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Author Topic: Tire Talk  (Read 2227 times)
TomC
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« on: March 26, 2013, 08:36:05 AM »

Tires are talked about quite a bit since tires are a big expense, only second to fuel burned. Just to be curious, I went on the Michelin commercial tire site to see how many tires are made. Michelin makes 29 different steer tires (all position), 23 drive, and 13 trailer tires in various sizes. I looked up 11R-22.5 and found they make 5 different all position tires. If you have a 4spd manual, a 6-71, 8V-71 or 6V-92TA, you don't really have enough power to take advantage of drive tires-and drive tires are typically more noisy. If you have an engine with over 400hp and either an Allison or multi spd transmission, then a drive tire would work for you.
Just to give you an idea of the 5 tires I found:
-XZA-1 first generation over the road all position tire-good tire, cheaper then the next tire
-XZA3+ 3rd generation over the road all position tire that is fuel efficient. Great tire, but has thinner side walls that don't like to be banged against the curb or go over curbs.
-XZE2 regional tire that is rated to 75mph. This is the tire I use-has reinforced side walls, but won't get much more then 80,000 miles of life out of them. Most of us would run out of time before miles anyway.
-XZU3 regional transit bus tire-very strong sidewalls and can carry more weight then the normal 11-22.5. But only a 62mph rating.
-XZY3 aggressive tread on/off road tire with 65mph rating. Great for logging and dump truck.
My point-as I've said many times before-tires are much more then big round rubber things that support the bus. They are the only contact with the road for traction. Since most buses are underpowered, braking is the main concern. El cheapo Chinese and Russian tires look good on the outside, but who knows how they perform? You can bet that the name brand tires like B.F.Goodrich, Bridgestone, Firestone, Goodyear, Michelin,
Sumitomo, Yokohama, etc do extensive testing on their tires. Both brakes and tires are not areas to be cheap with.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Oonrahnjay
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« Reply #1 on: March 26, 2013, 02:13:21 PM »

  I went on the Michelin commercial tire site to see how many tires are made.

     Thanks, Tom, good data. 
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

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Dave5Cs
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« Reply #2 on: March 26, 2013, 02:27:55 PM »

Ok here we go. I have the 12R x22.5 and when I had my tires off the other day I noticed the wheel size was 8.25. Now on that size rim steel rims can I put 11R x 22.5  ?

Dave5Cs
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Ed Hackenbruch
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« Reply #3 on: March 26, 2013, 05:46:06 PM »

Yes you can. Smiley
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1968 MCI 5A with 8V71 and Allison MT644 transmission.  Western USA
TomC
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« Reply #4 on: March 26, 2013, 10:05:27 PM »

If you can run 11R-22.5's rather then 12R-22.5's you'll find the availability far better on the road, since it is still a very popular truck tire. And keep in mind they make both 14 ply and 16 ply ratings. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
RJ
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« Reply #5 on: March 27, 2013, 12:14:55 AM »

If you have a 4spd manual, a 6-71, 8V-71 or 6V-92TA, you don't really have enough power to take advantage of drive tires. . .

Tom -

You've got to be kidding!

I just picked a random Michelin drive tire, the XDA3.  I notice that in the 11R22.5 size, that tire turns 495 revs per mile.

That's exactly the same tire revs per mile that thousands of GMC V-drive coaches had their powertrains developed around!

Granted, they weren't BMWs, but just like the Hare, they got you there.

So I'm having trouble understanding your thought process that a 2-stroke cannot handle "drive axle" tires.  Can you please elaborate?

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #6 on: March 27, 2013, 04:12:28 AM »

Tom,
 What's your opinion on a safe tire age, 5 years, 7 years or 10 years??

Thanks,
Ken
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« Reply #7 on: March 27, 2013, 05:02:02 AM »

There is always a lot of talk about tire RPM and the manufacturer's stated specs.  The correct way to discern  this is on a smooth level floor.  Make a mark on the tire and floor and roll the coach one full rev, measure and then do the math from a speedo chart.  When the tires are hot they also grow a little also, and change the rpm somewhat.  In calculating the RPM for the VSS on my Silverside we used the above procedure and came up with 497, even though the tire mfg. stated 504. 
JFYI.

