Thank you everyone for your thoughtful comments. I’m fully aware a smaller sprocket will increase the top speed, as KO said themselves. I wanted to keep the 62t sprocket so I could compare directly with the previous setup. Unfortunately, the KV rating of this motor makes it not handle high rpm the way the stock motor does. This was disappointing and resulted in slow test results. There is a lot of room for improvement so stay tuned!
These commmets amaze me. I had a bad experience KO customer service as well. These people refused to tell me what the gauge size was of the phase wires! You know what it is to pay $1500 for a motor and not have the company share such basic information. They are a Joke. Im running the motor, but with a bac8000 and am having a lot better luck.
Really what it comes down to is that the 30KW motor does not spin faster than the other motor. They have the same or similar top rotation per minute. Higher wattage effectively makes the power increase, not the rpm. This means you can have a larger sprocket on the motor or a smaller sprocket on the wheel. It's simple math.
From someone with years of experience with BLDC motors KO is 100% correct with their comment about the gearing. You can wind motors more for torque or more for RPM. You’ve optimised the gearing on the bike for the old motor which was wound for less torque and more rpm than the KO motor. The KO motor will require higher gearing to take advantage of the available power.
@@Jahsuke1 negative. Power isn't speed on the same gearing. Voltage is speed when it comes to motors. Current is power. That's why people keep mentioning kv. A low kv needs more voltage. High kv needs less to go fast.
@@Jahsuke1 He fully explained it in his comment and you still don't get it. If a more powerful motor makes less rpm on the output shaft it's going to be slower with the stock gearing regardless if it makes more power or not.
@@Jahsuke1 powerful motor doesn't necessarily mean higher top speed right off the bat. Powerful motor just means it can either get more torque or RPM or both, which depends on winding(of the motor itself) and actual bike gearing. What he's running rn is a really low gear ratio(larger rear sprocket) which is designed to make more torque to the wheels not necessarily top speed. It only worked for his last setup because his og motor was designed for high rpm low torque, so he compensated with a low gearing to get more torque to the rear wheels(which is needed for wheelies and for a from stop acceleration). The new motor has lower rpm but way higher torque so he doesn't really need the low gearing anymore. It's like a tall NBA superstar wearing really high heals while playing, it might work but not optimal. What he needs to do is get a higher gear ratio(less teeth in rear sprocket) to get a higher top speed. As it sits rn, what he's doing is kind of like putting a tractor transmission to a Bugatti Chiron then expect it to get higher top speed than stock... Just step back, relax and try to follow what the tech support suggests before calling the suggestion as bad/unhelpful cos most of the time those tech support knows what they're talking about especially if from niche but successful companies, and it's just users who fricked up and don't actually know how their stuff works(electrical/electronic/mechanical/etc).
Do you know how the motor is wired? If it has tighter windings you’ll need less teeth on the rear sprocket because that’s generating more torque and less speed than your previous motor. 30kw is sport bike territory you should be topping out at 100mph not 50
@@michaelj1371 I have a hypercruiser with cowling, at 16 kw and 96v on a qs 273 motor it tops out at something above 120kmh. But that’s mostly due to the cowling
Motor seems to be made for torque so having both 62 sprocket and 12 inch wheels puts no load on the motor, except on launch. I'd love to see your reaction with 48 tooth 19 inch rims. You should be pretty surprised.
My exact thoughts, if you do the math he is running exactly half the stock gearing, assuming the rear sprocket and wheel size is the only thing he has changed - that gives a top speed of 90mph on stock gearing. Hes a great youtuber but he could understand the bikes better. Another thing not even addressed is the flux weakening, which would also make a difference since the KO motors are rated to easily 8k rpm off the top of my head
@@dan4age with decent grip it will wheelie before getting wheel spin. he said he couldn't keep the wheel down which would explain the big differences in 1/8 mile times. but I agree 30kW with such light weight, short gearing and small wheels should want to wheelie all the way
It's kinda disappointing someone with so much influence would go into this with zero technical knowledge or know how on motors. One thing you cannot do is run over a 60T sproket on a KO motor, especially with those wheels, it's obvious just by the stator size/KV. Would love to help you out on the setup, definitely throw that 62T sproket away first!
He's stated in other videos he just got into motorcycles when he got his sur ron 3 years ago. So you have to take that into consideration anytime you take someone's advice. I don't know shit about EV's but I do understand how EV motors are wound and I really understand gearing. I agree though, most influencers don't know shit these days.
You can’t expect the same MPH out of a bigger motor while keeping the same gearing, You will loose top speed but gain torque. However having a bigger motor/more power will allow you to go down in sprocket size while still maintaining a lot of torque but also having top speed to go with it. Also you can tune your “Eco” as one of your power levels until KOs display is ready so you would have 2 power modes. The boys over at KO have the best customer service out of any company I’ve worked with, I find it hard to believe they didn’t steer you in the right direction unless you didn’t want the help from them. Change your gearing, spend some time building yourself a couple tunes for your liking and then give an honest review.
Yeah, its weird that he expect the exact same rpm from the motor. Spin speeds differ, but it has higher power output.. so just way smaller rear sprocket to actually max out that power.
Definitely doesn’t have good torque unless you run 20kw plus anything lower is dog shit and sprocket change won’t change anything I run a 60t with my bac 8k and stock motor at 8kw my top speed is his top speed running 30kw aka 60s I have a vid on my channel 12kw 75mph gps so he’s better off going back to bac and stock motor
As everyone has said, the motor is a beefy high torque low RPM. Once you have the right gearing and wheels it should be a beast! Can't wait to see the improvements!
Sur Ronster, don't worry, KO will get you sorted, lots of folks had these setbacks early on, your wheel/gearing will definitely need to be changed to get the results, fact is you don't need to run that large of a rear sprocket with this motor/controller, you will still have the low end torque. Most of us run with the controller in linear mode, I think with the smaller wheels combined with a smaller rear sprocket and some tuning you can run it in sport mode and you will be flying. There's plenty of videos on here along with Progressive E's work that shows the potential of this combo, the 12's change a lot so it will require some special tuning and gearing changes. I look forward to the next video once KO gets you sorted. If you don't already have a Domino throttle get one, it makes a big difference on how the throttle feels.
