An oversteer question

[Curt C.]

Are the solutions for oversteer (lower front tire psi, raise rear tire psi, tighten front end, loosen rear end etc.) the same for torque oversteer. On some medium to tight long sweepers I sometimes have trouble getting into the throttle without the rear coming out. Seems like you want more forward traction to solve this problem - ie. lower rear tire pressure, not increase it (latteral traction). Help, I'm so so so confused. Thanks for the responses

[DAVID GAGNARD]

Curt;

At a recent open track event I had a similar problem.... Although my car is a 65 Fastback,I think most things would carry over.....

First,chalk your tires,meaning talking some of the kids "window paint' and putting on the sidewall of all four tires going into the tread,that way you can see if your tires are "rolling over".

One of the driving instructers recommend I start with 40 psi in the front and 38 psi on the rears,cold tires....First session I was "loose" or had a slight but not too bad oversteer.... Tires were nowhere near rolling over on the sidewalls...

Next, he had me lower air pressure by 2 psi on all four tires,next session was a lot better, no loose condition,car had a very even and predictable four wheel drift with hard cornering....Still no tire roll over....

Third session,lowered air pressure 2 psi again on all four tires,got real loose with this pressure and tires began to roll over.... Came in and he checked the tires and I told him it went real loose, he said,well, now we have found the limits of your tires,back to 38 psi front,36 psi rears....

this is all on pure street tires,in the process of getting another set of wheels and some "racing" tires,probably Hoosiers...

Hope this helps;

David

[Roscoe]

Dave,

What size rims/tires are you running with 36psi? With the BFG's on my 15" rims I run 26 both on the track and the street.

Roscoe

[Curt C.]

His car is a lot heavier than a Cobra. I run R-26 F-24 with street tires and stock car slicks - Goodyears from Kraus.

[B. SMITH]

THERE COULD BE SO MANY COMBINATIONS OF TIRE PRESSURE CHOICES. I WAS VERY NEUTRAL AT 29 F AND 27 R BUT I WILL TRY THE METHOD DESCRIBED BY DAVID. IT SOUNDS LIKE A GOOD WAY TO GET TO THE CORRECT "PRE-BREAKAWAY" PRESSURE FOR MOST TIRES AND WEIGHT DISTRIBUTIONS.

B. SMITH

[Randy Rosenberg]

Here's a good reference: http://rogerkrausracing.com/overundr.html

Have Fun,
Randy R...

[DAVID GAGNARD]

Roscoe/Curt;

I'm running the Shelby Aluminum 10 spoke wheels,15x7,with some Wal Mart 215R60/15 tires.... This is my everyday street stuff.... I'm in the process of getting another set of wheels and some racing tires, probably Hoosiers....My car weights in at aproximately 3200lb with me in it at the track,a lot heavier than a Cobra....

The tire pressures I use were not neccassarily meant for a Cobra,but as an example as to what changes can be made with tire pressures and what happens when changing pressures.... There is little else on my car that I can change at the track to improve handling other than the driver right now,but some Cobras have adjustable shocks and adjusatable coil overs that can be changed easily at the track....

Also, was trying to point out that every car/tire combo will be different,chaulking the tires and "playing" with your air pressure is one way to find the limit of your tires on your car with your setup....It's also a lot of fun....BTW after a hard 15 minutes on the track I generally had a 2 to 3 pound build up per tire of air pressure and it was fairly even across the front and about 1 lb less on the rears....

David

[Curt C.]

The Roger Kraus stuff is really good. I have used it for some time now. I still have the question: Is torque oversteer the same as oversteer. For example: on corner entry I have no problems, car goes right in (no power being used here). Coming off the corner and getting back into the power is where I get into problems. If I had problems getting into the corner would this be oversteer? And, is coming out of the corner under power torque oversteer?

