Can too much grip hurt track times?
 

This discussion will be focused on track events (no autox).

It appears that some of track junkies have discovered that too much tire will actually hurt lap times. For example, you may scrub off too much speed during a corner when you have too much grip, thus increasing lap times.

So my question is, can too much tire increase lap times? What is the "optimal" track tire and wheel size? How can you explain the increased grip and decreased lap times from R-comps? Isn't running R-comps the equivalent to running wider street tires?

Yes if you mean too much width/etc. Rolling resistance increases with wide sticky tires. I'm faster with 225/45/17s over 235/40/17, not sure if it's the gearing (the taller tires save 2 shifts at sebring) or the lower resistance. Cornering speeds and entry/exit have been identical for me (ie normal variance).

I just don't buy the rolling resistance argument without any empirical data- show me a driver who picks a less sticky tire to avoid rolling resistance and I'll show you a driver in second place. Go watch ANY racing series, the guy with the softer/sticker tire is always faster on a lap time basis.

Saving two shifts on the other hand sounds like a valid cause. Figure 1-2 tenths per shift, according to most road racers I've talked to. YMMV.

Dave, I would also question tire construction, sidewall strength, and compound choice by the tire manufacturer. This can vary between tire sizes even within the same model. Additionally, if you're on street tires, these really need to be matched up to the right size rim for optimal performance. If you're on the correct width for a 225, going to a 235 on that same width width may actually be slower.

There is no such thing as scrubbing off too much speed in a corner because you have too much grip... The issue folks point to is rolling resistance and its effects on long straights, which most tracks have, in a low horsepower car like ours. Sometimes that effect is greater than the increased corner exit speed.

Miatas have the same type of behavior and I have seen people racing use narrower/lighter tires for that reason.

It's not just rolling resistance, it's also mass, and it's unsprung rotating mass. There comes a point where adding more tire doesn't add enough grip to make up for it.

To a point for sure. Run 285s on these cars and they will be slower. The car simply doesn't have the power to overcome the tires.

I think a few of of us have gone wider, and then scaled back. In every case that I know of, going past 235 resulted in slower lap times. There's more that just the resistance of the tires, weight (unsprung and rotational) is a huge factor.

In my case 225/45 Rivals are significantly faster (2-3 seconds) than 235/40 AD08s. However without the same compound I didn't want to post it as a test result.

This has been proven in other cars as well. A number of chump guys run narrower tires than they could because in their testing it was faster.

Yeah...AD08s suck. The Advan Neova was a hot tire 4 years ago or so and it's since been surpassed. The Rivals in particular are an outstanding tire.

As I mentioned, these are street tires. What width rims did you use? After compound choice, this is the second biggest factor in getting a street tire into its Happy Place.

loving my stock NT01s, fast, but for track only, sucky when cold on roads
sold my 225/45s, no thanks
like the 235/40 for DD but not for track, like the 215 best, light fast 100TW

I like the AD08s and have good luck with them. I would agree that they are surpassed by the next generation coming out now but I've been faster on them than Star Specs and RE11s. I also like their responsiveness.

The Rivals are a better tire, but one would hope that would be the case anyways. The CSG guys, Robi and some others have found the same with their testing. :shrug:

YMMV, for me, I don't believe that 235 and up will be faster with near-stock power levels.

I'm running 17x8s, there weren't too many easy to find 8.5" options in 5x100 back then.

ran 205 hoosiers (R6) this last weekend...good enough for 4th and 3rd with 3 well sorted multi-year racecars (BMW,RX8,RX7 1st gen) and 3 former ttd national champions in attendance.

what road course, curious>?

And I bet you don't have any empirical data to disprove either?

"Those guys" on TV have high-HP cars. Most folks race pretty low HP cars because racing high-hp cars is insanely expensive. You know that Mazda commercial that says "More Mazdas are raced on any given weekend then any other car"? The big part of that equation is the Spec Miata, so I will use that as an example.

3 key points:

1: Horse Power Matters:
Take a 125hp Spec Miata (Spec tire is 205/50/15) and put on 245 wide Hoosiers and they will be slower (assuming you could fit that massive of a tire on the car). The rolling resistance isn't just simply that you have a larger/stickier contact patch touching the ground but also that most race cars don't run 0 degrees of toe, they usually some variance of toe-in or toe-out front and back and thus the larger the tire the larger the resistance of the scrubbing from the non-0 degree toe setting. So now your 125hp has to "overcome" all this.

2: How weight affects rotational Mass (see #1 again)
Secondly the the "resistance" also comes from the fact that a larger tire is of course, more weight. Go to a dyno, do a pull, then put larger and/or heavier tires/wheels on and do another pull. What do you think will happen? Lower reading? You betcha! Guess what that affects? Straight line speed/acceleration and it also contributes to putting great heat into the brakes.

3: How crucial is operating temp to a tire. (re-read #1 and then add in weight of vehicle)
So going back to the Spec Miata, with that low weight and low hp if you put a big tire on it like a 245 R6 you will find it very very difficult (or impossible) to get it above 180 degree F. You will be racing below the tire's optimal heat range and thus, below it's optimal grip level the result is most often that you will not be faster than a slightly narrower tire that you can run in the optimal heat range as it will corner better and with lower rotational mass (and small scrub resistance) will allow your car to accelerate down the straight faster. I can talk intimately about the heat/grip characteristics of the Hankook C51 and why I absolutely will not run them again but yet would recommend them for certain cars. Another factor too is that some race tires will "grain" if you run them hard below their optimal temp further decreasing lap times.

So add it all up: Too big can yield too much scrub, too much rotational mass and in some cases, even less cornering grip.

I've personally experimented myself on my low hp ITA race car. I found that I'm faster for longer on a 205 R6 or C51 than I am on a 225 due to all 3 of those factors and I have data acquisition and lap times (and 2 championships) to prove it.

There is such a thing as too much tire. There's even a video with the FRS on youtube where they put on significantly wider tires and turned a slower lap time. How much more empirical do you need?

Buttonwillow. :D

One thing I'd like to note is that if there's too much grip, you may not be able to achieve the proper slip angle to corner the fastest...