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Adjusting Ride Height Using Coil Over Suspension

Motorsport Wheel Alignment Fundamentals

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I don't fully agree that adjusting spring preload to adjust ride height wont influence the suspension control .

I fully agree that pre load doent change sring rate and as long as the weight on the strut is more than the spring pre load it should theoretically have o affect.

However if the wheels leave the ground the amount off pre load I have set will influence the control my damper has when the wheel touches the ground again.

For example if I'm running 100kg of spring pre load there is always is a 100kg of force acting on the damper even if the wheel are off the ground this helping the damper keep control when the wheels touch the ground again. If you hit a bump and the vehicle comes off the ground and the spring is able to com off it seat by a 100mm at full extension when the vehicle lands the dampers shaft speed will increase drastically as there is no spring tension/resistance to control control the shaft speed for fist 100mm of travel till the spring starts to compress and giving the dampers a difficult task to keep control.

Pre load helps control damper speed when the suspension becomes unloaded....I race enduro bikes and we use spring preload to as a tuning tool not to adjust ride hight...for that we use internal spacers to limit full extension.

I do agree that with circuit racing you generally don't unload the wheels like you do in off-road racing so preload will have little gain.

Is my thinking correct?

Your thinking isn't correct. The damper resistance is independent of the spring resistance in compression, or extension for that matter.

What I believe is happening is you're confusing the affect preload has on initial compression with damper control, as they're both resisting the suspension compression. When the bike wheel is in the air there is, as per your example, still 100kg of load on the spring. When landing the wheel makes initial contact with the ground and needs to apply 100kg of load to the spring before it starts to compress the spring. From the rider's viewpoint, this will probably feel like a harder hit than with less preload, giving the impression the damping is firmer - it isn't.

You will probably notice this on stutter bumps, too, with the bike kicking more at the rear with a little less drive.

If you're otherwise quite happy with the static ride height, I'd suggest a longer spring, of the same rate, that will allow you to set the spring adjuster lower on the damper for the same static position. For the most part the bike will respond exactly the same, but there will be two, similar, affects when landing - it will be a little gentler and more controlled because the spring will start to absorb the landing forces more gradually and over greater travel, and at least as important, the damper will have extended further and so have more travel to resist the landing forces. Assuming you've high and low speed damper adjustment, you may find you can reduce the low speed a click or two.

There also seems to be a little confusion in the way the damper works - the greater the velocity the greater the resistance, assuming you mean a very light helper spring, rather than an unseated spring, the initial resistance to compression will depend on how quickly it is being moved - slowly will give little resistance, quickly will give greater resistance.

As you say, 'off road' competition is rather more complex than flat track/circuit stuff because there is not just a need to control the wheel assemblies, but control the chassis as it relates to the ground, especially when landing over jumps. Some of the 4 wheeler damper and spring setups are insanely complicated.

Gord thanks for your detailed explanations. I does make sense now.

I'd add to this discussion, the pre-load can/does have an effect at the point the tyre is transitioning from being off the ground to being in full contact, for the reasons you guys have been discussing already.

In the most part, I tend to avoid talking about it much because it generally leads to more confusion for people, until they understand that preload doesn't affect the rate for a linear spring (which I know you guys DO understand!)

In circuit racing, you can often spend a surprising amount of time with the car on 3 wheels. Preload can be a useful tool in tuning the transient balance at the point where the tyre is coming into/losing contact with the ground. But it is a much more nuanced effect, certainly compared to the concept of spring rate!