2 of my friends have the same set up and it runs great and they’re both doing 70+. You can have 2 power modes with the stock eco and sports switch. The egg rider is for the bac
Did they send you the old MX motor by mistake? I thought that the “factory spec” & RS motors had higher KV ratings (and thus more RPM).. not lower than stock. You should invest Dragy for more accurate performance metrics!
in the RC world, larger more powerful motors are less KV meaning less rpms and more torque. in this case you’d need to downsize the rear sprocket to gain that speed back because it has too much torque and not spinning as fast as the old motor
I was thinking the same thing. Coming from the Fixed Wing/Drone perspective. The other alternative would be increase the voltage. KO's specs say 48-100v. Ask Chi for a 96v battery!
You need to speak to Ben from KO he tuned my set up. It just takes a bit of time to dial things I had to ride the bike a little go back to him and he would change settings for me until it was perfect. I think this is the best way to do it. Also you should really consider changing your sprocket. The combo of sprocket and wheels is definitely massively limiting your potential on that set up. My set up now is an absolute monster. KO has the best customer support in the business.
@@MrXNITROx Also a gearing issue as well everyone who tunes these bikes knows that as you go up in power and torque you go down in gearing. The 62t sprocket is way overkill
Yeah I had the same , Ben and Ian from KO were amazing ! Ian spent 30 min solid tuning my controller with me and at the end I dropped my BAC 8000 and will never look back . Shame you have a bad experience. Also I think these guys are in the UK so maybe they didn’t respond cause of the time difference ?
@@briandhoward6137 yes after tuning but the rear sprocket is massive and he needs to drop to a smaller one to gain that speed. He won’t loose anything down low but gear ratios can’t be tuned by any controller.
@@ickypowwow6635 it had more torque so its prob designed for another ratio.. if he would tune it or gear it down in the rear he would most likely hit 60 quicker than the other setup
@@jal187 bro what are you guys talking about? If its the EXACT SAME SETUP BESIDES MTORO AND CONTROLLER then there should clearly be a power increase. Not to be a dick but I really don't understand how that needs to be explained.
it's because of the wider stator that's why it can't spin faster than a stock motor, the benefit with ipm motor (ko) vs spm motor (stock) is that ipm motor can sustain higher rpm without the magnets breaking, benefit of wider stator is that you have more torque with the trade off of the rpm, I don't see a reason to use a higher gear ratio when your motor has a ton of torque, its like driving only in 1st gear not to mention you're using a 12inch wheel which also gives off a ton of torque at the expense of top end speed
The thing is the stock motor spins faster but has less torque or power so you found the sweet spot with that size tire with that sprocket what you need is a smaller rear sprocket and bigger tires so the sprocket makes less rotations per motor rotation and you can also change out the front sprocket. If you’ve ever been on a mountain bike with front and rear gears you can change you’ll see this in action. The lower the gear the more power but the less speed the higher the gear the less power but more speed the way the air Ron is setup right now you could probably tow your truck. Put taller tires and you’ll see a difference then put a smaller sprocket on the rear or keep those tires and just try different sprocket sizes. In short the new motor spins slower but has more power output so just put in a gear ratio for more speed and less torque.
You got to change the rear sprocket for a smaller 1 with les teeth. if u get more power, like pulling power then it like having 2 horse's instead of 1. so making rear sprocket smaller you will get more top end but less acceleration. hope his helped. gr8 channel. thank you
There’s always a trade off between torque and speed. It appears that the KO has much better low end torque, so improving your gear ratio is the answer (as the KO engineers advised).
Sorry, but you cannot compare controller field weakning if you also change motor. You need to know the kv rating for the motors and compensate gearing. If one has more power, then also compensate for that. 🤓 Do some homework on the specs before misleading on the new setup 🙂 But it looks good 😁
I think what you may be missing is that, like engines, motors can be built in different configurations, and those different configurations deliver power differently. In this case, think of it as slider between torgue and RPM (this is oversimplified, but hopefully gets the idea across) - as torgue is increased, the maximum RPM of the motor decreases. This is expressed somewhat in the kv rating of the motor. Higher kv equals higher RPM (for a given voltage), but lower torque when compared to a motor of similar size and type but with a lower kv. This means their tech was correct in that you need to decrease the number of teeth in the rear sprocket. The motor obviously has the torque, so put it to good use with a higher gear ratio (larger tires would also work). This will help keep the front end down, and deliver a higher top speed.
Cool Video. As a drag racer. I’d like to share a little knowledge on standing starts. Drag racing the first 60’ is measured in time and is key to a good et. Trap speed in mph typically doesn’t vary much from a bad start and hood start. Irony bad start with spin will yield more mph. Time to accelerate was increased. Anyway. Point being. One Tenth faster 60’ roughly equates to three tenths off the 1/4 mile et. So the extra tq from the upgrade is slowing you start effecting your 1/8 et. I suggest a draggy as it’ll give you a lot of data points. Points where launch variables can be removed and use data like 330’ - 660’ et and speeds. Also the dirt bike looking unit riding beside you. What is that?
The KO prolly is lower KV then the Stock Surron motor but will provide more torque. And imho , I dont think it's fair to blame KO. Your gear ratio is geared for torque and not to mention , absurdly small wheels compared to the stock Surron wheel size so you can't expect them to test it on every single wheel and sprocket combo. If you want have more *top speed* , Bigger front sprocket OR Smaller Rear sprocket More *Torque* : Smaller front sprocket OR bigger rear sprocket.(Or increase the amps on the controller) Also , 30kw is a over-statement. The motor maybe rated for 30kw , but that doesn't mean you ARE pushing 30kw. The Chi battery you have is a 72v 38ah(37.8AH To be precise) of Molicel P42a 21700 cells in a 20s 9p config which gives you 405amp peak. At 72volts that gives you roughly ~29kw but that is highly not the case as I really doubt any manufacturer allows you to use it on the very limit of the cells and a 400amp BMS would be way too big anyway which is why some people bypass their BMS discharge but that's another story. The Stuttering MIGHT be because of the controller drawing too much amps but Idk . I've no idea what the KO controller specs are so it's all a theory.
Well you are smart with your gear ratio. If Surronster was actually pulling 30kw I am not sure it would even be drivable with all the torque from the 64T.
I'm running a 20kw tune on my KO and it's wicked fast. Give them a chance they will make it right. KO knows they didn't serve you the way they should have. This is the ultimate set up imo.
