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Old 12-03-2012, 08:54 PM   #1
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Help me set tire pressure

I just bought a set of TireMinder TPMS. To set it up correctly, I need to enter manufacturer's recommended tire pressures, so I called Country Coach tech support this afternoon. The rep asked me if I had it weighed, I told him not yet and inside pretty much empty; he then recommended 120psi for front and 115psi for rear.

I searched this forum, there were quite a number of threads on this topic. However the more I read the more I felt unsure if 120/115 is a little too high. most people were talking about 100psi.

What are the pressures on your wheels, on similar country coach 40 footers?
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Old 12-03-2012, 09:12 PM   #2
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Sounds like you may be getting the cart ahead of the horse. Get the coach loaded as you will travel, then weigh it. 4 corner weigh is best but at minimum weigh each axle. Then go to tire manufacturer's inflation tables for your specific tire and wheel position. Wen psi you determine from the charts is the psi you are looking for. Just for safety I add 5 psi above chart psi.
Hope this helps you get 'er done
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Old 12-03-2012, 10:12 PM   #3
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I suspect what the tech told you was correct for carrying maximum weight but you're nowhere near that in all probability. It would be fine (and safe) to inflate them to those pressures but if you're programming a TPMS I would think you'd want to do it only once so "get thee to a Cat scale" and get the right numbers.

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Old 12-03-2012, 10:20 PM   #4
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Quote:
Originally Posted by RickO View Post


I suspect what the tech told you was correct for carrying maximum weight but you're nowhere near that in all probability. It would be fine (and safe) to inflate them to those pressures but if you're programming a TPMS I would think you'd want to do it only once so "get thee to a Cat scale" and get the right numbers.

Rick
Most CAT scales I've seen won't let you get four "corner" weights and that's what you really need. Most of the tire manufacturers publish an RV tire guide. A copy of that from your tire manufacturer would set you on the right track. I have them for Michelin, GoodYear and TOYO and there may be others.
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Old 12-03-2012, 11:43 PM   #5
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Thanks everyone for your fast response. It seems I do need to weigh 4 corners at the earliest possibility. I am indeed nowhere near max load, maybe before I can get actual weight numbers I should set TPMS to front 115 and rear 110? currently it was filled with 105 psi all around by the tire shop where I bought the new tires.
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Old 12-04-2012, 11:39 AM   #6
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You should have a tire placard or certification label in your coach. This is the manufacturer's recommendation that you should use untill you confirm through scale weight, that you can run less.
HERE is a web page with general info and a worksheet on how to calculate your "corner" weights. I found a local builder's supply co that had a truck scale and would do the multi weight needed for RVs for about $10.

NOTE all the above applies to Motorhomes. If a reader has a trailer with ST type tires they should always run the inflation molded on the tire sidewall. They should still confirm they are not part of the 57% of owners that have one or more tire or axle overloaded.
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Old 12-04-2012, 03:11 PM   #7
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Hi sdlcrazier,
FYI, the weight on my rear axle is right at 20K (GAWR). You're drive axle should be the same GAWR (20K). Michelin says 95 PSI in all 4 tires. The front is a bit more tricky. There are many different front axle weight ratings for front axles. My front axle is rated at 12.5K. I am running 11.8K. Michelin says 105 PSI on the front tires.

This is FYI only. The tire manufacturer chart for PSI is your bible on this topic.
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Old 12-04-2012, 03:36 PM   #8
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the placard on the wall near driver seat shows max 120psi front and 110 on rear cold. the max load on all tires is 120psi. so, before weighing it, i am reluctant to put on max load, so i am going to pump up and set to 115 front and 110 rear. now i know i am safe and in line with everyone . upon weighing i might adjust these accordingly... thanks everyone.
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Old 12-04-2012, 04:25 PM   #9
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RV Safety & Education Foundation has a link to weighing

They call, do a short phone interview.. Come out, find a spot meet you weigh your rig (all 4 corners) and provide you with the proper pressure for YOUR tires (that's what the interview is about, Make and model and size of tire).

If you can not find a lower cost scale that can do 4 corner weights, Give 'em a call. or E-mail.
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Old 12-04-2012, 04:50 PM   #10
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If you get the axle weight and divide by two you will have a close enough weight for tires. Say front axle scales 18,000 pounds, I would just figure 9,000 for each side and base air pressure off this. We always run the same pressure on the steer of semi trucks as most alignment shops say a low tire on one side can cause it to pull. And they may very some side to side but not much. A motor home is a little different animal. Don't overload it, and try to balance cargo in the basement and coach. If it handles good then don't worry. Just keep tires to a correct pressure.
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Old 12-05-2012, 01:44 PM   #11
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If you get the axle weight and divide by two you will have a close enough weight for tires. Say front axle scales 18,000 pounds, I would just figure 9,000 for each side and base air pressure off this. We always run the same pressure on the steer of semi trucks as most alignment shops say a low tire on one side can cause it to pull. And they may very some side to side but not much. A motor home is a little different animal. Don't overload it, and try to balance cargo in the basement and coach. If it handles good then don't worry. Just keep tires to a correct pressure.
It is not unusual for axles to be out of balance by 1000# according to RVSEF.

Check THIS link here on iRV2
TYPE Class-A
RF - 4650#
LF - 4950#
RR - 9050#
LR - 7800#

As you can see these are a long way from 50/50.
As a minimum I suggest you calculate that you have a 55/45 side to side balance on the motorhome until you get data that confirms otherwise. You would select the inflation for all tires on the axle based on the heaviest tire load.
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