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?

Well run as stiff and low as you can without bottoming out lol. Sort of tongue in cheek but true.

Lower CG = better, but you need(by the book) at least 2" of compression travel. up to 3 is better. So run as low as you can without hitting wheels and with 2" of travel left in the shock. That's kind of a "by the book" recommendation. But two infallible truths:

1. Lower CG always better.
2. 2 inches of shock travel required.

Not my rules, just quoting, but I understand these two rules.

What is the suspension travel, front and rear? Shock travel, wheel travel?

Sub'd. Lovin the info.

My car was too low all the bit own braces bolts are nicely grounded down, lca also hit the track a few times lol. Not sure exactly what I raises it up to now but working well.
I kept breaking undertrays on track as well

I was referring to the set-up on my car would be a handful on a road course, it is just not set-up for high speed turns.

As far as the other poster who wrote lower CG=Good...well, yes in of itself, lower CG is good, but the Z33/Z34 roll centers start to go from meh to really meh once you get below about 1.5" from factory.

Easiest way to figure out how to spring a car is via frequency, which is easy enough to calculate using your corner weights, motion ratio and spring rate. There is a more involved means of calculating frequency, which involves chassis strength, bars, etc, but the above will suffice.

IMO, every off the shelf spring kit is going to be much to soft. They are made with a strong compromise to ride quality. That said, really good shocks will make even a 700-800lb spring entirely tolerable on the street.

Suspension travel =the amount of bump (compression) the shock has before it bottoms out. Unless you are using a lot of spring or ride on silky roads, you are going to want more than 2". The old rule of thumb 2" is really more geared towards true, single purpose track cars. In fact, formula cars often work on less than 1" of bump travel these days since most have a dedicated spring for aero load. I have run up close to 3" on BIG bumps with 1000lb springs for reference.

me too. never bottomed out the suspension when I was that low, but I did grind the flanges on my exhaust flat and all the bolts that held the undertray on too.

I actually bottomed out the front left suspension if I hit the berms very hard but that was mostly due a bad corner balance, once fixed I didn't bottom out anything either.

How mucha re you guys lower than stock?

I doubt you will find anyone much lower than 1.5" in the front and probably more like 1.25". I have been told we usually end up slamming our upper control arm into the body before we run out of suspension travel if you go much lower.

Also 03threefiftyz mentioned that below 1.5", the Roll Moment starts to get thrown all out of whack as well. I am not sure how to measure that personally but I am sure he speaks from experience.

That Voodoo spindle + camber arm that someone posted from Sema a few weeks ago would solve that problem and potentially allow you to go even lower. I can only imagine what they are going to charge for that part though.

this was the lowest, no idea on how much vs stock
https://fbcdn-sphotos-e-a.akamaihd.n...67907162_o.jpg

Your coils have 9 or 10" springs Martin?

That would be a really tall spring. I use 7" up front and 6" in the back..

not sure I'd have to look up specs, if I had to guess 6 or 7"

I believe I'm at an inch. I'm now on 18's so I have more clearance there and I've have raised my car little by little over the past year so I feel I'm near a perfect height for my coilovers. First of the year I'm going to be ordering and custom setup. I want higher spring rates and valved to properly.

Custom what?

Custom coilovers.

Depending on what that will cost, maybe you could do some fortune auto 510's.

We have similar setups, or will be when complete. Here's my survey I did for them and their response. Of course they will build them properly with valving etc.

"Based on your intended usage and vehicle, I would recommend:
15k front and 13k rear spring rates."

Meant brand.

Well first I love true type coilovers only. No doubt there's a slight advantage there. There's only two companies I know of at the moment that make true type for our cars. One being JRZ's. Definitely the most over rated coilover there is with a price that's flat retarted (only speaking of there entire level setups). Course they are from another country so I assume cost would be more. Every track guy I know at the track has said this to me.I just don't believe in spending crazy money for certain things.

But as another true type coilover is Stance GR+. No doubt under rated. I have track eight days on these and they are awesome. Yet they are only one way adjustable. The springs rates are 13K and 6K rear. In which on a true type setup 6K rear is the same as 11K OEM setup.

After contacting Stance they will build any setup you want for our car. So I'm looking at about $2200. This spring rates of my choice, custom valving, and separate compression and rebound with external reservoir. They have coilovers up to $3.5K.

I got the 14K/11K Fortune 510. It is not stiff enough for track use only. At the middle click range, the car felt exactly like stock. I didn't notice a difference until the very top end of the clicks. Even then the car is still not stiff enough. Everything seems to be working like it should, but $2000 on the coilover was such a mistake. I should have just gone with the sway bars and camber arms instead. I am still pissed I lost my datalogs, now I don't know what the exact difference is.

And they are OEM design? You only posted one damn pic and its super close up of just 2 shocks :gtfo2: haha

Weight of our cars are a big factor. Just going up in spring rates doesn't seem to be the only effective way to help with handling. I've been told by a great respected Z driver that 18K in the front is where to start. If not at least 15K.

Sways have always been the biggest gain of all my Z cars.

Besides Shamu I will have the lightest Z here with a full cage. But I'm not in any spec form of racing. Nor will I ever. I've have cut weight in areas that you wouldn't never see if you were looking right at it. My car will be corner balanced in the next few weeks for finally numbers. And I still haven't gotten my single exhaust and 2pc rear rotors.

Yes they are, special order a set from a vendor here. 14/11K 510s. It fits fine and works like it should, but for $2000 I was expecting a lot more in terms of performance.

JRZ has a lot of winning pedigree, but they haven't been my choice when I dropped big money on shocks (twice). IMO, 18k would be in the upper range for a street tire car (with aero) up front. That is what I use with a 315 A6 on the front. I haven't looked at Fortune dyno's, but lower priced shocks tend to be mired in considerable cross talk, that makes them difficult to fine tune. I question how many valving options there really are for stance. They use a small shaft, etc, which would relegate them to ripping off Koni pistons and/or making their own. My guess is all they do is vary the shim stack and can pressure, then slap a "custom valved" sticker on the box.

I just had these built...I am excite:
http://farm8.staticflickr.com/7413/1...4b5593b5_c.jpg
Replacing these:
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