Michelin X Line Energy Z

[Bill Gerrie]

I can't agree more with luvrbus then that as I know 2 people that did exactly that. The 12 R is a much better handling tire and smoother ride.

[richard5933]

Here's the actual difference between the 12R and 11R both 16ply rated-based on the Michelin XZE.
12R- loaded radius is 19.8" and 11,600lbs would be 90psi
11R- loaded radius is 19.2" and 11,600lbs would be 100psi.
So running 11R's you'd loose 6/10" in height and have to run 10 more psi-in my book that's well worth the convenience factor of having 11R's instead of 12R's. Good Luck, TomC

The radius is only half the story. With regard to the ride height, the tire diameter is important. The 11r is almost two inches less than the 12r in diameter, which would drop the ride height 1".

[richard5933]

Re: tire rubbing the internals...

Same 12R size tire, one Goodyear, one Michelin,

One of them would rub one of the bars under an MC8, one wouldn't.

Just the nature of the beasts, slightly different bulge, one just touched, the other didn't.

Noticed the dirt missing shortly after tire swap, swap 'em back, dirt began to accumulate again.

MC8 steer like battleships, so the mechanics had it freed up as far out as we dared, when this was discovered.

Interesting the subtle difference between two "same size" tires.

Experiment and adjust.

happy coaching!
buswarrior

Even with the same tire manufacturer and same tire. Toyo offers their M170 in two widths - 13.0 and 13.6

Obviously one would be more likely to rub than the other.

[TomC]

To clarify-loaded radius is the distance from the ground to the axle when mounted with rated load and air pressure in the tire. All this talk about over an inch isn't true. 6/10" is all the difference your bus would be between the 12R and the 11R. Good Luck, TomC

[luvrbus]

To clarify-loaded radius is the distance from the ground to the axle when mounted with rated load and air pressure in the tire. All this talk about over an inch isn't true. 6/10" is all the difference your bus would be between the 12R and the 11R. Good Luck, TomC

Actual drop on a Eagle measuring from the body to the pavement with 11R x22.5 is almost 2 inches, so they go with 11R x 24.5 but I'll take your word on the 6/10 of inch  since I don't recall the brand of tire

 

[Geoff]

Something not mentioned here is the mph difference in running shorter tires.  I run 315 80r 22.5's for the GVW on my 2 axle RTS @ 36,900 lbs.  Tom is good at calculating top speed.  I like the taller and wider 315's.

[richard5933]

To clarify-loaded radius is the distance from the ground to the axle when mounted with rated load and air pressure in the tire. All this talk about over an inch isn't true. 6/10" is all the difference your bus would be between the 12R and the 11R. Good Luck, TomC

There are two variants of the Toyo M170 in the 12R22.5 size. One is nearly identical is size to the 315 size, with a loaded radius of 19.8"

The M170 in size 12R22.5 in the narrower width is only 19.0" loaded radius. This is the one I'd be installing, because it's the one that would help with the clearance issue. The wider M170 is the same width and same loaded radius as the 315s, and would most likely have the same clearance issue.

315/80R22.5          19.8" loaded radius
12R22.5                 19.0" loaded radius
11R22.5                 18.6" loaded radius

So, the drop from the current 315 size to the 11R size would be 1.2"

As it is, going from the 315s to the 12R would be dropping the ride height down .8" and make getting the tank hose on more difficult (impossible in some places). Going down another 1/2" would be worrisome if I hope to be able to empty the tank without too much cussing.

Top speed is not a worry right now. With the 315s I can hold a cruising speed over 70 with no problem on flat roads. As it is, the speed can easily creep up over 75 if I'm not watching. I like to keep it to around 65 at the most.

[RJ]

Richard -

My Les Schwab dealer just got back to me today with some "inside" information on the Toyo M170s in the 12R22.5 size that you see on their commercial tire website.

SKU #546090 is the current production tire, and the ones put on my coach a few weeks ago.

SKU #546310 is the new replacement for the 546090 as current stock in the system is depleted.  It has a slightly different tread pattern, slightly higher load/speed numbers, has a slightly taller static loaded radius (19.7 vs 19.0), and a slightly wider overall inflated width (12.4 vs 12.0.) This new tire is also smaller than a 315/80R22.5, but not by much.  Biggest difference is the 315 has a greater weight capability and, surprisingly, a lower speed rating! (At least in the Toyo line, others may be different.)

Anyway, thought you'd find this info interesting as you ponder new shoes for your coach.

FWIW & HTH. . .

[richard5933]

Thanks for the updated information RJ.

That confirms what I've been thinking, but I discovered a part of this that confuses me.

If the tire is contacting the airbag on full turns, it's most likely the corner of the tread that makes contact. I suspect that the width of the actual tread is the same on both of these two model variants, so the only real difference will be the loaded static radius.

The current production tire, the one with the smaller radius, is probably going to be the one with the most clearance between the tire and the air bag. However, it will be the one that gives me 0.7" less clearance under the bus. Maybe not that much, but I worry that it may be enough of a drop to make putting the black tank hose on more difficult or not possible in some locations.

There are so many variable with this that it really gets to be mind boggling after a while.

[sledhead]

I had the 12's on the MCI when I first got the bus then went to the 315's but went back to the 12's because it FELT easier to steer

Dave