Beauty is pain, as they say! Just stumbled across this channel, its honestly really nice to see concise and well explained topics regarding suspension, which as I look into it seems more and more like an occult magic.
The wheel bearings would be subject to an added moment as a result of the wheel spacer as you said. On the other hand the bearings do have to be able to withstand this to some degree, because this is what cornering forces would impose anyway- although only periodically, not permanently. This brings me to my question/topic suggestion: what are the loads that a car suspension are typically designed for?
The question should be wheel offset to be more clear. Some cars are more sensitive than others. My sports car was actually sold with both high offset (negative scrub) and low offset (positive scrub) depending on version, with the same suspension. Both works well, it just changes the feel a little bit during braking for example, and the Steering effort of course. For an FWD car i would definitely be more careful with Offset changes.
Fascinating video and channel! Question for you about the bearing load line (which runs in the center of the wheel).. my car came factory with a 7in wide wheel, if i change the wheels for a 8in wide wheel (and the offset remains the same).. would using a 0.5in spacer correct the bearing load line?
PS, you are touching on a topic that I see is causing a lot of confusion in people and I am working on a video to address it. Wheel offset is a dimension from the centerline of the wheel to the mounting face. Since it is measured from the wheel centerline, it is not effected by the wheel width, so if you mount 8" wheels instead of 7" wheels with the same offset, the bearing load line will not move.
Great explanation! So many people forget this also applies to wheel offset as well. But when modifying stock cars, the options for changing kingpin location and angle are often limited, and we have to take the good (Track width and contact patch) with the bad (Scrub radius). I have definitely felt the effects of going too far and it really kills the feel of the car, even when it's faster.
Your best bet in that case is to get an updated suspension kit. More and more are available bolt on, and correct old cars flawed design, on top of adding whatever you need for your application. Grip or drift knukles have different mouting points and allow different suspension settings. And example of that is what gktech offers for nissan S chassis. You get larger track, more steering angle if you wish, more or less ackermann, built in lowered car, bump steer correction and so on. If you want your car to handle, the first step is to put sticky tyres on it, the second is to install that kind of thing.
Hello thank you for explaining this make alot more sense, i have already installed 15mm spaces which are far less from the tolerances than your example of 50mm, my car is a Audi TT mk3 do you think its okay given the tolerances of only 15mm or would you suggest I remove them and never use spaces regardless of the depth. Much appreciated:)
Hi Huibert, would I be correct in saying that scrub radius is also affected when changing the diameter of the tire? Something to consider perhaps for the off-roaders
You are correct, because of the kingpin angle. As the diameter of the tire grows, the angle of the kingpin axis means the point where it intersects with the ground moves outboard, making the scrub radius less positive, or more negative.
@@suspensionsexplained So, given no change in wheel offset and therefore kingpin offset, a larger diameter tire will not affect the moments impinging upon the suspension during acceleration or impact but will affect the moments during braking? Given this, the only way to accommodate a change in tire size without a change in any of the moments is to modify the angle of the kingpin axis as well. I presume this would generally mean changing the suspension components. This personally interests me because I am in the market for a long-travel IFS kit for a Toyota Tacoma. IFS kits include longer upper and lower control arms to increase the range of articulation but I am curious to know if the kits are actually designed to maintain factory kingpin offset and scrub radius with a given tire size, which if I presume correctly, is especially important for emergency situations such as sudden braking or encountering a patch of black ice. Good questions to ask before buying. Thank you for your time!
Great explanation! Now I'm curious, does changing the wheel offset by a good amount change this relationship at all? I'm thinking not, based on your diagram? I've got a 2006 WRX which had +55 offset 18x7in wheels originally with 215 width tyres and now had +38 offset 18x8.5in wheels with 245 width tyres. I remember forum members arguing that the offset change would wreck the wheel bearings faster, even though there is no wheel spacers installed? I am thinking that is incorrect. Maybe an idea for a video?
Yes, unfortunately, what you did has the same effect as a wheel spacer would. The change in offset changed where the wheel center is located on the suspension just the same as if you had used a spacer with your original wheels. In your case though the change was 55 - 35 = 17 mm, so not nearly as drastic as the example I used.
@@suspensionsexplained Wouldn't the wider tire, coupled with the camber, change where in the contact patch the centre of the upwards force is? +17mm offset, but +30mm width, the inside of the tire is going to be +2mm
I understand!! But….. how about if is 10MM or 15MM spacers? Not something….. significant like 50MM per wheel? I just wan a opinion cause if even like that parts will be damage eventually I don’t want them cause parts for a German SUV are very expensive!
Thank you. It was very informative. Knowing that, how one could find, or estimate/calculate, kingpin offset and scrub radius of their car? I have a winter wheel set that has slightly different offset and I was wondering how big effect it may have.
With the increasing prevalence of 3d scanners you could check online to see if anyone has scan data. Not likely someone will have it for your specific car, but you never know. You can also sometimes find partial schematics or drawings if you spend a lot of time googling, but that's rare.
you forgot a very important factor, if you have a negative scrub let's say 15mm and you add a small 10mm spacer you tend to go toward zero scrub which is much worse than changing scrub direction as it can cause inherent suspension instability called squirm
I can’t believe it. A no-nonsense, unemotional and well informed video about wheel spacers? Thank you.
Beauty is pain, as they say! Just stumbled across this channel, its honestly really nice to see concise and well explained topics regarding suspension, which as I look into it seems more and more like an occult magic.
I figured a doctah would want something even more technical, haha. I agree!
