tires

[HB of CJ]

TomC is on to something here.  Also try your local heavy truck wrecking yard for good take off's in 11R x 24.5's.  Sometimes a package deal includes good Alcoa wheels, steer and drive treads and mounting/balancing.  Good luck. 

[Lin]

Sean,
     You are certainly right that one must make sure the tires are in the load and speed range you require.  My MC5a had 11R22.5's when I got it, so my first thought was to replace them with the same.  I did find them to be commonly available.  I considered changing back to the 12R22.5's the bus must have originally had, but due to cost and local availability, I did not.  As far as ride height goes, I thought that there was only 1/2 inch difference.  Would that really be noticeable or change the ride characteristics?  This is not a rhetorical question, I don't know.  I think that the tires I got are load range G, but the numbers came out to several tons more than my GVW.

[Sean]

Sean, you mentioned when we were visiting that you like block treads on the drive tires.  Is there really a significant difference when you are on dirt,

Yes, there is a great deal of difference, not only in dirt, mud, and sand, but also in snow.  We spend enough time on beaches and dirt roads that we would not be without them.  The decision was driven by real experience:  we got stuck in the mud up to our axle in, believe it or not, a developed campground.  I had not started blogging yet back then, so unfortunately I can't point you to the horrid tale.  Suffice it to say we waited four hours for the gigantic tow truck.

and do you get more road noise?

Yes, we do.  For some people, this might be a deal-breaker, but we did not find it to be excessive.  Of course, unlike bus passengers, we're not riding upstairs over the drive axle -- we're 25' ahead of it, in the cockpit.  Many things, including the cockpit heater/air conditioner, the power steering box, and even my driver's window fan are louder than the road noise from the drive wheels up here.

Any other factors to consider on that choice?

Yes: tread life, and tire rotation.  The tread life of open-shoulder, block-tread traction or "M&S" tires will not be as high as for "rib" type highway tires.  We're coming up on 100k on these tires, and they are past 70% by my eye.  I'm going to guess that, while we could probably get another 50-70k on them, there'd be so little depth to the tread left that they would not meet our original objective.  I will probably trade them in while they can still be retreaded and buy a fresh set, so I'm figuring I'll get only about 120k miles on these overall.

The tire rotation issue contributes to that problem:  You will not be using the same tread on your steer axle, and probably not on the tag either.  So we can only rotate the drivers with one another, and the steers with the tags.  By having a single tread design on all eight, you can get more tread wear:  the steer and dives will tend to round off the shoulders, while the drivers tend to flatten the centers.  So you move the steer/tag wheels to the drive axle and vice verse, which tends to even out the wear.

It's not a trade-off everyone would make, but it works for us.  I would not trade my block-tread drivers for rib tires.  So much so that when we bought these tires, we really wanted to go to the 315/80R-22.5, but no one had them in stock in block tread (worldwide -- we called the manufacturers, and only Michelin would even commit to having a batch coming out "in about three months"), so we stuck with the 12R-22.5.

HTH, and great to hear from you again.

-Sean
http://ourodyssey.blogspot.com

[Sean]

...  As far as ride height goes, I thought that there was only 1/2 inch difference.  Would that really be noticeable or change the ride characteristics?  This is not a rhetorical question, I don't know.

That depends, and it's hard to make comparisons.

I had to hunt around for a tire that came in both sizes so I could make an apples-to-apples comparison.  From the manufacturer's data, the "static loaded radius" of their 11R22.5 tire is 0.6" less than the 12R22.5 (the overall diameter is 1.4" different).

However, remember that load and inflation will affect sidewall flex and how the tire sits when actually on the ground under the vehicle.

In this particular example, the 11R tire is rated for  6,175 pounds at 105 psi, whereas the 12R tire is rated for 7,390 lbs at 120 psi.  If you put a 6,175 lb load on the 11R tire at 105 psi, the tire will "compress" much further than that same 6,175 lbs on the 12R tire at 120 psi (naturally).  Of course, the load tables will tell you that to carry the 6,175 on the 12R, you will only need to inflate to 95 psi, which will result in more deflection.  So the real question is what inflation pressure does the coach manufacturer recommend for the stock tires -- it is possible that the engineered ride height could be as much as an inch different between these two tires at the same load.

My bus only sits 6"-8" off the ground at normal ride height, so, for me, that inch would be significant (although I'm actually too heavy to use the smaller size).  For, say, a Crown, the difference might not even be noticeable. YMMV, as they say.

HTH,

-Sean
http://ourodyssey.blogspot.com

[Rodsmc5c]

   
   Are you in NH?
       Rod from Bow

[TomC]

Sean- Michelin has two drive tires in the 315/80R-22.5.  One is the excellent XDN2 GRIP that is a traction/snow tire with matrix siping that gives great traction in both dry, wet and snowy conditions.  It is a moderate lug for mud.  The other is the XDY3 that is a heavy lug tire that would probably be noisy, but the best for soft and muddy situation.  Personally- I think the XDN2 GRIP is an exceptional tire-have a couple of fleets running them and the wear and traction reported is better than any other tire.  Plus they ride very well.  Good Luck, TomC

[Sean]

Tom,

When we put our drivers on, the XDN2 had just come out.  And, as I wrote, they were on three-month backorder in that size.  We couldn''t wait that long.

That tire is on our short list for when we replace the drivers, but,to be honest, Michelin has done nothing to make me want to spend money with them (see my recent posts on the other board).  We'll see when the time comes.

-Sean
http://ourodyssey.blogspot.com

[Joebus]

I purchased 4 OHTSU 12r22.5 in SC for 1675.00 installed. These are Japanese make. The load range and speed limits fit our need (MC8) I believe they only have one model in this size.