Toyo open country AT3 poor wet weather performance

[ChrisMA1B]

Under real world testing, the hydroplaning performance of different tires run at the same pressure and load on the same vehicle will hydroplane at different speeds. I'm curious where you found that equation - can you share it?

I don't remember exactly where I saw that, but I know that NASA did some testing on aircraft tires, and the NHTSA did research on highway vehicles. I was working as an expert witness on a personal injury highway accident case some years ago, and I found the formula I quoted. I think that NASA came up with a different formula for aircraft (I believe that it was 10 times the sq rt of the tire pressure, which maybe was different because of lift and ground effect...

You may be correct that "real world" might have turned up some differences, but I do not know. There are variables, such as depth of water and ambient temperature, etc. I have observed some vehicles hydroplaning on the highway, and it seemed that it was well below "cruise speed." I looked it up again, and it turns out that there are several formulas - I just found one on the Purdue Univ website that says 10.35 times the square root of tire pressure. So for a tire at 36 psi, that would be over 62.1 mph, which I have seen as demonstrably wrong. The bottom line is that hydroplaning is dependent upon tire pressure, so driving on the highway with underinflated tires is a risky proposition. Lowering tire pressure off-road is very different, since off-road speeds are far lower. Just make sure one reinflates before going back on the highway.

 

[uraniumrich]

I don't remember exactly where I saw that, but I know that NASA did some testing on aircraft tires, and the NHTSA did research on highway vehicles. I was working as an expert witness on a personal injury highway accident case some years ago, and I found the formula I quoted. I think that NASA came up with a different formula for aircraft (I believe that it was 10 times the sq rt of the tire pressure, which maybe was different because of lift and ground effect...

You may be correct that "real world" might have turned up some differences, but I do not know. There are variables, such as depth of water and ambient temperature, etc. I have observed some vehicles hydroplaning on the highway, and it seemed that it was well below "cruise speed." I looked it up again, and it turns out that there are several formulas - I just found one on the Purdue Univ website that says 10.35 times the square root of tire pressure. So for a tire at 36 psi, that would be over 62.1 mph, which I have seen as demonstrably wrong. The bottom line is that hydroplaning is dependent upon tire pressure, so driving on the highway with underinflated tires is a risky proposition. Lowering tire pressure off-road is very different, since off-road speeds are far lower. Just make sure one reinflates before going back on the highway.

Thank you for the information. I didn't get that you were trying to emphasize that it's important to run the proper tire pressure to help prevent hydroplaning. I read the Purdue paper you referenced. The paper makes it clear that the equation is a simplified equation, so it does not take into account other factors (such as tread depth, tread design, water depth, etc.) The equation gives an easy way to calculate a rough estimate of the speed where tire hydroplaning may occur. I'd guess that it's never a good idea to run an under-inflated tire on a paved road regardless of road conditions.

 

[markofky]

I swapped out my stock FE wheels and tires after purchase this summer to TRD bbs 18” wheels and at3 275/70/18’s. I’m running them at 35psi and they have been great all summer.
However, once the rains started here in the PNW, they have been crazy slick and unsettling to drive.
The road on my daily commute is steep with many off camber turns and I’ve felt the LC FE slip and slide all over (no leaves on the road either).
For one, I would have thought the full time 4WD would help and 2 the AT3’s updated rubber compound would grip better.
Has anyone else experienced greasy type driving in the LC in the rain around corners?
Think the tires need to acclimate more?
Thanks for any advice or feedback.

Same vehicle and same tires here in 285/70/17 and find the wet traction easily as good as what I once thought was best in the rain which if the Michelin Defender LTX/MS.