Will larger tire size induce cupping??

[Dylan]

Morning fellas. I'm going from the stock 265/65r17 tires to a 255/75r17 (32x10) tire. The guy at firestone told me not to go with the C rated tire but instead the AB. The AB is a 113s, the C is a 115 I believe. He told me that if I go to the C rating then it will be prone to cupping. I've not seen anything relating the load to cupping on tire wear. Can anyone confirm?

 

[DC runner]

Heavier tires put more wear on your shocks, or if your shocks are old and weak, they can cause cupping.

Cupping is basically your shocks are unable to keep your tire on the ground all the time, so it "bounces". That bouncing causes cupping over thousands of miles.

I won't say in your situation, that will happen. If you shocks are still in good shape, and the move up isn't that tremendous, then you will probably be fine.

 

[Dylan]

So with my current stock shock setup, is it advisable to go with the AB? I intend to upgrade the shocks eventually, but don't want to subject new tires to uneven wear if it is likely to happen.

Furthermore, if I do go with the AB, and later replace my shocks as intended with Bilstein 5100s...will a lower load (AB) be affected the same way by adding newer shocks? Or is this a one way street in regards to going with larger tires on stock suspension.

 

[MarkinWMich]

When I got my second set of tires after my first lift, I went from the stock P-rated tire to a set of C-rated BFG Mud Terrains 255/75R17's. Right from the start, the team at Discount Tire had a difficult time balancing them. He had almost a full pound of weights stuck over one of the wheels, and it still wasn't right. In fact, I got about 3 blocks away from the Discount Tire and had to turn around because the steering wheel was bouncing like crazy. Another tech rebalanced them all, but honestly, I don't think they ever were balanced right. I bought 5 tires and rotated them, including the spare, every 5K. I eventually got a good 60K out of them (a 50K tire), and still had a lot of tread, but a few of the tires were horribly cupped and had a lot of vibration...I had to swap them out. So, it may be that it was a heavy, knobby, off-road tire. It may be that it was a C-rated tire. It may be that the techs on that day didn't have a complete understanding of what they were doing. I don't know.

I've got a set of E-rated BFG All Terrains 265/70R17's and these are much smoother on the road.

So, I don't know if there is actually something about all C-rated tires, that particular C-rated tire, your tech is a genius, or he was trying to baffle you with the BS.

Personally, I think it has a lot more to do with the condition of your shocks, your alignment, and the balance of the tire and wheels.:shrug:

 

[ebg18t]

Personally, I think it has a lot more to do with the condition of your shocks, your alignment, and the balance of the tire and wheels.:shrug:

I completely agree with this. :thumb:

OP- Having run C, E & P tires I feel it has more to do with proper alignment and the use of quality shocks. If you run shot/worn shocks you can't expect tires to wear evenly.

IMHO I would replace your 10 year old shocks first, get it aligned then get some new tires. The 255-75-17 is a great size.

 

[Dylan]

Alright, thanks for the insight. FWIW, I'm getting an alignment...in fact I'm getting the lifetime alignment they offer, so once i do the shocks i can align it again.

My tires currently wear evenly. My shocks aren't "shot", but they are not new. Will new shocks, even unlifted OEM size, be good enough for a larger rating like a C? Or do larger tires require a beefed up shock? I'm going to get 5100s all around most likely.

The stock 265/65r17 110T AB size would have a load range of 2337 lbs with a height of 30.6" and 38 lbs per tire, 44 psi.

The P255/75r17 113S AB size would have a load range of 2535 lbs with a height of 32.1" and 43 lbs per tire, 44 psi.

The LT255/75r17 111/108R C size would have a load range of 2405 lbs with a height of 32.1" and 43 lbs per tire, 50 psi.

So the C rated has a lower load range, same height, and same weight per tire.

I'm surprised i haven't seen any mentions about upgrading shocks in other tire threads about the same topic. Plenty of people going the 265/70 route on stock setups.

Any other thoughts??

 

[Dylan]

So the Firestone guy called me back saying he got confused, thought I was going to an E load. He took back what he said and confirmed the C load should be fine....so now I'm confused based on what others said in this thread.

 

[BlackWorksInc]

Heavier tires put more wear on your shocks, or if your shocks are old and weak, they can cause cupping.

Cupping is basically your shocks are unable to keep your tire on the ground all the time, so it "bounces". That bouncing causes cupping over thousands of miles.

I won't say in your situation, that will happen. If you shocks are still in good shape, and the move up isn't that tremendous, then you will probably be fine.

Spot on, cupping is typically a function of weak/worn shocks and/or shocks not strong enough for the unsprung weight. Meaning that if you're running factory shocks on a 33" LT Mud Terrian set-up you will most likely see cupping as the factory shocks and springs just can't manage that extra weight properly.

So the firestone guy called me back saying he got confused, thought i was going to a E load. He took back what he said and confirmed the C load should be fine....so now I'm confused based on what others said in this thread??

My Nitto Terra Grapplers are E load if I remember right and they haven't shown signs of cupping. Then again I am running a LT285/70R17 with a 2.5" OverLand Warehouse lift kit with 700lbs springs; so my suspension easily manages the extra weight I run.

 

[Drak]

So the firestone guy called me back saying he got confused, thought i was going to a E load. He took back what he said and confirmed the C load should be fine....so now I'm confused based on what others said in this thread??

This is what I was thinking as I was reading the thread really.
An E tire is generally heavier and stiffer, w/ stiffer sidewalls and less flex.
With weakened shocks, would tend to 'bounce' more (thus cup) than a C tire which has softer sidewalls and more flex/give to them.
So I would agree with his amended statement, E's would create more havoc on weak shocks than C's would.
E's - harder, heavier, stiffer = more bounce w/ weakened shocks.
C's - softer, lighter, more sidewall flex on hand to absorb road irregularities.

 

[drewm]

I think the extra 10lbs a tire you get by running E load pales in comparison to the rear axle weight. I wouldn't expect cupping unless your shocks are totally shot or tires are unbalanced to the point your tires are leaving the ground a lot.

Also the difference in my Cooper AT3 between the C and E load is around 2 lbs which is nothing.

 

[Dylan]

I'll get better pics posted later. Here they are on the newly acquired PC black SR5 wheels.