My car needed new shocks about five months ago. Fortunately, there's group buy on a coilover system that I can get into. I love the increased performance. Probably the dampers aren't stiff enough for frequent track use, but enough for me to have fun for spirited driving. I find the coilover pretty streetable, which is nice.

Enough of my intro. I have a question regarding preload. Before that, let me show you guys a few pics (I guess it may help, but couldn't hurt)




http://lh4.google.com/image/vi ... xyNeCEw/s800/P6021372.jpg

As you can see, the fronts has a pillowball top mount (adjusts camber), adjustable endlink mount (not real sure what's the true function of it) and adjustable lower mount (ride height for the most part). The rear is only ride height adjustable. All shocks have adjustable damping (36 levels). Bump and rebound are adjusted simultaneously.

The car lose about half of its available stroke when it's on the ground. The question is if I decide to make minor ride height change (I guess within half an inch, may be a bit more) by turning the spring seat/perch, do I increase preload? If I change the rear ride height, will that increase spring preload at the same time? I talked to the manufacturer's tech support. They said if I change the ride height through the front spring seat instead of the lower mount, I'm changing preload. They also say changing the rear ride height in any means will change preload also. I don't think that's right since I still have plenty of travel left before extra pressure can be put on the springs for the front, and I can't put extra pressure for the rear spring unless I go as high as it can go. What's the true answer?

Note: The manufacture default for the front spring location is where the spring has no room to move up and down easily without putting tension to it, just like the pic for the fronts before they go on the car. The rear has no default location. The stock top cap is used for the rear coilover as part of the assembly.

Yes, it increases preload, but that doesn't matter. On your car the motion ratio will remain pretty much constant, so the preloads only effect is to raise your ride height.

More preload = less droop travel, and more bump travel (because of a higher static ride height)
Less preload = more droop travel, and less bump travel (because of a lower static ride height.

Preload does NOT effect the rate of the spring, despite what many a website will tell you - they are talking rubbish.

Set the preload so that the static ride height is where you want it (this may also be acheivable via the adjustable bottom mounts you say you have).

At your chosen ride height make sure that the camber is sensible (manufacturers recommendation would be fine, maybe a touch (0.5°) more negative if tyre wear isn't a problem.

Minimum preload is when, with the spring/damper unit OFF the car, the perch just touches the spring. You DO NOT want the spring to start rattling around when you hit full droop. Maximum preload is when you run out of droop travel (i.e. the car is at maximum ride height) or the springs go coilbound.

I would like to set the static height through the adjustable front lower mount, but the hole was enlarged 1/8 inch too big. I didn't want to go through the trouble of setting it right, so I just turn the spring perch/seat up to my desired height.

The manufacture tech support also states that changing the preload (by moving the front spring perch/seat up) will also change front damper rebound rate. Since the motion ratio is constant, it doesn't change the rebound rate, right?

I have the front camber set at -1 degree (I think that's the most negative front camber recommended by Toyota). The rear is a torsion beam, so it's stuck at -1.5 degrees. I don't see any kind of bad camber wear (probably my tire is too hard lol. I use Michelin MXV4 Plus). The current setting is sufficient for me at the moment. Since I have cracked front bump stops (Probably the road is crappy enough that I hit the bump stop without knowing it did), I may change the front camber. If I change the front camber to -1.5 degrees, wouldn't the car start to be less responsive? Will it be not suitable for frequent freeway driving (let's say 300+miles in a day under hot weather)?

Also, what's the true function of the endlink mount? It's adjustable and I know it'll affect body roll if they aren't in about the same location for sure. What else can it affect?

I don't see how the spring preload will change the damper rate - the damper can considered separately. Unless of course the damper rate varies though it's travel (it shouldn't), in which case static ride height might change it. If someone else knows differently (damping isn't my strong point) then correct me.

-1° front is probably about right. You don't want too much more. More will increase grip (slightly), but probably give the car more oversteer and wear/heat your tyres too much. If you're happy with it, leave it. My point was that altering the ride height changes the camber, so you'll need to reset it (which you have). A lot of people fit lowering springs thinking it'll improve the car, but forget about camber curves.