Hey my man, just chiming in as a mechanic and long time motocross racer. The bike has more hit down low than the stock motor. The KO is slow up top. You need to change the drivetrain. Just like a different transmission in the same truck will give you totally different power results......You need to take the hit off the bottom by regearing it with in turn would move that power up top where you want it. Let me know if you will be doing another video, really appreciate your content. I see you around sometimes, im just in Oside.
@@Mayhemjach absolutely, but you have to tune the motor manually in the bac8000. If you dont know how to tune a motor in a asi controller it will be hard for you to get the motor running smoothly
I didn’t see an eco switch on your bike, if I remember right, I’m pretty sure the KO will default to ECO mode if there is no switch. I’m running 15 kw on a similar setup and it wants to flip over at 10mph and 40mph. I have hit 65mph but my front wheel starts getting spooky. I’ll bet I can hit close to 80 with my 16 inch amd 56 tooth. 72 chi max and KO controller and RS motor.
I'd assume the acceleration at the start being commented on would suggest it has higher torque and that it tops out due to lower rpm, and so if by slow you mean the speed that the motor is spinning you are correct. If your have one gear you're either going to tune for acceleration, top speed, or a balance. You can do the same with gears which will determine the range for high top speed or faster acceleration which would result in faster gear changes. It's the same for all motors. Car typically have 5 or 6 gears. My bicycle has 9 on the back wheel (derailleur). Power tools have lower rpm for cutting and higher rpm for polishing.
Definitely a tuning issue. Are you on their discord channel? Almost always have someone on there. I can hit 62mph with my KO combo and that's with a 58t sprocket and 19/16 dirt bike wheels and tires. Plus, you should be able to use the eco mode on your display. Mine has 2 modes, eco and sport. They are supposedly coming out with a display too.
Just a quick thing: The KV isn't making it not handle high RPM as well, it just doesn't spin as fast. if it has a lower KV rating it will make much more torque but spin slower as kv is rpm per volt and you have to adjust gearing accordingly.
Yes its called " Final Gear Ratio" and yes involves wheels size-tyre size and front&back sprockets and of course the engine characteristics as power/rpm etc
HECK YES FU YT notifications I'm here now. Been waiting for it to make it to your channel...lots of people have been having good results but you're a bigger channel and a bonafide hard ridin user, so we'll know if it's weak... *proceeds to enjoy video*
i would change to a 30 tooth sprocket especially for the ko motor your gear ratio is definitely a huge problem and also l check your tune i’ve gotten to seventy mph with the ko motor easily
i think it because its really strong magnets in the motor meaning its all about the torque, it explaines the chunkieness you were talking about and the lack of speed, and more torque.
Let me dumb this down for the Americans and petrol heads out there: What Mr.Ronster did in the video is the equivalent of sticking a 13 litre 600HP Semi truck Diesel engine in a stock Mazda RX7 and complain about the top speed. The RX7 comes with a much less powerful motor spinning at a whopping 8000RPM and has a final drive chosen to make use of its power band. Putting the more powerful engine through the same transmission will equate to an obvious lower top speed. The whole reason Ronster swapped to the bigger sprocket to begin with was to make use of the stock motors increased RPM due to raising the voltage of the battery (and perhaps the BAC’s field weakening settings). If he instead would have listened to the KO support and kept the original drivetrain of the Sur Ron the results would have actually been useful. This video really put unjustified blame on KO and I think you owe them a follow up video actually listening to the experts. Shame
Smaller sprocket for sure, has more than enough torque to handle it. Motor is basically just running out of rpm probably why it's choppy. I'd also make sure all the grounds are good high voltage would make the bike stutter as well
Its true when you wind a motor for Torque that you lose a bit of RPM.. you can lose quite a chunk actually. So with the right gearing that thing will keep pulling. Believe me.
Try a BAC8000?!? I would have expected more from KO in customer service. You being “the man” regarding surron’s, they should have sent you specs and everything to be 100% dialed in. Sad day for this company. Thank you for the honest review.
I have binge watched your videos for 3 days straight now. I love your videos. I think im going to get a s2r plus e scooter. I heard it is high quality scooter.
The back tire has mass clearance if you kept the same rear sprocket and increased the diameter of the rear wheel to fill in the large gap, the bike would still lean forward for the back tire bigger than the front, but possible to increase the size of the front wheel or add a spacer or longer forks to get the handlebars higher up
Just paused 6.5 minutes in, haven't read any comments. I just wanna say, the dealer rep sounds right. Put a smaller driver on. With more power, You'll be ok with lower gears to get a better top speed.
my suggestion is use optimum lap to find your best gear ratio, choose fsae car, give your tire coefficient 0.9 or something like that and put your motor data. Do not forget this motors have so much rpm and after 6000rpm the torque slows dowmn but that too it downs to 29nm. After that but your final drive and go in a straight line track. If you check your optimum lap and real life data you can find the right coefficient of friction, after that make a chart for a ideal ratio. But every one should put this in mind, gear ratio is all about your feeling if you dont race on a track. I like high torque in low speeds and i liked your first ratio. Nice video, want to buy ko motor and i hope after finishing your video i dont get upset about stupid ko motor. I literally send 5 mails to that guys to get rpm current data. They dont even response. And also i have seen tests with 72/60v compressions it really doesnt matter. And lastly, torque gets higher when you have more current. With low current motor will act like small tiny miny motor.
You ran into a problem I had back in the day with hop up motors on electric rc vehicles. The hotter motors had fewer turns, so less torque but capable of much higher rpms. No one told be I had to gear the truck down. So my hop up added some acceleration but not to end and only lasted a few battery packs because the gearing was preventing the motor from spinning as fast as it wanted to. Got a new motor and smaller pinion gear and top speed went up and the motor ran cooler.
It seriously gear ratio if you can't see that you're blind put a longer gear on it and you'll haul ass and you can have all the torque and power you want but if you have no gear it ain't going nowhere
its like going from a gas to diesel engine and expecting it to be as fast with the same rear gear. There is a reason for example BMW 335d's run a 2.81 rear gear where as the 335i runs a 3.46
Isn't it just more power? So it can run smaller gear ratios. Different motors have different max rpm ratings.. but more kv should give you more power, so it exactly is about changing the gear ratio.
having a background in RC racing they are 100% correct about the gearing and when u add in factor that your wheels are smaller than original it make it that much worse u can actually burn it up with to low of you could be amazed and what a simple proper gear ratio would do to that bike
I’m still buying KO because they came out and publicly made a comment about this. They admitted they dropped the ball and came clean before this video went live. They may have not prioritized your issues but I don’t anticipate any issues with mine as I don’t run that wheel and sprocket setup you do. I like my 17” Super Moto wheels and would only drop down to a 14” for a local Karting track.
