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Tire Inflation w/ Bus Air
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really informative data, thanks! Where did you weigh your wheels? Most scales in my area are on ramps and not sure It is possible to drive with only one side on the scale.
Two things the document said: store the tires on cardboard, plastic or plywood. What do most folks use? Inflate to the side wall pressure. So if I got that, over winter I ignore the load-based pressure and inflate to what the tire says?
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Like Tom I have had my wheels weighed individually and the side to side difference was negligible. Our weights were done by the SD State Police at a rally, but there are companies that offer individual wheel weighing for those who want to get specific. I think one company offers the service at FMCA rallies for example.
The tire pressures are determined by the manufacturers and they are established to provide both performance and tire life. One thing that can never be repeated enough that everyone should know and understand is if you are going to deviate from the tire pressures understand one very important fact that tire manufacturers agree on. Any tire that has been run at 20% less than the specified pressure is JUNK. The tire has been ruined. It should be scrapped.
The reason for such a statement is because running a tire at 80% or less of the required pressure damages the cords. The damage is invisible. But the probable outcome of continued use is what the tire manufacturers describe as a zipper failure. The tire fails catastrophically, with the sidewall opening as though there were a zipper around the carcass. It is a blowout. A tire that needs 100 PSI, but is run at 80 PSI has been damaged.
So regardless of whether you run the specified pressures, or exceed them, at the very least make certain you never allow your pressures to go below the required pressures.
I would be very afraid of tires on a used coach if I saw signs the owner was careless with maintenance. If an owner is not going to keep maintenance up to date, it is unlikely a pretrip tire pressure check will be done (or a brake check for that matter).
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David,
If your current wheels at 8.25″ or 9″ wide, and they likely are, you can move to 315s. The only other caution would be that your wheels may not be rated for the maximum capacity or pressure as a 315. This is not a big deal because you don’t need the 130 psi or 9090 lb capacity of a 315. 8.25″ wheels are likely rated for a maximum pressure of 120psi and 8,000 pounds.
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Liam,
Some scales may have enough of an apron around the scales to get one side off on the concrete. There is a Q-T near me at exit 306 in Adairsville, GA that has the room. I have weighted individual wheels there many times. You do have to explain what your doing, or they’ll look at you as if they saw Jon at a Rolling Stones Concert.
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Liam,
You can also check with your local Department Of Transportation (DOT) officer, the ones that check out the big rigs, and they will have the portable scales in the trunk. At least here they are willing to weigh them for you.
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I drove in my truck this morning to check out the 3 local truck stops (I live near the I-70 and I-81 interchange so there are plenty) and found one with grass level with the side strip – the other CAT scales are the type built as a ramp. I will head-out soon to try it. I assume with the drive on one plate and the tag on the other, you still get a good weight even with the wheels that close to the edge of the plates?
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Liam.
Just be sure you split all 3 axles on separate platforms. It’s easy, but you might need someone to help make sure the drive and tag are not on the same platform.
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ok, just back from a weigh-in. Before I fueled-up and filled my fresh water tank to the top. I had to get out of the bus to push the intrrcom buttons, so no people in the weight. I was slightly heavier on the driver side but within the margin of error using the tables.
Steer = 13940
Drive = 18300
Tag= 9020
So if I add 800 pounds for 6 people assuming people weight distributed fore and aft that bumps the steer up 2 columns in the table to 14740. The other 2 axles are way under minimum so ignore. If i then add the 5 you all add then my pressures would be 105, 90, 90
Did I do that right?
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Those numbers are almost identical to what my XL used. I would say they are correct.
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Looks close to mine Liam, 105, 95, 85.
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Liam,
Did you say your tanks were empty when weighed? If so, fill them and reweigh. Here’s the weights of my 99 XL (no slides) with full fuel tank and 1/2 a tank of water and less than a 1/4 tank in gray and black water tanks, also no passengers. The stuff in the coach was about as much as I would ever carry.
Front DS: 7,400
Front PS: 7,400
Added for passengers and fluids: 500 per wheel
Front Tire Pressure Weight 7,900, 115psi per Michelin + 5psi = 120 psi
Drive DS: 10,800
Drive PS: 10,100
Added for fluids 400 per wheel position
Drive Tire Pressure Weight 10,800+400=11,200, 85 psi per Michelin, I run 95-100 and will monitor for uneven thread wear.
Tag DS: 6400
Tag PS: 5900
Added for fluids 200 pounds per wheel
Tag Tire Pressure Weight 6400+200=6,600, 90psi per Michelin, I run 95-100
Although the differences between DS and PS weren’t much on my coach I saw well over 1,000 pounds difference at a recent rally. The biggest differences were on coaches with slides.
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Gil, If you have an actual 15,300 on your steer axle and 315 tires what chart do you refer to? This one shows 105 PSI for an axle weight of 15320 for XZA tires. I understand adding 5 PSI, but not 15.
http://www.michelintruck.com/michelintruck/tires-retreads/load-inflation-tables.jsp
I’m cool with folks wanting to overinflate their tires because it is safer than underinflation, but to folks asking for advice the chart says based on your 14,800 plus 500 pounds says 105 is the pressure and your 120 is misleading. What charts are you using?
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Jon,
I think you are using the truck chart instead of the RV chart, http://www.michelinrvtires.com/michelinrv/tires-retreads/load-inflation-tables.jsp. This chart states 115psi for 7,950lbs.
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Gil, I had fuel and fresh water 100% full. I stopped by the new State Police barracks to ask if they do portable scale weights and they said “yes” if you are commercial, but if you are private “then we would have to do it for everyone!” Gee, we wouldn’t want EVERYONE being safe as they hurtle down the highway! And this was hagerstown where every teenager at a check-out counter calls me honey or sweety 😉
Thanks everyone – and someone steal a scale and bring to the next rally!
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Gil, your own figures show a weight on the steer axle tire of 7650 that includes your 500 pounds above the axle weight. As I look at the RV chart http://www.michelinrvtires.com/michelinrv/tires-retreads/load-inflation-tables.jsp
it calls for 105 PSI.You are inflating for a single tire weight of 8530.
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