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.

 

[Blue Bear]

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.

 

[b407driver]

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.

Of course any given tire would need to be at the optimal pressure to prevent hydroplaning to the extent possible under a given set of conditions. The assertion that the equation applies to all tires equally is simply... well, wrong. That would imply that a bald tire would perform identically to a tire with any sort/combination of tread, lugs, channels, etc.

I could see using such an equation to try to prove that someone running incorrect tire pressure may have created an accident, contributed to increased severity, etc., but beyond that, I don't know how it applies to the fact that different tires demonstrably react differently to conditions under which hydroplaning can occur. And, as an aside, airplane tires are relatively homogeneous in regard to basic tread design compared to car tires.

 

[markofky]

Of course any given tire would need to be at the optimal pressure to prevent hydroplaning to the extent possible under a given set of conditions. The assertion that the equation applies to all tires equally is simply... well, wrong. That would imply that a bald tire would perform identically to a tire with any sort/combination of tread, lugs, channels, etc.

I could see using such an equation to try to prove that someone running incorrect tire pressure may have created an accident, contributed to increased severity, etc., but beyond that, I don't know how it applies to the fact that different tires demonstrably react differently to conditions under which hydroplaning can occur. And, as an aside, airplane tires are relatively homogeneous in regard to basic tread design compared to car tires.

Wow! More simply stated, and back to the OPs inquiry, my tires grip well in rain and I like them

 

[trek805]

We dont get rain so I dont know. How are they in earthquakes?? In So Cal

 

[Piggy]

Sorry to bring up a dead thread, but I just couldn't figure out why there are such polarizing opinions about this tire...

Seems the LT and the SL have different siping?

Could the explanation be that simple?

 

[WookieBait]

Sorry to bring up a dead thread, but I just couldn't figure out why there are such polarizing opinions about this tire...

Seems the LT and the SL have different siping?

Could the explanation be that simple?

View attachment 63206

Lexus appears to have some sort of tire they put on the GX that has the same name but different specs as well to add to the confusion.

For what little it's worth I have the plain Jane version of this tire in standard load and have not experienced any issues in snow, mixed conditions, light or heavy rains. I drive like a grandpa though so I'm hardly pushing the limits of tire grip or capabilities on road.

 

[ERROR504]

These are the specs of the ones I got from tire rack:

• Size: 265/70R18
• Style: Blackwall
• Eco Focus: N/A
• Load Range: SL

• Serv. Desc: 116TService Description
• UTQG: 600 A B UTQG
• 
  Severe Snow Service Rated: Yes

I have not had any issues with them in several years rain. They performed pretty well in some light/moderate snow. These toyos are awesome and have no complaints with them.

 

[Altitude]

There’s some confusion on using all-terrain tires in inclement weather, and maybe a misguided sense that all-terrain tires are universally “better” than other tires.

The name of the game in snow and rain is maximizing the tire’s contact with the road. AT tires by nature have voids in the tread which are designed to grip irregular surfaces like rocks, and move loose material out. They do that well but they do it at the cost of contact patch size. With rain, the AT tread patterns do well enough moving water away from the contact patch but the tread voids give up a lot of contact real estate in the process.

AT tires can be effective in heavy snow because the road surface in those conditions is similar to loose dirt or sand, and an AT-style tread pattern is useful to maintain grip. But on hard packed snow, ice, or wet roads, which is what we all mostly deal with, the tread pattern provides no advantage. In fact, compared to a very good highway tire like the Michelin Defender, AT tires will predictably underperform in those conditions. Siping does help.

In winter this is made even worse by hardening of the rubber compound in cold temperatures. Ultimately that further constricts contact patch size.

This is why most winter tires, even those that are designed for trucks like the DMV-2, have tread patterns designed to maximize contact patch size in the snow and do not have aggressive AT-looking tread patterns.