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Author Topic: wheel sizes...differences?  (Read 2483 times)
turbobrat930
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« on: November 28, 2008, 11:25:19 AM »

Ok, So I am looking at the market right now and the busses for sale. I know that the Alcola wheel seem to be the right choice. But, I am wondering on the different sizes. I see most are 22.5" diameter but some are the 24 or 24.5" diameter. Which are better? Is it a personal preference? Is there a greater tire selection with one size wheel verses the other? Can gearing be changed that much between the two? If one is definately better than the other, and the bus that I end up buying has the least desirable of the two, how much do new or a good set of used wheels cost nowadays? Are there differences in the cost of tires or longevity of the tires between the two sizes?

Thanks again.... and hope everyone had a wonderful Thanksgiving holiday, spending it with family and friends...

regards, Brad
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makemineatwostroke
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« Reply #1 on: November 28, 2008, 12:20:45 PM »

turbo, at one time the 24.5 were the most popular because the trucks used that size that is not the case any more to get 24.4 on new trucks they need to be ordered as 22.5 have become the standard size I changed to 12R 22.5 from 24.5 11R and never regretted it.FWIW the 22.5 is a world wide standard    
have a great day
« Last Edit: November 28, 2008, 12:44:50 PM by makemineatwostroke » Logged
RJ
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« Reply #2 on: November 28, 2008, 02:50:43 PM »

Brad -

Another perspective, and this only applies to GMC coaches:

GMC designed the powertrain around tires that turn 495 revs per mile.  On the 4106 model, the results were 60 mph @ 1650 rpm with the stock 4-spd transmission and 4.125:1 rear axle.

GM powertrains sit side-saddle across the back of the coach (except for the Scenicruiser), consequently there is a bevel gearset that directs the prop shaft in the proper direction to the rear axle.  Fourth gear is 1:1 in the stick, and the bevel ratio is 0.808, yielding a 3.333:1 overall final drive.  (1:1 x 0.808 x 4.125:1)

However, many folk have converted their coaches over to the V-730 automatic, which has a 0.875 bevel gearset.  The math ends up giving you an overall ratio of 3.609:1, roughly a 5% engine rpm increase at any particular road speed, with subsequent drop in top speed and fuel mileage.

Since the 4.1:1 rear axle is the "tallest" available for the V-drive layout, the ONLY way a GMC owner can pick up some of that lost 5% is by going to tires that turn LESS than 495 revs per mile.  In many cases, this requires changing from 20 or 22.5 wheels to the larger 24.5 rims.

Lots of 22.5 tires turn right around or slightly more than the magic 495 rpm for GMCs, but very, very few turn less.  OTOH, looking thru the 24.5 sizes, one can find several that turn less - I've even found one 24.5 Bridgestone model that turns 470 rpm, which almost, almost matches the OEM road speeds for those who have opted for the automatic.  Obviously, if one has 22.5s on the coach now, and wants to bring back that OEM performance, they'd have to switch to 24.5 rims.

Enough about GMCs and their unique requirements. . .

Two-stroke's right, however.  The tire market is definitely going to the 22.5 as more popular.  They're also switching to metric sizing for the HD tires, something we've had in the auto side of things for the last what, 15 years or so?

MCIs and Prevosts have normally come from the factory with 12R22.5 tires.  Stock "bus size" tire for the last couple of decades.  Not always easy to find at your local truck stop at Oh Dark Thirty when you need one - the challenge then takes on your wallet big time.  Depending on the situation, and if you don't have a spare hidden away behind the front bumper, sometimes you can limp on by using a tag tire or outside dual for a short distance.

As I said earlier, metric sizing is starting to make inroads with the HD tires now.  The familiar 12R22.5 crosses over to a 315/80R22.5, but there's a caveat here, also:  Highway vs City.

Yup, there are different bus tires for transit vs highway use.  All HD tires are speed rated (passenger cars are too, for that matter), with the majority of transit bus models rated at 50 or 55 mph.  The major difference between highway and city tires is the sidewalls.  Transit tires have much heavier sidewalls, because those drivers thoroughly believe that the cement curb is part of the braking system, so they're scrubbed often.  That and in the hotter SW climates, transit brakes generate a tremendous amount of heat as they drive a block and stop, over and over.  So the tires are designed for the heavier heat load in the bead area, and the heavier sidewalls to resist curb scrubbing.  Ride quality is not a major concern for this market either, for that matter.

Obviously, then, highway tires are built to different criteria - a comfortable ride at 70+ mph, with lots of airflow to help keep temps reasonable (although inside duals run hotter due to less airflow).  You also get your choice of steer, drive or all-position tires, just to keep the matrix interesting.

Point here, tho, is if/when shopping for tires for your coach, make sure you're getting highway rated, not city-transit rated.  May look the same, but they aren't.  Do your homework.

New Alcoas or Accurides run about $350 or so each, new steel Accurides are about $100.   Sometimes you can score a good deal on a set from a truck boneyard, many have.

FWIW & HTH. . .

 Wink

« Last Edit: November 29, 2008, 10:58:10 AM by RJ » Logged

RJ Long
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« Reply #3 on: November 28, 2008, 06:08:36 PM »

RJ,

Really great write-up....Thanks.

Question, if the trucking industry is going to 22.5 and you have to special order 24.5 in some cases...why is 22.5 so hard to find at a truck stop facility?

Can I get the same options in both sizes at the same price?  I think 24.5 offered more options and prices but that may be oldschool dated info.

