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Topic: Newb Tire Pressure question. Cold PSI? (Read 747 times) previous topic - next topic

Newb Tire Pressure question. Cold PSI?

I just bought my coach, a '93 U300 40 foot GV, about a month ago. The tires are two years old. I haven't driven the coach since I got home from NAC.

I do not know what my actual axle weights are. I read several threads on tire pressure and I'm a bit confused. We are heading out tomorrow morning on our first trip and once the engine is warmed up and leveled to ride height I want to check tire pressure. One tire appears low but I'll know for sure tomorrow.

The side walls on the two year old Michelins show max air of 110#. Should cold PSI be 100#?

Thanks for your patience.

Jeff
1993 U300 40ft GV SE
Build # 4344

Re: Newb Tire Pressure question. Cold PSI?

Reply #1 –
Air pressure for the tires is determined by the weight on that tire. The maximum air pressure is the pressure that is required when the tire is at maximum weight. Air pressures are given as cold air pressure.

Roland
1993 U280 4341
2010 Jeep Liberty
The Pied Pipers

Re: Newb Tire Pressure question. Cold PSI?

Reply #2 –
Jeff, welcome,

I have essentially the same coach and run 100 psi cold all the way around, never have had a problem. This is 10 psi over the rating on the chassis plate. I don't think adjusting each corner to the exact psi for a certain weight is necessary, while others may do this. Roger's suggestion to be a little over-inflated is good. I have several friends with SOB coaches that have tires just barely capable of carrying their coach empty, you won't find this problem with a Foretravel.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Newb Tire Pressure question. Cold PSI?

Reply #3 –
Jeff,

If you do not know what axle weights are then the safe thing to do is inflate to max psi (110) when the tires are cold (in the morning before driving).  There may be a plate over by the driver's side in the front that says what the gross axle weight is and what the tires should be inflated to for that weight.  If you find it then inflate to that psi..  When you have a chance get each axle weighed if not each corner so you know what your actual loaded, ready to go weight is.  It is better to be over inflated (up to the max psi) than under.

Somebody else might have more specific info.

I check my tires every morning when we are getting ready to leave even though I have a tire pressure monitoring system.  It is a good habit to adopt.
Roger
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Newb Tire Pressure question. Cold PSI?

Reply #4 –
Thanks all, I really appreciate it.
1993 U300 40ft GV SE
Build # 4344

Re: Newb Tire Pressure question. Cold PSI?

Reply #5 –
Lots of different opinions on this one. I max out the cold temp on the sidewall. 110 psi all the way around on our U300. Always have, always will.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Newb Tire Pressure question. Cold PSI?

Reply #6 –
Opinions galore, gotta love it.  For this ole dog, I always ran 105 psi in all six, but had a long chat with Wayne, so I figured what the H, so set all at 85psi, actually I got to liking that setting after 1500 miles, but the mind sez up to 90 psi, so I did.  Funny, it drives nicer at 85 on my light weight 36'
FWIW  I would never have beleived it.

Re: Newb Tire Pressure question. Cold PSI?

Reply #7 –
I used to drive in snow and ice.  The over inflated tires run on the center rib basically.

I have had overinflated hydroplane in heavy rain and skate on ice. 

Plus rides worse. 

Running adds ten pounds to the cold number I have heard. 

My tires were adjusted by previous owners all over the place.

A tread depth gauge shows they vary across them a lot.  Not flat on the ground.  Not good if conditions were severe.  Which they normally are not.

Cheap tread depth gauge shows what the correct number actually is.

Keep a log book.
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Newb Tire Pressure question. Cold PSI?

Reply #8 –
On our '93 GV 40', the PO used 100 psi all around - worked fine for him.  I've used 100 psi all around for the 2 years we've owned it - works fine for us.  All 6 tires are wearing evenly across the treads, and coach rides very smoothly at that pressure.  Centramatics also help the ride.

The important thing is to CHECK the pressures REGULARLY, when tires are COLD, with a ACCURATE gauge.  I've had good luck with the tools linked below.  The straight-back/straight-forward air chuck is especially handy for reaching the valve stem on the inside rear tires.

Air chuck:  POWERTANK - CO2 Air Systems

Pressure gauge:  POWERTANK - CO2 Air Systems
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Newb Tire Pressure question. Cold PSI?

