New for Suspensions!

[Claude Rouelle]

P^squared,,

It seems we are on the same wave length

Just a simple question (answer of which can be useful to many readers here): How will you change the ride height?

Claude

[P^squared]

For suspension systems employing a pullrod / pushrod actuation mechanism, ride height adjustment is simply a matter of varying the length of the pull/push rod ( vary the distance between the bracket on the wishbone, and the bellcrank mounting point ).

This task becomes easier if you have opposite handed rodends at the two ends of the tube. Then it simply becomes a matter of turning this tube to vary its length.

Similar adjustment can also be achieved with direct acting dampers as well.

Using spring preload to get the same effect would limit your droop travel, while ( in extreme cases ) also altering suspension characteristics in bump.

[Claude Rouelle]

P^squared,

I assume you are thinking abut a car with pull or push rod, no direct activation

In that case

1. IF you use the spring perch position to change the ride height you will effectively change the amount of your damper possible droop and bump travel but you will also change the position of your rocker and in some case that will tremendously change the motion ratio and therefore your wheel rate (remember that the wheel rate (or if you want suspension stiffness) is related to the SQUARE of the motion ratio) If I was you I would not adjust your ride height with the spring platform (some call it perch) unless you really know that you are doing and have beforehand tested all different adjustments on a setup pad with scales

2 . I have seen teams in FS competitions changing the front and rear ride heights for the acceleration, apparently putting the ride heights back where they wanted them for the skid pad event and not finding back the car handling they were used to. Static corner weight and crossweight can be VERY sensitive to pull or push rod length change. on a FS car 0.5 kg (1 lb) between the LF and the RF static corner weight can be a huge difference) I have seen students and professionals completely screwing up their car handling and making it very asymmetrical (with for example understeer in left end corners and oversteer in right end corners and systematically looking, again for example, the LF wheel in left hand corner entry....) by changing the pull or push rod length with a difference of only a 1/2 turn, if not less. That is why a) unless I am working with a very experienced team I would not change any push or pull rod unless the car is on setup pad with 4 scales) b) I think there is an advantage of using shims (instead of rod end length or turnbuckle) to adjust the ride height with push or pull rod: usually less mistake are made as you can always double check the length of the installed shims stack, while many students do not meticulously measure the eye-to-eye (rod end center to rod end center) of their push or pull rod length (PS: I assume that your chassis and the rest of your suspension is symmetrical in both geometry and stiffness..... with no asymmetry in rod ends and damper residual friction) but that is another - big - chapter!!!)....

Here is a proposed solution to avoid any of the mentioned pit falls; when you design your rocker make sure you have 2 holes for your push or pull rod: one for low (or "normal") ride height and one for high ride height as for acceleration. When you change for one to the other ride height you will have less risk of creating an asymmetrical car. Be aware though that you motion ratio will be different.

If you have direct actuation you can imagine having 2 pick up points on your chassis for your damper/ spring units.

Hope this helps

Claude

[P^squared]

Claude,

There are potentially better ways of doing it with a direct actuating damper.

http://www.fsae.com/forums/showthrea...g-Damper/page7

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