Thanks again,

John
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« Reply #4 on: November 28, 2008, 06:22:20 PM »

My old Crown Super Coach had 12R x 22.5 tires mounted on 2 hole and 4 hole steel Budd type wheels.  I was told the 2 hole version was slightly stronger, but this only applys to steel wheels.

The plan was to mount surplus "take offs" 11R x 24.5 truck tires already mounted to Alcoha wheels.  Yeah, lots of truckers are going from 24.5 back down to 22.5 wheel and tire sizes.

Another source that may save $money$ (and be fun) is to get to know your local heavy truck wrecking/recycling yard.  Be amazed at the good stuff available for sale for little cost.

Sometimes they may have sets of tires and wheels from trucks that don't need them any more, like taken off wrecks.  $Deals$ with mounting might be had.  HB of CJ Smiley Smiley Smiley
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TomC
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« Reply #5 on: November 28, 2008, 07:12:04 PM »

My transit came with 12R-22.5 at 485rpm.  Because the 12R is harder to find on the road, and I wanted the largest tire on my bus since transits are lower than highway buses, I changed to 11R-24.5 at 473rpm.  With 4.56 rear axle ratio and the V730, that works out to be 1898 at 60mph.  I run just a bit less than that at 1835rpm which is 58mph.  With my engine turned up to 2400rpm, I can get a top speed of 75mph if needed.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
turbobrat930
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« Reply #6 on: November 28, 2008, 07:13:34 PM »

Thanks to all that replied...and RJ, WOW...What a detailed response That is exactly what i was looking for. So, the 22.5" wheels and tires are becoming the industry norm, then that is what I will look for. Thanks again.

I understand on the GM coaches in reference to the gearing. I was wondering if that was the reason on any of the other coaches... but if the tire selection is better with the 22.5....and that is what is on most coaches...then thats what I will go with..

I am also probably going with a MCI.... unless a Majorly good deal happens on another brand of coach.

Thanks again,

Brad
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Len Silva
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« Reply #7 on: November 29, 2008, 06:28:55 AM »


.............Another source that may save $money$ (and be fun) is to get to know your local heavy truck wrecking/recycling yard.  Be amazed at the good stuff available for sale for little cost............


One precaution here, the tires may have been flat spotted in the course of the wreck that brought the truck into the yard.
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« Reply #8 on: November 29, 2008, 07:50:37 AM »

Just a comment on 24.5's.  North American trucks are just about the only on road trucks that use 24.5 rubber.  22.5 is the norm in the rest of the world.  Just go to any tire site and see how many 22.5's are offered compared to 24.5.  Michelin is making a X-One RV version now that is better riding then the truck version.  If I had a Crown, Gillig, or PD4501 with tandems, the big single X-ones would look really cool.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
luvrbus
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« Reply #9 on: November 29, 2008, 08:48:46 AM »

you guys going into Mexico with the 24.5 need to carry a extra one they are about impossible to find down south, we waited 4 days on 24.5 tire for a friends bus when traveling there         good luck
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letz4wheel
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« Reply #10 on: November 29, 2008, 11:09:07 AM »

RJ,

Question, if the trucking industry is going to 22.5 and you have to special order 24.5 in some cases...why is 22.5 so hard to find at a truck stop facility?

John.
I think you are speaking of RJ's post. What he said was the 12/22.5, found standard on the MCIs and Prevosts,are hard to find in truck stops. The truck standard is the 11/22.5 and they can be found in any truck stop that sells tires. Did I just muddy the waters or did that help?
Doug
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« Reply #11 on: November 29, 2008, 01:43:27 PM »

TomC,

Now I'm curious and hoped you would explain why trucks went to 24.5 from 22.5 and then back again??

As much as I hate duals I do like the idea of having a spare already on the ground when one goes flat. Those big singles don't appeal to me at all and they must cost a mint.
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Gary '79 5C
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« Reply #12 on: November 29, 2008, 05:48:20 PM »

Gus,
I believe US trucks are split almost evenly between the two sizes, but the 22.5's weigh less and that equates to better mileage. Also the trailers can be taller with the smaller tire which results in larger cargo volume.

Gary
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« Reply #13 on: November 29, 2008, 05:58:02 PM »

Gary,



OOOOOOOOO, that makes so much sense it must not be true.  Thank you for the only answer I have ever heard that makes sense.

Doug,

You cleared the water.  I didn't pick up on the 11 and 12 thing.  So why don't we go with 11's that are more common?   I know that a narrower tire rolls easier and weighs less.  Honest question now, really.

John
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"An uneducated vote is a treasonous act more damaging than any treachery of the battlefield.
The price of apathy towards public affairs is to be ruled by evil men." Plato
“We can easily forgive a child who is afraid of the dark; the real tragedy of life is when men are afraid of the light.”
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luvrbus
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« Reply #14 on: November 29, 2008, 06:45:25 PM »

I have ran 12R 22.5 on every bus I owned and they have never been a problem to find anywhere in the USA I have traveled, who knows where this got started from.I cut one in McCall ID and the dealer there had 4 in stock.Who would want to buy one at a truck stop if you don't have one of the tire co's fleet card a $400.00 tire at a truck stop will cost you $600.00   

JohnEd, I buy my 12R 22.5 every 4 years from what I think is the best tire dealer in the USA located in your state of OR Les Scwap Tire and they always have the 12R 22.5 Toyos or other brands in stock.I also drive to Eugene to have brake and alignment work done from one of the best Dick Kaiser at Kaiser Wheel and Alignment.Buses drive better and ride better with the 12R 22.55 or the metric version,  in my opinion

good luck
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