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Author Topic: Tire size 900x20?  (Read 7663 times)
TomC
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« Reply #15 on: May 01, 2009, 09:45:16 PM »

Gus-you are correct-I wrote it wrong.  Even wheel diameters are TUBE type tires-like 20" and 22".  TUBELESS is with a .5 at the end.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Sean
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« Reply #16 on: May 01, 2009, 10:28:55 PM »

I guess some are making up tire sizes.  ...

Tom, I think it is simply a case of the Javascript size calculator, for which Dallas posted a link, not actually being in any way cognizant of what sizes are actually manufactured.  It's just a straight across calculator, converting inches to the nearest 5mm increment and vice versa.  I believe it translates the aspect ratio for any pre-metric size to 80%.

-Sean
http://OurOdyssey.BlogSpot.com
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Jerry32
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« Reply #17 on: May 02, 2009, 12:21:48 PM »

I put larger wheels on mine and used 11R24.5's which keep the hieght up for clearance as the 11R22.5"s are smaller around. Jerry
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« Reply #18 on: May 02, 2009, 04:29:20 PM »

My question is can I switch my front 12r22.5 tires and wheel with a 11r24.5 on my 83njt mci-9 ?
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Sean
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« Reply #19 on: May 02, 2009, 11:06:52 PM »

I put larger wheels on mine and used 11R24.5's which keep the hieght up for clearance as the 11R22.5"s are smaller around.


and

My question is can I switch my front 12r22.5 tires and wheel with a 11r24.5 on my 83njt mci-9 ?


I hear this all the time:  11r24.5 are cheaper and easier to find than 12r22.5.  Both true, however, I have studied the cost difference and the availability issue, and, frankly, most of us will not save enough over the lifetime of our buses to justify the expense of changing the wheels.

The short answer is, yes, you can change wheels.  Make sure you get the correct mounting (hub-pilot versus stud-pilot aka "Budd"), correct hub bore, and correct bolt holes for your application.  Then, make sure you recalibrate your speedometer, and, if DDEC-equipped, the DDEC RPM parameter.  Lastly, measure your wheel-by-wheel weights to get the correct load range and inflation for the new tires.

Remember that the 24.5 wheels will give a stiffer ride than the 22.5 wheels under all conditions.

-Sean
http://OurOdyssey.BlogSpot.com
« Last Edit: May 02, 2009, 11:12:45 PM by Sean » Logged

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Sean
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« Reply #20 on: May 02, 2009, 11:08:48 PM »

(deleted - posted in error)
« Last Edit: May 02, 2009, 11:12:12 PM by Sean » Logged

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TomC
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« Reply #21 on: May 02, 2009, 11:11:59 PM »

Sean- I'm not quite sure how a 24.5 can ride stiffer then a 22.5.  Both a 11R-22.5 and 11R-24.5 have the same aspect ratio making the side wall height the same on both tires-sidewall height is where you get the tire ride.  I have 24.5's on my bus, and when I first put them on, my mechanic said he had never felt such a smooth ride compared to 12R-22.5's.  So how do you explain that? (no insult intended!).  Good Luck, TomC
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Sean
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« Reply #22 on: May 02, 2009, 11:14:54 PM »

Sean- I'm not quite sure how a 24.5 can ride stiffer then a 22.5.  Both a 11R-22.5 and 11R-24.5 have the same aspect ratio


Tom,

Sorry, I was perhaps not clear.  I said that the 11R24.5 would be a stiffer ride than a 12R22.5.  You can't really compare 11R24.5 to 11R22.5 -- they have vastly different diameters and load ratings.

-Sean
http://OurOdyssey.BlogSpot.com
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RJ
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« Reply #23 on: May 03, 2009, 02:36:35 PM »

Happy Camper -

Don mentioned that you have an RTS.  The original factory tires on your coach were 12R22.5s.  This tire size was chosen for a vehicle in revenue service.

For RV use, many busnuts have gone to the smaller 11R22.5 size, for various reasons - mostly because the 11s are less expensive than the 12s. 

Generally speaking, unless your interior is outfitted with marble floors and granite counter tops (i.e. HEAVY), this isn't a problem.

As Sean said, however, it does mess with your speedometer readings, fuel mileage and ground clearance.  These may, or may not, be a concern to you.

The bus/trucking industry is slowly converting to metric sizing, just like automobiles use.  It will be awhile, so a lot of the old numbers are still current and useful, but that's changing.

Most newer coaches are coming with 315/80R22.5 tires, which, as has already been mentioned, is approximately the same size as your 12R22.5s.  Not enough difference to really quibble over.

HOWEVER -

Be aware that bus tires are made in a couple of different configurations - one for regional or city use, and one for long-haul or highway.  The difference is in the sidewalls primarily - those designed for city/regional use generally have heavier sidewalls, because transit bus operators thoroughly believe that curbs are part of the braking system when pulling into a bus stop. 

City/regional tires also have a lower speed rating than highway tires, usually 50 mph vs 70-75 mph.

So be careful when shopping for tires - do your homework!!

FWIW & HTH. . .

 Wink
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happycamperbrat
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« Reply #24 on: May 03, 2009, 08:45:01 PM »

Wow! I am impressed with all this info! You guys have all given me loads to think about with the tire issue. And a special hello to you Don and thank you for letting me and my mother see your beautiful coach (she still is talking about your mirrored ceiling)!

It seems tires are the single biggest expense with a bus over the lifetime of it. My tires LOOK like brand new, but they are 8 years old and that scares me from what I have read. I would definitely buy brand new for my steers but I am looking for a cheaper way for my back tires on my RTS.

Thank you,
Teresa
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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post
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