Heavier wheel/LT tire combo "skipping" across pavement?

[Nechaken]

Question for you guys that have gone to a heavier wheel/tire combo.

In summer, I run Cooper AT3 LT (ie E-range) tires on tuffant steel wheels. I live in CO where we have some windy roads with less than great pavement quality. I've noticed when cornering over bumpy/broken pavement, sometimes the car seems to "skip" a bit, with the result being the radius of the turn seems to widen without corresponding steering input. Nothing that sets off the DSC or anything, but does feel a bit disconcerting. (Slow down, I know)

Has anyone else experienced this? Each wheel and tire comes in just under 90lb, so about 20lb heavier per corner than stock tire on stock rim. So I'm wondering if the suspension is now a bit underdamped, with the wheel not being pushed back down hard enough after a bump lifts it. I was considering trying to find a set of takeoffs of the Defender 18" wheels (or something similar). Alternatively, it could just be the Coopers are much firmer than passenger tires and that's contributing to it.

Thoughts? (Suspension is fine, car is recently aligned, etc.)

 

[mm3846]

I had Coopers on my D1 and hated them on the road, I found them unpredictable and they sucked in rain.

What’s your tire pressure?

 

[Nechaken]

I had Coopers on my D1 and hated them on the road, I found them unpredictable and they sucked in rain.

What’s your tire pressure?

I've played around quite a bit, from 42/46 to 55/60. The skipping is less pronounced at the lower pressures, of course, but I'm guessing that's pushing it in terms of load capacity if I have 4 people and camping gear and ice and firewood etc in the back. I actually can't complain much about the tires other than the skipping effect. I saw that Tire Rack did a comparo and referred to them as having an "unforgiving" ride over impacts. I guess that's the tradeoff for puncture resistance.

 

[ryanjl]

I run 38 psi front and 40 psi rear on my 265/65/18 e-rated tires on my Defender steelies. I think you're running too high of pressure. The sidewall on an e-rated tire is stiff enough that you don't need to run high pressures.

 

[mm3846]

I run 38 psi front and 40 psi rear on my 265/65/18 e-rated tires on my Defender steelies. I think you're running too high of pressure. The sidewall on an e-rated tire is stiff enough that you don't need to run high pressures

Yup I think you only need to run 2-3psi above stock on that size E rated to meet factory GVWR.

Remember you don’t need to run the higher PSI in the rear when empty, it’s just spec’d that way in the US.

I also shredded two AT3s in my D1. Not to discourage you since you’re already running them, I know some people like them but I sure didn’t.

 

[ktm525]

Unsprung weight is a real killer to ride and handling. That poor stock shock assembly is trying to control the heavier wheel/tire combo. The best solution would be proper shock valving for the increased unsprung weight but that would be $$$$$$.

 

[Nechaken]

I run 38 psi front and 40 psi rear on my 265/65/18 e-rated tires on my Defender steelies. I think you're running too high of pressure. The sidewall on an e-rated tire is stiff enough that you don't need to run high pressures.

I've always thought you were supposed to add pressure when running E-rated tires. At least pickups and such that can be spec'ed with E-rated tires work out that way. Granted on an F-250 they're probably planning for 3000lb of construction materials in the bed or a horse trailer or something.

I was thinking the following:

Stock Continental 4x4 Contact load rating / max PSI works out to 47 lb per PSI, meaning based on factory pressures they're planning on handling weight of 1700 front / 1931 rear (per tire)

AT3 LT in 265/65/18 has 3305lb rating @ 80 PSI which works out to 41 lb per PSI. Based on the factory load distribution, that comes to 42 front / 47 rear.

Obviously its not a linear relationship and it'd be cool if Cooper published load inflation tables. But this seems like a reasonable starting point.

Yup I think you only need to run 2-3psi above stock on that size E rated to meet factory GVWR.

Remember you don’t need to run the higher PSI in the rear when empty, it’s just spec’d that way in the US.

I also shredded two AT3s in my D1. Not to discourage you since you’re already running them, I know some people like them but I sure didn’t.

I can bring the rears down and see what happens. Were your AT3s also E-range? I went with E-rated tires here in CO due to all of the sharp rocks and such, so far they've been pretty durable. Very firm ride, however. Tire rack seems to love the General Grabber, but it doesn't come in 265/65/18. Even if I got some money back from selling the Tuffants/ AT3s, I'd prefer not to spend the $$ to replace the whole tire / wheel setup.

Unsprung weight is a real killer to ride and handling. That poor stock shock assembly is trying to control the heavier wheel/tire combo. The best solution would be proper shock valving for the increased unsprung weight but that would be $$$$$$.

Yeah, that's my thought about moving to a lighter alloy wheel. At least the AT3s are (comparatively) light compared to other E-tires. No idea how I would find someone to modify the air spring/shock.

 

[f1racer328]

No idea how I would find someone to modify the air spring/shock.

Could throw in Bilsteins.

https://cart.bilsteinus.com/details...4047164&Submodel=3017349710151427203&Pos=Rear

This is the shock for the rear. These are stiffer than the OEM shocks.

 

[mm3846]

There are countless other people running that wheel and tire combo without issues and even heavier tires, too. I’d start checking all your suspension bits after settling on the air pressure.

My AT3s were E rated as well.

 

[djkaosone]

Like everyone said, try running it close to oem tire pressures. I run mine at F40:R45, which is slightly over oem (F36:R42).