Mark
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TomC
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« Reply #8 on: March 27, 2013, 08:00:57 AM »

RJ-How're Doin? I said that the lower horsepower buses won't be able to take advantage of a drive tire-not that they can't handle a drive tire. With the lower horsepower, it is just plainly hard to spin the tires-unless you're in really slippery clay type mud. Then-how often does that happen? Also with snow-if it gets to that point that your drive tires are spinning, you should either have chains on, or my choice just plainly be parked. You can run drive tires on your bus if you want-it won't hurt anything. But-an all position tire will get better fuel mileage-less rolling resistance.

As far as tire life-it really depends on where you park the bus. If you're parked outside in a hot desert region with the sun hitting the tires, 7 years would be it. If you park indoors in mild climate 10 years or more would be it. The bottom line is to inspect the tires for bulges and cracking sidewalls. The tires have a hard job to do. Make sure the tires are up to the task with proper inflation (should use a system like PressurePro to keep track of tire pressure while driving). My first set of tires I went 14 years. I replaced them when I started to see sidewall cracking. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #9 on: March 27, 2013, 08:39:07 AM »

Tom,
 You mentioned pressure sensors. I recently purchased several late model Alcoa wheels. Some of the wheels have pressure sensors inside the wheel that are part of the valve stem assembly, a bigger version of the ones that are installed in automotive wheels that have the pressure monitoring system from the factory. I think the wheels I have came from an MCI. Are some of the late models coaches equipped with TPMS from the factory now?

Thanks,
Ken
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TomC
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« Reply #10 on: March 27, 2013, 11:23:46 AM »

I can't speak for MCI, but I know Freightliner trucks the TPMS is still an option. This is sort of weird to me since cars have had them standard for several years now and truck tire pressures are more critical then cars. Do figure? Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #11 on: March 27, 2013, 11:39:04 AM »

MCI uses the Smartwave system TPM by Bendix fwiw
« Last Edit: March 27, 2013, 01:24:59 PM by luvrbus » Logged

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chessie4905
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« Reply #12 on: March 27, 2013, 02:22:08 PM »

maybe the revs per mile is derived from taking the average between full tread and worn/discard tread.
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« Reply #13 on: March 27, 2013, 08:47:32 PM »

SAE paper J1025 explains how tire rpm is determined.
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Jim Keefauver/1985 Wanderlodge PT36/6V92TA/MT654CR/East Tn.
RJ
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« Reply #14 on: March 27, 2013, 09:21:18 PM »

If you have a 4spd manual, a 6-71, 8V-71 or 6V-92TA, you don't really have enough power to take advantage of drive tires. . .

I said that the lower horsepower buses won't be able to take advantage of a drive tire - not that they can't handle a drive tire. With the lower horsepower, it is just plainly hard to spin the tires - unless you're in really slippery clay type mud.

Tom -

I'm sorry, my friend, but I'm still not getting your point.  What's the "advantage" to a drive tire you're talking about?  Why would you want to spin the tires anyway, as mentioned in your response?  To dig yourself in deeper?

FWIW & HTH. . .

 Huh
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RJ Long
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Fresno CA
Uglydog56
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« Reply #15 on: March 27, 2013, 11:20:48 PM »

The rear tires on my Crown are Bandag recaps, 11R 24.5.  The tread looks like a set of mudders for my wife's jeep.  I can maneuver it around in the muddy vacant lot next to my house, while my dually pickup spins and gets stuck.  I think that is to which TomC refers.
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Rick A. Cone
Silverdale, WA
66 Crowny Crown "The Ark"
TomC
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« Reply #16 on: March 28, 2013, 11:44:35 AM »

Like Rick said, some of us are more adventureous then others. If you go into mud and soft sand, a traction drive tire will many times get you out. But-my point with a 4 spd manual, the 1st gear is so high, mud and sand will just let the tire settle in and won't have enough power to pull it back out of the trench-hence a traction tire would be useless.
I run only all position tires on front and back of my bus since I will never get off road and will never be in snow (living in L.A., I can do that).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
RJ
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« Reply #17 on: March 28, 2013, 07:28:22 PM »

Thanks, Tom. . . Now I get your point.