The wheel bearings would be subject to an added moment as a result of the wheel spacer as you said. On the other hand the bearings do have to be able to withstand this to some degree, because this is what cornering forces would impose anyway- although only periodically, not permanently. This brings me to my question/topic suggestion: what are the loads that a car suspension are typically designed for?
The question should be wheel offset to be more clear. Some cars are more sensitive than others. My sports car was actually sold with both high offset (negative scrub) and low offset (positive scrub) depending on version, with the same suspension. Both works well, it just changes the feel a little bit during braking for example, and the Steering effort of course. For an FWD car i would definitely be more careful with Offset changes.
Fascinating video and channel!
Question for you about the bearing load line (which runs in the center of the wheel).. my car came factory with a 7in wide wheel, if i change the wheels for a 8in wide wheel (and the offset remains the same).. would using a 0.5in spacer correct the bearing load line?
PS, you are touching on a topic that I see is causing a lot of confusion in people and I am working on a video to address it. Wheel offset is a dimension from the centerline of the wheel to the mounting face. Since it is measured from the wheel centerline, it is not effected by the wheel width, so if you mount 8" wheels instead of 7" wheels with the same offset, the bearing load line will not move.
Great explanation! So many people forget this also applies to wheel offset as well. But when modifying stock cars, the options for changing kingpin location and angle are often limited, and we have to take the good (Track width and contact patch) with the bad (Scrub radius). I have definitely felt the effects of going too far and it really kills the feel of the car, even when it's faster.
Your best bet in that case is to get an updated suspension kit. More and more are available bolt on, and correct old cars flawed design, on top of adding whatever you need for your application. Grip or drift knukles have different mouting points and allow different suspension settings. And example of that is what gktech offers for nissan S chassis. You get larger track, more steering angle if you wish, more or less ackermann, built in lowered car, bump steer correction and so on. If you want your car to handle, the first step is to put sticky tyres on it, the second is to install that kind of thing.
Great chanel! I love it!!! What do you think about increasing the length of the upper and lower wishbones instead of using spacers?
LOVE THAT E TYPE!
Just for you, John.
Hello thank you for explaining this make alot more sense, i have already installed 15mm spaces which are far less from the tolerances than your example of 50mm,
my car is a Audi TT mk3 do you think its okay given the tolerances of only 15mm or would you suggest I remove them and never use spaces regardless of the depth.
Much appreciated:)
Hi Huibert, would I be correct in saying that scrub radius is also affected when changing the diameter of the tire? Something to consider perhaps for the off-roaders
You are correct, because of the kingpin angle. As the diameter of the tire grows, the angle of the kingpin axis means the point where it intersects with the ground moves outboard, making the scrub radius less positive, or more negative.
@@suspensionsexplained So, given no change in wheel offset and therefore kingpin offset, a larger diameter tire will not affect the moments impinging upon the suspension during acceleration or impact but will affect the moments during braking?
Given this, the only way to accommodate a change in tire size without a change in any of the moments is to modify the angle of the kingpin axis as well. I presume this would generally mean changing the suspension components.
This personally interests me because I am in the market for a long-travel IFS kit for a Toyota Tacoma. IFS kits include longer upper and lower control arms to increase the range of articulation but I am curious to know if the kits are actually designed to maintain factory kingpin offset and scrub radius with a given tire size, which if I presume correctly, is especially important for emergency situations such as sudden braking or encountering a patch of black ice. Good questions to ask before buying.
Thank you for your time!
But why is rwd positive and fwd negative?
Great explanation! Now I'm curious, does changing the wheel offset by a good amount change this relationship at all? I'm thinking not, based on your diagram?
I've got a 2006 WRX which had +55 offset 18x7in wheels originally with 215 width tyres and now had +38 offset 18x8.5in wheels with 245 width tyres.
I remember forum members arguing that the offset change would wreck the wheel bearings faster, even though there is no wheel spacers installed? I am thinking that is incorrect. Maybe an idea for a video?
Yes, unfortunately, what you did has the same effect as a wheel spacer would. The change in offset changed where the wheel center is located on the suspension just the same as if you had used a spacer with your original wheels. In your case though the change was 55 - 35 = 17 mm, so not nearly as drastic as the example I used.
@@suspensionsexplained Wouldn't the wider tire, coupled with the camber, change where in the contact patch the centre of the upwards force is?
+17mm offset, but +30mm width, the inside of the tire is going to be +2mm
Great explanation, thank you ..)
I understand!! But….. how about if is 10MM or 15MM spacers? Not something….. significant like 50MM per wheel? I just wan a opinion cause if even like that parts will be damage eventually I don’t want them cause parts for a German SUV are very expensive!
Thank you. It was very informative. Knowing that, how one could find, or estimate/calculate, kingpin offset and scrub radius of their car? I have a winter wheel set that has slightly different offset and I was wondering how big effect it may have.
Unfortunately, without the drawings or CAD of the suspension it would be almost impossible to measure those parameters.
@@suspensionsexplained Is it available from manufacturer or some other sources? 2019 Chevy Bolt.
With the increasing prevalence of 3d scanners you could check online to see if anyone has scan data. Not likely someone will have it for your specific car, but you never know. You can also sometimes find partial schematics or drawings if you spend a lot of time googling, but that's rare.
you forgot a very important factor, if you have a negative scrub let's say 15mm and you add a small 10mm spacer you tend to go toward zero scrub which is much worse than changing scrub direction as it can cause inherent suspension instability called squirm
Stay under 38 mm. My car handles better. Will shorten life of hub bearings. If I need to change them, no biggie.