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View Full Version : Auto-X wannabe suspension tech (warning newbish)


Maeda
05-21-2003, 03:13 PM
Ok, so it's come time to start studying suspension...

What i've come to understand
Body Roll - Side to side leaning
Camber - How vertically tilted the wheels are (more means more grip but also less tire patch)
Toe - How horizontally tilted the wheels are (toe in toe out)
Castor - rebound?
Chassis Flex - how the chassis dampens or absorbs road information( or imparts it to other parts?)

Ok, I'm pretty sure I don't want the stiffest suspension created by man because it imparts the road information on to the tires correct? And too stiff a suspension also dulls road input to a minimum right? Like most everything with cars i'm looking for a balance?

So, if I upgrade my busted springs, to something like 6 kg front 4 kg rear, i'll have less body roll, but more stress to the tire?
Same thing goes for just about everything else right?

What happens if i get a nice tire with a small side wall? where does that force go? increased tread wear?

How much body roll do you need to drive well... so I guess i'm asking how much input do you need to drive well? Is that all driver dependant?

Lastly!
How do I tell if the car is understeering? isn't that a matter of opinion? I thought understeer is a per-turn condition?

sorry for the vast amount of questions, but then again i know nothing, and i can't really find the theory behind suspension tuning in the search... so i thought i'd try to hit it on the nose...

BTW. Is there a maximum boost-ish book thats on suspension instead of turbo? A Suspension bible so-to-speak?

AKADriver
05-21-2003, 04:41 PM
Caster is also known as kingpin inclination. It's an angle between the steering axis and vertical. If you look at the front struts (the steering axis) in the car, you'll see that they're slanted back a few degrees. Caster can only be adjusted in our cars with aftermarket tension rods, set shorter to pull the bottom of the strut further forward. The effect of caster is to create negative camber on the outside tire when the wheel is turned.

Chassis flex is bad. It allows suspension parts to move in ways they weren't designed to move, affecting suspension geometry.

Changing spring rates won't affect wear on the tires so much (though handling biased strongly to one end of the spectrum or the other can create uneven front/rear tire wear). Cars come delivered with soft springs primarily for comfort. At some point, though, a spring can be too firm to adequately allow the suspension to move over surface irregularities on the track.

Same with a hard sidewall tire - that bump force goes to the springs and dampers (where you want it) but also to the bushings, chassis, and your butt (where you don't).

Body roll is preference, and it's affected by the amount of grip you have. With a high-performance street tire in the stock size, the stock suspension is a good learning tool. But to some people it's upsetting. As grip increases, also, the ultimate amount of body roll you'll experience will increase.

Understeer is when the front tires begin to slide before the rears. 99% of production car suspensions are tuned for this to happen in steady state cornering. Just about any car can be induced into under/oversteer in certain situations, though; a rally driver's "flick", a yank of the handbrake, or even just jumping off the throttle, can send my normally understeering VW into dramatic oversteer.

As for books, I know Carroll Smith's "...To Win" series are good (Drive To Win, Tune to Win, etc). There are others as well, some people will surely chime in.

Maeda
05-29-2003, 10:07 AM
Originally posted by AKADriver
There are others as well, some people will surely chime in.

Chime in people! I still need help =\

shameless bump...

AREITU
06-01-2003, 04:11 AM
From what I gather, caster is the angle of the shock tower in relation to the ground. Turn your wheels all the way in one direct, and see how they're tilted? That's caster.

German cars have a TON of it, presuemably to increase steering feedback, lessen understeer a little, and tighten turning radius...

240racer
06-07-2003, 09:41 PM
if you want the bible on suspension it's called Racecar vehicle dynamics by Milliken. http://www.millikenresearch.com/rcvd.html

it's kinda an engineering text with lots of math, but I own it and really like it.

there are lots of other books too:
http://www.amazon.com/exec/obidos/ASIN/1557880646/builyourownracec/102-9976560-3102552
check those out.