Also (I was looking this up earlier because it’s come up a few times) but the voltage and current leaving your controller and going to the motor doesn’t have to match the current or voltage leaving the battery. If the motor voltage is lower on this controller than the other controller then even if they both had the same kV windings you’d end up with a lower top speed
Try changing your rear sprocket into a smaller one or a taller wheelset because that motor has so much torque, that has so much power at start and its slow at the top end because you didnt change your gear ratio and you have smaller tires than the stock ones
doesn't (or shouldn't) matter though. its the same rpm/volt as the stock motor, so should be able to manage higher speeds given its a IPM motor and thus should respond better to field weakening than stock. It may well be tuning (ie controller imposing an artificial acceleration limit), but the notion that 'because gearing the top rpm & torque is lower' is nonsense.
love the vid bro. do you think you could make a new video of the price breakdown of all the parts on your bike and just all the money it costs to have a bike like yours. Thanks bro keep up the good work love u
the way brushless inrunner motors work is they have kv, the higher the kv means the faster it will be able to spin but will have less torque, the lower the kv you will have less rpm but more torque. from what i can see the ko motor has a lower kv meaning its not as fast but it has more torque. torque is always more useful as it will keep temps down and as you can change the gear ratio with that extra torque you will be able to hit that higher speed. I'm sure some kind of tune will be needed but its a new product and it is how things are. try putting a smaller sprocket on the bike and go back to the 16" wheels. torque is always better than higher rpm.
My knowledge of ebikes are limited. But i know that electric motors has a Kv-number (not kw). Kv= the RPM (revolutions per minute) a motor does per Volt that is put into it. My best guess i that your gear ratio is way of!
Most definitely should out preform the stock motor and the bac4000. Unless this works better I will stay stock motor and back 4000. I get 50+ on my set up. Your expectations should be high for a set up like this. Lots of hype over this set up. Seems to be hype in your experience. Love your content on the surrons.
Y'all are out of ur fkn minds if you need to go faster than 55. I don't believe the suspension on these things would even hold up to what I would do with it. Thing is too small to be going 60-70 mph ur nuts.
You should maybe get in contact with the guys from Progressive E. They have a youtube channel which they were having somewhat having issues like yours or worse, as they were one of the first one to get the KO motor and controller to test it out, but they finally got all the bugs out of their tune.
i super respect this honest af review man. been looking into KO but they have some work to do it seems. will keep rockin my solid bac4000 build. OL RELIABLE.
Thank you everyone for your thoughtful comments. I’m fully aware a smaller sprocket will increase the top speed, as KO said themselves. I wanted to keep the 62t sprocket so I could compare directly with the previous setup. Unfortunately, the KV rating of this motor makes it not handle high rpm the way the stock motor does. This was disappointing and resulted in slow test results. There is a lot of room for improvement so stay tuned!
Yo
These commmets amaze me. I had a bad experience KO customer service as well. These people refused to tell me what the gauge size was of the phase wires! You know what it is to pay $1500 for a motor and not have the company share such basic information. They are a Joke. Im running the motor, but with a bac8000 and am having a lot better luck.
ill be at the houston megaride! You can test my bike brother @surronster
Man stop being stubborn. Put a 48T and you can do 0-60 in half that time. That motor is crazy. Don’t you want to have to have fun?
Really what it comes down to is that the 30KW motor does not spin faster than the other motor. They have the same or similar top rotation per minute. Higher wattage effectively makes the power increase, not the rpm. This means you can have a larger sprocket on the motor or a smaller sprocket on the wheel. It's simple math.
From someone with years of experience with BLDC motors KO is 100% correct with their comment about the gearing. You can wind motors more for torque or more for RPM. You’ve optimised the gearing on the bike for the old motor which was wound for less torque and more rpm than the KO motor. The KO motor will require higher gearing to take advantage of the available power.
More motor power= more power it should still have a higher top speed than stock homeboy
@@Jahsuke1 negative. Power isn't speed on the same gearing. Voltage is speed when it comes to motors. Current is power. That's why people keep mentioning kv. A low kv needs more voltage. High kv needs less to go fast.
@@miscellaneousguy3803 totally agree ! So much blush it if I on this thread it melts my mind .
@@Jahsuke1 He fully explained it in his comment and you still don't get it. If a more powerful motor makes less rpm on the output shaft it's going to be slower with the stock gearing regardless if it makes more power or not.
@@Jahsuke1 powerful motor doesn't necessarily mean higher top speed right off the bat. Powerful motor just means it can either get more torque or RPM or both, which depends on winding(of the motor itself) and actual bike gearing.
What he's running rn is a really low gear ratio(larger rear sprocket) which is designed to make more torque to the wheels not necessarily top speed. It only worked for his last setup because his og motor was designed for high rpm low torque, so he compensated with a low gearing to get more torque to the rear wheels(which is needed for wheelies and for a from stop acceleration).
The new motor has lower rpm but way higher torque so he doesn't really need the low gearing anymore. It's like a tall NBA superstar wearing really high heals while playing, it might work but not optimal. What he needs to do is get a higher gear ratio(less teeth in rear sprocket) to get a higher top speed. As it sits rn, what he's doing is kind of like putting a tractor transmission to a Bugatti Chiron then expect it to get higher top speed than stock...
Just step back, relax and try to follow what the tech support suggests before calling the suggestion as bad/unhelpful cos most of the time those tech support knows what they're talking about especially if from niche but successful companies, and it's just users who fricked up and don't actually know how their stuff works(electrical/electronic/mechanical/etc).
Do you know how the motor is wired? If it has tighter windings you’ll need less teeth on the rear sprocket because that’s generating more torque and less speed than your previous motor. 30kw is sport bike territory you should be topping out at 100mph not 50
the stator itself is much wider than stock, this motor is literally made for torque, his gear ratio is literally like driving a car in 1st gear
Ninja 400 around 30kw weighs around 360lbs top speed 105mph
Bro if he put a 48tooth on it and not that stupid big sprocket used for the stock motor. It would be doing 70.
