# Tire pressure and hydroplaning resistance



## XtremeRevolution (Jan 19, 2012)

I had a trip planned to visit my cousin who is back from the military this weekend, leaving tomorrow afternoon and arriving there around 11:00PM, central. However, I noticed this on the weather forecast. 










I'm driving from Chicago to the southern tip of Illinois into North Tennessee, which will practically be in the "red zone." I will check the weather tomorrow to decide when to leave based on when the storm is expected to hit the hardest. 

So, I need to make some preparations. My understanding was that a high tire pressure places more pressure per square inch of road area and traps less water overall, thus "slicing through" water more easily. However, I have over my time spent here learned and accepted that max sidewall pressures come with a compromise in wet handling traction due to the heat barrier mentioned before. 

So, what tire pressure would be recommended for very heavy rains? I am expecting completely soaked roads during big downpours, and my biggest concern is avoiding hydroplaning.


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## CruzeDFB (Mar 3, 2013)

I found this on Wiki Answers 

"Absolutely, and if one tire is more flat, thus wider, it will or could cause a spin out and loss of control. 

It is directly related to the square root of the tire pressure. According to testing cited by the NTSB (National Transportation Safety Board) the speed at which a normal tire will begin to hydroplane is 10.35 x the square root of the tire pressure. So, if the recommended tire pressure for your vehicle is 36psi, the speed at which you can expect to hydroplane would be 62 mph. Let that tire pressure go down to 25psi and you're hydroplaning speed drops down to 52mph!"


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## spacedout (Dec 7, 2010)

Last summer running 40psi in my 16in firestone FR710's they sucked in the rain. Well today I got a chance in similar conditions to drive at 34PSI, I think they were actually worse! Might be the less tread depth with 15,000 more miles though. 

If I were you I would just split the difference between your normal PSI and door place card. I suspect your MPG will be almost as good as normal. I loose about 5mpg highway when it rains, mostly due to the defogger and AC use I believe(I loose similar MPG in the summer using the AC).


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## XtremeRevolution (Jan 19, 2012)

CruzeDFB said:


> I found this on Wiki Answers
> 
> "Absolutely, and if one tire is more flat, thus wider, it will or could cause a spin out and loss of control.
> 
> It is directly related to the square root of the tire pressure. According to testing cited by the NTSB (National Transportation Safety Board) the speed at which a normal tire will begin to hydroplane is 10.35 x the square root of the tire pressure. So, if the recommended tire pressure for your vehicle is 36psi, the speed at which you can expect to hydroplane would be 62 mph. Let that tire pressure go down to 25psi and you're hydroplaning speed drops down to 52mph!"


That was my understanding as well. My tires are currently at max sidewall pressure. I just wanted some confirmation on this. I'm not taking any chances.


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## Robby (Mar 1, 2013)

Yeah, that can be a tough one to consider.

The biggest reason rolling resistance is reduced with higher pressure is because the tire presents a smaller 'footprint' front to rear.
The side to side 'footprint' stays about the same due to the way the radial belting maintains the tire tread width.

So, knowing that Chevrolet, in conjunction with the tire maker, determined that 35 psi (ambient) was the best compromise for cold/hot/wet/dry handling as well as acceptable tread life and rolling resistance on this tire mounted on this vehicle.

Hydroplaning is, to degree, the result of inadequete tread depth, causing the tire to ride up on the water rather than pump it out of the tread........I've read your depth measurements and that isn't an issue in your case.
But, I do think it important to maximize the footprint length to minimize slip potental.

The other side of the coin.....a shorter footprint puts more weight on the ground per sq. in. possibley enhancing traction, comes into play.

All the thoughts to say, probably should run at the specified pressure......and do slow down a bit.....any tire regardless of tread depth hydroplanes under the right conditions.

Have a safe trip.

Rob


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## obermd (Mar 3, 2012)

I would expect the smaller "front to back" footprint of a higher pressure tire to increase hydroplaning resistance because the water doesn't spend as much time trapped under the tire in the treads. This would explain the NTSB's results.


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## XtremeRevolution (Jan 19, 2012)

Thanks guys. I'll probably keep them the same simply to maintain hydroplaning resistance. Going to replace the wipers as well since they're 22k miles old and are starting to smear.


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## Gravity (Apr 6, 2013)

:1poke: so if all you are worried about is "hydroplaning resistance" then sure more psi will help you "slice" threw deep water. you know those old sayings that are fun but true when you really get down to it? like "there is no replacement for displacement". If i had to come up with one on the spot for this thread it would be "Contact patch is King". Any gains from psi "slicing threw standing water" are lost if you have to turn, stop, change lanes quickly accelerate hard etc. so while you might not hydroplane as fast with more PSI in your tires if you do hydroplane it will be alot harder to regain control of the car especially if it goes into a skid. 

Stuff like this is so subjective that in the end it really doesnt matter one way or the other. I have driven countless high performance cars at bridgestone "ride and drives" (which are all done on wet tacks) to test out there products against the competition. and the most important thing i have learn from them is that bar anything else the most important item on a car is the tires. if you have premium tires on your car its going to handle well, if you bought FR710s or goodyears (pretty much any of them they are all horrible in the wet they get stuck on wet grass), then your going to have a bad time in the rain regardless of what PSI your running.

By far the most asked question i get from customers is "are those good tires" and of coarse the people that ask this question are the people that want the cheapest tire they can buy. not to pick on *spacedout* but buying FR710s (firestones economy tire) and expecting them to be good in all conditions is insanity. Firestone has a great tire (Precision touring) that is like 15 dollars more a tire and not only lasts long but out performs the FR710 by leaps and bounds. The performance gained (and safety because of it) is worth way more then 60 dollars.

Yes i realize i went on a huge rant sorry about that.


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