[DAVID GAGNARD]

Curt;

I'm by no means an expert on all this,just relaying my expeirences....If going into the corner you are fine and coming off the corner you are "loose" or have oversteer,it could also be applying to much power on exit and breaking the rear tires loose.... Had that problem at Nashville in one sharp U turn to the right,downshifting to second and getting on the power a little too hard and having to "chase" the rear end which was messing me up for the next corner.... I began "feathering" the throttle and that helped some,one session I tried running this corner in third gear and seeing how it would do.... My lap times came down because I was not having to chase the rear end and being in third gear I could just floor it coming off the corner and I actually could run the next two S's wide open and because I came off the corner slower,I actually went faster overall.... Goes back to the old saying "sometimes you have to slow down to go fast". I proved it right... Luckily with my gearing and tires I could run thru the course in third gear and only had to shift to fourth on the long straight-a-way..

I'm not real familar with "torque" oversteer or quite sure exactly what you are describing..... I call an oversteer or loose condition when the rear end wants to come around on you,weather going in or coming out of a turn,understeer or tight is when you go into a corner or come out of a corner and the front doesn't hold and it wants to go straight instead of turning,those terms are what I call it,not nesccasarily what others call it,just my terms and understanding of it....

I'm assuming what you mean by torque oversteer is the rear end wants to come around on you under power???? If so,then all I could suggest is working with rear tire air pressure and feathering the throttle or even possibly staying in one higher gear thru that corner thereby when you get back on the throttle you will not have as much torque or power going to the tires soo fast....

Hope this helps,if we have any road race guru's out there,please chime in,I'm all ears....

David

[Curt C.]

David, I appreciate your input. Yes, your understanding of my deifinition of torque oversteer is correct. Go check out that link posted above at Roger Kraus and check out all the remedies for oversteer. I am trying to figure out if the solutions apply to both oversteer and torque oversteer. Someone here knows the answer.

[Sheppard]

hate to do this to you....but if your're loose off the corner you need to also think about the steering wheels and their relative position.... loose off can be made worse if the front tires are turned slightly....you shouldn't be hard on the throttle until the front wheels are parallel with the desired direction of travel...but if your're still loose off the corner...then youn neeed to do something to shift/transfer weight aft so that the rear tires bite...if under power the car pushes up or towards the outside of the corner and the rear wheels are digging in....then the car is tight off the corner..its all about a progression......but you must start with the condition at entry to the corner ....once you get the car to turn into the corner without being loose....then work towards a more neutral off the corner set-up...you can always withhold power..... a bad push off is worse that loose off because you have to adjust with entry speed rather than just holding back power......slow in makes you slow off better that the car turns in and you feather the throttle off....just my humble opinion

[flipper35]

If your shocks are adjustable, you can adjust those (bump/rebound) for more weight transfer out of the corner without affecting the entry much.

[DanElam]

Don't guess on the tire pressures or try to use chalk. (Use chalk for suspension stuff, but not for tires.) Borrow (or buy) a tire pyrometer. They tell you exactly what you need to do for your tires. In many cases, it can also help you make adjustments for camber. But for a particular setting, it will tell you very quickly how to get the pressure straight. Until you know you have the pressure dialed in, you are wasting time on the other stuff.

Springs are a common problem too. A lot of cars have too much spring which lets the car hop. If you've got some unusual engine combination, it's not hard to result in a need for spring settings that are different from someone elses car.

At the end of the day it might just be you have too much HP for your tires. My guess is that 351W puts out gobs of power. From the pics, I can't see what kind of tires you have, but I am guessing street tires.

You might be able to adjust your apex a little early and learn to slide it through the corner if you are always bringing the back around on a late apex, but my guess is that it doesn't matter.

[coyled]

Curt, Dan is right on with tire temps. That will tell you where to go with tire preasure. I also run the goodyear bias ply slicks. Not that this will apply to your car but I start around 18 pounds cold and wind up at 25 to 27 hot. Scott

[Curt C.]