@@michaelj1371 I have a hypercruiser with cowling, at 16 kw and 96v on a qs 273 motor it tops out at something above 120kmh. But that’s mostly due to the cowling
@@michaelj1371 he can still get away with 42t and still have massive torque
You’re running a 62t and a 12 " wheel, that’s like staying in 1st gear is why there’s no top speed
He does that so he gets more torque for wheelies
Motor seems to be made for torque so having both 62 sprocket and 12 inch wheels puts no load on the motor, except on launch.
I'd love to see your reaction with 48 tooth 19 inch rims. You should be pretty surprised.
My exact thoughts, if you do the math he is running exactly half the stock gearing, assuming the rear sprocket and wheel size is the only thing he has changed - that gives a top speed of 90mph on stock gearing. Hes a great youtuber but he could understand the bikes better. Another thing not even addressed is the flux weakening, which would also make a difference since the KO motors are rated to easily 8k rpm off the top of my head
No way it's 30kw it would be impossible to keep down with short gearing and small tyres, it's not even spinning the tyre something is wrong
@@dan4age with decent grip it will wheelie before getting wheel spin. he said he couldn't keep the wheel down which would explain the big differences in 1/8 mile times. but I agree 30kW with such light weight, short gearing and small wheels should want to wheelie all the way
@@dan4age There's no load on it because of gearing.
Yeah seeing this I am thinking why such a large sprocket on rear
It's kinda disappointing someone with so much influence would go into this with zero technical knowledge or know how on motors. One thing you cannot do is run over a 60T sproket on a KO motor, especially with those wheels, it's obvious just by the stator size/KV.
Would love to help you out on the setup, definitely throw that 62T sproket away first!
the blind leading the................ blind?................ dumb ? man's a FOOL. a eejit
He's stated in other videos he just got into motorcycles when he got his sur ron 3 years ago. So you have to take that into consideration anytime you take someone's advice. I don't know shit about EV's but I do understand how EV motors are wound and I really understand gearing. I agree though, most influencers don't know shit these days.
You can’t expect the same MPH out of a bigger motor while keeping the same gearing, You will loose top speed but gain torque.
However having a bigger motor/more power will allow you to go down in sprocket size while still maintaining a lot of torque but also having top speed to go with it.
Also you can tune your “Eco” as one of your power levels until KOs display is ready so you would have 2 power modes.
The boys over at KO have the best customer service out of any company I’ve worked with, I find it hard to believe they didn’t steer you in the right direction unless you didn’t want the help from them.
Change your gearing, spend some time building yourself a couple tunes for your liking and then give an honest review.
What you said Koby , Hit up Ian he is a top guy and super patient if you don’t have computer skills like me hahah. The KO combo is a monster !
Try a smaller sprocket, it will definitely go faster it already has good torque awesome video 😱
Smaller rear sprocket
Yeah, its weird that he expect the exact same rpm from the motor. Spin speeds differ, but it has higher power output.. so just way smaller rear sprocket to actually max out that power.
Smaller sprocket on the rear and bigger gear on the motor
@@flotareciever sprocket has a ton to do with it lol
Definitely doesn’t have good torque unless you run 20kw plus anything lower is dog shit and sprocket change won’t change anything I run a 60t with my bac 8k and stock motor at 8kw my top speed is his top speed running 30kw aka 60s I have a vid on my channel 12kw 75mph gps so he’s better off going back to bac and stock motor
As everyone has said, the motor is a beefy high torque low RPM. Once you have the right gearing and wheels it should be a beast! Can't wait to see the improvements!
I tuned my motor then farted really loud , my boxers are soggy and brown . Help
@@TwofourA there ain't no mechanical fix for that chief, go get the washing machine
@@Ferrari255GTO it’s flooded with brown sludge mate , it’s a non starter
@@TwofourA i mean, if you don't try you don't know. You will probably have to replace it afterwards though.
Thats retarded.. it was faster before.. if he changes the gears ⚙️ on the old set up it will be faster to.
Sur Ronster, don't worry, KO will get you sorted, lots of folks had these setbacks early on, your wheel/gearing will definitely need to be changed to get the results, fact is you don't need to run that large of a rear sprocket with this motor/controller, you will still have the low end torque. Most of us run with the controller in linear mode, I think with the smaller wheels combined with a smaller rear sprocket and some tuning you can run it in sport mode and you will be flying. There's plenty of videos on here along with Progressive E's work that shows the potential of this combo, the 12's change a lot so it will require some special tuning and gearing changes. I look forward to the next video once KO gets you sorted. If you don't already have a Domino throttle get one, it makes a big difference on how the throttle feels.
2 of my friends have the same set up and it runs great and they’re both doing 70+. You can have 2 power modes with the stock eco and sports switch. The egg rider is for the bac
Who thr fuck wants to do 70 in a toy bike 😂😂😂
Did they send you the old MX motor by mistake? I thought that the “factory spec” & RS motors had higher KV ratings (and thus more RPM).. not lower than stock.
You should invest Dragy for more accurate performance metrics!
in the RC world, larger more powerful motors are less KV meaning less rpms and more torque. in this case you’d need to downsize the rear sprocket to gain that speed back because it has too much torque and not spinning as fast as the old motor
Yeah I think this is the only plausible explanation.
I was thinking the same thing. Coming from the Fixed Wing/Drone perspective. The other alternative would be increase the voltage. KO's specs say 48-100v. Ask Chi for a 96v battery!
First person with a brain in the comment section
This guy gets it, it fries my brain that he is spending $xxxx without understanding how the basics work.
well done for reading everyone elses comments first
All motors have a max speed. (in combination with the voltage). its pretty ignorant to assume KO are are responsible for your bad gear ratio
I'm no scientist but the 64 sprocket and wheel size could be throwing this all off.
Recomend 40 tooth sproket
You need to speak to Ben from KO he tuned my set up. It just takes a bit of time to dial things I had to ride the bike a little go back to him and he would change settings for me until it was perfect. I think this is the best way to do it. Also you should really consider changing your sprocket. The combo of sprocket and wheels is definitely massively limiting your potential on that set up. My set up now is an absolute monster. KO has the best customer support in the business.
this seems biased and contrary to the video
@@MrXNITROx I doubt it, controllers have many settings. Tuning them is not intuitive.
@@MrXNITROx contrary in what way? this is clearly a tuning issue rather than anything else.
@@MrXNITROx Also a gearing issue as well everyone who tunes these bikes knows that as you go up in power and torque you go down in gearing. The 62t sprocket is way overkill
Yeah I had the same , Ben and Ian from KO were amazing ! Ian spent 30 min solid tuning my controller with me and at the end I dropped my BAC 8000 and will never look back . Shame you have a bad experience. Also I think these guys are in the UK so maybe they didn’t respond cause of the time difference ?
