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Author Topic: 11-22.5 verses 11.24.5 tires  (Read 8856 times)
Lin
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« on: December 19, 2007, 10:09:23 PM »

Pardon my ignorance, but so 22.5 and 24.5 refer to the rim size or could I, since I need all four rear tires, move up from 11-22.5 to 11-24.5 without changing rims?  If so, what are the real benefits and drawbacks?
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TomCat
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« Reply #1 on: December 19, 2007, 10:24:45 PM »

Rim size and tire size will need to be the same. Width is specific as well.

Jay
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JohnEd
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« Reply #2 on: December 19, 2007, 10:53:29 PM »

Jay,

This is an old, old topic.  I haven't gotten an answer from the board that really satisfied me.  Talked to some Nuts in person and they made very good sense.  Here is my take:

The 24.5 is more common by oodles and gobs.  With that popularity comes more competition and price breaks.

You can also run excellent "take off trade in tires" for a couple years and then trade them for newer takeoffs and save a lot of money.  Truckers wear them out in a couple of years but we never wear them out but must change because they go over the 5 year limit or they start cracking.  Got bucks?  go Michelin for $500 a copy. 

The aluminum rims that make our bus run smoother is cheaper in the 24.5 cause there are hundreds on sale used every day.  22.5 is harder to come by used.

Carefull, those 24.5 come in some really heavy duty versions.  Get a tire with too high a weight rating and you will absolutely NOT BELIEVE THE HARSHNESS OF THE RIDE.  You can do that with 22.5 tires also.

The 24.5 tire is taller than your stock item and gives you a taller high gear and higher cruise.  You sacrifice bottom end and might have a problem starting on a slight grade.  Autos don't have this concern as much and those with 10 speeds ignore the issue.

Hope I didn't give you more questions than answers.

John
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TomC
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« Reply #3 on: December 20, 2007, 06:54:35 AM »

22.5 and 24.5 refer to the rim diameter.  Typically the width should be 8.25, sometimes 9.00 for 12" or 315 tires.  On 22.5's (the most popular wheel size for big trucks and buses [europe doesn't use 24.5]) some of the sizes are 7.5, 8, 9, 10, 11, 12, 235, 245, 255, 265, 275, 295, 305, 315, 365, 385, 425, 445.  So you see, just saying you have 22.5's is like saying you have a 4 wheel car. 
RPM differences- 11R-22.5 are 501rpm, 11R-24.5 are 478rpm.  Good Luck, TomC
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« Reply #4 on: December 20, 2007, 07:01:38 AM »

Thank you TomC, again, for providing accurate information!
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JC
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« Reply #5 on: December 20, 2007, 09:32:25 AM »

..and to make things even more interesting is the difference between 12R22.5's and 11R24.5's.... not much except the rim diameter!!
Though the rims are different diameters, the outer diameter (thus RPM) of these two is almost exactly the same. (look them up if you don't believe me, it's true! 479 vs 485)

I had to figure all of this out when one day I needed new tires for my Crown (on the road, a tire went bad) and got stuck at a place that only had a pair of 11R22.5's, Michelin XZA3 style, instead of the 12R22.5's that were on the rest of my bus.  The ones they had were 2" less diameter than the XZU2's I was running, but that was the only way I was making it out of there so I put a pair of 'em on the front and away I went, with a somewhat shorter bus in the front now. 

What ASTOUNDED me was the difference in road noise- the XZA3's made such a change inside as we drove that my wife and I immediately figured out that we could TALK to each other rather than YELL at each other while on the freeway.  It probably reduced the inside cab noise by half!!!

I decided that I'd love to put the right sized tires back on the front when I got home but alas, Michelin doesn't make a 12R22.5 in the XZA3 series, and since they were SO QUIET, I was a bit disappointed.  Upon more researching, I found that they DID make it in 11R24.5... and when I looked up the RPM's and found them to be almost the same I was REALLY happy, (and later to remember that my Bluebird bus -that needed new fronts anyway- had 11R22.5's all around-) so when I got back I stuck the just-purchased tires on the bluebird, and got new rims and  XZA3 11R24.5's for the front of the Crown, which brought it back up to the correct height off the road.  Confusing? You bet!!
Of course the Crown's front rims n tires are no longer interchangeable with the rears but I can live with that being that the tire diameters are now the same again, and it's so nicely quiet to drive now.

