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Author Topic: 11R 22.5 tires to replace 12R 22.5's??? Should I?  (Read 21895 times)
Angola Coach Conversion "Aesop's Tortoise"
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« Reply #15 on: June 24, 2010, 12:07:41 PM »

Michael -

To thoroughly confuse you, be aware that the truck tire industry is very quickly moving to metric sizing of their tires, something that the auto industry did almost 20 years ago.

Thus a 315/80R22.5 is roughly the same as a 12R22.5.  11R22.5s cross over to roughly 295/75R22.5, but  beware:

Another consideration that has been alluded to above is the number of "revolutions per mile" of the tire.  Two tires the same size, from two different manufacturers, will often turn different rpms.  Looking at the Bridgestone chart, I found 489, 492, 507 and 517 rpm for the same size tire in different versions!

The taller the tire, the fewer rpm, which also translates into slightly better fuel economy and a higher top speed, at the expense of slightly worse gradeability (downshifting sooner)  Obviously, more rpm gives you the opposite effect.

A final caveat:  Be careful of the dealer that's got a smokin' good deal on some "bus tires".  Tires are also speed rated, and he may be trying to unload a set of transit bus tires that have been sitting in his shop for awhile.  Transit tires are limited to 50 or 55 mph - they're designed for stop/go traffic and banging curbs all day, not hi-speed runs on the Interstate.

New steel wheels might also be a thought - they run about $100 each - so your tire shop could have the tires mounted and balanced in advance for you.  (Pretty Alcoas run $300+ if you want to go that route.)

Do your homework, it pays to shop around!!

FWIW & HTH. . .


RJ Long
PD4106-2784 No More
S13406 1978 MC-5C Converted
S14947 1980 MC-5C Shell
Cheney WA
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"Foolish Pleasure" 35' MC5A

« Reply #16 on: June 24, 2010, 01:17:52 PM »

Thankfully, my MC5 came with Michelin tires and I wouldn't guess that I'd have to replace them in my lifetime. But they are 12R-22.5. I had a rock caught between my duals and didn't know it and it ruined the side wall of the inside tire.  Thankfully when I was at Fred Hobe's he had a tire and wheel I could use so I replaced it.

I have a friend who owns a 2004 Prevost and racks up milage you wouldn't believe. Last year he replaced all his tires with Toyo's and loves 'em. And if he wasn't happy the world would hear about it

My speedometer is off just about 10%. I think Beaver Coach lines used 11R-22.5 tires. I can live with it because the GPS gives me the accurate speed over the ground and that's what I go by and transpose that to RPM's. I drive my bus by the Tach...but that's another story.

We're I to replace my tires it would be 11R's and if I had 24.5 wheels....I'd lose them ASAP.

That's my .02.


True friends are difficult to find, hard to leave and impossible to forget.
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