Spraying Tires with Water

[jdp526]

A buddy of mine can't understand why so many people at our autocross events are spraying tires with water between runs. It's definitely hot down here in Texas right now so tires are building up some heat, but I wouldnt think they would heat up beyond the optimum tire temp for best traction. Most people complain about their tires getting 'greasy' after several runs even though they are spraying them.
I dont notice many people checking tire temps and pressures. I haven't found much info on the max tire temp for the best performance from street or R tires, except for a one article that mentioned a range of 165 to 185 for street tires and 185 to 220 for R compounds.
I guess they are trying to cool down tires and reduce the tire pressures, but wouldnt they be better off building up heat and reducing pressures based on tire temps to achieve better tire performance?
I can only get the FC tires up to about 125-128 so it seems like I would see an improvement in traction if I could get more heat into tires.

[Keith Carter]

Seems like a tale of monkey see - monkey do. If they're using regular air in their tires, it would benefit them keeping the tires as hot as possible to maintain as close to operational temps and pressures as possible. It would also make me think that they are prematurely heat cycling (hardening) their R compound tires if they purposely cool them between sessions if they can stay that hot with ambient temps in Texas.

[cooleyjb]

Your FC is light. Many of those Street tire guys are in 2500-3000 pound cars. They can get the tire temps over 200 without trying very hard. I know when I had an STX WRX it was really easy to overheat the tires and be slipping and sliding around. It was never about air pressure. It was always about the tire temp.

[jdp526]

I will measure some of the tire temps on other cars at the next event to see just how much heat they are generating.

[Robert Puertas]

Lots of things are happening on street tires that don't apply to slicks on a formula car.

1. Street cars are heavier, and not nearly as well balanced.
2. Street tires have softer sidewalls, which flex and create heat.
3. Street tires have tread which flexes to create heat.
4. Street tires have a compounds which are designed to work in a lower temp range than racing slicks are designed for. (Not unlike race brake pads vs. street brake pads)

[Dick R.]

For most open wheel race tire autocross situations spraying tires doesn't seem to be needed for the reasons noted. Spraying the radiator(s) is more common. If you do, please don't let the water go to where I have to drive through it (hence cooling/wetting my tires just before a run . . . ).

Dick
CM85

[ChrisInAtlanta]

Back in the days I drove a BMW M Roadster, I did an event in Ozark, Alabama. Mid-summer + very high grip concrete. I corded ALL FOUR new DOT Hoosiers in eight runs. Not quite back-to-back runs, but not far from it. And not just a few cords showing. The starter, on my last run, told me that my tires were corded. I just laughed. I mean, these were new tires, so it could only be a joke. . . Ah, youth.

Real slicks, that nearly all of us here use, like much higher temps. A much-smarter-than-I high level competitor told me that if you can hold your hand on the tire, it's not as hot as you'd like it to be.

Chris Eckles

[Joe_914]

Yep the current Hoosier Crack that many autocrossers buy is the A6. It was develped to grip cold as in 100 to 130 degrees. under that and they slide, over 150 they slide. Either way they will wear fast if they slide. Had a local guy running a Boxster S on A6's quick turn around runs of 40 seconds fairly fast lots of transitions (lane change) type features. He hit a wall on times and started falling off I touched his tires and they were screaming hot and I could not keep my hand there for long. We sprayed heavy and he dropped 1.5 seconds.

Blythville NT around 56-60 second runs at high speed high G course, the CM guys were lightly spraying thier tires and heavy spraying the radiators. it was HOT HOT HOT outside. Thier R25B Hoosiers had a nice even graining on them.

Keep the tire happy and it will reward you.

What is happy for a Hoosier R25B ??? core temp with a probe pyrometer. I would think around 150 to 170.

[M.Sauce]

With the ambient temperature being 100 plus and the pavement temps probably in the 135 range,if you have an A compound Hoosier tire you are going to overheat the tire right away.Cooling it down with water will help for the first part of the course and there is time to be made up there.Anytime you cool a tire off with water when it is that hot outside I would think it probably does not help the the life of the tire either.Sometimes the conditions are just not good for tire wear and grip.Adjusting pressures will help some but you are still asking a tire to work at temperatures outside of its working range.

[iamuwere]

With two drivers in an F500/FMod in autox, on hot summer days, cooling the Hoosier 25a and 25b was absolutely necessary or times would drop off. There is some critical temperature that works in autox and beyond that temp it starts to slide. Interestingly, I would run the same tires in club racing and they would get greasy at the end of hot day, but it would still be quick. There is some difference on solo surfaces and the type of energies put through the tires.

Jim
(solo nat champ---codriver sister multiple solo nat champs)

[Tom Maycock]

As you can see from the follow up posts, autoxers are well aware of the temperature factor.

It used to be that having a co-driver was absolutely vital to do well at national tour events and the national championships, because it was the only way to keep the tires warm enough to work well. Although I haven't run the current Hoosiers myself, my understanding matches what you've read above--i.e. that the issue these days is keeping their temperatures low enough.

