Yokohama Tires

[Tikvah]

Okay, so if I'm reading right... there is still an advantage in price to the 12R 22.5 over the 315 80R/22.5  ?

[Sean]

I have a nice pair of 315/80R22.5 on my front steer.

It's time to replace my drives.  Can I buy the 11R22.5s for my drive and leave the steers where they are?

My discussion above referred to 315/80R22.5 vs 12R22.5.  The 11R22.5 is a completely different animal.  I do not believe that the 11R22.5 would be an approved fitment for an MCI-9 (or -8, or -7).  For starters, the load range of an 11R22.5 is significantly lower than for a 12R22.5.  Even if you weighed the coach, though, and determined that the 11R would have sufficient capacity, it is also a significantly smaller (diameter) tire.  Not only will that lower your fuel mileage AND your top speed, it might also allow parts of the coach to drag when you would not otherwise expect it.

I definitely would not recommend changing from either a 315/80R or a 12R to an 11R22.5.

What about the tag?  Does it need to be the same as the drives?

Here again, mixing 315/80R and 12R22.5, so long as each axle has the same tires all the way across, should not be a problem, but the same can not be said for mixing either of those with the 11R22.5, since it is so much smaller.  If you have the larger tires in the front and smaller in the back, your coach will ride nose-up, and vice-versa.  And if you have a separately suspended tag like MCI (as opposed to my tags, which share an air supply with the drivers), you would have to adjust the tag suspension for the different size, otherwise you could end up with too much or too little weight on the drivers.

I thought I was hearing just the opposite... 11R would give slightly better mileage than the 12R

I think you may be confusing this with the 11R24.5, which is, again, a completely different animal.  Yes, this is the tallest tire you can get, and has similar load characteristics to the 12R22.5, but it would required changing wheels from the 22.5" rims you have now to 24.5" rims.  Make sense?

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

Okay, so if I'm reading right... there is still an advantage in price to the 12R 22.5 over the 315 80R/22.5  ?

Yes, as I wrote earlier, the 315/80R22.5 (in a similar brand/model) will carry a higher base price than the 12R22.5, PLUS it will carry more FET.  Together these can add 30% or so to the price for any given tire.

-Sean
http://OurOdyssey.BlogSpot.com

[Tikvah]

Thanks Sean... that does make sense.

Well, I'll start shopping for 12R 22.5

Dave

[wal1809]

I am running Double Coin and Ling Long.  I have had nary a trouble with either brand.

[TomC]

Just to clear up some rumors going around about the difference between tires.  This is straight from Michelin, and with the same model of tire which is the XZE-.
315/80R-22.5, 42.3" in diameter, 19.5" rolling radius, 492rpm
12R-22.5, 42.6 in diameter, 19.8" rolling radius, 486rpm
11R-22.5, 41.3 in diameter, 19.3" rolling radius, 501rpm.
So changing from a 12R to 11R, your coach will be .5" lower, and if you spin 1800rpm at 60 with the 12's, you'll spin 1855rpm with the 11R's.  Personally-if you have 13,200lbs (16ply) or less on the front axle, you can switch to the 11R, pay less, and have them readily available at most truck stops.
Good Luck, TomC

[gus]

Just one point about tire size codes, the 315/12/11 widths are overall tire width when inflated, not the tread width. The 315 is almost 13" wide. The 11 and 12 are in inches.

[Low Class]

I have often wondered why most of the older buses run 12-22.5 tires?  The GM's and MCI's aren't that heavy.  My (old) Wanderlodge is approximately 12500-19000-7000 axle weights.  When I bought it, all the tires were 11's load range G of all things.  The fronts (GY G357) were overloaded a couple hundred pounds.  The old bus drove fine.

Came replacement time.  I stayed with 11's on the rears and upgraded to 295-80 Mich XZA2 on the front.

I have no idea if it is the wider tire or a quirk of the XZA2 but now my Wanderlodge is true to it's name.  It is sensitive to pavement texture. Some pavement it runs straight as an arrow and some it wants to go every direction but straight.

My point is from my limited experience is that wider is not always better.

[muldoonman]

I am running Double Coin and Ling Long.  I have had nary a trouble with either brand.

Is that really the names of the tires? That sounds almost comical. No offence.

glen

[muldoonman]

I am running Double Coin and Ling Long.  I have had nary a trouble with either brand.

[Sean]

...
12R-22.5, 42.6 in diameter, 19.8" rolling radius, 486rpm
11R-22.5, 41.3 in diameter, 19.3" rolling radius, 501rpm.
So changing from a 12R to 11R, your coach will be .5" lower, and if you spin 1800rpm at 60 with the 12's, you'll spin 1855rpm with the 11R's.
...

All true, Tom, but while the raw numbers (e.g. half an inch) sound small, they are more significant in percentages.

On my coach, 0.5" would be 6.25% of my ride height.  I don't have the ride-height spec on an MC-9 in front of me, but I am guessing 0.5" is somewhere around 4%-5% of ride height on that coach.

The difference between 501 RPM and 486 RPM is 3%.  So that's 3% off the top speed, and probably about that much off fuel economy as well.

Again, I would not mix 12R and 11R on the same coach; at the very least, I would try to have the same size on the steers and drivers.  For a light enough coach, you could make the case that switching to 11R22.5 all the way around could save a couple hundred bucks in tires up front.  I would argue that you'll probably give that money back in fuel over the life of the tires (by my math, around 230 gallons of extra fuel).

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[TomC]

Just because an engine is running 3% faster does not necessarily mean it is using 3% more fuel.  As an engine turns faster it produces more power, so with a faster running engine at the same mph, you'd be actually be using less pressure on the gas pedal.  But with higher rpm comes higher friction.
If you keep the same rpm and let the mph lower down, you'd probably get about the same mpg.  Granted you're not covering as much ground, but with the lower mph, you have less road and air friction.
Many people like to see the savings on tires right now in a big lump sum.  Seeing the savings over the life of the tire isn't what most will be looking for.  Just the mere fact of using the wrong tire will use more excess fuel then the difference between tire sizes (like an off road or heavy lug tire compared to a fuel efficient highway tire-this can make up to a 5% difference in fuel mileage).  Good Luck, TomC

[WEC4104]

Can anyone tell me if there is a metric equivalent to the 11R22.5 size, that can be run on the same rims?   Next time I'm tire shopping, the extra choices might be worth considering.

[TomC]

The metric version of the 11R-22.5 is either the 295/75R-22.5 or the 275/80R-22.5.  But once again, it is a low profile tire and you will loose both height (about a half inch lower on your bus) and rpm.  The 11R is 495-500rpm, and the others can be 505-517rpm.  Practically all over the road trucks are now using one of the two metric tires above.  Good Luck, TomC

[Scott & Heather]

Thanks Sean and RJ. Couldn't have paid for a better answer.


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