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Tire pressures
After getting several different numbers from supposedly “knowledgeable people”, I want to get the facts from the people on this forum.
I have Michelin 315’s 22.5 tires and need the correct tire pressures please.
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14 Replies
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After you weigh your bus by each axle go to Michelin tire pressure chart find your weight in the 315’s and that’s your suggested minimum PSI.
Cost to weigh at Flying J about…. $100
FWIW…..As the Flying J is just across I-49 from our bus barn a couple of years ago I weighed the bus with 90 gals of fresh water and fuel in-between empty / 1/4, empty holding tanks.
2005 Marathon XL-II 2 / slide
Went back to scale after filling the fuel tank, increase weight was evenly distributed between steer and rear axles.
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PSI 85 90 95 100 105 110 115 120 125 130 Maximum load & pressure on sidewall kPa 590 620 660 690 720 760 790 830 860 900 LBS Single 6415 6670 6940 7190 7440 7610 7920 8270 8690 9090 S 9090 LBS at 130 PSI Dual 11680 12140 12790 13090 13540 13880 14420 15220 15820 16540 D 8270 LBS at 130 PSI KG Single 2910 3030 3150 3260 3370 3450 3590 3750 3940 4125 S 4125 KG at 900 kPa Dual 5300 5500 5800 5940 6140 6300 6540 6900 7180 7500 D 3750 KG at 900 kPa -
Here’s Prevost’s motorhome tire pressure calculator site.
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George…… could you share with us what the “knowledgeable people” had to say.
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Georges,
The posts above are correct and all owners who have not yet done so should weigh the coach and inflate the tires to the pressures called for in the Michelin chart for their tire size. These are cold inflation pressures.
Everyone needs to keep in mind if a tire is driven at pressures 20% less than the specified pressures the tires should be treated as unroadworthy. They are considered damaged by the manufacturers and taken from service. They may look OK but have the potential to suddenly fail catastrophically. Tire pressures are critical to your safey.
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There is only one way to establish the MINIMUM tire pressure. You MUST have your coach weighed when fully loaded and it MUST be weighed at each wheel position. Any other method of establishing minimum tire pressures are guesstimates.
Personally, and Jon disagrees with this approach,I always err on the side of safety and will never run my tires at the MINIMUM tire pressure. I run my drtives and tags at 100 psi even though Michelin’s minimum would be 85 and 90. I run my steers at 120 even though the minimum is 105-110. Okay, I mat sacrifice a bit in ride, although I can’t feel it. Our coaches are too heavy to worry about wearing the center of the tread out early due to my pressures. All I’m doing is improving sidewall life and safety. Keep in mind the load/inflation table only tells us what the minimum pressure is.
If you insist on running at the minimum pressures, make sure your pressure gauge is calibrated.
Your best reference is the Michelin RV guide. It’s better than the Michelin Truck guide. http://www.michelinrvtires.com/michelinrv_en_us/toolbox/reference-material.jsp
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The “advice” was offered by a certified detroit diesel mechanic, an RV dealership and a Bluebird owner. The numbers were anywhere from 95 on the rears/100 front to 110 lbs all around! They made me dizzy. Thank you all for the (as always) excellent advice.
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Gil,
Running tires at pressures in excess of the pressures shown in the Michelin chart is satisfactory. The chart defines the ideal pressures and wasn’t intended I don’t think to be minimum, but the pressures that assure long life, even tread wear, comfort, and best performance with respect to skidding and or braking.
The minimum is 19% below the recommended pressures. One percent less causes tire damage if you can believe what all the tire companies say. They all agree 20% less than recommended pressure causes non-repairable tire damage so any pressure above that magic number by one PSI is the minimum. (I’m being absurd to make the point)
A lot of folks who own Prevost coaches have spent a lot of money to change from 315 to 365 tires just so they could run their tires at lower pressures to improve the ride so I suspect while extra pressure provides a better margin for safety in the case of a slow leak for example, most will want to use the chart for inflation pressures.
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Take your bus to a truck scale (like CAT) and weigh each axle. Use a tire load chart such as listed below (for your brand tire) to select your air pressures. Some owners like to go a few % higher to give you a little margin. If you really want to dial it in you can weigh each tire patch. Some conversions can have a weight difference side to side as well.
You will with nearly 100% certainty require different air
pressures at each axle. -
Dan said that because most busses will have different weights at the front and rear – and even side to side as he said. So you might end up running different pressures for the different tires. When you weight it you’ll have to put the bus on the right spots to get the axel weights. CAT scales are at most of the bigger trucks stops. I think it was about 40$
Our bus was exactly like that… 105 in the rear and 130 in the front. I ended up getting 365’s for the front because at 130 the front tires were like rolling on rocks. Now I can run 105 in the front. Much nicer ride.
And Livemore is the new wine country!
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Since Walt fired one over the bow,(-: I have to chime in. We stayed in Paso Robles for about a week in mid January, absolutely gorgeous! The Redhead (aka The Wino) put a serious dent in the budget visiting the wineries.
We’ll have to add Livermore the next time we get back out there.
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Was substantial hair cut also part of the Paso Robles trip?
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Definitely weigh each axle separately
on your coach and use the “load chart” for your brand of tires.The last time I weighed our coach (late 2016) it
cost $70 the first time and $10 each subsequent time in a 24hr.
period.It wasn’t specifically CAT scales but it was the truck stop
across the street from the CAT scales. It was just more convenient
at the time. 🙂 -
Go to Jeff’s ETLC and get a service done, while there, you can get individual axle, side to side weights at the same time, and NO extra charge. Then refer to the tire chart.
It would make a good road trip from Calif.
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