Slicks in the WET

[15Degrees]

First off hi everyone! I'm new to this site, and had a question.
If you had to run slicks in the wet and you were only allowed to adjust tire pressures.
What would be the optimal choice for tire pressure (no real number needed)?
Also there is no standing water. Just a slick wet track.
A. Normal Tire Pressure
B. Higher Tire Pressure
C. Lower Tire Pressure

[vikram_d]

In my opinion you should run normal pressure. Higher or lower would affect the contact patch.

[thisisatest]

if you were aiming for equal running pressure, your cold pressure would likely have to be a bit higher as the water will cool the tire pretty efficiently.

[15Degrees]

if you were aiming for equal running pressure, your cold pressure would likely have to be a bit higher as the water will cool the tire pretty efficiently.

Thanks that makes sense. What would be optimal for uneven pressures?

[Paul]

I think running higher than normal and shrinking the contact patch will help against aquaplaning, essentially helping the tyre to push through the water film...

[Roland Ehnström]

On the other hand the load on the tires will be far less than normal, since you will be going at about half the normal speed, so that would tend to make the optium pressure a lot lower.

[bobster30]

In karting we use higher pressure because you cut through the water and because you have a smaller contact patch, your tyre temperture will be higher

[Jersey Tom]

Probably bump the cold pressures up a bit since you won't be building up nearly as much - but I wouldn't fuss over it too much or go back and forth over "optimal" footprint this or that.

Dry compound slicks with any amount of water on the track will be inescapably poor with not much you can do about it. Might be some other mechanical setup gains worth doing especially if you have to put the power down, but driver talent is really what's going to make all the difference in the world.

[15Degrees]

Thanks so much for the replies everyone.

I also forgot to mention how this post came about! I have 2 old cars with stock suspension with street tires. 97 Honda Civic and a 1990 Mazda Miata. The Honda had over inflated front tires by 5lbs. And the Miata had under inflated front tires by 3lbs. But they both under steered mid corner at the apex or just before in dry conditions. When the tires on both cars were set back to recommend manufacturer tire pressures, both cars were able to negotiate the corner without any undsteer mid corner. Everything is exaggerated in the wet, so it got me thinking there could be a good chunk of time to be gained with properly inflated tires while racing in the wet on slicks.

Everything just seems to contradict itself when thinking about tire pressures in the wet. Initially I was thinking a lower pressure (under recommend pressure) would give more grip by increasing the contact patch. But as others have already stated the water would actually be cooling the tires thus lowering the tires pressure already. Another thing that was mentioned above was the decrease in cornering speed, which would also contribute to lower tire pressures. I'm going to go with the higher pressures and let you guys know how it works out!

Plus also I know that driver factor in the rain is the #1 deciding factor. But this assumption of tire pressures is assuming that everyone is of equal driving skill. I've been working on trying to minimize horizontal load on the tires and being smooth.
Even if it's only .01 a lap from properly inflated tires I'll take it. Over 20 laps assuming one is consistent...that could make for a good finish. [-o<

[Jersey Tom]

The Honda had over inflated front tires by 5lbs. And the Miata had under inflated front tires by 3lbs.

How are you defining "under" or "over" inflated? Compared to placard / owner's manual inflation? Bear in mind those stated inflation pressures for tires is pretty well entirely dictated by highway safety, not performance. Best pressures for raw performance may be significantly different than placard numbers.

Initially I was thinking a lower pressure (under recommend pressure) would give more grip by increasing the contact patch.

Common misconception is that lower air pressure = bigger footprint (I hate the phrase "contact patch") = more "grip." Simply not true, not in the wet nor dry conditions. For all tire & vehicle combinations there's some set of inflation pressures which is best. Some are very sensitive - little above or below the sweet spot and you're junk. Some are very insensitive - little above or below and it's of little or no consequence.

As an aside - same goes for tire temperature.

[Andres125sx]

Best way to figure it out is to test it by yourself

Best and easiest way to make a comparison would be testing both at the same time, for example, do some laps with standard pressure in the front wheels and lower pressure on the rear ones, then standard/higher, then lower/standard, then higher/standard.

Even if differences are really small this way they will change car´s behaviour, telling you what pressure is providing more grip directly, no need to do any interpretation or comparison between different stints

If you do it, please post the results!

[gambler]

My kart pushes the nose on wet tracks without standing water, so I may try more psi in the rears with normal hot psi in front should I find myself in that situation again.

[BanMeToo]

Call me a fool but I would do the opposite... bump up the front pressures a bit.

[gambler]

Foolish never, we try both. Thanks.

[Scootin159]

My kart pushes the nose on wet tracks without standing water, so I may try more psi in the rears with normal hot psi in front should I find myself in that situation again.

Could also be because with less overall surface grip, you're not getting as much chassis flex, and thus you have too much grip on the inside rear wheel. Might want to look into options to soften the chassis to get similar flex to what you have in the dry.