smackboy1

I'm new at autoX so could use some advice. Thanks.

I noticed that as my autoX school went on, my tires would get progressively more "greasy" feeling. It was about 100* outside and I was running maybe 5-6 runs at a time with maybe 2-5 minutes between runs. At the end of the day I was sliding all over the place and someone commented that I probably overheated my tires. The tread looked like Edward James Olmos' face and felt pretty hot and gummy (I don't have a pyrometer). I had F 36 psi R 44 psi cold in the morning and didn't check them during the day (I didn't notice anybody else checking their tires). The tire wear comes right up to the edge of the tread but not over onto the sidewall.

Will overheating the tires permanently affect them? What can I do to get rid of the "greasy" feeling? How do I know when it's time to replace my tires?

Joe Weinstein

overheating is mostly temporary. You should have checked your pressures a few times
as they got hotter. Your stick may have gone away because of heat-induced over-
inflation. You should ask around for the ideal temperature range for your tire, and
in a case where it may go over, you can use a water spray bottle to cool them off
between runs. Street tires should be replaced when the tread is too low to be safe
in the conditions you drive. If there's rain, replace at the wear bars. If only dry, you
can go lower.
Joe

Mussl Kar

You get the greasy feeling because your tires are getting far to hot. Prob over driving them also. You can easily get them over 160 degrees by overdriving them. I use a garden sprayer with water and soak my tires between runs and I can feel the difference. You also may want to get one of those infared laser temp guns. Not a lot of $ but very helpfull to know what is going on. I'm still a noob at autox with only 9 events under my belt. A week ago my tires werer getting really hot on the morning sessions. I changed my driving style and they ran a lot cooler in the afternoon. 3-4 seconds faster too.

Kerry

This is an interesting topic to me right now. I've run a bunch of auto-x the past five years, but only on street tires so I never paid any attention to tire temps. Just ran my first 15 runs on Kumho 710's (thanks for the advice, Joe!). I'd bought Accutech pyrometer to check the temps so as to determine the correct pressures. The runs were on concrete, air temp was 88deg F, made six runs and checked the temps immediately after the end of the run. I never saw a temp over 124deg F. To quote the Tire Rack:
"While the ECSTA V710 tread compound operates well over a broad temperature range, it is most effective in the 180° to 220° F range, with 200° F being optimum for most applications."
I have to assume there is no way I'll be overheating a tire running autocross.

Mike Murphy

How old are your tires?

One thing not yet mentioned is the quality of the air in the tires, or more accurately the lack of moisture in the air in the tires. If you have a lot of moisture in your tires, then presumably when the tires get way too hot, the moisture could boil and cause over-inflation.

I would think about getting some good, clean, low-moisture air put in your tires. It's not necessary to get Nitrogen, although in most cases, the Nitrogen will be almost completely dry, thus achieving the effect you're after with low moisture air.

Dr. Car

Water suspended in air won't "boil."

Starting with those pressures cold in the morning, your pressures later in the day were certainly way too high. Yes, tires get greasy and the ability to perform at high temps varies widely from one tire to another.

For A/X you want to keep most r-compound temps no higher than the 130's. Regular street tires are OK to higher temps, but on a hot day very few tires will work their best after multiple laps without spray cooling (I use an insecticide/fertilizer sprayer). If there's a recommendation of 180-200 for the Kumho V710, that's certainly for track use, for a/x it won't work as well at those high temps. All top SCCA autocrossers on those tires spray them to keep them far, far cooler.

With street tires, I would generally recommend not worrying about a sprayer, but do keep track of your tire pressures and get a pyrometer to compare temps in the outer 1/5, middle and inner 1/5 of the tire. You can adjust pressures, alignment and driving style to equalize temps across the face of the tire. But that's a complicated topic...

Mike Murphy

I'm not sure I am following you. I was under the impression that since water suspended in air is considered a vapor, and vapor pressure increases with temperature, vapor pressure can form bubbles inside mixture.

But even if water can't boil, I have found that many times, inside the tire, the water has condensed to liquid form, and you can actually see a puddle at the bottom of the tire if you deflate the tire and take it off the wheel. If that water gets hot enough, it can boil and actually cause the tire to explode (rare).

Dr. Car

Water as a vapor is already a gas. When liquid water boils or evaporates, it becomes a gas. Like any gas, be it CO2, O2 or whatever, it will increase in pressure as temperature goes up when it is in a confined space. But different gasses respond differently to temperature.

When you see liquid water in a tire, I wonder if it would evaporate long before getting to the boiling point of 212 (actually the boiling point will be higher under pressure). Never heard of tires exploding from boiling water ... only race tires should be heated to those temps, and I'd hope they are maintained well enough there isn't water inside them. Got links to technical articles about this phenomena? I'd like to know about it.

Mike Murphy

Tell you what - let's take this discussion over to the racing section. No sense in using up this thread. Or we can just agree that moisture is bad inside the tire and has a dramatic affect on tire pressures, which put under stress and heated. Agreed?

Vlocity

IF you felt the front to rear balance was about right at your cold pressure, you might drop tire pressure 2-4 PSI on fronts and rear at your next event and see of the problem returns.

Once you find that magic pressure, be sure to get that cold pressure for reference the next day and keep good notes. I actually keep a little binder with my sway bar settings, shock settings, tire pressures, toe etc. etc.

If you ever start doing Driver Education events your set up will change dramaticly from your autocross set up.

You should also "chalk" the side wall or pay attention to the tire "rollover" Most tires will have a little triangle part way over, where the tread transistions to the sidewall and you do not want to exceed this point.

Street tires generate a lot of heat because of the tread depth....track & autocross tires are shaved to reduce this problem......All and all as you progress you will likely want to buy a set of dedicated sticky tires and not risk chunking your street shoes.

Good luck and I hope this helps a little. As someone else mentioned, you may have also been overdriving the car. Smooth is fast.

Ken

Dr. Car

I'm really completely unfamiliar with the phenomena of water in tires causing problems when they get hot. I'd be interested to hear facts or anecdotes about it from veterans in the racing & DE forum. Just seems hard to imagine that race tires are used enough to build up much condensate inside them, but I cannot make any claim to knowledge on whether this happens much.

Mike Murphy

This board has a lot of good information, which is why using the search function has really helped me out at times...

I did a quick search and found quite a few topics related to air moisture in tires. It mostly comes up when people are discussion putting 100% Nitrogen in the tires instead of 78% Nitrogen (outside air).

https://rennlist.com/forums/showthre...ht=water+tires
https://rennlist.com/forums/showthre...moisture+tires
https://rennlist.com/forums/showthre...moisture+tires

Vlocity

I've been through about 30 sets of tires on my 928 and I can honestly say I have never seen moisture accumulation of any type within the tire. While there can be some moisture, most shop air is run through a moisture filter....I even have a filter in my small garage set up.

Ken

Mike Murphy

Yes, all good air compressors setups should have good drier in place, but some people fill up at the local gas station and if you want to have fun one day, put in a quarter in those crappy little compressors and you actually SEE water shooting out of the hose.

auto-xr

Running PS2s I usually set the fronts to 34 and the rears to 38 for AX. I monitor the tire temps too and adjust accordingly. Seems to work out well.