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Author Topic: Tire pressures  (Read 1205 times)
Emcemv
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« on: December 30, 2012, 12:59:33 PM »

I've got all my tires set at 100 psi......what pressure is everyone running?
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Bruce & Nancy Fagley
1973 MCI MC-7 Combo Freighter
450HP DD 8V-92T 2000 Reman
HT 740 Allison
Woodbury CT.
belfert
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« Reply #1 on: December 30, 2012, 01:23:16 PM »

I run 85 PSI in the front and 75 PSI in the rear, but that is only the right PSI for my bus.  I would never recommend anyone use those pressures for their bus unless it had the same axle weights as mine.

The best thing to do is get the weights for each axle when you are loaded for a trip and then set the PSI based on the tire inflation chart for your tires.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
wildbob24
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« Reply #2 on: December 30, 2012, 03:48:07 PM »

What Brian said.

I'm running 85psi in the front and 80psi in the rear. Front axle weight is 9600#. Rear axle weight is 16,800#. Tires are 11x24.5

Bob
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P8M4905A-1308, 8V71 w/V730
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Eagle Andy
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« Reply #3 on: December 30, 2012, 06:01:12 PM »

Like you I have run 100 # in mine for 5 years and 10,000 miles and no signs of bad ware. it's just what turck boss at our shop said to try and it seems to be working for us.
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1968 Model 05 Eagle # 7481 Miles City MT
Emcemv
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« Reply #4 on: December 30, 2012, 06:14:06 PM »

I have searched through all the info I have on the bus and can't find that the PO had it weighed. GVWR is 36,500 on 3 axles. I plan to have each axle  weighed this year.
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Bruce & Nancy Fagley
1973 MCI MC-7 Combo Freighter
450HP DD 8V-92T 2000 Reman
HT 740 Allison
Woodbury CT.
RJ
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« Reply #5 on: December 30, 2012, 06:46:30 PM »

Bruce -

Brian's correct - you need to adjust your tire pressures based on the load each axle's carrying and the tire manufacturer's inflation table for your tire size and load range.  As an example, the 4106 I recently owned weighed just over 20K stripped.  Doing the research gave me 80 psi front, 70 psi rear.

When you weigh your coach, you should do so in "ready to roll" trim, thus a full fuel tank, a full freshwater tank, all of Mama's stuff inside, food, groceries, etc.

Rolling across the scales, you should get a front axle weight, three axle weight (whole coach), two axle weight and last(tag) axle weight.  A little math will help you determine the drive axle weight, at least close enough for these purposes.

Once you have each axle's weight, divide that by the number of tires on each axle, in your case by 2, 4 & 4 (since you've got duals on the tags).  That will give you the average weight each tire's carrying.  I take that number and add 200 lbs as a fudge factor, then go to the inflation tables to find the corresponding pressure.  If the weight falls inbetween, use the higher psi.

FWIW & HTH. . .

 Wink
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RJ Long
PD4106-2784 No More
Fresno CA
TomC
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« Reply #6 on: December 30, 2012, 09:55:31 PM »

No guessing here-go to your tire manufacturers site and pull up your tire model with the tire inflation table. Then go weigh your bus with you and the tanks full by axle. Then compare the weight to the tables and run the tires at that inflation or about 5psi higher.
My bus weighs 11500lbs front and 20500lbs rear. With 11R-24.5 16ply Michelin XZE's I run them at 90psi. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Tony LEE
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« Reply #7 on: December 30, 2012, 11:11:15 PM »

The tyre tables have separate sections for single tyres and dual tyres which takes into account that each tyre on a dual carries more than half the weight.

Tyre jockeys tell you 100psi because it is a nice round figure that is really easy to remember. Lowering to the recommended values should give you a better ride and better braking.
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Scott Crosby
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« Reply #8 on: December 31, 2012, 04:48:42 AM »

I got all new tires last year and the tire shop set them to 100.  I had it like that for 6 months.  Then I checked the chart for my tires, and took the bus to get it weighed at the truck stop.  Front was 5,000 lbs and rear was 14,000.  Those are 80psi settings for both on our chart.   The ride is so much better, I had no idea it would such an improvement in ride.  Night and day difference and well worth the $15 it cost to get the axles weighed. 
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Emcemv
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« Reply #9 on: December 31, 2012, 07:43:18 AM »

Looks like I have to make it a priority to get it weighed in the new year! Thanks to all for very detailed answers. Right now it has Michelins all around but new tires will be needed in the next couple of years as these are quite old.

Happy new year to all!
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Bruce & Nancy Fagley
1973 MCI MC-7 Combo Freighter
450HP DD 8V-92T 2000 Reman
HT 740 Allison
Woodbury CT.
plyonsMC9
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« Reply #10 on: December 31, 2012, 10:09:26 PM »

Yes, and also, watch the pressure after tire shop services.  I've had them do some veeerry ODD things with my tire pressure.  Even after I told them not to mess with the other tires, and / or exactly what PSI I wanted in the new tires.  Totally surprising.  Be careful out there!

Kind Regards, Phil
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Northern Arizona / 1983 - MC9
Tony LEE
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« Reply #11 on: December 31, 2012, 11:57:00 PM »

Quote
Those are 80psi settings for both on our chart.   The ride is so much better, I had no idea it would such an improvement in ride.

You only have to spend time on badly washboarded roads to realise that tyres ARE part of the suspension - provided they are given a chance to help.

Last time I got new tyres on the toad, I made sure they at least went through the motions of torquing up the wheel nuts correctly, but it wasn't possible to keep tabs on what the tyre changer was doing. Got home and found that the hardest tyre was pumped up to more than double the pressure of the softest one. None was within 5 psi of another and this was with tyres that should have been at 24psi.  Lazy &^%%^**#@
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