Reply #9 –
I'll jump in on this one. Tie pressure is based on weight, speed, tire construction. Simple. Get your load rating on the tires, get the weight on each corner, determine your average max speed. We are about 29,000 lbs. we average 57 mph, we have H rated Contenentals. I air them to 90 psi and let them get down to 85 before taking them up again. I get seven years out of them with no problems. The ride is great and so is the handling. Can't see any reason for 110 psi just because the sidewall says that's the max.
Larry
1996 U295 36'
Build # 4805
Actually we sold it but just like to lurk

Re: Newb Tire Pressure question. Cold PSI?

Reply #10 –
I'm sure that airing your tires to the published pressure per weight is a good thing to do. But if your not that detail oriented, running the tires between 100 and 110 is my choice. My tire shop said it may not ride quite as comfortably at the high pressures but it reduces the chances of a blow out.  FWIW
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Newb Tire Pressure question. Cold PSI?

Reply #11 –
Jeff,

Until you can get individual wheel weights (best) or axle weights, look at the GVWR plaque near the driver's area.  It will give correct tire pressures for the original tires IF the axles are loaded to their full GAWR.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Newb Tire Pressure question. Cold PSI?

Reply #12 –
Thanks Brett.
1993 U300 40ft GV SE
Build # 4344

Re: Newb Tire Pressure question. Cold PSI?

Reply #13 –
Tire pressure is determined by weight, tire load rating, at cold temps.  Since you are new, it will be an ongoing journey as you find there are things you " have to have" in the coach- which will add to weight.  Another factor is do you drive with full water, 1/2 water, no fresh water at all?  100 gallons of water @8lbs/gal is another 800 lbs.  Just an example of how weight can and will change as you go down this fun road.

We live full time in our coach, always start off with empty holding tanks and full fresh water tank- that way we are good for a week or more if we don't hook up or want to go into a campground.  I run 100 PSI all the way around, tires are wearing well, handles fine.

Do what works for you now and don't be afraid to experiment a little to find what you really like.  Just be sure not to be under inflated  as that could be unsafe.

Have fun and cya down the road
Ted & Karen
2001 U270 36' - sold after 12 years full timing

Re: Newb Tire Pressure question. Cold PSI?

Reply #14 –
The correct tire pressure listed for all vehicles take into account comfort/ride. Tires will only carry their maximum weight as listed on the side wall at the maximum cold pressure listed. RV/vehicles in storage will require higher pressures than listed on the side wall unless under the maximum weight for that tire or the vehicle has been partially or fully jacked up to take the weight off the tire. Each manufacture will give pressures for storage, low speed (under 5 mph) in the case of heavy equipment in an online chart.

Operating your vehicle in high temperatures at lower pressures increases the tire temperature and makes it more susceptible to impact damage from potholes, etc. Tire manufacture max pressures also stop faster and handle better with less tread squirm/distortion.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Newb Tire Pressure question. Cold PSI?

Reply #15 –
I ran 100 lbs until a couple of months ago, had my rv weighed, full of fuel and water and loaded. Lowered my pressure by 10lbs
and really improved the ride
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Newb Tire Pressure question. Cold PSI?

Reply #16 –
Quote from: oldguy –
I ran 100 lbs until a couple of months ago, had my rv weighed, full of fuel and water and loaded. Lowered my pressure by 10lbs
and really improved the ride

Countless discussions with Rv owners who ran max sidewall pressure as a Foretravel sales manager and invariably your results matched everyone else's.

The wet area test to a dry piece of white concrete seemed to show the actual contact patch.

Noticeable with over inflation that the edges were not as dark on the ground.  Go back correct the pressure and drive through the water again.  The mark was the same all the way across.

Remember a bunch of days doing this more than once a day with interested owners.

Old tires then but the pilots showed the same differences that were originally on the first unihomes
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: Newb Tire Pressure question. Cold PSI?

Reply #17 –
Do not run the tires at the pressure stated on the sidewall unless you want a harsh ride. Read the data plate and then set the tire pressure to that value--if you still have the original size and manufacturer. A 10 PSI difference in tire pressure can make a significant difference in ride quality.
David and Carolyn Osborn
1995 U320C SE 40' Build 4726 Feb 1995
FMCA 147762
Motorcade 17186