Will a 1200x22.5 run with a 315/80x22.5 on the same drive axle???

trailblazer2 · April 22, 2007, 06:11:38 PM

I need to buy (2) new tires to replace the worn out ones on the left rear drive axle. I have 1200's on the back of the coach and 315/80's on the front. I want to take the 315/80's from the front (about 65% tread) a place them on the inside back,placing the 1200x22.5 on the outside. Thereby putting fresh 315/80's on the front.I was told by the tire people that the radius is about the same,only a yifference in the width.I have always put new rubber on the steer!Whatuh yalll say??

Bill

chargePlus · April 22, 2007, 07:06:29 PM

I don't know how it is with buses, but I know on cars and light trucks I've been told and have read that you should put the new rubber on the rear tires because of the handling differences caused by the differences in traction between the older tires and newer tires. If you put the new, higher traction tires up front you can get into oversteer much more easily. If you put the higher traction tires in the back you have an understeer situation. Most folks can handle an understeering vehicle better than an over steering one.

Unless you are Bo & Luke Duke, in which case oversteer is a way of life.

- John

pvcces · April 22, 2007, 07:11:58 PM

Bill, if I recall correctly, there is a small difference in revolutions per mile between the two kinds of tires. If there is no interference in the wheelwell from running them on the rear, I would only install duals as matched pairs.

This would mean that I would use the pair of 315s on one side of the rear and a pair of 1200s on the other side. The problem with this is that there will be some difference in the way the rig corners, depending on whether you are turning left or right.

One bus operator did not recommend using new tires on the front. The operator would put new tires on one side of the rear and run them for a time, then move them to the front after they were broken in.

65% left sounds to me like you might as well leave the 315s on the front and put a pair of new on the one rear corner. We have one 315, and we run it on the front for just these reasons. The rears control the stability and the front does not notice the difference in size.

For what it's worth.

Tom Caffrey

TomC · April 22, 2007, 10:12:44 PM

Highly recommend you put 4 new identical tires on the drive. Here's the difference in the two tires-Michelin XZA2 Energy 315/80R-22.5-- 19.5" loaded radius and 492rpm (revs per mile). Michelin XZE 12R-22.5-- 19.8" loaded radius and 486rpm. Doesn't sound like much, but with 8rpm difference between the two, the 315 will be the one scrubbing since the 12R is slightly taller and will be taking more of the weight. Do yourself a big favor, don't mix tire sizes on the same axle, and on drivers, all tires should be the same make and model for maximum life and least likelihood of tire failure. If you want to mix tire size on the steer or the tag, that won't hurt. Good Luck, TomC

RJ · April 22, 2007, 10:30:28 PM

Bill -

EVERY tire manufacturer recommends not mixing tire sizes on the drive axle, especially with duals. Are you going to second-guess the factory?

Besides what TomC mentioned, if you put the 315s on one side and the 12Rs on the other, you'll increase the wear rate of the spider gears inside the differential, since the axles will be turning at different rates.

Your bus, your tires, your $$$

FWIW & HTH. . .

Jeremy · April 23, 2007, 04:44:39 AM

Quote from: TomC on April 22, 2007, 10:12:44 PM
Highly recommend you put 4 new identical tires on the drive. Here's the difference in the two tires-Michelin XZA2 Energy 315/80R-22.5-- 19.5" loaded radius and 492rpm (revs per mile). Michelin XZE 12R-22.5-- 19.8" loaded radius and 486rpm. Doesn't sound like much, but with 8rpm difference between the two, the 315 will be the one scrubbing since the 12R is slightly taller and will be taking more of the weight. Do yourself a big favor, don't mix tire sizes on the same axle, and on drivers, all tires should be the same make and model for maximum life and least likelihood of tire failure. If you want to mix tire size on the steer or the tag, that won't hurt. Good Luck, TomC

I bought a new tyre last year of the identical type to my existing tyres, and I would say that the difference in size between the new tyre and the older worn tyres was at least equivalent to the size difference between the two types of tyre mentioned by TomC (19.8" - 19.5"). My instinct at the time (and I stress that I don't have the knowledge or experience of TomC) is that such a small difference in size would cause no problems, simply because doing what I did (ie. installing one new tyre) must be common practice. I don't believe that truck or bus operators usually buy four new tyres if only one needs replacing, even if that is what theoritical 'best practice' dictates.

