Proper ride height for Track
 

As the title says. I've always been told you have to allow for travel in the suspension. So what's that leave? Would it be get the car as low as possible without rubbing under max load? Or is it as long as the car is corner balanced properly it all falls into place. Or both?

Subd.

Someone has to know the height were things start to bind or another word if I'm using it wrong, we're going to low starts to hurt the travel of parts. We need someone like in the subi community with RCE where they would dyno (not a HP dyno) a car with their springs and they had all the computers and travel info and such to see what worked best.

I do know, unless you build new spindle arms like we saw that one company do, normally you don't go very low because of the binding issues. Somewhere in the 1/2" area maybe. Every car is probably different though. For example RCE refused to make a "lowering spring." They wanted a performance spring. So 10mm and 15mm drop were your only choice. Any lower and you'd hurt performance vs help it.

That's what I like. I know lowering to some extent is needed for better aero dynamics or reduced drag.

You have to watch your shock travel. Think you want to be about in the center of it when sitting still. If you go too low. You are out of shock travel when hitting a bump, and you have to have the compression damping set too hard to resist bottoming. And that stiffens up the ride too much.

Lowering the car lowers the CoG to improve mechanical grip.

If you have a splitter/flat-floor/diffuser then you'll get some down-force, but the underside of a Z34 is pretty dirty from an aero perspective, so we are really limited to splitter and wing and that is really about killing hi-speed lift than anything else.

In terms of the amount of bump and droop, I would not go any lower than 55-60mm of bump and that implies a front wheel rate of 400 lbs/in as a minimum (this is about 2.5 times the OEM Z34 wheel rate).

Because I like to run the rear a bit softer, you'll need some rake on the car, but beware roll-centre height differences that are more than 6-8".

This can be difficult to do with OEM suspension, and unless all the bushes are changed for solid (heim joints or - say- delrin bushes), it will all be moot in any event.

You do not want your car to hit the bump stops under braking (will trigger the ABS or provoke a lock-up), or in roll (in roll the spring rate rises dramatically depending on bump-stop material) and the will cause understeer at front or oversteer at the rear if it happens - and it will be dramatic !! If the corner is bumpy and you are a millimetre off the bump-stop, then hitting a bump can be the difference between a dynamite corner entry/exit and the car flinging itself at the scenery with zero time to catch it.

This is one reason why I run 18" wheels with small diameter (645mm-650mm) tyres because I get a free CoG drop of 25mm and the suspension angles remain (near-enough) to OEM settings.

However, a car setup for the track will not be a pleasant daily drive or even road drive as it will be too stiff to counter low ride height, have no compliance, follow tracks in the asphalt and generally be a PITA.

Tread your own path.

RB

Very nice info. Makes a lot of sense.

Depends on track first then spring/coil setting for the tire

So if you will bottom out adjust the coils/springs fittingly then not too stiff depending on what the tire can handle...

Stiffer and lower setups are more for road courses

Stock height/no sway bars/high spring settings/slicks are for auto x setups...helps with turn in

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No, most classes are camber limited for Z. The camber is more important than the ruined roll centers in autocross (especially on concrete). We lower the car as much as possible that doesn't run out of shock travel and/or cut the tire down. You also won't find a Z racing on this planet that does not have a front roll bar. I tested 4 different ones myself.

There are a million variables on how to set the car up for a given purpose (road race, autox, etc). Rules for the class generally trump your initial set-up goals, so you make some sacrifices along the way.

For heavily aero'd cars, by that I mean flat bottom, front air damn splitter/winglets, multi tiered rear wings, etc), the ride height is CRITICAL! The aero grip from maintaining proper ride height (something like 4-6cm) trumps mechanical grip from a softer set-up. That said, you still want the springs as soft as you can go to maintain this.

Suspension set-up is also heavily dependent on tires. If you are going to run 300mm super soft avon hillclimb tires, you are going to have to run a much different set-up than 400tw michelins.

My car is probably a full 2" lower than stock (this is with very short motons at the time). Even though the one side is loaded, you can see that the other side is off the ground, but all that much higher than what a factory ride height would be. 1000lb spring on the front/ 850lb in the rear. A little on the soft side for concrete at 2900lbs and 315 A compound hoosiers. If you tried to run this set-up on a road course as is, it would be a hell of handful.
http://farm6.staticflickr.com/5496/9...178c47e7_c.jpg

experience/knowledge corrects me...

:thumbup:


edit:

forgot where I am

:tup:

Well then I have no Fing idea where to start haha.

Sub'd

These springs are close to those that the Z34 NISMO RC ships with and are what I would expect as a start for road-racing on slicks - or sticky R-spec's - with large front bar (1.25" or maybe 1.5" hollow) and a small rear bar, but only when the suspension bushes are stiffened right up.

I'm not sure why you'd consider this to be a handful on a road-race circuit unless you reckon it would be too twitchy given the stiffness in the suspension - but our circuits here in Australia are (relatively) smooth - there are a few (like Wakefield Park in NSW and Sandown in VIC) that are bumpy, but the really quick ones like Phillip Island are quite smooth and reward driver committment and a stiff chassis.

Anyway, back to the OP - beware running the car too low, suspension arms need to remain relatively flat and you need enough "bump" to avoid bottoming under braking and bumps which will make the car lock wheel(s) and dart/break-away with little warning

RB

Subd

Im in

So with all this being said. How do I decide what's a proper spring rate for a particular weight of the car?