Thanks for the responses guys. Yes, I have a tire pyrometer which I use to ensure consistent temps across the tire patch. I run the Goddyear bias play stock car slicks. Motor yeilds 380 RWHP. My biggest problem lies in the long sweeping 120 degree turns. I get in fine, hit the apex and then start trying to get on the throttle easily coming out. However, because the turn is so long, front tires are still turning and the rearend has tendency to step out. I have been reading the Skip Barber book. It recomends hitting a later apex in these types of situations. I will be on the track (2.5 mile roval at Las Vegas Motor Speedway) the 29th and 30th of this month with a brand new set of tires. We shall see if I can beat that turn apexing later than usual.

[DanElam]

Get a little video from the track, will you? We are going to run the Spec Racer National Championships at Las Vegas later this year and I'd like to see the track.

The Skippie book talks about late apexing if you are pushing to the edge. It wasn't meant as a comment on the handling. It means you have turned too early if the wheels are straight.

If the turn is 120 degrees, there is a good chance that it is a double apex turn. Which turn is giving you the problem? It might just be that you've got more HP than traction and there isn't going to be much that you can do.

Good luck. Sounds like you're on it!

[Curt C.]

Hey Dan,

I will try to get a tape. I believe one is already available on the NASA site. Per the Skippy book "The most common approach to hairpins, especially tight ones, is to form a single late apex that allows higher corner exit speeds, critical if the corner leads onto a long straight." He also talks about the double apex move as you mention. I thought the late apex would work better because it seems when I am half way around the corner and starting to go really slow is where I struggle. I want to get on the throttle but the rear will have nothing to do with it. I will try both moves.

Here is a pic of the track. You see that area up in the right hand corner that looks like a big grey circle? That turn is the one that gives me grief. The turn has been cut out on the 2.5 mile roval course as shown in blue. However, when we run the interior only, it is in use. No question, the car has a lot of HP and little weight. I am just looking for ways to minimize the negatives of this combo.

[DAVID GAGNARD]

Curt;

Looking at the diagram of the track,it is very similar to a lot of road courses used on or at NASCAR tracks....If the run you are talking about is the big left hand sweeper,it looks as if it uses the track apron,and they usually have little or no banking....The Nashville track is very similar and uses a very similar left hand sweeper on the track apron before getting on the banked front stretch...It is easy to get "loose" in this sweeper,I've tried running it low,middle and high and the results are all about the same.. Basically what I do is run it in the middle and run a steady speed that I'm comfortable with.... This sweeper is pretty quick,looked at the speedometer a few times going thru it and was doing from low 60 mph to high 60 mph before hitting the straght....

David

[Curt C.]

Its the little grey circle inside the oval (to the left of the Apron turn you are speaking of). It is, for all intents and purposes, a 180 hairpin. You come into it from the straight, make a left and then start the long right. David, the turn you are speaking of (turn 11) is lots of fun. You can pretty much go full throttle. However, as you graduate to the tri-oval, you hit what feels like a dip where the track starts to bank. It upsets the car slightly, but really unnerves the drive (me). One of these days I will get enough guts and punch it all the way through around the turn and see how fast I can go before darting back to the inner road course right before turn 1. I can't get enough of this stuff.

[DAVID GAGNARD]

Curt;

I see what you are talking about now,turn 5,sharp left hander (u turn)....If that's the one,the only thing I could think of would be to try a very late apex...Go in high and wait until the very last second to turn into the corner..At Nashville one session an instructor was riding with another guy helping him out,they were behind me for that session,when it was over he came walking to me in the garage,I figured I was in for a good cussing,but instead he wanted to ask a few questions about my car and offered some advise....Told me I drove a good line for most of the corners but, as with most beginers,tend to "turn in" too soon,he advised to try turning in a little later on a couple of turns..... He said it is a "classic" beginer mistake.....

Looks like a very fun and fast track layout,would love to run it someday....

David