Droop Travel

[theawesomeone]

Quick question for the suspension gurus. When using spring rates high enough such that the weight of the car only compresses the springs 1-2", are there benefits to having droop travel beyond the point at which the spring is fully unloaded? In other words, to have the suspension extend further such that the spring would actually be loose. This would be for a mid-engined racing car, about 2000 lbs, spring rates about 700 lbs/in front, 450 lbs/in rear. I can see that in a corner, when all the load has been transferred off say the inside front tire, instead of the tire coming in the air, the weight of the unsprung mass could still be touching the road. However, there are several racecars that routinely lift tires in the air.

 

[GregLocock]

There's no good theoretical answer, I suspect. One way round that is to use multi rate springs, and travel limiters, and then decide which compromise works for you.

With GE cars lifting a wheel provides the maximum restoring moment to get the car flat again and the aero working properly.

Cheers

Greg Locock


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[JayMaechtlen]

Don't forget to restrain/retain the springs so that they stay in position at full droop!

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[evelrod]

More from the practical side. Having the springs unrestrained in such an exaggerated 'droop' makes for some very interesting "moments" when all comes back together with the roadway...usually exiting a turn at speed. I can tell you from personal experience, that is NOT the best thing to happen if you are in a group of cars.

I race two cars that are noted 'wheel lifters'...Lotus Cortina and Mini Cooper. One front, one rear. The Locort is McP strut with 300# springs and a 1" anti roll bar that, in concert with restricted rebound on the Koni inserts keeps the springs in contact with their seats. On the Mini, a rear bar and similar rebound limits on the GAZ's limit wheel travel...again, not a good idea to have the links to the primitive Mini suspension system go slack and probably fall out. ;o(

Several production cars have used limiting 'straps' or such to prevent too much droop. I just have not seen 'droop', or at least, excessive droop as a problem in modern cars. Road cars and NOT the off road monstrosities that have wheel travel approaching or exceeding TWO FEET!

Rod

 

[theawesomeone]

Thanks for the replies guys. If I wanted to have droop travel past the point where the springs are unloaded, I can put in extremely low rate "helper" springs to keep everything in place. I'm just not sure if there's any benefit in doing so. I found it interesting that some F1 cars use zero droop in the front, meaning it's already at maximum extension at its static ride height.

 

[GregLocock]

"some F1 cars use zero droop in the front" .../because/ they are GE aero cars.

Cheers

Greg Locock


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