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Author Topic: Tire Size  (Read 11321 times)
Fred Mc
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« on: July 02, 2007, 11:30:28 PM »

My bus (GM PD4106) currently has 12R 22.5 tires on it . Are these the common tire size that truckers use. If not, what tire size should I go to.

Thanks

Fred Mc.
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tekebird
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« Reply #1 on: July 02, 2007, 11:37:42 PM »

not a truck common size.

trucks commonly run 24.5's

.
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Gary '79 5C
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« Reply #2 on: July 03, 2007, 02:39:22 AM »

Tekebird,
No offense, as I am out of my league to speak on trucks, However here it goes. My opinion was that most trucks today run the 24.5's but in looking at truck 4 sale mag's at the fuel stops, I see more and more late models with 22.5's. I am assuming for less weight, more fuel mileage ? ?
If you ask why I am looking at ad's of trucks for sale, you have just joined my wife's line of questioning.

Have a great day,
Gary
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bruceknee
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« Reply #3 on: July 03, 2007, 02:50:39 AM »

Some trucks run 22.5's, some 24.5's. The most tire for your money is an 11r22.5 16 ply. They will be a couple of hundred dollars less than a 12r22.5 and work fine on a bus. There is less than an inch difference in the height of the tires.
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kyle4501
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« Reply #4 on: July 03, 2007, 04:52:15 AM »

Weigh your bus to determine the actual load carried by the tires. Then buy a tire that will do the job.

You need to do more than a simple axle weight as one side may have more stuff & result in tire problems if the tire rating is marginal for the axle.
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« Reply #5 on: July 03, 2007, 05:06:54 AM »

I'll defer to NJT as he is one of the truck experts on the board
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TomC
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« Reply #6 on: July 03, 2007, 07:59:41 AM »

From being in the trucking industry for over 30 years, I can tell you that the 11R-24.5 was the industry leader for many years.  Now that the trailers are tallers, they needed a smaller tire.  The standard of the industry tire now is the 295/75R-22.5 or 275/80R-22.5 (Michelins size).  No real advancements have been made on the 12R-22.5.  But the tire now is the 315/80R-22.5 (metric version of the 12R).  Michelin just came out with a 315 that will take up to a 20,000lb load on the steers approved at 65mph (was 55mph before).  I changed to the 11R-24.5 since it is the biggest tire in diameter and I have a transit that is low to start with.  Changing from the 12R to the 11R-22.5 would be a good change, except you'll loose about 16 revs per mile (making the bus a bit slower at top speed).  Tire speed is as follows- 11R-22.5=502rpm; 12R-22.5=486rpm; 315/80R-22.5=489rpm; 11R-24.5=478rpm.  Technically, the 12R and 315/80 are supposed to be on a 8.25" or 9.00" rim-of which you probably have a 9.00" wide rim.  The 11R's can run on either a 7.50" or 8.25" wide rim.  My guess is that a 9.00" rim could facilitate a 11R tire, but check with your tire man.  So changing from the 12R to 11R-22.5 will make your 80mph top speed now a 77.5mph bus.  Still a better choice than the 12R.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #7 on: July 03, 2007, 08:11:26 AM »


My bus (GM PD4106) currently has 12R 22.5 tires on it . Are these the common tire size that truckers use. If not, what tire size should I go to.
 

Fred -

The magic number you should be interested in is 495.  That's the number of revs per mile that GM designed the 4106's powertrain around.  Going to a tire that matches that rpm, regardless of rim size (22.5 or 24.5), will give you OEM performance out of your coach.  Buried in the specifications for all commercial tires, you'll find the revs/mile spec for each size/type, which is a factor you should be considering.

Going to a tire that turns more than 495 revs/mile will lower your top speed and increase your fuel consumption.

Going to a tire that turns less than 495 revs/mile will have the opposite effect.

IF you have a V-730 instead of the OEM 4-spd, there is a Bridgestone 11R24.5 tire out there that turns 470 rev/mile.  Installing this tire will bring the overall performance almost back to OEM, with the exception of fuel mileage.

Then there's the issues of load range and speed ratings.  You don't want to purchase tires that do not have sufficient load range to support the weight of your coach fully equipped, nor do you want to purchase tires that are speed rated at only 50 or 55 mph (transit tires, commonly).

I will agree with Gary, however.  It does seem to be that more and more trucks are running 22.5s.  Besides being a lighter tire, therefore increasing the load they can carry, I think they're also switching due to the newer engine's torque characteristics, allowing them to run overdrive transmissions.  TomC has noted some of this in his post above.

Also note that the manufacturers are switching over to metric sizing (315/80R22.5 for example), something else to scratch your head over.

Just remember that magic number of 495 as you work thru this.

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #8 on: July 03, 2007, 02:56:49 PM »

I just installed four Toyo M122 11:00R 22.5 14 ply tires on the rear of my 4104.

The dealer said it is his best selling truck tire.

I've had two of these on the front for just over a year and am very pleased with them.
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tekebird
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« Reply #9 on: July 03, 2007, 03:00:19 PM »

Toyos are very popular around me Mid Atlantic,  very good tire value

the 12r22.5s are still made in Japan and can be hard to find.  When I bought my last pair of tires they were backorderd with an expected delivery time of 6 months.