Slightly changing in topic - the original question asked about swapping tyres between front and rear axles - but how advisable is this? Is the reduced traction of a steer tyre on the back axle axle likely to ever cause a problem? Are there economy gains? Are there any laws restricting what you can do? I'd always assumed that putting drive tyres on the front would be illegal, and that steer tyres on the back would be legal but not ideal, especially for a bus conversion / motorhome that might leave the tarmac on occasion. Steer tyres are quite a bit cheaper to buy than drive tyres (here at least), so if it's acceptable to run steer tyres all round I might do that at some stage

Jeremy

tekebird · April 23, 2007, 05:59:50 AM

I run all position as do most coach companies in the US so they can move tires at will.

Having different size tires on the same set of duals will greatly increasssse your odds of a tire failure, due to one tire being loaded moreso than the other ( the larger of the two) while the smaller one goes along for the ride for free.

as for same axle mixxing, Possible issues if tires are grossly different in size, but not too likely IMOH

if you move your steer rear, be sure to pair them on the same side.

Also, tires should almost always be bought in pairs., i would not concern myself with matched paiirs on tags though

Len Silva · April 23, 2007, 06:00:08 AM

Just uneducated theory kicking in here.
It seems to me that if you have different size tires on the rear axle then the differential will always be "working" as if you were in a constant turn, and one side will be doing all the driving even when doing straight down the road, thus putting all the wear on the larger wheel.

Len

JimW7 · April 23, 2007, 06:06:43 AM

Bill, I would have to agree with TomC. Years of driving has shown me not to mix tires sizes on any drive axle. If anything, take the two from the left side, and use them as the outside duals, and the right side ones on the inside, and run them untill you can replace the four together. If the fronts were the same size, always run new on the fronts. These are the most important tires on your rig. If you mix duels,a smaller tire, even 6 RPM's, they will scuff and heat, if you put those two smaller ones on one side, your axle will wear the spiders, and create a lot of heat. Maybe the dealer might have something there that you could match that would have the same tread as the right side? Just my thought, Jim.

tekebird · April 23, 2007, 06:09:25 AM

A truckin mag just did a tire article said not to mix on same set of duals.....as the larger tire will heat and fail as it is carrying the load for both tires

trailblazer2 · April 23, 2007, 06:32:06 AM

Thanks ;for all the good angles on this thing! I am really pleased with all the knowledge this board shares!
Bill

Jerry32 · April 23, 2007, 06:57:43 AM

Bill I had that on my bus when I drove it back from SC and the 12R22.5 is larger in diameter and will be carrying all the load. I found the 12 was overheating and finally blew out. So my advice is stick to the same size tires together Jerry

Busted Knuckle · April 23, 2007, 09:18:02 AM

When we buy tires we either buy 2 steers, or 4 drives. Then we take the old tires and use them on the tags, or as spares! I run drive tires down to the tread marker and have them regrooved once, and run them down again. Then it's time to replace them. I run steer tires for a while then, when I need a tag tire I rotate the steers back to the tag and either dispose of the worn out tags, or if I have 1 that still has plenty o' tread on it I'll keep it as a spare! I do regroove tags 1 also, so my spares are just that a spare to get me home so I can replace either a pair of steers or a set of drives which ever the case maybe! That way I always have matched tires on each axle, and good tires all the way around. We never run a regrooved tire on the steer, unless it's just to get it home as a spare! Just the way we do it, but keep in mind under normal operating conditions my coaches see more miles a month than a lot of you put on yours in a year! And we are hauling 30-59 people at a time, so safety is maximum priority here when it comes to tires! Because in our business , we're only 1 accident away from being out of business!
FWIW! BK

tekebird · April 24, 2007, 04:21:30 AM

BK,

Wondering why you run drive tread in TN/KY? When operators in the snow belt run all Pos. year round?

tekebird · April 24, 2007, 04:26:08 AM

Also: Keeping in mind I just woke up and have not had coffee yet......

I dont think left to right tire size is a huge concern ( thats left duals vs right duals).....It does make some difference in a liited slip and certainly does with a locker

But any time your bus is not driving straight the tires on one side have a different RPM than the other side.....thats not tearing up your diff.

My neck of the woods for those who don't put new all around.....

New Steer. 75% those go as a pair to a drive axle

Drive tires when worn go to tag