droop limiting?

[autodoctor911]

Why limit droop on race car suspension.

I would like to know why in many cases limits to downward travel of the wheel/tire are imposed, purposely unloading a tire completely, rather than let it continue to droop and bear at least some load and continue to provide traction.

I have seen this in the original design of the suspension and also as an retrofit/upgrade on some open wheel race cars with limiting straps, etc.

Why do this?
how can it be beneficial to lose all traction at one corner?

Ideally, wouldn't you have plenty of downward travel at each corner to keep weight from suddenly transferring to the other tires?

[Greg Locock]

The idea is to rapidly alter the balance of the car as you approach the cornering limit, for instance, if you limit the travel of the inside front wheel in a particular corner, the front axle will tend to understeer more once it hits the travel limit, due to tire load sensitivity. A more gently approach, using springs inside the shock absorbers, is used on road cars, to improve the ride.

[apexspeed]

I would like to know why in many cases limits to downward travel of the wheel/tire are imposed, purposely unloading a tire completely, rather than let it continue to droop and bear at least some load and continue to provide traction.

I think you are rolling two subjects into one with this question. Droop limiting is not the same as having no vertical load on a droop limited wheel. The droop limiter will not cause gravity to turn off; if an inside wheel is off the ground, it is not because of the droop limiter, it is because all of the load has transferred off of that wheel.

[Belatti]

I use droop travel limiting in front suspension of low power open wheel cars in a couple of tracks I need to.

The reason? Susp geometry is restricted to the original car supplier and the inside front drags the car in fast full throttle corners. Droop limiting improves speed there but makes the car understeer in mid speed corners and hairpins. Of course, if the laptime balance is positive you prefer using it.

[autodoctor911]

What about the required steering or ?suspension? geometry "drags" the inside front tire on fast turns?

Are you having to run a lot of static toe due to poor Akerman qualities?
Isn't it going to drag a lot on the straight as well?

or Maybe the Akerman affect is too great at small steering angles(large radius turns) and diminishes, or is helpful at larger steering angles(tighter turns)?

I think I can see how the droop limiter is benefiting most of the time now though. On corner exit, as the car pitches back from acceleration, the droop limiter is reached and helps load the inside rear wheel more, giving better traction for acceleration out of the turn.

Is this correct?

I also see how droop limiting at the rear would help the car rotate on turn in, especially trail braking and especially with a locked diff.

[dynatune]

As indicated above it is often used to create a sudden load transfer on an axle provoking a rather pronounced US or OS tendency. There is however also another "effect/benefit" that is somewhat less known. Once the inside wheel is in the air all the load transfer on that axle has by definition "finished", any additional lateral g on the car can only "create" load transfer on the axle where the wheel is still on the ground which in case of a droop stop on the front this would be the rear suspension which then would create a tendency for more oversteer. One can for instance see this in F1 cars running around Monaco where in slow corners the inside wheel is quite often in the air.

Cheers,
dynatune, http://www.dynatune-xl.com

[Belatti]

What about the required steering or ?suspension? geometry "drags" the inside front tire on fast turns?

Are you having to run a lot of static toe due to poor Akerman qualities?
Isn't it going to drag a lot on the straight as well?

or Maybe the Akerman affect is too great at small steering angles(large radius turns) and diminishes, or is helpful at larger steering angles(tighter turns)?

I think I can see how the droop limiter is benefiting most of the time now though. On corner exit, as the car pitches back from acceleration, the droop limiter is reached and helps load the inside rear wheel more, giving better traction for acceleration out of the turn.

Is this correct?

I also see how droop limiting at the rear would help the car rotate on turn in, especially trail braking and especially with a locked diff.

In the cars I mentioned open diff its used (not locked) so I dont use droop limiting at the rear.
The ackerman indeed has a value I dont like and drags in the corners. I dont mind it drags in slow speed corners (you have to brake anyways) but there are some full throttle 200km/h corners and a 120HP car suffers a lot if the fron inner drags.

So, with the bad ackerman setting you limit droop at the front and you gain at those fast corners without the need of extreme toe that drags in straights.