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Rally/off road suspension geometry

Suspension Tuning & Optimization

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Hi.

For a long time now I have been trying to understand things like anti-dive, anti-squat, roll center and so on.

But what I struggle with is this:

Does (for example) anti-dive also affect how the damper/spring handle bumps in general?

If you add a lot of anti-squat, will the car then handle bumps porly?

In rally and rallycross (european rallycross) you need to run a very soft suspension.

So it seems natural to think that a lof of Anti-dive and anit-squat (on a RWD car) would be beneficial?

But maybe not. And if not: maybe a third element spring to handle anti-dive would be smart?

Any input is greatly appreciated. Thanks' :)

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I have watched the anti-effects video a few more times.

So these anti-effects do not play any role if you are just rolling over bumps (like at the end of the straight before you hit the brakes, or rolling through a long corner). The individual dampers and springs will work just like they should (do all the work).

The anti-effects play a role during longdidudinal weight transfer, so in the braking or acceleartion zone (and especially heavy breaking and heavy accelerating?).

So if the car dives so much under braking that you are bottoming out, you could add anti-dive.

But that also stiffens up the front suspensoin during that brakes phase, meaning you get less grip (espcieally in rough/bumpy surface).

So for rally/rallycross it is probably better to just add ground clearance (all though that might be a disadvantage during the middle section of the corner).

On a rallycross car having grip under braking and accelartion on extremely uneven surfaces is crucial (usually more uneven than many "modern" rally stages).

So I guess zero anti dive would be a good place to start?

But then if you go to tracks with very clean/good tarmac braking zones you could add anti-dive (if you don't wont to add stiffer springs, since that would change the ballance. And you might not wont to change rear springs because there is gravcel sections out of the corner).

Soft springs (2hz?) and very good dampers.

And then potentially a front heave spring (3rd element) could help with anti-dive?

In rallycross you often start 5 cars side by side on relatively good tarmac and drive only 5 laps. So the race is actually like 50% dragrace. The car that leads in to the first corner will often win the race.

So you probably want some anti-squat for a perfect launch. (25% to start with?).

Then on the other hand, traction out from the corners is also extremely crucial , and here the gravel or tarmac is often very bumpy (often transitioning from tarmac to gravel as you exit the corner, with deep ruts).

But if you have gravel out of the corner you are feathering the thottle, so the weight transfer to the rear not not so big, and the negativ effect of anti-squat might not be a problem. Only if you have bumpy/uneven tarmac where you are accellerating hard?

For referance, this is the type of Rallycross I am talking about (RWD, 250-350hp, about 1000kg, 57% of the weight over the rear axle): https://www.youtube.com/watch?v=EbXpSpIxow4

And in this video Andreas Bakkerud (top contender in FIA World Rallycross Championship) is commenting together with Andrew Coley on how soft setup the fastest guy has (he was by far the fastest the whole weekend).

We usually reply within 12hrs (often sooner)

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