You have to remember you also have smaller wheels so that will throw the gear ratio out of whack
He got 50+ on the stock motor with the same wheels, the KO should be faster on the same set up.
@@briandhoward6137 yes after tuning but the rear sprocket is massive and he needs to drop to a smaller one to gain that speed. He won’t loose anything down low but gear ratios can’t be tuned by any controller.
He didn't change the gear ratio though so what do you mean? that is irrelevant when those wheels were on it for both tests
@@ickypowwow6635 it had more torque so its prob designed for another ratio.. if he would tune it or gear it down in the rear he would most likely hit 60 quicker than the other setup
@@jal187 bro what are you guys talking about? If its the EXACT SAME SETUP BESIDES MTORO AND CONTROLLER then there should clearly be a power increase. Not to be a dick but I really don't understand how that needs to be explained.
it's because of the wider stator that's why it can't spin faster than a stock motor, the benefit with ipm motor (ko) vs spm motor (stock) is that ipm motor can sustain higher rpm without the magnets breaking, benefit of wider stator is that you have more torque with the trade off of the rpm, I don't see a reason to use a higher gear ratio when your motor has a ton of torque, its like driving only in 1st gear not to mention you're using a 12inch wheel which also gives off a ton of torque at the expense of top end speed
The thing is the stock motor spins faster but has less torque or power so you found the sweet spot with that size tire with that sprocket what you need is a smaller rear sprocket and bigger tires so the sprocket makes less rotations per motor rotation and you can also change out the front sprocket. If you’ve ever been on a mountain bike with front and rear gears you can change you’ll see this in action. The lower the gear the more power but the less speed the higher the gear the less power but more speed the way the air Ron is setup right now you could probably tow your truck. Put taller tires and you’ll see a difference then put a smaller sprocket on the rear or keep those tires and just try different sprocket sizes.
In short the new motor spins slower but has more power output so just put in a gear ratio for more speed and less torque.
You got to change the rear sprocket for a smaller 1 with les teeth. if u get more power, like pulling power then it like having 2 horse's instead of 1. so making rear sprocket smaller you will get more top end but less acceleration. hope his helped. gr8 channel. thank you
Its simpel, motor got much more power, but the rpm are lower.. smaller sprocket, and it will be faster, and acceleration Will be the same
There’s always a trade off between torque and speed. It appears that the KO has much better low end torque, so improving your gear ratio is the answer (as the KO engineers advised).
Just wanted to let you know I'm extremely impressed at how quick the quality of your videos have improved nice work!
Since the motor is super powerful wouldn't a high gear ratio be no problem for torque and give you good top speed?
cant wait to see this thing in person in November!🤘
Sorry, but you cannot compare controller field weakning if you also change motor. You need to know the kv rating for the motors and compensate gearing. If one has more power, then also compensate for that. 🤓 Do some homework on the specs before misleading on the new setup 🙂 But it looks good 😁
Do some homework........................ any homework!........................... please
I feel like the big sprocket is messing with your top end
I think what you may be missing is that, like engines, motors can be built in different configurations, and those different configurations deliver power differently. In this case, think of it as slider between torgue and RPM (this is oversimplified, but hopefully gets the idea across) - as torgue is increased, the maximum RPM of the motor decreases. This is expressed somewhat in the kv rating of the motor. Higher kv equals higher RPM (for a given voltage), but lower torque when compared to a motor of similar size and type but with a lower kv.
This means their tech was correct in that you need to decrease the number of teeth in the rear sprocket. The motor obviously has the torque, so put it to good use with a higher gear ratio (larger tires would also work). This will help keep the front end down, and deliver a higher top speed.
Great way of explaining it
Cool Video. As a drag racer. I’d like to share a little knowledge on standing starts. Drag racing the first 60’ is measured in time and is key to a good et. Trap speed in mph typically doesn’t vary much from a bad start and hood start. Irony bad start with spin will yield more mph. Time to accelerate was increased. Anyway. Point being. One Tenth faster 60’ roughly equates to three tenths off the 1/4 mile et.
So the extra tq from the upgrade is slowing you start effecting your 1/8 et.
I suggest a draggy as it’ll give you a lot of data points. Points where launch variables can be removed and use data like 330’ - 660’ et and speeds.
Also the dirt bike looking unit riding beside you. What is that?
The KO prolly is lower KV then the Stock Surron motor but will provide more torque.
And imho , I dont think it's fair to blame KO. Your gear ratio is geared for torque and not to mention , absurdly small wheels compared to the stock Surron wheel size so you can't expect them to test it on every single wheel and sprocket combo.
If you want have more *top speed* ,
Bigger front sprocket OR Smaller Rear sprocket
More *Torque* :
Smaller front sprocket OR bigger rear sprocket.(Or increase the amps on the controller)
Also , 30kw is a over-statement. The motor maybe rated for 30kw , but that doesn't mean you ARE pushing 30kw. The Chi battery you have is a 72v 38ah(37.8AH To be precise) of Molicel P42a 21700 cells in a 20s 9p config which gives you 405amp peak. At 72volts that gives you roughly ~29kw but that is highly not the case as I really doubt any manufacturer allows you to use it on the very limit of the cells and a 400amp BMS would be way too big anyway which is why some people bypass their BMS discharge but that's another story.
The Stuttering MIGHT be because of the controller drawing too much amps but Idk . I've no idea what the KO controller specs are so it's all a theory.
Big thumbs up 👍 for the honesty!
My top speed is 76mph on 12 wheel set up but 42T sprocket. Also KO set up
Well you are smart with your gear ratio. If Surronster was actually pulling 30kw I am not sure it would even be drivable with all the torque from the 64T.
@@lonecoyote5454 was planning to put 58T. I guess thanks to his video I will keep mine at 42
Can you do a consistant 70 mph or just burst of 70 mph+?
@@Hunter_Heart almost WOT. I tried from 83V down to 67V on a freeway. My top at 67V still at 68mph and no overheating
I'm running a 20kw tune on my KO and it's wicked fast. Give them a chance they will make it right. KO knows they didn't serve you the way they should have. This is the ultimate set up imo.
64t and 12’s is the issue. Sprocket that thing down and try it. A mid 50 would do a lot better
Great video, with a another banger, i get excited when I see you post!
