So my dad is a pretty smart guy and an engineer so i tend to take his word for most things. But idk what to think about this. Yesterday while driving to my dads house my car didnt feel right while driving so i checked my tire pressure and it was all over the place with these new wheels i just got used, so i changed them all to 35psi which i think is right for our cars, no? While i was doing this my dad came out and said to over inflate them because its starting to rain alot here. And he explained that it would make the tread bulge out making them more resistant to hydroplaning, kind of like a motorcycle tire. Is this good ok to do? Or should i just have them at the recommended specs?

 

I'll let more experienced users chime in about street driving, but when I was filling up for Autocross (in the rain, lots of rain), I referred to:

TireRack inflation pressures for competitive driving:
http://www.tirerack.com/tires/tirete....jsp?techid=58

 

Hmmm that's an interesting article, thanks for that. Kind of confirms what my dad said (for track use atleast). but I don't know why would be any different for street driving especially since I do most of my street driving on the freeway at 50-60mph

 

Not a hydroplane expert. But engineering background here.


Increase in tire pressure will decrease in the surface area of the tire contacting the pavement. Higher pressure on the tread means that the contacting treads will dig in deeper through water obviously reducing the hydroplane.

Just searched on wikipedia, and hydroplane speed is proportional to the square root of tire pressure. Which means you will have to travel 1.4 times faster to hydroplane when tire pressure being doubled. Your dad is right. Over inflation will reduce the possibility of hydroplane.

 

Now that we established that it is good. For our cars what would be a good pressure to run? I set them to 40psi. Would that be good?

 

This

However

Less contacting surface area means less overall traction. The tire is designed so that all of contact patch is touching the ground (thus the name "contact" patch), when you overinflate, it starts reducing the contact patch (think motorcycle tire). Since not all of it is touching the ground, you're basically throwing most of its features out the window and greatly reducing its performance all while only wearing it out in the center as well which is a whole other issue. Your dad is correct but when you’re not hydroplaning and just driving in the rain, your want as much tire on the road as possible. You don’t want a bus filled with nuns and child prodigies to cross your path and only have motorcycle-like contact with the ground on a 3000lb. car. . . in the rain.


Having the right set of tires would be of much more help; the more tread on them the better, of course. Deeper tread= better water evacuation/channeling.

 

Thats a good point i didn't think of, but would it bring up the point of more of the weight on a smaller part of the tire, would it actually improve breaking because the tire would dig more onto a slick road. instead of spreading that weight across more of the tire that is on the slick road. And keep in mind by upping the tire pressure on a car tire it would minimally affect the contact patch since it is a flat tread and not a round tire like a motorcycle.

 

You're right but the less contact patch, the less of a threshold before it skids or VSA/ABS comes on i.e. going back to less traction. I used the motorcycle just as an extreme example.

In my opinion, the more (flat) contact patch, the better. For what it's worth, I'm far from an engineer but I've been selling tires for about four years and have gotten to do cool tests/training sponsored by the manufacturers.

Best advice I can give ya is run the recommended psi which I beleive is 32 or 33psi, and invest in a good tire. If you do a lot of wet driving, obviously wet traction is a factor you wanna look for. My personal recomendation is the Michelin Pilot Super Sport or the Bridgestone Potenza S0-2 as a plan B. Do some reading on the super sport, theres even a couple threads on this site about it.

If you really want to maximize your wet traction, your best bet is to take your car and do tests with different pressures.

Hope this helps!

 

think of your favorite supercar and its tire widths

 

I totally agree with ducatikid749.
For OP's subsequent question, increasing tire pressure will obviously have pros and cons.
It will reduce the possibility of hydroplaning, which means you can go faster without hydroplaning.
Second, once you are hydroplaning, you have close to zero braking capability. So there's no point of discussing braking capability once hydroplaning.

Now, assuming you are traveling BELOW hydroplaning speed, your grip won't improve with a higher tire pressure.
For instance, if you are stuck in mud, you lower the tire pressure to get more grip.
Now that is assuming you have enough tread left to drain out the water when driving. If not, you are probably hydroplaning again.

So I guess there's no perfect answer. If it's raining a lot, and you are on a highway, increasing the tire pressure will raise the hydroplaning speed but you will lose some of braking power.

If you lower the tire pressure, you will have more chance to hydroplaning, but will have enough grip. So that would be more suitable for slow stop-and-go traffic, where you won't go fast.

Again, it all depends on so many factors.

Please correct me if anyone finds any mistakes.

Thanks