Understeer problems

[JohnPaul]

I'm trying to figure out why my car was understeering and how to fix it.

I'm running take off tires in decent condition but don't know how old or how many heat cycles they have.

The Pushing (alot) came towards the end of the day on slow speed turns. I'm not sure if the tires were shot or if I was driving harder and forcing the push and therefore requiring a setup or drivering adjustment.

I guess the first thing to do is new tires. Which I will do but it's a shame because the tires don't look so bad.

I'd like to try any type of car adjustment/setup for a few laps before the tires so I can see if can any better so the new tires will even better.

Any suggestions of what I should look for or do (simple stuff) if this continues after (or before) the tire change?

[cooleyjb]

I'm running take off tires in decent condition but don't know how old or how many heat cycles they have.

Don't chase setup on bad or unknown tires.


I've pulled tires off my VD that had 15 heat cycles and were completely crap that looked just like tires with a couple of heat cycles.

[Mike B]

1) Get new tires. You'll chase your tail trying to balance a car on worn (or unknown) tires.
2) Not sure what you have for ARBs, but try softening the front or stiffening the rear for a session.
3) If the bars help, try going the same direction with springs.


Oh yeah, welcome to Van Diemen ownership...

[S Lathrop]

New tires are step one. Step two is to do a way better job of analysising the problems you might be having than you described here.

The new tires will solver you problem for a while. But if you wait until you notice that the car is under steering again you will have already ruined a good set of tires. If you get the car balanced then the tires will last at least 100 miles and not go off balanced.

My advice is to take very accurate tire pressure readings with a guage that you can see 1/4 lbs increments. Take reading immediately before going on the track and immediately after you come off the track. Compare the change in pressure of the front and the rear tires. If one end increases more than the other you have a balance problem. Fix it right then. Otherwise the tires will deteroriate at different rates and you will not be able get the car balanced.

Balance is not a grip problem. It is a problem of reaching the limit of one end of the car before the other end gets near the limit. Divide the corner into entry, mid corner and exit. Get the first part fixed first. Note carefully the difference between high speed and slow corners. Draw a map of the course yourself and make good notes about every corner. The better you debrief yourself the better and sooner you will get the car fixed.

[JohnPaul]

Thanks guys, first thing is new tires. I had the car setup by James Lee so I'm assuming the car should be balanced but I hear that VD are notorious at understeer and may take more fine tuning. I think that a little looser up front and tighter in the rear should be tried in small increments.

Compare the change in pressure of the front and the rear tires. If one end increases more than the other you have a balance problem. Fix it right then.

Ok. but what is the fix? (dare I say) adjusting air pressures?

Balance is not a grip problem. It is a problem of reaching the limit of one end of the car before the other end gets near the limit. Divide the corner into entry, mid corner and exit. Get the first part fixed first. Note carefully the difference between high speed and slow corners.

I'd say late mid through exit on slow corners

[glenn cooper]

so you could imagine how suprised I was when I bought my RF99 FC car, and prior to conversion to FB, ran it. It felt great, railed corners, even won the FC race.

I ran the same dampers on the Novak car, still had not touched them (for real), and even though the car was now 200 lbs lighter, still ran the same 450 front and 600 rear springs. The thing railed, absolutely railed everywhere.

I made little changes to ride height every now and then, and of course softened it way up for wet, but never experienced anything close to "the dreaded VD understeer" I had heard so much about...

GC

[Brandon Dixon]

Dave Weitzenhof has put together a document that you should look through. It's on the NEOhio website:

http://www.neohio-scca.org/comp_clin...ut%202005a.pdf

[RobLav]

Van Diemen's need rake. More than you think. What year Van Diemen is it? If it is RF99 or RF00, check the tubes behind the driver for cracking.

[S Lathrop]

You just got the correct advise. Ride height and rake first. Get the car as close as you can by changing rake. Up in the rear to make the car loose. Also run as close to the ground as you can. You should be adjusting ride height in 1mm to 2mm increments. You need an accurate and repeatable way to measure ride height

A good setup is only the starting point. You must tune that setup.

Hot tires mean that those tires are working harder. Make the cold tires work as hard.

[formulasuper]

What tire compound are you using? When I tried R25 Hoosiers on my Ralt I experienced the same problem as you towards the end of the session. With R35's no more problem.

[JohnPaul]

Van Diemen's need rake. More than you think. What year Van Diemen is it? If it is RF99 or RF00, check the tubes behind the driver for cracking.

It's an 06-07 DP04 like Beattie's and Cooper's.

Dave Weitzenhof has put together a document that you should look through. It's on the NEOhio website:

http://www.neohio-scca.org/comp_clin...ut%202005a.pdf

Very Helpfull, thanks.

You just got the correct advise. Ride height and rake first. Get the car as close as you can by changing rake. Up in the rear to make the car loose. Also run as close to the ground as you can. You should be adjusting ride height in 1mm to 2mm increments. You need an accurate and repeatable way to measure ride height

A good setup is only the starting point. You must tune that setup.

Hot tires mean that those tires are working harder. Make the cold tires work as hard.

I'm going to have James Lee re-adjust the ride height and rake as advised. Back to your last post what was the fix if the front/rear hot air pressures don't equally go up? just adjust the air pressure to match at hot temps?

What tire compound are you using? When I tried R25 Hoosiers on my Ralt I experienced the same problem as you towards the end of the session. With R35's no more problem.

I'm running R25 fronts and R35 rears. I'm going to use both R35's on the new set.

[S Lathrop]

The rise in tire pressure is often a more reliable indicator of car balance than a tire temperatures.

I always have a target tire pressure that I want to run. I reset the tire pressures to the target before I send a car out for the next run.

You described a low speed mid to corner exit push. I would have raised the rear ride height 2 mm or 3 mm. Reset the tire pressure to target, say 16 to 18 psi and do another run.

I would expect that the next time in you might say that the push was less but the car was stepping out at corner exit. I would raise the rear 1mm and reset the TP to target and send you out again. This time the car should balance just right, no push and no stepping out.

The car may not be real comfortable. So you would tackel that problem. When a car does one thing in a slow corner and something else in fast corners, it indicates that you have something too soft. You might raise the front ARB or just raise front TP and see what happens. 1 psi of thire pressure raises the tire spring rate 30 to 50 lbs. Do something so you have another data point. Even if the change makes the car worse, you will know what to do next to bring the car right.

[donotello10]

That explains why I sheared off front skid plate(jabroc) bolts and the plate itself under braking. The other item is the steering rods are shorter than the FE baseline length of 17 1/8" so I suspect toe-in or neutral setting, will find out when I do the alignment.

Duh, should have read this thread before trying the car.

[Jnovak]

I believe that Coop's car was a 99 VD and not a DP 04. I also made some changes to the rear geometry and everyone liked the cars.

[glenn cooper]

It's "Old Thread Ressurection Week" here on Apexschpeed!

The Cooper mentioned by JP is Lil Bruvva Ben's car, the blue one, which then became the Mayer car, which then...

[romoman]

It's "Old Thread Ressurection Week" here on Apexschpeed!

The Cooper mentioned by JP is Lil Bruvva Ben's car, the blue one, which then became the Mayer car, which then...

At least it's a good thread with some great info for people.

[glm34]

With my limited knowledge and being rather new to driving I went through this similar problem last year. It was so bad I felt like I was driving on ice. After changing tires, suspension, wings etc with no results, we decided to check the shocks. The were very low on pressure. Once I got the correct pressure in the car became balanced and the under steer went away for the most part. It was like night and day. I ended up purchasing a shock gauge.