I tried R-compounds for the first time on Sunday at an autocross. Instead of giving me more grip, all they gave me was a lot of problems with oversteer. I had five decent runs on them. They were 205/50ZR15s (Kumho Ecsta V700s).

First run: 26 psi front, 26 psi rear. The rearend stepped out a lot (I spun) and the sides weren't rolling over much so I lowered the pressure.

Second run: 26 psi front, 24 psi rear. The rearend was still hairy and while I didn't spin I had to plow through a cone on two separate occasions to save a spin.

Third run: 26 psi front, 22 psi rear. This was the fastest run yet, but again I wasn't pushing it because I was afraid of spinning.

At this point I was talking to the experts and they all recommended I UP the pressures a lot.

Fourth + fifth run: 32 psi front, 32 psi rear. Still very slippery, didn't seem to have much grip. The front end slid around a lot.

Can anyone tell me what I should have set the pressures at? The tires were borrowed so I can't try it again, but I'd like to know for future reference . The car's never been that tailhappy before, and it was kind of worrying! Thanks guys!

 

What was the temperature?

What were the surface conditions?

What are the basics of your setup?

Did you make any other changes before the event (new rear sway bar, etc)?

I assume from your website you have a CRX?

What is your alignment?

What were the circumstances of the spins? Trailbraking? Transitions? Steady state loose?

Scott


[Modified by celica73, 9:02 PM 2/11/2003]

 

Generally speaking you will want to run tire pressures in the 35-40psi range.

It's always hard to tell what people mean when they say a car is loose or that the rear end stepped out. For some people if the back end just wiggles they call it a near spin, where as some people only call it loose if you're looking out the side windows. The fact that you were spinning a bunch also indicates to me that you need to be on the gas more and not lift as much.

 

Those pressures seem really low to me. I ran closer to 36F/38R in the ITR on V700s. On colder days when the tires never warmed up (lower pressures) it felt like the whole car just skated around (and not the good kind of 'Hoosier' skate, but the bad kind of 'Kumho' skate ).

 

There was an EV700 AutoX pressure thread just a few days ago....

https://honda-tech.com/zerothread?id=407861

I ran the pressures that .RJ suggested in ~40F weather and the car had great stick. Started out with 29.5 front and 32 rear cold which put the fronts around 35 hot.

Your pressures seem low, but just to say your car had too much oversteer doesn't really tell us anything. Too many variables from driver, to suspension setup, to alignmnent, to track surface, etc etc etc etc.


[Modified by SPiFF, 5:13 PM 2/11/2003]

 

So the pressures were too low huh? I figured I should keep them lower since the car's so light (2050 lbs) and I'm surprised you guys ran higher rear tire pressures. Though since everyone's telling me that lowering pressure on R-comps makes them more prone to spinning, higher pressures in the rear make sense

 

From my experience with the V700s, i'd say going by amount of roll on the sidewalls is a really, really bad indicator. The problem with these tires is that if you're way off on the pressures they just dont generate enough grip to roll on the sidewall and then it becomes sorta vicious cycle where since they dont roll, you try to reduce the pressure, so they grip even less and roll even less, so you try to reduce the pressure, etc. etc. I got caught up like that when I just started using these tires, mostly from inexperience. After a while, i just stopped looking at the sidewalls and started listening and feeling what the car was actually doing and the amount of grip generated. And basically, i learned the hardway that these tires like about 40psi hot maybe a couple of psi less on colder days.

 

The old "chalk on the sidewall" trick just does not work that well.

Buy yourself an inexpensive surface thermometer to get temps off of the tire's tread. Taking temps from the middle and both sides you will get a better idea of what pressure to run.

Higher temp in the midde = overinflation

Higher temps on the sides = Underinflation

Higher temp on the inside edge = too much negative camber

Etc.

Also, I see lots of posts about Hondas that "Oversteer" which is a good trick because they plow like pigs (understeer) in stock form. If you examine your driving style you are probably lifting at about the apex, or even worse braking at the apex.

Here is your new driving tip of the day- Brake in a straight line. That means going as fast as you can into a turn and then completing your braking before you turn the wheel.

Scott

Scott

 

Cold and or wet weather just isn't a good time to measure of a DOT race tires capabilities.

that being said, my celica used to have serious snap oversteer when trail braking or with any lift during turn in.

The solution for me initially was tire pressures (I kept going lower in the rear, and that did help me), and eventually, I got an alignment that stabilized it.

With any car that has passive rear steer (the Celica is one example, the RSX is another, and ithe CRX as well, according to you), it often helps to get rid of some of the negative camber in the rear. In the celica I was at -1.7 degrees and I could never get the back tires to roll over. That meant in transitions and at turn-in I didn't have all of the tire on the ground (remember negative camber takes away some grip until the suspension is loaded).

Since I couldn't ever use the tires 100% I had the car re-aligned with -1.3 degrees of camber in the rear, and suddenly all was well. It was like a new car.

Anyhow, It sounds like you need a bit more development, and warmer weather before you pass judgement on the tires. Believe me, on a 65-70 degree sunny day you will like them.

Scott

 

Thanks for the input guys

It was too cold to even get the rear tires heated at all - they were cool to the touch even after spinning on them and after doing six runs (my car was being dual driven). The fronts were heating nicely, but the rears were not getting any temp.

I'm positive I wasn't braking during the turn, or even going into the turn - I'm not cool enough to trail-brake just yet I did all my braking before the turn; in fact, I was evidently braking a couple tenths too early (according to senior driver's opinions). The spin was probably due to lifting, as I was getting the tail to hang out nicely on the rear sweeper by reducing throttle, but I still think that the tire temps/pressures had a lot to do with it.

If I ever get a chance to run R-comps again I'll be sure to use the info about tire pressures

And hopefully one of these days I can afford an alignment!

 

If you were lifting and getting the rear to come around, the next step is to learn to lift and add power in the apex. By lifting and then adding power you are "shifting the weight" of the car.

For example, you want the rear of your car to rotate during a turn, lifting off the gas makes your rear light and it will rotate. To stop the rotation be fore you spin, get back on the gas and that will shift the weight of the car forward and stop the rear's tendency to rotate.

Sometimes you will hear a driver "blipping" the gas throught a turn, in reality he is shifting the car's weight forward and back through the turn.

Scott

 

When you say to get back on the gas when the tail starts to come out, should I also be trying to steer into the turn - ie countersteer? Or just keep the wheel pointed and wait for the rear end to follow?

 

It depends on how far and fast the rear end comes out. Sometimes it only takes throttle and other times it takes full lock and throttle. If you do counter steer be sure to unwind the wheel as you begin to regain grip in the rear tires.

 

Yes I've had fun with the 'pendulum' effect before

Thanks for the info

 

if your rear tires were still cold, theres your main problem. fronts are near up to temp so they got grip, rears dont. when front has more grip than rear, thats called oversteer. i have that problem as well when i run my kumhos. but i got a lot of rear spring as well, rear end comes out just making long sweepers.

i think you already realize that you compound the problem by lifting during the turn. if youre not going to attempt trail braking, just go in with your foot giving just a bit of throttle, not coasting, and ease into full throttle at the apex.


[Modified by Tyson, 6:06 PM 2/12/2003]