The point of all of this is how astounded I was at the noise differences between tread designs.  Had I not done it this way, I'd have never guessed that treads would have any major effect upon the sound levels inside the bus while on the freeway.  Never!  It's an ENORMOUS difference.  IF you have a noise problem up front and can use the XZA3 series tires, I highly recommend trying them out!!!!
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Lin
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« Reply #6 on: December 20, 2007, 09:50:47 AM »

Interesting about the noise.  Is there any independent noise rating on tires?  Finding this stuff out one tire at a time could be rather inefficient.
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« Reply #7 on: December 20, 2007, 09:58:48 AM »

JohnEd....Good post! Helpful and ...

I agree with you about the discussions over the years.

FWIW

RCB
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« Reply #8 on: December 20, 2007, 12:04:26 PM »

RCB,

Thanks!

Lin,

One of the nuts I talked to a few years ago was 79 years old and had had his Eagle for 15 years.  He had 22.5 rims on her in Alcoa all around.  In conversation he shared he should have gone to the 24.5 rim because he would have had more options and lower prices.  He also mentioned that his best friend owned a tire shop and he bought new at cost.

Please understand that this and the rest of it isn't "my lie".  I am passing along data that I think is good based on my and others judgement of the sources and filtered through my processor.  Of which sources, by the way, I think TomC is among those on the highest tier.  When he or many others I could name and I disagree I simply stand corrected.  I might still check but I won't argue with that ton of first hand experience and actually feel privileged to have access to that much first hand info.

keep on keeping on,

John
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« Reply #9 on: December 20, 2007, 03:43:36 PM »

Here is first hand info- I changed from 12R-22.5 to 11R 24.5 on my MC8.
   Used Alcoas that I inspected b4 I paid, $100 each. Nice Takeoff Tires with more than 50% tread, Goodyears on the front and Continentals on the rear, 2years old, $100 each from trucker that I know, off his personal truck.
    I have driven an identical bus (MC8)with new Michelin 22.5 on new Alcoas and the ride is nearly identical to mine. Both tires have 480 rpm, 12R 22.5 and 11R 22.5
   There is no difference in the gearing, take off speed or top end speed.
Just a lot eaier to find the 24's.........and a lot less $$$, My setup cost $1400 for the wheels and tires
 ( I run steel inners on the duals) Just my opinion, but I've BTDT. Chuck
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RJ
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« Reply #10 on: December 20, 2007, 08:25:48 PM »

Lin -

Let me add my nickel's worth to the discussion.  As you may have discovered, there's a whole lot of info out there - buying a commercial tire is a LOT different than buying something for your car.

22.5 and 24.5 refer to the wheel rim's diameter, so you cannot fit 24.5 tires on 22.5 rims.  Well, you could, but they wouldn't hold air.  Like trying to put a 15" tire on a 13" rim. . .

Be aware that the HD tire industry is converting over to the metric system that's been common on automotive tires for awhile now.  Remember when we had such sizes as FR70-14?  Nowadays those same tires would be P215/75R14.  Well, that's what's happening to the truck tires we use on our buses - what used to be the common (on MC-8s and 9s for example) 12R22.5 tire is quickly being replaced with 315/80R22.5.

As TomC said, 22.5 rims are becoming more and more popular on the newer trucks.  There's a couple of reasons for this:  First, both the aluminum wheel and tire combo in 22.5" weighs less with almost the same load capacity, so they can carry heavier loads, which = more $$/load.  Second, the newer 4-stroke engines have a "sweet spot" several hundred RPM lower than our old two-strokes, and often have more torque, too.  Consequently, with proper rear end and transmission gearing, trucker's can obtain equal or better fuel economy, again which translates into more $$/load.  And at $3.25+/gallon, they're looking to maximize the $$/load every trip.  OTOH, this creates a good opportunity for us busnuts, as finding used 24.5 rims in the truck boneyards, especially Alcoas, becomes easier as older equipment is retired.

When shopping for tires, regardless of rim size, be aware that different manufacturers may say that their tire is an 11R22.5 or 11R24.5, but compare them closely.  You'll find, for example, that one brand may turn 490 revs per mile, while a competitor's same size turns 504.  May not sound like much, but if you had a matched set of the 490s on one side of the drive axle, and a matched set of the 504s on the other, then your differential is going to be operating like it's turning a corner all the time, increasing wear on the spider gears inside.  One other thing is that the more revs/mile, the more fuel you're going to burn, which is kind of a moot point in a vehicle with the aerodynamics of a brick.  There may or may not be a speedometer/odometer error, but that's not something that's a big issue, normally.