A good water sprayer was a must with the first generation of Falken Azenis, which were *the* tire to have in the early STX (street tire) class days. I was skeptical myself about the need to spray those things down until I experienced it myself. Co-driving a friends prepped WRX for the first time, I was pretty fast early in the day but couldn't figure out why my times plateaued despite seemingly driving the car better and better on each subsequent run. But having watched all the other WRX guys spraying down tires between runs, I realized that ours had indeed got *very* warm.

The car sat through the last heat, and then we went out for a couple of post-event fun runs. The grip difference was like night-and-day--easily 1.5 seconds faster on a 60-second course.

So, yeah, the guys and gals with water sprayers probably DO know what they are doing.

Tom

[Jim Garry]

Interesting back and forth here with opposite experiences. For my C Mod FF my co-driver and I have only rarely sprayed tires and I don't think it made a difference.

At Test and Tunes we've run back to back to back to ... etc. runs and the car gets faster and faster. Not 100 deg out but about 90 deg.

I can't explain the two opposite experiences discussed on this thread.

[Tom Maycock]

I don't know that there's that much disagreement.

The key point is that there is a big difference between heavy(ish) street cars on either street tires or DOT R compound tires on one hand, and lightweight open wheel cars on slicks on the other. It is pretty rare to see the formula car guys spraying down tires, but not uncommon to see folks with a heavy car on 140 treadwear street tires spraying like mad on a hot day.

There's also a pretty broad spectrum just with street cars depending on the particular tires used--some need/handle a lot more heat than others.

Autocrossing tends to be an exercise in coping with sub-optimal tire temps.

If you're lucky, you get some nice warm-but-not-too-hot days in the middle of the year where the tires come up to temp reasonably quickly on your first run and never get overcooked.

But it's just as common to have a super-hot day where keeping tires from overheating is a challenge, or way-too-cold mornings where the tires never get close to optimal temps.

I remember the last time I ran my Miata on Hoosiers. It must have been about 35 degrees out before the first morning run. The Hoosiers were practically rock hard, and literally were not round--the flat spot that had formed while the car sat in grid was making thunking noises as I rolled to the start line. Fred Flinstone had softer tires and more grip than I did on that first run. The starter waves you off and you just try to do your best to build some temps while keeping the thing pointed in the right direction, hoping for a decent second or third run.

Tom

[F five hunj]

I've never sprayed an F500 tire, and I must say that even with 2 drivers I've never gotten them hot enough.

Even 4 back to back runs at Toledo for the Pro is just a tease, they're just getting there by the end of the 4th run.

[Dick R.]

I've never sprayed an F500 tire, and I must say that even with 2 drivers I've never gotten them hot enough.

Even 4 back to back runs at Toledo for the Pro is just a tease, they're just getting there by the end of the 4th run.

Maybe you don't drive as hard as IAMUWERE who is national champ.

Dick
Never a CM national champ either.

[Jim Garry]

Tom the way I read it, some of the light formula car guys say to spray and others do not. Yes, there's agreement about heavy versus light cars. But two people who have light cars said it is necessary to cool the tires with water.

[Locked]

When do I spray my tyres? When the guys that are leading start spraying their tyres!

[Dick R.]

I think the bottom line is that if you run 25B tires in autox and if you actually get to the limit of the open wheel car (easier said than done), you might start checking tire temps so see if cooling is needed before the next run. More likely to be an issue with 2 driver cars with runs closely spaced.

Dick
Still trying to get to the car's limits.

[Dick R.]

When do I spray my tyres? When the guys that are leading start spraying their tyres!

Sounds like a good trick for them to use to slow you down. Set a really quick time that is ahead of all the other guys and then slow them down by cooling tires hoping they will copy you.

Dick

[ChrisInAtlanta]

What is happy for a Hoosier R25B ??? core temp with a probe pyrometer. I would think around 150 to 170.

Naw, I'm nearly certain that the happy temperature for these is 200-220 F. So, putting your hand on the tire face is kinda like dipping your hand in boiling water. . . I tried to find this at the Hoosier site, without success. A couple of tire types, sprint and GT, had these temps and some types up to 260.

Though on my F500, new-ish tires grip like the dickens at near ambient temps. They just get awesome when properly hot. I have never felt my tires "go away" when very hot, but I have rarely had a co-driver. Or been a national champion.

Chris Eckles

[Tom Maycock]

Tom the way I read it, some of the light formula car guys say to spray and others do not. Yes, there's agreement about heavy versus light cars. But two people who have light cars said it is necessary to cool the tires with water.

Yeah, I see what you mean--some disagreement even among the formula car crowd.

Suffice it to say that spraying tires is pretty clearly a good idea in many cases, but in others, the old "YMMV" thing applies.

[TedV]

to spray or not to spray? it depends. Do what the car wants and the driver likes the feeling best.

On the Hoosier A6 it will have more ultimate grip with some heat but will have a more loose/vague feel. Cold will feel more crisp, too hot will loose grip. If tires get too hot, like in summer, folks will use R6 compound.

For formula car slicks the best temp for grip and long life generaly is around 180. Its sort of a bell shaped curve where the details depend on the particular compound. Good grip coming in around 160 and getting greasy in the 200 to 220 range. These are the rubber core temp down close to the cords, not the surface temp. Tire surface sheds heat too quickly. General formula car tires are too hard for autocross. Were the people spraying 200 degree water on the tires?