Hoosier A6 - 150F too hot?

noahfleming · **Posted:** Wed May 25, 2011 4:39 pm

Guys,

I'm still learning how these new tires work ...

At the NCCAR event, my front tires got up to about 150F, with the rears maxing out at about 140F. Is this too hot for Hoosier A6s? I kept my pressures at about 34-36 PSI as I was not rolling over on the sidewall (or even close) - I guess my question is whether ya'll think these tires were getting too hot from being run too soft. The RX-8 weighs about 3K and has double wishbone suspension.

Thanks!
Noah

Chuck Branscomb · **Posted:** Wed May 25, 2011 7:39 pm

Hoosier says 110-140F. Were your measurements from a probe? If not, then the actual probed temp would have been hotter.

Either GRM or SCCA mag did a test sometime back with the A6 on a skidpad and did something like 20 laps. What they found was that as temperatures grew hotter, the ultimate grip did not really fall off, but the slip angle required to get max grip increased. I think they went over 160F. The A6 feels sloppy as temps rise which you might notice toward the end of long run where you need bigger steering inputs to get to the ultimate limit.

http://www.tirerack.com/images/pdf/warranty/HOOSIER.pdf

michaelsmiller · **Posted:** Wed May 25, 2011 9:28 pm

Noah,
Your pressures do not sound that far off. I played with mine until I got the most consistent temperatures between three locations across each front tire. I was running 32 front and 35 rear at NC CAR. The only reason that the rear is higher is to balance the car. The temperature consistency only really matters on the front of my car. Hoosiers make the Miata a little pushy. I find that the outside for the front tire is usually the hottest. NCCARR seemed to be a little easier on my tires than most places. I vary the fronts from 32 to 34 depending on location and add 2 to 3 psi to the rears. I run Laurinburg at the highest pressure. Everybody probably has a little different way of figuring this out. I adjust my tires in a manner that makes the car feel good to me. I don’t know if my method results in the fastest time but I do drive with a little confidence. Others may rely on data acquisition systems to compare different runs at different tire pressures. I actually only sprayed the front tires, the rears didn’t get too hot. Hoosiers seem to like the heat better than V710’s.

Keith Quistorff · **Posted:** Thu May 26, 2011 8:27 am

Noah - the pressures you mentioned are in the ballpark - your temperature measurements indicate whether you need to go up or down a few psi. General rule of thumb is if the temperature at the center of the tire is higher than the average of inside edge and outside edge temperatures, drop the tire pressure; if the temperature at the center is lower the the edge average, raise the tire pressure. Based on personal past experience, I would start with ~36-37 psi in the front, 32-33 psi in the rear and use the pyrometer to adjust from there. Of course, if you already have pyrometer data at specific pressures, adjust from there.

As for other useful info you gain from your pyrometer measurements: if outside edge tire temperature is significantly higher than inside edge temperature, camber is less (negative) than ideal - this is typical of most stock class cars as they generally can't get enough negative camber. FWIW, I generally measure edge temperatures about 3/4 to 1 inch inside the physical edge/corner of the tire.

Were you pushing the front and/or spinning the rear tires much on Sunday? (might help explain the high temperature readings)

Chuck Branscomb · **Posted:** Thu May 26, 2011 8:52 am

Found some links to the articles I was thinking about.

Quote:

The October 2008 issue of Grassroots Motorsports contains an excellent article testing the relationship of tire temperatures vs. grip. The subject tires were 205/45R16 Hoosier A6 tires mounted on a Mini Cooper S. To keep things consistent, Tire Rack's 200-foot skid pad circle was used to provide steady-state cornering, perfect for testing lateral grip. Conventional wisdom states that a race car's tires will gain grip with increased tread temperature. Likewise, many of us have experienced how cold tires can lead to decreased traction in those first few turns of an autocross. The result of the test was that although the A6 tires are optimized for lower temperatures (120 to 140), they remained fast even during high temperatures and extended lapping sessions. The tires were abused to temps of 200 degrees, but the lap times never changed significantly. Although the grip did not change significantly, as the temperatures built, the slip angle required to generate maximum grip increased along with a general loss of precision in steering feel. While ultimate grip is important, precision and confidence are mandatory for fast autocross laps, which might explain why autocrossers like cooler tires. (9/08)

