Don't mix LR tires on same axle

[sreigle]

I learned something the hard way yesterday. I was not satisfied Alko-Kober had properly aligned the axles they replaced on our Montana so asked the Keystone Service Center to check them out. The axles are fine but do need alignment. However, Keystone won't foot the bill for this one since it was my fault, not theirs. I'm not sure that's fully correct since we've had some tire wear issues since day one but that's moot at this point.

The cause of misalignment - Back when we had that last Goodyear tire go bad, the one with the big bubble, we had some miles to cover and I didn't want to be without a spare for that far. The dealer in that small town doesn't carry Goodyear. So I bought a used tire, same size, from that dealer. The problem is the Montana came with Load Range D tires even though the placard says they're E rated tires. The used one I bought was LR E. Yes, the D's do have weight rating to handle the weight of our Montana. The tire dealer put, at my request, the E tire on the ground and I kept my D spare as the spare.

Keystone tells me having different LR tires on the same axle is a no-no. Apparently they have different rolling resistance that causes the E tire to cause the axle to drag on that side in comparison to the side with the D tire. I was told this can cause an alignment problem with the axle that requires it be realigned. Soooo, Keystone made us an appt with an alignment shop in Elkhart, IN, (we're in Goshen right now) for early Monday morning. It will cost me $75 if they have to align one axle, $150 if two. Live and learn, I guess.

Keystone also checked to see if they could put on a new tire to replace the one worn out on the inside but didn't have any D rated tires in the factory so they put my D spare on the ground and put the E as my spare. So I need to go buy a new tire real soon.

Thought you all might want to be aware of the load range situation. Sure was a surprise to me.

Also, some may recall I posted the rim to rim measurement on one side was an inch longer than on the other side. Keystone checked it out and found there is not a problem there. I was told the axle is allowed to move on a turn and shortly after a turn can measure as much as an inch off. They said you have to drive straight for a ways, such as the length of their parking lot which is roughly 50 yards, to get a true reading.

[NJ Hillbilly]

The mixed rating issue is a valid one. Rolling resistance may be one thing but what comes to my mind is the size and operating pressure. A D rated tire runs at 65 psi (I think, correct if wrong) and an E rated tire runs at 85 psi. Mounted tires are dimensionally the same until they are put on the trailer. The D rated tire flexes a little more and has a more pronounced buldge. This bigger bulge in the sidewall means that the rim is slightly closer to the ground than the other tire. This cocks the axle slightly and causes the other "E" tire to ride slightly to the inside of it's tread causing wear to the inside.

Think of an axle with a 15" diameter wheel on one side and a 16" diameter wheel on the other. Doesn't look much different but the axle is not level.

Hope this helps.

John

[sreigle]

John, I think you've nailed it and explained some things I didn't understand. I just now posted in another thread a copy of a memo from Keystone about the D and E tires. They note the D's are 1 inch less in diameter than the same sized E's, causing 1/2 inch difference in coach height. And the D's are narrower than the E's as well. So I think you're explanation is dead on and more relevant than the rolling resistance comment I made. I wasn't real sure about that anyhow. The other thread is 'axle update'.

Thanks.