By endlink mount, do you mean the bit that attached the coilover to the wheel upright? It simply moves the ride height up/down without changing preload. In some ways it would be better to use this, as you'll have more spring length to play with (as long as you ensure the spring cannot come off the spring perches at droop.

If you have preload or the mounts different side to side you'll change the handling slightly, probably by preloading the anti-roll bar (sway bar) and moving the corner weights (which aren't at all critical on a road car) around. Best to keep things pretty symmetric if you can.

To put it simply, set the ride height. Ensure camber is okay. Use as little preload as you can if you do adjust your mounts, but don't worry if not. Then set your dampers to a sensible setting - probably around the halfway point on the adjustment, erring slightly softer (more for trackdays when you are not remotely concerned by ride comfort, just wheel control).

Enjoy!

Quote from tristancliffe :

I don't see how the spring preload will change the damper rate - the damper can considered separately. Unless of course the damper rate varies though it's travel (it shouldn't), in which case static ride height might change it. If someone else knows differently (damping isn't my strong point) then correct me.

I don't think any fluid dampers are completely linear as you get compression effects near either end of the travel. Dampers are supposed to work best when kept in the middle of their travel.

Also, unlike the linear dampers in LFS, it is typical four most dampers to have seperate 'fast' and 'slow' responses, although it would only been on top end shocks that these become seperately adjustable. That way you can have a soft ride over bumps without the body bouncies like mad after going over speed humps. I haven't seen the damper curves used in Ferrari Challenge at work, but I know they were obtained from Ferrari. Fast damping is only about 10%/30% critical (bump/rebound) but is a lot higher at slow speeds (quite close to critical I'm told, but as stated I've not come across it yet). It is of course worth mentioning these are from the 430 racecar (so much stiffer) but I doubt any modern roadcar would have linear dampers.

Quote from tristancliffe :

By endlink mount, do you mean the bit that attached the coilover to the wheel upright?

The endlink mount is the black tab that below the spring seat of the front coilover. One side of the endlink goes there and the other end goes to the front sway bar. I notice it can control body roll since I find the car lean more when making right turns and use that to correct the problem. But would like to get a better understanding of what it does.

I also heard if you lower the car too much, it'll affect the roll-center especially vehicles with double A-arm (my car sure isn't one since there's only one lower arm on each side). In my case, I can get it to be at whatever ride height without affecting it too much or it's the opposite?

Quote from madbikes :

The endlink mount is the black tab that below the spring seat of the front coilover. One side of the endlink goes there and the other end goes to the front sway bar. I notice it can control body roll since I find the car lean more when making right turns and use that to correct the problem. But would like to get a better understanding of what it does.

I also heard if you lower the car too much, it'll affect the roll-center especially vehicles with double A-arm (my car sure isn't one since there's only one lower arm on each side). In my case, I can get it to be at whatever ride height without affecting it too much or it's the opposite?

Ahok. When the car is at it's ride height, you want to set those so that there is no load on the sway bar. In pitch/dive the roll bar should remain free, and only come into play in roll (as I'm sure you know). You shouldn't use these adjusters to control body roll in any other way - stiffer bars or different drop links are the only ways to do that sensibly.

Raising and lowering the car will move the static roll centre. Lowering the car will lower the RC, and vice versa. At the same time you will also be raising and lowering the CoG at that end of the car, but by a different amount (the CoG is fixed on the car body, whilst the RC is defined by the movement of the suspension arms). So raising and lowering the car will change the roll couple (the effective distance between the RC and the CoG), which will change the balance of the car (less so if you do that same at the rear). However, unless you are really dropping the car to Touring Car levels of ride height, or are routinely driving the car 'On The Limit', the change will be pretty negligable I'd have though.

So my overall advice still stands. Set the ride height to what you want, keeping the difference between front and rear roughly the same. Make sure the springs won't go loose at droop. Reset the camber. Make sure the sway bars are unloaded when the car is level. Drive. Enjoy.

If it was for motorsport use you'd have to look more closely at roll centre heights and roll couples, but that's a bit too much effort for a road car if you ask me.
So my advice still stands

Thanks