Quote:

The November 2008 issue of Grassroots Motorsports included an excellent article exploring how tire pressures impact grip. Similar to the previous test that measured grip vs. temperature, an autocross-ready Mini Cooper S running Hoosier A6 tires was used together with a 200-foot skid pad. Rear tires were held constant at 55 pounds and the fronts were raised and lowered in 5-pound increments from 50 to 20 and back up again. Despite the pressure spread of 25 pounds, the lateral grip only ranged between 1.012 and 1.057. However, from behind the steering wheel, the testers noted quite a bit of difference. At the highest lateral grip (1.057 at 30 pounds pressure), Steering precision and feedback was significantly reduced, the outside front tire emitted a noticeable low groan or growl, and the tire was really rolling over onto the shoulder. In conclusion, the article indicated that a setup that feels good might not be the fastest, and the fastest setup doesn’t always feel good. Back to the white shoe polish, I guess.

For reference, the above summaries of the testing are from this page: http://yellowstonescca.com/pages/tips.htm (I'm not endorsing this site...just pointing out where the summary of the GRM tests came from).

With regard to the second test of tire pressure, I'd just point out that this was a steady state condition on a skid pad which is pretty much a rarity in autox where there is a HUGE demand for accurate transient response (coupled with ultimate grip) on a continual basis. Hence any conclusion from a skid pad on what pressure creates the fastest skid pad lap (highest g) likely has little correlation with the pressures needed on a typical autox course in my opinion.

Matt McGrain · **Posted:** Thu May 26, 2011 9:24 am

michaelsmiller wrote:

Hoosiers seem to like the heat better than V710’s.

I'm starting to find this out too and I like it. With the V710's I ran last year, even with spraying, I'd try to drop times while being a little more and more aggressive and there were some runs that I just could not do it because the tires were 'giving up' the grip. The A6's I'm running this year seem to be the opposite, even without spraying.

The runs in group 4 at NCCAR were pretty quick intervalwise, and even with the heat, the tires felt pretty good. I'm sure the grippy new surface out there played a part too.

So is the rule of thumb to keep the temps pretty equal across the contact patch for maximum grip and/or tire life?

KendtEklund · **Joined:** Tue Mar 27, 2007 7:29 pm **Posts:** 1204

On the tire pressure thing, Les told me this weekend that "Hoosiers like pressure" - I'm glad I listened.
I had been using lower pressures like I had in the V710s, but running 36F and 34R seemed to make a big difference in feel and drivability, even if ultimate grip may have been little different.
I know not all the hotshoes made it to NCCAR, but Les just shy of FTD and me within 5 tenths makes me

Chuck Branscomb · **Posted:** Thu May 26, 2011 11:41 am

Hoosier recommends the following min safe cold pressure:

Quote:

When tuning at reduced pressures use the following formula to determine the minimum safe pressure: Divide the total vehicle weight, including
fuel and driver, by 100 to arrive at the minimum safe pressure. Example: Your car weighs 2750 lbs. as raced. The minimum safe (cold)
pressure is 27.5 psi.

So for something like the M5 at 3920lbs plus my 205lbs = 4125lbs = min safe cold pressure of 41psi. This is 6psi or so higher than I'd run with BFG R1s for example.

Keith Quistorff · **Posted:** Fri May 27, 2011 1:57 pm

Matt McGrain wrote:

So is the rule of thumb to keep the temps pretty equal across the contact patch for maximum grip and/or tire life?

Yes, except having a little more heat in the outside edges is generally better for braking and launch - indicates you have more contact area when pointed straight.

THSCC Forums

Hoosier A6 - 150F too hot?

Who is online