Sidenote: The Toyos made in japan give off some no so pleasant oders when warm.
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Sean
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« Reply #10 on: July 03, 2007, 04:14:01 PM »

Fred,

I'd like to reinforce a couple of points already made, and add a few notes.

First off, yes, 12R22.5 is a very common size on trucks.  Not so much for the trailers, but definitely on class 8 tractors.  11R24.5 is arguably a more common size, especially if you count trailer tires (bearing in mind that the truck tire market is divided into drive tires, steer tires, and trailer tires, and you'll only want steer, drive, or "all-position" tires).

If your concern about "common size" has to do with cost, I would venture a guess that the 12R22.5 tires will not cost you enough more, over the life of the coach, to justify changing wheels.  Changing wheels might lead to other issues as well, such as having to recalibrate speedo, cruise control, etc..

If your concern about "common size" has to do with availability in case you need one someplace on the road, you are likely to have slightly more choice in the 24.5, but not enough to matter.  Most tire dealers stock at least one 12R22.5 (that is, if they are big enough to stock 24.5 as well).  And we've had no problems finding used tires in that size, either.  In either case, if you have, say, Bridgestone R250s on your coach, and you blow one and want to replace it with an identical R250, it is just as likely the dealer will have to order it in either size.

If you want to change tire sizes, whether or not that also involves changing wheel size, you need to be certain that whatever tire you choose can handle the load.  Factors to consider are the rated load at max pressure, the pressure you will have to run to carry the load you will actually have, and any derating necessary due to speed (some tires require load derating above 55, 60, or 65 MPH).  So the advice to weigh your coach wheel-by-wheel is really mandatory if you wish to change.

If your existing rims are 8.25", you can fit the 12R22.5 you have now, or the 11R22.5, which will have a lower load rating, and likely more revs/mile.  If your rims are 9" (unlikely, but people have been known to change them), then the 11R22.5 is not an approved fitment.  If you go to the larger wheel, you will be looking at 11R24.5, which will have a load rating closer to the 12R22.5 you have now.

Other factors to consider:  The 22.5 wheels give a softer ride than the 24.5.  This is why many truckers use them, and it is why buses were almost exclusively fitted with this diameter wheel.  As has already been mentioned, you need to pay attention also to revs/mile, which vary among tire models even in the same size, and will vary more if you change wheels.

Also, tires with higher load ratings can (and should) be run with lower air pressure.  So even in 12R22.5, a Load Range H tire will likely need less pressure than a Load Range G, for example.  (Load range has a direct relationship to the older "Ply Rating" system, which has nothing at all to do with the number of plys in the tire, and a close relationship to the actual rated load in pounds.  Note the rating is different for single vs. dual applications for tires which can be dualled.)  Lower air pressure will, again, mean a smoother ride, and may also mean improved traction in soft surfaces.  This is the other reason you need your correct weights -- so you can inflate the tires according to the manufacturers' "load and inflation" tables.

Lastly, choosing tires can be daunting.  There are lots of brands, but only a handful of manufacturers.  There is a lot of unsupported anecdotal "information" floating around, including on these boards ("don't buy brand X; brand Y is best, never rotate tires to the opposite side, etc.).  You probably can't go wrong with any of the major brands -- just make sure you get fresh product as shown on the DOT code (it is not uncommon to get "new" tires that were manufactured two or even three years ago).  And shop around -- pricing differences can be high between different dealers, even right across the street.

HTH.

-Sean
http://OurOdyssey.BlogSpot.com
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tekebird
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« Reply #11 on: July 03, 2007, 05:25:47 PM »

isn't the 11r22.5 the common low profile 22.5 for trucks?

the 12r22.5 is the suposed rare to find on the road tire becuase it is a bus tire primarly now days
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Dallas
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« Reply #12 on: July 03, 2007, 05:37:17 PM »

According to what I've learned over the years, the 70-75 metric sizes are the lo-pros.
295R7522.5
275R7522.5

The 11.00R22.5 is a full sized tire (80% width to height ratio).

Another BIG reason trucking companies went to 22.5" rubber is that the FET on them is a whole bunch less than on 24.5" tires.

Trism, CFI, CF, UPS, CR England, Transport America, Celedon, Swift, Werner, Schneider, JB Hunt, among most others, all use lo-pro 22.5's.

Dallas
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luvrbus
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« Reply #13 on: July 03, 2007, 05:44:26 PM »

Doug, here in the west the 12r 22.5 and the metric size of this tire are easy to find at a good price because they are used on the log trucks on the steering axle
« Last Edit: July 03, 2007, 05:46:24 PM by luvrbus » Logged
tekebird
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« Reply #14 on: July 03, 2007, 05:51:57 PM »

Luvrbus, I was being a smartass when I said that about being rare.

theya re not rare...granted your Road service guy may not have one on hand but unless your in BFE ( email me if your not sensative and I'l give you that meaning if you don't know it) you should easily be able to find one, perhaps  not the brand/ tread design you run...but the correct size withing 24 hours.

thats why buses carry spares.  get a flat......replace with spare and arrange for another tire down the road a bit and keep on busin"
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