Help from the track day/race guys here.


Some time ago I picked these charts up off the NZHondas forum. For the sake of credit where it's due, apparently they were developed by Greg Simmons (Spa Design/Penske) and published in "Competition Car Suspension". They were written for the BMW M Coupe, but the basic technical ideas should apply to most vehicles.

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With the pressures that low do you not see the tyre wall scrubbing?
I tried low pressures once. Car had no bite at the front and felt like jelly. And when i came in the sidewall had took some action. This was with about 2 degrees camber.
 
What suspension is on the car, and what is the springs rate.
On this, there are several thing that I would like to investigate.

1. Roll centre: If you are very low your front roll centre might be out, this will decrease roll resistant.
2. Spring rate: Depending on what you are using the car for, you might be running a very high or low wheel frequency.
3. Compression valving: if you are using R888 and there aren't enough compression force, you are probably not pushing the tyres down to generate the grip that it can produce.

Just a few thought that hit my head when I saw this on the suspension side of the things.

As with everything, it is all a package.
Geometry plays a role, tyre pressure plays a role, driving style plays a role.
So you got to just slowly peel that onion one layer at a time to get to the answer in the middle.

Jerrick
 
I have tried about 24 PSI warm and without power steering it was seriously hard to turn, I also felt like the car wouldn't change direction as quick with really low pressures. Lower pressures will improve grip in a straight line in a FWD car but I can't see anything lower than about 26 PSI hot doing much for a fwd Honda on a circuit


Really as low as 7 psi!! I have seen the driftworks AE86 a few times here at the Irish drift championship and its impressive but you would think that the tyre would come off the wheel with that little pressure and so much power going sideways! I try to get to as many rounds of the IDC as I can and my mate competes in the NI drift series. Great form of motorsport imo and its only going to get bigger



Setup wise I use OEM front and rear ARB's, 16k spring rates, about - 2.5 front, -1.5 rear camber and zero toe to keep things well behaved, my local circuit is quite fast with 1 x 120mph corner and not too twisty so I don't want the rear to be too lively. For a more technical circuit I would probably add a small amount of toe out on the rear


Like i say i will give it a go and see what occurs. I really can't see it gain me any grip but it's worth a shot.

Yes just 7PSI. They were having issues at JDMallstars (before it became Driftallstars) at the Birmingham wheels venue with tyres coming off rims. These guys are running no stretch either. Ask your mate about tyre pressues and see what he sais about more grip. Just out of curiosity.

16K springs is real hard man. All round? Setup sounds good. Mine has just 1 degree at the rear.

Jesse:
We don't run front camber arms. The passenger side is at 2 1/3 and the drivers side is just inder 3. We have so far only driven Oulton park which is a right handed circuit so leans on the passenger wheel (the one with 2 1/3)
 
Thanks for the info NZracer. They all look to make sense to me.

Murray: No side wall rubbage at all. The car is light and 22PSI hot is well enough. We don't even have large amounts of wear on the outside of the tread let alone the wall.

Jerrik:
Had a conversation with you over winter while i was building it.

We run Meister R coileys with uprated spring rates of 10KG front 8KG back. About 5mm preload all round. We also run the buddyclub roll centre correcting ball joints on the front so roll centre is good on the car all round.

I don't understand point 3. Well, i do however i don''t know how to answer or investigate this.

I know its not driving style. Without being big headed i came from drifitng so know how to chuck a car to get the back out and this has massive amounts of grip at the rear compared to the front. I would say geo and tyre pressure were to blame.
 
It is a front wheel drive car, and therefore it does work differently vs. a rear wheel driver car.
You see FWD race car around the track and sometime you see the rear wheel lift off the ground, there is a reason for that.

One of the trick in building a good fast track FWD car is to limit rear compression travel.
That way when you brake and turn in, the rear damper top out.
This try to lift the rear wheel off the ground.
The reason for this is because you want keep that front wheel hook for as long as you can and put as much weight on it as possible, as that is the bit that is generating traction.
The only problem with this design is that you cannot really use this on a road car, as it would be pretty uncomfortable and dangerous in low grip surfaces (think cold wet morning in winter).

Of course there are other bits also, springs rate play a role, damper plays a role.
FWD car is an odd setup as a good fast road going setup isn't really optimal for track use.
Because for safety sake, you want the rear to grip harder than the front; if you are going to crash you want to front end to hit the wall instead of side way if that make sense.
However, for track use, you want that rear end to be loose so you can turn in, and that mean swapping the wheel frequency (springs rate) so the lower end is at the drive wheel.
Otherwise, the only other solution is like you say, tune tyre pressure, anti-roll bars, or just change your driving style with lift off over steer.

There are a lot of way to tune a car, the problem is the more "focus" you make it for one thing, the less it is able to do others.
If this is a trailered to track only car driven on slick, we can make a suspension that will work for that on the track, but it will try to kill you as soon as you hit some uneven country roads.

Jerrick
 
My AO48's I run at 28 hot, this is in a stripped out Metro so bloody light, same pressure more or less for classic Mini's (650kg), your tyre pressures seem v low to me.
 
I run 28psi too. You need pressure to support the tyre - a lot of load going through them!

Low pressures only for cold wet days as the extra deflection creates heat through elestomeric hysteresis.
 
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