Charley Hoyt

Now that I moved up to a dedicated race car I am finding that I have a lot to learn. One of my questions is about driving on racing slicks. My question is, to get the best times how far should they be pushed? If I am pushing them to the point where I can feel lateral movement (side slip) is that an indicator that I am pushing them to far? What is an optimum/acceptable slip angle / amount? I know that they give much less warning when approaching the edge of their capabilities.

Thanks for the help,
Charley

B Stead

Neither racing slicks or R-comps stay sharp for very long. They just have a limited number of heat cycles in which they work.

If the tires are sharp and have a small sliding that is a very hot driver. If the tires are off and have a small sliding then the driver is probably not running hard enough to know how bad the tires are.

One thing, fresh race tires have a lot of squiggle. The drivers that can benefit from them just run very hard and let them squiggle. The squiggle is often read on data recordings as being continuous correction of sliding but it's not.

If the car develops a strong understeer then the tires are bad. If the car newly becomes throttle steerable then the tires are bad. Club instructors often insist that the driver rotate the car but that's what can be done when the tires are bad. When the tires are good the car just pulls enormous traction and doesn't do much anything else. (Well, that's assuming that the corner entrance speed is good. If the entrance speed is not good then a lot of power can be used at mid-corner.)

Basically, racing on 300 treadwear tires would be a less volatile situation. Or the Nitto and Toyo R-comps have a reputation of being less delicate than other R-comps
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rithsleeper

Good info and new way for me to look at it. Thing that I feel I want to comment on is the "I know that they give much less warning when approaching the edge of their capabilities."

I couldn't disagree more. I heard for so many track days as a novice how I should stick with a street tire because I can hear them and they are more forgiving. I have had 100% the opposite experience. On a street tire if they ever let go I had to just hang on for the ride. With a racing tire (continentals, hoosier, and toyo) I catch slides all the time, feel the slip angle and constantly can push the limit and still be in control. I feel so much safer. I honestly can't see the reason everyone has this adversion to racing tires for anyone but seasoned track guys.

B Stead

Oh, that point. Race tires give less warning at their limit ?

Well, fresh race tires pull enormous traction which also tends to pull the speed down through the corner. And so there is not much feeling of sliding but just building g-forces early in the corner, strong g-forces at mid-corner, and receding g-forces late in the corner.

But that's race tires that are very fresh and sharp. They just don't stay that way for more than two or three heat cycles.

And again, fresh race tires do have a lot of squiggle but the traction is enormous.

Also, I keep assuming that the driver has good entrance speed into the corner. That's a situation of adding a small amount of power in the second half of the corner. A different driving style could produce a different result.

Tire slip angles ?

A tire that works at low slip angles is simply a faster responding tire while a tire that works at high slip angles is a slower responding tire. They could both have equal mid-corner traction but the tire that works low slip angles would have more traction on the turn-in. But it's possible for the tire to be too fast reacting for the driver.

And a slide simply happens at the point where the tire tread can no longer deform under increasing cornering load. That's the maximum tire slip angle as on the particular car setup.

The tire that works at low slip angles is a stiffer and stronger tire than the tire that works as high slip angles. But again, both types of tire can work
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RX-Ben

The optimum slip angle differs for each compound. And the behavior past that optimum point varies as well. Typically, you are looking in the 6-7deg of slip range (which will feel like very little). Some tires may have a bit of a plateau after their peak traction slip angle, others will fall off quickly and you will to be more careful around their limit.

If you are used to operating in the 6-7deg range, you will feel some slippage and also feel some things through the wheel. But, it is relatively minor. The urge is to slide more, b/c of course more is better and it feels faster, but it is not. If you have a datalogger, you will quickly and plainly see this for yourself.

Charley Hoyt

Thanks for the advice. I am really enjoying the slicks. The sutra traction is really nice.

Bill Dearborn

Have only had tires let go a few times over 22 years of doing this stuff. Each time was when I encountered a surface where the grip level changed drastically. When the surface doesn't change all that happens when you exceed the grip of the tire is you take a larger arc through the turn. For example if you can take a 100 ft radius at an X max speed and the next time you go through the turn you add a few mph all that will happen is the radius will increase by a few ft. Break aways where the car spins around are usually due to driver error with throttle input.

Bill

Charley Hoyt

Thanks Bill.

Bill32

No, it means you're almost there.
With the light weight car, you should be drifting just a little in the medium and high speed corners. And your steering wheel corrections will have to be much quicker than in a Corvette.

Until you start logging your tire temps, track temps and pressures, you won't know if the side slip is a good thing or a bad thing.

Heat cycles will affect the side slip by quite a bit. On the Fords, the Goodyears will run at the front of the pack for 4 cycles, the harder American racers will go 6 cycles before they start to fall off and you start to slide more in the corners.

You usually can add 1 more cycle if you break in the tires correctly (scrub them in). We scrub in 2 or 3 sets on the first test day and put them in the trailer.

We mark the number of heat cycles on every tire.

Don't worry about slip angles unless you have a very sophisticated data logger.

Again, it's all in the tire temps (and they must be taken correctly).