Literally saw a video last week of a moto mini with KO motor combo going past a guy on his Surron and he was pushing 98+
Hey my man, just chiming in as a mechanic and long time motocross racer. The bike has more hit down low than the stock motor. The KO is slow up top. You need to change the drivetrain. Just like a different transmission in the same truck will give you totally different power results......You need to take the hit off the bottom by regearing it with in turn would move that power up top where you want it.
Let me know if you will be doing another video, really appreciate your content. I see you around sometimes, im just in Oside.
I´m running the KO Motor with a Bac8000 and have tuned it pretty good.
This thing is sick with a Bac8000
The bac works well with the lo motor? I was thinking about just grabbing the motor
@@Mayhemjach absolutely, but you have to tune the motor manually in the bac8000.
If you dont know how to tune a motor in a asi controller it will be hard for you to get the motor running smoothly
Gearing makes sense.
Have to regear my r/c truck when using different esc,motor combos. Not only for going faster, but also for heat.
I didn’t see an eco switch on your bike, if I remember right, I’m pretty sure the KO will default to ECO mode if there is no switch.
I’m running 15 kw on a similar setup and it wants to flip over at 10mph and 40mph. I have hit 65mph but my front wheel starts getting spooky. I’ll bet I can hit close to 80 with my 16 inch amd 56 tooth. 72 chi max and KO controller and RS motor.
I'd assume the acceleration at the start being commented on would suggest it has higher torque and that it tops out due to lower rpm, and so if by slow you mean the speed that the motor is spinning you are correct. If your have one gear you're either going to tune for acceleration, top speed, or a balance. You can do the same with gears which will determine the range for high top speed or faster acceleration which would result in faster gear changes. It's the same for all motors. Car typically have 5 or 6 gears. My bicycle has 9 on the back wheel (derailleur). Power tools have lower rpm for cutting and higher rpm for polishing.
well you have tiny drive wheel and huge rear sprocket and small front one and the motor has more torque and less rpm so what do you expect
Bro this is amazing the bike is now a fully costum build keep up the good work👍🙃❤️
Definitely a tuning issue. Are you on their discord channel? Almost always have someone on there. I can hit 62mph with my KO combo and that's with a 58t sprocket and 19/16 dirt bike wheels and tires. Plus, you should be able to use the eco mode on your display. Mine has 2 modes, eco and sport. They are supposedly coming out with a display too.
Just a quick thing: The KV isn't making it not handle high RPM as well, it just doesn't spin as fast. if it has a lower KV rating it will make much more torque but spin slower as kv is rpm per volt and you have to adjust gearing accordingly.
Just change the back Chainring (Make it smaller) so you get a higher topspeed.
Yes its called " Final Gear Ratio" and yes involves wheels size-tyre size and front&back sprockets and of course the engine characteristics as power/rpm etc
HECK YES
FU YT notifications I'm here now.
Been waiting for it to make it to your channel...lots of people have been having good results but you're a bigger channel and a bonafide hard ridin user, so we'll know if it's weak...
*proceeds to enjoy video*
I think the wheel size also might have something to do with it or the size of the front sprocket
100 Points to Surronster 🙌 Honesty is the Best Policy, loved this vid bro
i would change to a 30 tooth sprocket especially for the ko motor your gear ratio is definitely a huge problem and also l check your tune i’ve gotten to seventy mph with the ko motor easily
Do you still have a Sur ron with KO motor? If you do, can you do a consistant 70 mph or. bursts 60 mph like 4000 BAC/stock motor setup?
Dude, how in the heck do you do all this work on you Surron with a helmet on… you’re insane!!! Props dude lol
Come on dude.. Give it the gearing it deserves..
More power needs more gear..
That’s the way the world works..
Sick bike dude!
i think it because its really strong magnets in the motor meaning its all about the torque, it explaines the chunkieness you were talking about and the lack of speed, and more torque.
Let me dumb this down for the Americans and petrol heads out there:
What Mr.Ronster did in the video is the equivalent of sticking a 13 litre 600HP Semi truck Diesel engine in a stock Mazda RX7 and complain about the top speed.
The RX7 comes with a much less powerful motor spinning at a whopping 8000RPM and has a final drive chosen to make use of its power band. Putting the more powerful engine through the same transmission will equate to an obvious lower top speed.
The whole reason Ronster swapped to the bigger sprocket to begin with was to make use of the stock motors increased RPM due to raising the voltage of the battery (and perhaps the BAC’s field weakening settings). If he instead would have listened to the KO support and kept the original drivetrain of the Sur Ron the results would have actually been useful.
This video really put unjustified blame on KO and I think you owe them a follow up video actually listening to the experts. Shame
Brooo you're truck is wicked clean, i like it!
Smaller sprocket for sure, has more than enough torque to handle it. Motor is basically just running out of rpm probably why it's choppy. I'd also make sure all the grounds are good high voltage would make the bike stutter as well
Its true when you wind a motor for Torque that you lose a bit of RPM.. you can lose quite a chunk actually.
So with the right gearing that thing will keep pulling. Believe me.
Try a BAC8000?!?
I would have expected more from KO in customer service. You being “the man” regarding surron’s, they should have sent you specs and everything to be 100% dialed in.
Sad day for this company.
Thank you for the honest review.
Check logs from the BMS to see if it’s actually pulling 30kw
I have binge watched your videos for 3 days straight now. I love your videos. I think im going to get a s2r plus e scooter. I heard it is high quality scooter.
Love the videos, keep it up!
The back tire has mass clearance if you kept the same rear sprocket and increased the diameter of the rear wheel to fill in the large gap, the bike would still lean forward for the back tire bigger than the front, but possible to increase the size of the front wheel or add a spacer or longer forks to get the handlebars higher up
Get a smaller rear sprocket. A motor with more torque isn't going to spin the wheel any faster without some changes
Just paused 6.5 minutes in, haven't read any comments. I just wanna say, the dealer rep sounds
right. Put a smaller driver on. With more power, You'll be ok with lower gears to get a better top speed.
