I've got my last autocross of the year coming up, and the temps are rather low.
Given an ambient temperature of around 40 degrees F, which would have the best grip?
- a regular high-end summer tire, 140 TW, eg a Star Spec
- a high end UHP all-season tire
- a performance winter tire
Would it change if you added R-Comps?
Has anyone figured out where the crossover(s) is/are for grip vs temperature?
A Toyo R1R would be my choice, even over R-comps at that temp.
R-comps don't typically start working until the temps are at least 50-55.
Per
I've had good luck with Toyo R888's in cool temps and poor luck with Hoosier A6's.
No real experience with street tires in cold temps. Weird.
Drop pressures too, so the tire can build some heat & be more compliant.
Since tires will build less heat, lowering the pressure would be counter productive. Check the pressures after your first run, before they get a chance to cool.
scardeal wrote: Given an ambient temperature of around 40 degrees F, which would have the best grip? - a regular high-end summer tire, 140 TW, eg a Star Spec - a high end UHP all-season tire - a performance winter tire - R comps
First, get a co-driver. In those temperatures in my experience, the best is 140TW with a co-driver and tire blankets. And a co-driver.
The question above was mostly theoretical about the different tires. I only really have Star Specs, but I was wondering for future reference.
Practical question: Should I be running hot laps to retain the most heat possible in my tires?
Addition: I'm working on the codriver part...
Per Schroeder wrote: A Toyo R1R would be my choice, even over R-comps at that temp. R-comps don't typically start working until the temps are at least 50-55.
I ran an autox in March of this year. It was a sunny day in the low 50s and on my Kuhmo R-comps I had no - repeat, no - grip. Even last weekend, in the low 60s, I had to take a 15 minute highway drive before my second set of runs to get some warmth back into the tires so I could actually use the gas pedal on course.
As I learned this weekend (temps in the high 50s), it definitely isn't Hankook RS-3s. They were SCARY on the first couple runs of each heat, and the only time they worked half decently was when I had a friend take my car out for an "instructor run" in between my normal runs. I love these tires when it's 80 though.
I've used Yokohama R-comps before in temperatures right around 40, and it was like driving on an oil slick. I'm sure street tires would've been way faster.
scardeal wrote: The question above was mostly theoretical about the different tires. I only really have Star Specs, but I was wondering for future reference. Practical question: Should I be running hot laps to retain the most heat possible in my tires? Addition: I'm working on the codriver part...
Being that you are talking about a CCM event that I think is on a seal coat, yes, hot laps would be a requirement. That lot is a PITA to get right at this time of year. Not that it's much easier to drive in the middle of July, though.
My well worn Kumho SPTs worked well this weekend. I was really trashing them hard with back to back runs on a first gear only course. So they were getting heat. But they have also dominated on cold days at previous more regular events. It might also help that they are the smallest size SPTs(205/50R16).
I'd try the Continental DW or even DWS before the more extreme summer tires. Maybe Pilot Super Sports? Think smaller tread blocks. I doubt the winter tires would work as well as the all-seasons though. If it is really cold the UHP all-seasons might really be the best.
Chalk up another one who's experienced ice skating on R-comps (Kumho V710s) below 50ish degrees. I know I had some general setup issues on my E30 at that point, but I was starting to think of the pedal on the right as just a yaw randomizer... I'd swear the back end went sideways faster than the car went forward.
iceracer wrote: Since tires will build less heat, lowering the pressure would be counter productive. Check the pressures after your first run, before they get a chance to cool.
I'm confused...
The lowering of pressures makes intuitive sense to me in terms of increasing carcass hysteresis to get some heat into the tires.
[EDIT: I gotta be more careful chucking around 50-cent words... I think hysteresis really applies mostly to what's going on at the tread layer as it deforms and returns at the contact patch under cornering/acceleration/deceleration, and I should've just said "carcass deformation"...]
Are you suggesting that in terms of getting an idealized contact patch, you'll need to start as high or higher due to decreased gain in temperature and thus pressure in cold conditions? Or am I even further in left field than I think?
alfadriver wrote: Being that you are talking about a CCM event that I think is on a seal coat, yes, hot laps would be a requirement. That lot is a PITA to get right at this time of year. Not that it's much easier to drive in the middle of July, though.
The CCM lot is definitely hard to deal with. I agree. And the temperature doesn't help at all.
Maybe I can haz 90+ points Sunday?
In reply to ransom:No I believe your right-dropping the pressure will result in a lot of tire flex which in turn generates heat.Optimizing the contact patch at that point is not going to help if its stone cold. I ran my hoosier slicks 3 lbs lower than normal(not dot r's)the last event and the grip was way better than expected considering it was about 3 degrees above freezing,overcast and windy.Obviously not a warm day type of grip but I still set the event ftd by 3 seconds on my 1st run.A co-driver helped as did the rain that came just as the 3rd runs were starting-no one was going to go any faster in those conditions.
iceracer wrote: Since tires will build less heat, lowering the pressure would be counter productive. Check the pressures after your first run, before they get a chance to cool.
Uh... Thx, but I'll continue to lower my pressures when it's cold.
When I was starting out, the guy I could never beat showed up for an event on high performance summer tires. It was cooooold. Like 28 when we went out for our runs. I was on Kumho V710s. He was sure the street rubber would work better in the cold. It was the first time I beat him.
If there isn't ice on the surface, you'll get enough heat in an R Comp to get more grip than any street tire, at least in my experience. If the choices are Summer, All-season (never the right answer) or winter, it's a no brainer. Summer tire for sure. I love my Blizzaks, but they're nothing next to my Goodrich G Force Sports if there's no ice/snow - at any temp.
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