NOTE:  If you have a GMC converted from a stick shift to a V-730, the bevel gears inside the transmission have an effect on top end performance.  For these, it's recommended that you use 24.5" tires with the LOWEST number of revs per mile to bring the performance back to near OEM.  This does not apply to T-drive coaches, only V-drive GMCs.

HD tires also come in different types of tread patterns, namely "Drive" for the drive axle, "All-Position" for any axle, and "Steer" for the front axle.  Generally speaking, drive axle designs have more aggresive (= noisy) tread patterns, which may or may not be important in your neck of the woods (snow country, anyone?).  A somewhat rule of thumb is the more aggressive the tread pattern, the noisier the tire, altho there are some all-position that are quite quiet. 

Load range is another thing to consider.  This is the rated weight the tire's designed to carry.  Even this can vary between sizes and manufacturers, so again, shop carefully.

Might I suggest that before you spend your hard-earned $$ on some new tires, take your coach in "ready-to-go" mode (full fuel, water, all the goodies inside, etc.) and run it over a set of commercial scales to find out not only how much it weighs, but how much weight is on each axle.  These figures will help you determine what load range tire you need, as well as determining what tire pressure you should be running, based on the tire manufacturer's published tables.

One final point:  Whatever tire you decide on, make sure it's rated for 75 mph.  There are "bus tires" out there that are specifically designed for transit buses, and most of those are speed rated at 50 or 55 mph max.  These are designed with heavier sidewalls, because transit drivers believe that curbs are part of the bus's braking system, so they bang 'em all day long.  These heavier sidewalls generate a LOT of heat at highway speeds, enough that for safety reasons, the manufacturers restrict their speeds.

Do your homework and choose what's right for you.

FWIW & HTH. . .

 Wink

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RJ Long
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Lin
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« Reply #11 on: December 20, 2007, 09:48:16 PM »

Thanks for the comprehensive info.  I will look into take-offs because it seems just pitiful to waste new tires to age, but since I would be looking for four (I'd like to have same on same axle), I am not expecting to get away with it.  Unless there is a big bonus in savings on the tires, it may not be worth bothering to change to rims either.  I like the idea of less noise, so I will also try to specify a less aggressive tread.  Being substantially driven by price though, I am sure some compromise will be in order.  Thanks again.
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« Reply #12 on: December 20, 2007, 10:18:43 PM »

Russ,

That is one heck of a post.  Thanks.

I visited my local truck store today.  I asked the owner if 24.5 rim truck tires were more popular than 22.5.  He said that "today" they are running about 50 50.  I asked if it had always been that way and he told me that up until a few years ago the 24.5 was much more popular on trucks.  He also mentioned that all the tires were going to the wider versions to be kinder to the roads and even duals were being replaced with a single wide tire.  I mentioned that fatter tires were less economical and wore out faster and he agreed that was true as a generalization and those double wide dual replacements were working out to cost the operators a lot more than they planned.  (generalizations are never true universally) (generalizations are NEVER true....hummmm)  I shared that the best wearing tires I had ever had were those old 19.5 by 8 inchers I had on the Winnie.  He agreed that those skinny tall tires set the record.   More fuel for the fire and a confirmation for TomC and maybe me.

John
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« Reply #13 on: December 20, 2007, 10:26:44 PM »

Lin,

You want 4 take offs of the same manufacturer, model and tread depth/wear.  You can do that.  Really!  Call around.  $100 per tire or less and try for Mich or Conti or other main brands that are known to be good.  Weight rating is critical for ride quality.  Specify that if one of the tires needs more than 4 pounds of weight, the deal on that tire is off.  There is an amt of weight that indicates a "second" in quality and avoid those.  I don't know what that weight is exactly for 22.5's.

HTH,

John
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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.”
—Pla
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« Reply #14 on: December 21, 2007, 06:55:13 AM »

I just bought 4 take-offs from a friend of mine trucker. Virgin Ohtsu 11R22.5, 50% tread, 3 years old, $100 a piece. The cheapest retread I could find was in Spokane for $180. I'm happy, the old girl gets reshod at a reasonable price.
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
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