Oversteer Problem

[Nickel Dime]

I'm new to racing and this is my first post so please bear with me. I run a Datsun 510 in ITC. The car seems to be well balanced and neutral at turn in (unless I over cook it). At VIR I haven't really noticed too much of a problem. In 90 degree turns I get a nice controlable 4 wheel slip angle. But I went to Roebling Road recently, with it's fast 180 degree sweepers, and about 3/4 of the way through the turns I was fighting to keep the rear of the car behind the front. I realize some of this is my lack of experience and the loose nut behind the wheel but I was wondering if there is an adjustment I can make to help late corner oversteer without sacrificing too much at turn in. Keep in mind with 90 some HP, throttle induced oversteer is a fantasy I hope to some day experiance.

Any ideas?

[Festus E. Simkins]

Here are a couple three things you can do. I am assuming that you have adjustable sway bars.

1. Soften the rear sway bar if you have one.

or

2. Stiffen the front sway bar

or

3. Adjust tire pressures. Typically increasing tire pressure will increase grip. That is to a point. The tire pressure thing can be real touchy. However, if your tire pressures and temps are spot on I would leave them alone and work with the sway bars.

4. If none of this works remember "slow in fast out." You may have to alter your driving style for these types of turns. I would rather enter a turn a little slower and be able to power through it than dive in and have to make a lot of corrections in the middle of the turn.

5. John Saucier once asked me when I was having a similar problem... "How old are the tires?" They had several heat cycles on them. Bought new tires and problem was gone. Lap times dropped 3.5 seconds. Only cost about $650 and change.

Just my .02. Hope it helps. :D

[Nickel Dime]

That's a good point about tire pressures and age. The tires were a year old. It was an HPDE track event (seat time is seat time) and I didn't want to kill my new tires. As for air pressure I've kind of been winging it by the seat of my pants. I really need to find room in the race budget for a pyrometer. Do you suggest an IR or probe style?

[gran racing]

The "only option" is a probe style. For your budget reasons, instead of buying one, at the next event you attend, walk around and and find someone else who is using one and ask for their assistance. If you're nice enough, maybe they'd be willing to take the tire pressures and temps when you come into the pits after a hot lap.

[orlando_wrx]

In my experience probes are best for tire temps, and IR for brake rotors, just be sure if you get an IR to get one that goes over 888 degrees. I second the above comments on adjustments to set-up and driving style, but also add that rear toe could also be looked at, maybe just a pinch more toe in at the rear? That is, if it's not worn tires that are the culprit.

[ITANorm]

Rear camber angles are also a possible issue. Since your car is good in moderate speed sweepers but goes away in high-speed ones, it's possible you're overheating one edge or the other of the rear tires. A good probe-type pyrometer is your indespensible friend!

[Daryl DeArman]

MHO:

The fact that it is on exit only, I'd suggest looking at the rear toe. You may have too much toe out or too little toe in depending on perspective. Go 1/16 to 3/32" more toe in than whatever you have now and try it out.

The other thing to consider is through longer corners the outside rear coil spring or shock may be bottoming, are you hitting the bumpstops? ANy of those will make your effective rear spring rate go very high very quickly=oversteer.

[Nickel Dime]

Thankx for all the input.

I'll take the car to the alignment shop and get it looked at. I don't know if the toe can be adjusted on the rear but it's worth looking into. When I bought the car, the camber on all 4 corners was around -4 degrees. Not knowing any better I have left it there. The pyrometer I'm going to buy (that I had no idea was going to be so expensive) should help me figure out where the camber should be as well as tire pressures.

I just saw a picture of my car, taken from behind, just about where things were getting intresting and there does seem to be a bit more body roll than I expected to see. I don't think that it was bottoming out the suspension but you never know. I'm looking into adjustable shocks but I'm having a hard time finding them for a 35 year old Datsun 510. I have no idea what the spring rates are or if I could find stiffer ones.

Too my thinking if I stiffened the spring rate or dampeners (in the rear) it would increase the rate of weight transfer thus (with everything being the same) it would oversteer sooner in the turn. But in watching cars turn the ones which corner flater seem to be faster. As you can tell suspension setup is a foreign language to me.

Another thing is, I don't want to make too many changes at one time because I won't know which helps and which hurts.

[dickita15]

The easiest trick to see if the shock is bottoming in to put zip ties tightly on the shock piston rod (the shiny thing) and push it down to the shock. After the session you can see how far the shock compressed.

[lateapex911]

And to take Dicks comment further, use shoe polish or some other easily scuffed marking material and "paint" the parts of the suspension and body that are likely to hit each other in a bottoming scenario, like the bump stops, etc.

Another method is to remove teh spring and move the suspension by hand through it's travel to see where it might contact..

There are a few ITC 510 guys who lurk here, you migth want to fish for setup ideas in the specific Datsun section. I know Stan posts here and has/had a 510...not sure if he's running it regularly though.

[Daryl DeArman]

Another thing is, I don't want to make too many changes at one time because I won't know which helps and which hurts.
[/b]

You are already ahead of many.

Sorry OrlandoWRX--I didn't read that you had already suggested rear toe as a culprit.

[Harvey]

Welcome to Roebling Road. This is what you are going to get until the repavement.

[Nigel Stu]

Roy,

Welcome to the world of racing and racing a 510! :023:

I've gone through some similar handling issues as you seem to be having. First off, contact Jeff Winter out in Colorado (www.rallye-sport.com) - he can hook you up with the suspension you need to get that car around the track. He has helped me quite a bit.

I'm guessing from your camber numbers that you do not have a slotted RR cross-member yet - and with that much camber, you just are not using enough of your tires to give you enough traction. I have some 'before' shots where you can see the inside RR tire is almost entirely off the ground due to the camber/body roll combination - no contact - no traction so you are relying on the outside tire to do ALL of the work.

You'll need to slot to change toe as well (as that RR susp compresses, it adds a bit of toe-out). Once you get that taken care of, you can get camber to where it needs to be and toe set right so the car will retain its neutral handling throughout the corner. You'll have to play with the sway bar, I am currently trynig to figure out if the car is faster WITHOUT a RR bar...


I have more info if you need it - you can reach me at benschaut -at- hotmail dot com

[Nickel Dime]

Thanks Ben, I don't think the rear cross member has been slotted and I'm positive it hasn't been done for toe adjustments. I'll look in to that. I want to go to adjustable dampers. I have been told that 240Z struts (with a spacer on top) will work in the front but can't find any info for the rear shocks. Do you have any suggestions?

Thanks for the help