Love the videos and u inspire me so much and im thinking about getting a surron but the price is a big number for a bike, keep the videos going
my suggestion is use optimum lap to find your best gear ratio, choose fsae car, give your tire coefficient 0.9 or something like that and put your motor data. Do not forget this motors have so much rpm and after 6000rpm the torque slows dowmn but that too it downs to 29nm. After that but your final drive and go in a straight line track. If you check your optimum lap and real life data you can find the right coefficient of friction, after that make a chart for a ideal ratio. But every one should put this in mind, gear ratio is all about your feeling if you dont race on a track. I like high torque in low speeds and i liked your first ratio. Nice video, want to buy ko motor and i hope after finishing your video i dont get upset about stupid ko motor. I literally send 5 mails to that guys to get rpm current data. They dont even response. And also i have seen tests with 72/60v compressions it really doesnt matter. And lastly, torque gets higher when you have more current. With low current motor will act like small tiny miny motor.
Props for keeping it honest 100%
He actually clueless about Ko-Moto,pretty funny from where I’m sitting
Thst burn out was sick
How much did you have to spend for every versions?
You ran into a problem I had back in the day with hop up motors on electric rc vehicles. The hotter motors had fewer turns, so less torque but capable of much higher rpms. No one told be I had to gear the truck down. So my hop up added some acceleration but not to end and only lasted a few battery packs because the gearing was preventing the motor from spinning as fast as it wanted to. Got a new motor and smaller pinion gear and top speed went up and the motor ran cooler.
It seriously gear ratio if you can't see that you're blind put a longer gear on it and you'll haul ass and you can have all the torque and power you want but if you have no gear it ain't going nowhere
its like going from a gas to diesel engine and expecting it to be as fast with the same rear gear. There is a reason for example BMW 335d's run a 2.81 rear gear where as the 335i runs a 3.46
Isn't it just more power? So it can run smaller gear ratios. Different motors have different max rpm ratings.. but more kv should give you more power, so it exactly is about changing the gear ratio.
Love your videos man keep up the good work❤love from Nepal 🇳🇵
Try it with the stock 48 tooth rear sprocket!
having a background in RC racing they are 100% correct about the gearing and when u add in factor that your wheels are smaller than original it make it that much worse u can actually burn it up with to low of you could be amazed and what a simple proper gear ratio would do to that bike
I’m still buying KO because they came out and publicly made a comment about this. They admitted they dropped the ball and came clean before this video went live. They may have not prioritized your issues but I don’t anticipate any issues with mine as I don’t run that wheel and sprocket setup you do. I like my 17” Super Moto wheels and would only drop down to a 14” for a local Karting track.
Na I’m good tbh 😮
Also (I was looking this up earlier because it’s come up a few times) but the voltage and current leaving your controller and going to the motor doesn’t have to match the current or voltage leaving the battery. If the motor voltage is lower on this controller than the other controller then even if they both had the same kV windings you’d end up with a lower top speed
Not sure it’s already been said but without a switch it defaults Eco mode.
Yea,he’s probably in Eco,he should really spend sometime learning about Ko before posting a video on it,he is totally clueless.
@@stevemech3787 yea I’m excited for bro. Once he gets it right that fuckers going fly. I want to share my tune lol
discord would have got him right in 20 min.
You'll get it figured out, Mr. Ronster. You always do. :B
Try changing your rear sprocket into a smaller one or a taller wheelset because that motor has so much torque, that has so much power at start and its slow at the top end because you didnt change your gear ratio and you have smaller tires than the stock ones
doesn't (or shouldn't) matter though. its the same rpm/volt as the stock motor, so should be able to manage higher speeds given its a IPM motor and thus should respond better to field weakening than stock.
It may well be tuning (ie controller imposing an artificial acceleration limit), but the notion that 'because gearing the top rpm & torque is lower' is nonsense.
love the vid bro. do you think you could make a new video of the price breakdown of all the parts on your bike and just all the money it costs to have a bike like yours. Thanks bro keep up the good work love u
This E-bike is red
holy shit, sur ronster thats epic! keep up the great work!
the way brushless inrunner motors work is they have kv, the higher the kv means the faster it will be able to spin but will have less torque, the lower the kv you will have less rpm but more torque. from what i can see the ko motor has a lower kv meaning its not as fast but it has more torque. torque is always more useful as it will keep temps down and as you can change the gear ratio with that extra torque you will be able to hit that higher speed. I'm sure some kind of tune will be needed but its a new product and it is how things are. try putting a smaller sprocket on the bike and go back to the 16" wheels. torque is always better than higher rpm.
"it's a new product and it is how things are" bro this is a 3k upgrade, id be fucking heated lmaoooo
Yo bro I love your video’s so much when I watch your videos you just make my day keep it up suronster
My knowledge of ebikes are limited. But i know that electric motors has a Kv-number (not kw).
Kv= the RPM (revolutions per minute) a motor does per Volt that is put into it.
My best guess i that your gear ratio is way of!
you forgot to blur out the plate at 1:25 but since its custom i dont think itll work the same as a reg plate im not sure
Bro I am your biggest fan. Love you hard work, if you have a dream to chase, nothing can stop you. Love you bro. Can I get a shout-out
No im his biggest fan
Bros trying
Most definitely should out preform the stock motor and the bac4000. Unless this works better I will stay stock motor and back 4000. I get 50+ on my set up. Your expectations should be high for a set up like this. Lots of hype over this set up. Seems to be hype in your experience. Love your content on the surrons.
Y'all are out of ur fkn minds if you need to go faster than 55. I don't believe the suspension on these things would even hold up to what I would do with it. Thing is too small to be going 60-70 mph ur nuts.
You should maybe get in contact with the guys from Progressive E. They have a youtube channel which they were having somewhat having issues like yours or worse, as they were one of the first one to get the KO motor and controller to test it out, but they finally got all the bugs out of their tune.
Yea I copied their tune out of the gate it’s really close to personal preference. butter
bro it's like a car, if you want torque on the higher end change the gear ratio
i super respect this honest af review man. been looking into KO but they have some work to do it seems. will keep rockin my solid bac4000 build. OL RELIABLE.
You are as stupid as this clown if not dumber. Blind leading the blind
Ay, I just want a surron soooo badly but it costs soo much!
Its like moped tuning, the gears ratio does make a big difference, especially with powerbands on 2t
30kw what why it doesnt wheelie whole time?
Gearing. Poor configuration.
Stop lying to the people dude. The KO controller is about 1000$. The Bac8000 is about 1500$. Stop lying
Yeah dude so much in this video that don’t add up hey. Ko guys are super helpful and my ko combo rips shreds of my old BAC set up
Wow that customer service is horrible.
loving the vids bro and how’s the truck going it looks sick