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Author Topic: tire size / inquiring mind wants to know...  (Read 3315 times)
coolbus
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« Reply #15 on: June 18, 2007, 09:45:50 PM »

okay, here's what the VIN plate says:

FRONT~   13,000lbs           Tires~   12R22.5         Wheels~   22.5X8.25

DRIVE~      22,000lbs          Tires~   12R22.5         Wheels~   22.5X8.25

AUX~       10,000Lbs          Tires~   12R22.5          Wheels~   22.5X8.25

My question:

Is a 12R 22.5 tire (as spec'd on VIN plate) shorter than a 11R 22.5?  Huh The 11R is definately too tall; rubs on the tag position.

The design of the bus makes it look as though the tag should be a shorter tire, since there is no wheel well inside the bus above the tag like there is on the drive axel & front axel. However, the VIN plate does show same size tires all the way around. Maybe less wheel travel on the tags?

This is a puzzle for me; I don't understand these tire sizes. Is it possible that the PO put on different (taller) tires so as to change gear rato?

Again, the bus currently has 11R 22.5 tires on front & drive axel; the tags are 10R 22.5. If I put a 11R 22.5 tire on the tag position, there is serious clearance issues with the height of the tire. Is a 12R the same height as a 10R? Seems odd to me.

thanks

Mark
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tekebird
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« Reply #16 on: June 18, 2007, 10:13:27 PM »

12r is a "standard" bus tire size

good chance some bright individual was screwing with your ride ht...trying to make it perform/handle better....LOL

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TomC
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« Reply #17 on: June 18, 2007, 10:37:02 PM »

The 12 will be taller than the 11 which is taller than the 10.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
prevost82
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« Reply #18 on: June 18, 2007, 10:44:54 PM »

Mark ... maybe the rear ride height is not set up high enough. If you look at my bus it isn't running flat, the rear is sitting a little higher than the front of the bus in a nose down attitude. Does you bus have a wheels-up air switch by the brake switch?  Most Prevost tag can be lifted.

Ron
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Stan
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« Reply #19 on: June 19, 2007, 05:20:56 AM »

Your bus gets more unusual with every post. I don't think it is possible to have no wheelwells  on your bus and get full suspension travel. Is it possible that the previous owner removed the wheelwells? Another strange thing is the weight distribution from your VIN plate. As a normal rule, tag axles with a single tire only carry 30% of the drive axle weight. With tires two sizes smaller than spec, you will have to reduce the weight on the tags to about 4000# by reducing the pressure in the tag air bags.
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TomC
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« Reply #20 on: June 19, 2007, 06:45:15 AM »

You could go as small as a 265/75R-22.5 and still have sufficient tire to take the rated 10,000lb load rating of the tag axle. As to tire size, the only reason that 12R's were originally used, was they were the only tire that could take that kind of loading-realizing that tires when the bus was built were still nylon bias ply tires.  Now with the excellent steel radials, you can go smaller and not have to worry about loading.  At 13,000lb you could use either a 11R or 295/75R-22.5 16 ply for the front.  For the rear at 22,000lb, a normal 11R or 295/75R-22.5 at 14 ply would be enough.  Most converters will not come close to the gvw rating for passenger carrying capacity.  For instance, my bus is rated at 13,000lbs front and 23,000lbs rear.  I went to 11R-24.5's that are 16 ply since they will take that amount.  At full pressure, the 16 ply tires will take 14,000lbs front and 26,300lbs rear.  With only 10,500lbs front and 20,500lbs rear, I run 90psi all around, and that is even a bit high.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Hartley
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« Reply #21 on: June 19, 2007, 07:02:01 AM »

It occurred to me that there might be an error in the description of tire clearance.

When you say the tag hits the support. Is that with the bus up and running with the suspension aired up or when it is sitting with no air pressure?

Generally speaking many buses when they have no air in the suspension will sit all the way
down to the stops which usually are barely high enough to keep from touching stuff.

My RTS sat really low and if I didn't have the wheels straight the front tires would bend the wheel well rubber trim, My MC9 does the same thing without air. My tags look like they would almost touch without air pressure but with full pressure they have 7 inches of clearance. These things have a lot of travel.

There can be from 3 inches to 14 inches of clearance depending on what bus and suspension settings.

From the picture you posted it looks like someone has lowered the ride level or there was no air pressure to hold the bus up. In that case this whole issue can be misleading and what people will tell you may not be the exact answer.

Air it up and check the clearances, Then let us know what you find. Anything else is conjecture.

Dave....
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coolbus
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« Reply #22 on: June 20, 2007, 10:37:51 PM »

This is what happens when the WRONG size tire is used in the tag position...
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coolbus
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« Reply #23 on: June 20, 2007, 10:45:29 PM »

Check out all the shredded rubber! The tire was rubbing on the airbag, as well as the steel structure mounting the airbag. The tire was rubbing so bad. it rubbed thru within two - three blocks after mounting it up!  The top of the tire was also rubbing, but no damage occured as a result.

The tire I used was a 11.00 R 20.  I thought they were the same diameter as a 11.00 R 22.5?  My mistake.

Now to replace an otherwise perfectly good airbag... and find a couple good tag tires...

Mark
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TomC
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« Reply #24 on: June 21, 2007, 12:16:15 AM »

11.00R-20 = 12R-22.5.  10.00R-20 = 11R-22.5.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #25 on: June 21, 2007, 01:00:46 AM »

Maybe you have the wrong rims on the tags.

The offset is wrong.Huh?

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