Spring Explanation - bump, droop, compression, travel, diameter, rate (Part 1)

In this video I go over springs - their rates and how to understand them, diameters and how to select the right mounts, bump vs droop or compression vs extension.
This is the first part. In the next video ( • Shock Explanation - tr... ) I cover the shock/strut and how that impacts the overall suspension travel, how it impacts bump vs droop or compression vs rebound/extension.
All this is leading up explanation to what and how I am going to be adjusting on my Ohlins R&T because Ohlins don't play nicely with camber plates (they were made to work with stock top mounts), and there is only a limited amount of total suspension travel.
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[@sr20dett1000]

I have a e46. Almost all the coilovers come with pitch not flat ride. The only one I found that comes with flat ride is kw street comfort. The coilovers I want comes with a stiff 457lb front spring rate. I want to switch that to the front to the rear and the front change it to a 225lb should give me a 10% flat ride. I'm just confused on the spring length. I don't mind if it's over dampened.

[@mrgizmo7975]

@sr20dett1000
Welcome to the E46 family :). So with a 225 spring you will need to preload it about 2 inches more (assuming it's the same unloaded height as the 457, say like 7") to get to the same ride height as you would with a 457. Does the shock body have enough threads to adjust the bottom spring collar upwards that much? What length spring is the 457? I might try to get the 225 in at least an inch taller, that way the extra inch of unloaded length will only require you to preload it 1 inch via the collar on the shock body.
The other point you made, yes you will probably be over dampened. Normally shocks are valved to take about +/-20% spring rate. You will be going down almost 50%. So even at full soft shock setting you might still be getting a subpar ride quality. Maybe call kw to see if they can custom valve the fronts for your specific intended needs?

[@sr20dett1000]

@@mrgizmo7975 I'll probably get a 9 or 10 inch spring. It has a helper spring too. I think if I use the same spring length the coils will bind.
I'm using this spreadsheet
www.fatcatmotorsports.com/FCM_Ride_Harmony_BMW_E46_M3_Online/FCM_Ride_Harmony_BMW_E46_M3_Online.htm

[@mrgizmo7975]

Yeah swift/hyperco make custom springs and they publish the free height and the total travel on the springs before coils bind. Good to see you are already using Shaikh's site. 👍 You only need the helper if the primary spring is not tall enough to stay seated at full shock droop.

[@sr20dett1000]

@@mrgizmo7975 the length of the 457 is 7 inch with a helper springs. The 457 spring deflection1.86 inch spring loaded is 5.14. the 225 will deflect 3.79 inch loaded 3.21. Won't it coil bind with just 3.21 left.

[@mrgizmo7975]

What is the total travel of the kw front strut? And what is the bump component (remember the shock will compress a few inches as well to sit at equilibrium height with the spring and what will be left to compress until bottoming out is the bump travel). If shock bump component is more than 3.21 before it reaches bump stops, you will have coil bind. Think of it slightly differently, if you remember stock front strut, the spring rate is about 170, and the unloaded total length of the spring is about 11-12 inches. So you will need to get a pretty tall spring, if you want to run a 225, which is not that much stiffer than stock front. That said, outside of valving the kw front strut to take such a low rate, I dont know the total travel it has and whether you will be able to run a 10-11 inch spring on it (like physically get the spring on the bottom collar and be able to tighten the top mount on it).