Understand about the geared-high 1st (and reverse, for that matter).  But then again, the OEM gearboxes were never designed for the type of operation we busnuts put them to.

FWIW & HTH. . .

 Smiley
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RJ Long
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Fresno CA
luvrbus
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« Reply #18 on: March 28, 2013, 08:02:39 PM »

Why would one give up a +or- 1inch of width to go from a 12r22.5 to a 11rx22.5 you tire experts enlighten me or humor me tire manufactures have said for years the wider the tire the less rolling resistance is that BS  or what ? 

As a Eagle owner for years I can tell you a Eagle with 12rx22.5 tires drives and handles a lot better than one with 11x24.5 plus they have 4000 lbs more GVW and the wider 315's 22.5 are even better IMO
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RJ
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« Reply #19 on: March 28, 2013, 08:46:02 PM »

Why would one give up a +or- 1inch of width to go from a 12r22.5 to a 11r22.5?

Clifford -

Simple answer?  $$

The 11s are cheaper than the 12s.

FWIW & HTH. . .

 Wink
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RJ Long
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TomC
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« Reply #20 on: March 28, 2013, 08:59:56 PM »

Less rubber on the ground and the higher air pressures, the less rolling resistance. Also the less amount of tires means less rolling resistance-this is why 18 wheel trucks are going to super singles so to only have 10 tires flexing.

As to the difference between 12's and 11's-if your bus weighs within the limits of an 11-why pay for a 12? And as stated, usually only buses use 12's and most everything on the road uses either an 11 or the lower profile metric version of an 11. Trucks and buses are now switching to the metric version of the 12 which is the 315/80R-22.5-which is a big chunk of money more then a 11.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #21 on: March 28, 2013, 09:07:35 PM »

Yep and trucks have a lot more caster built in than a bus if I remember right a Eagle was 3 degrees tops maybe 3.5 
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TomC
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« Reply #22 on: March 28, 2013, 09:10:19 PM »

When I found out how close in ratings the 11R-24.5 16ply is compared to the 12R-22.5 16ply, this is why I changed my bus from the 12's to the 11R-24.5.
12R-22.5- 7390lbs per single tire; 6780lbs per tire on a dual
11R-24.5- 7160lbs per single tire; 6610lbs per tire on a dual.

And on my bus, even though I have a 13,000lbs front and 23,000lbs rear, I only carry 10,500lbs on the front and 20,500lbs on the rear-hence even with the 11R-24.5 16ply tires that can take 120psi, I only run 90psi. My ride is very good with the tire pressure and the tires don't run hot.

Caster is a function of factory requirements to overpower the power steering. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #23 on: March 29, 2013, 06:10:46 AM »

another function of caster is to keep the vehicle going straight. Non power steering vehicles had very little caster as it is harder to turn a vehicle with more caster. The vehicle with caster will lift as it turns. 
Clifford If you find an Eagle with that much caster in it it will be rare. 2-2 1/2 is all you ever see. That front end was started long before power steering was used much. The design has never changed. That is why it is very important to keep things tight in an eagle front end.

Wayne
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« Reply #24 on: March 29, 2013, 06:31:18 AM »

I knew it wasn't much Wayne the buses like the Eagle even the Prevost with the IFS are limited on the caster they are nothing like a straight front axle bus or truck the narrow tire just don't work on the front IMO
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« Reply #25 on: March 29, 2013, 06:52:04 AM »

FWIW, we run 315's on our steer and 12R's all the other positions. We need every bit of the 315's on the front. We are 45K with a medium load.

We can get stuck on a banana peal (my guess is that goes for most). We haven't spent the money on the open shoulder tires, because if it get's at all soft we seem to just sink. That is one of the reasons we carry tire chains with us year round. Been times when grass has just been steep and slippery that we have needed chains. Otherwise it is pavement for us (except that isn't always fool proof...LOL)

John
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MCI 1995 DL3. DD S60 with a Allison B500.
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