Tire Pressures

[Don SC]

How much air pressure should I run in my tires- both the 5thwheel and the truck?

The 5er tires say 80psi on the sidewall, and so do the truck's tires. What are the guidelines for air pressure?

[mptjelgin]

Both the truck and trailer should have sticker that give you tire pressure. On the truck it will often be in the drivers side door jamb. On the trailer it will generally be a sticker on the side somewhere. 

If you can't find any stickers the safest thing to do would be to run all of the tires at their rated 80 psi, and then get the hitched setup weighed either at a truck scale (like a CAT scale) for each axles weight, or even better tire-by-tire at one of the SmartWeigh events sponsored by SKP's. With that specific knowledge you can use tire manufacturers weight-vs-load tables to determine appropriate pressures. 

[rynosback]

37 minutes ago, mptjelgin said:

Both the truck and trailer should have sticker that give you tire pressure. On the truck it will often be in the drivers side door jamb. On the trailer it will generally be a sticker on the side somewhere. 

If you can't find any stickers the safest thing to do would be to run all of the tires at their rated 80 psi, and then get the hitched setup weighed either at a truck scale (like a CAT scale) for each axles weight, or even better tire-by-tire at one of the SmartWeigh events sponsored by SKP's. With that specific knowledge you can use tire manufacturers weight-vs-load tables to determine appropriate pressures. 

I agree completely with what he said.

[gjhunter01]

52 minutes ago, mptjelgin said:

Both the truck and trailer should have sticker that give you tire pressure. On the truck it will often be in the drivers side door jamb. On the trailer it will generally be a sticker on the side somewhere.

If you can't find any stickers the safest thing to do would be to run all of the tires at their rated 80 psi, and then get the hitched setup weighed either at a truck scale (like a CAT scale) for each axles weight, or even better tire-by-tire at one of the SmartWeigh events sponsored by SKP's. With that specific knowledge you can use tire manufacturers weight-vs-load tables to determine appropriate pressures.

Good advice.

 

Greg

[Don SC]

OK. The truck door sticker says 60 psi in front and 75 in the rear tires.

Camper sticker says 85 psi for both axles'  tires. I'm getting new Goodyear Endurances for it tomorrow. 1st camping trip coming up this weekend.

[mptjelgin]

Are you sure about the 85 psi on the trailer?  From what I can see the Goodyear Endurance trailer tires are available in Load Range "D", which is 65 psi, and Load Range "E" which are 80 psi maximum cold inflation pressure.  An 85 psi inflation pressure is unusual.  

You'd mentioned that your current trailer tires state 80 psi, which would be the common Load Range "E" tires often found on fifth wheel trailers. 

[Ray,IN]

On nearly all RV-type trailer tires, they are operating at or near their maximum load rating, and should be inflated to sidewall maximum pressure for that and another reason. Tandem axle tires are subjected to severe sidewall stress' when making a sharp turn, lower pressure allows more sidewall deflection.

I once saw a guy make a spot turn with his 5er on new blacktop, it rolled the bead away from the rim enough to lose pressure in the tire.

I always complied with the federal tire placard on my dually when towing our 5er,  the tires wore evenly and each set lasted about 45/50,000 miles.

[pethier]

I have some confusion on tire pressures.  I have a 34-foot Damon Challenger diesel pusher.  It has 19.5 tires which state on sidewall max pressure 120 PSI.  Tires were at 100 PSI when I got the unit used, so I have been using this.  Tires got warm, not hot, on the road.  I could not feel a difference across the tire.  This was true whether or not I was towing my car trailer

The data plate on the motorhome calls for 60 PSI.  This seems really low to me.  Should I try running them that soft?

 

(On my car trailer and my 3/4-ton Suburban, I run 80 PSI in the loadrange-E tires on the trailer and the back of the Suburban.  The front of the Suburban runs 50.  Oddly, I had arrived at the 50-80 split on the Suburban before I found that 50-80 is actually the spec from Chevrolet.)

[Kirk W]

2 hours ago, pethier said:

I have some confusion on tire pressures.

The proper inflation pressure for your tires depends upon the weight on each wheel. All tire manufacturers publish inflation charts for the tire size and models they build. If you go to the manufacturer's website and find the tire you have and size that it is you should find a chart that lists the proper inflation pressure for each of a wide range of individual wheel weights. To do this accurately, you need to have the motorhome weighed when fully loaded for travel and with a full fuel tank. You need the weight on each wheel. If you don't have that you can use a truck scale that weighs by the axle and if possible weigh a second time with only one side on the scale. By doing that, a little math will give you the weight on the side not weighed alone. You should always run the same pressure in each tire on the same axle so use the heavier side to choose pressure. You can and usually do run different pressures in different axles. 

[Ray,IN]

Something to remember about load/inflation charts, they show the MINIMUM air pressure to support the corresponding load. This means if you inflate to that pressure, you are operating your tires at 100% of their load capacity, You decide it that is prudent. Heat is the #1 enemy of tires, lower inflation allows the sidewall to flex more, which equals more heat buildup.

[Kirk W]

13 hours ago, Ray,IN said:

This means if you inflate to that pressure, you are operating your tires at 100% of their load capacity, You decide it that is prudent.

While this is true, if you operate at maximum inflation pressure you will cause poor tire wear and a stiff ride. 

[Ray,IN]

10 hours ago, Kirk Wood said:

While this is true, if you operate at maximum inflation pressure you will cause poor tire wear and a stiff ride. 

For a motorized RV this it true, that's why the federal tire placard in the vehicle states required air pressure for the GVWR, instead of the tire sidewall pressure. Pull-type trailers OTOH seem to be always near the GVWR, thus the recommendation by ST tire mfgrs to use sidewall pressure.

Personally, I've always thought trailer mfgrs should use heaver tires to greatly reduce tire problems, instead of creating the situation where ST tires are continually operating near/at their maximum weight rating.

[TireHobby]

Motor Home owners seem to always give information on this subject that is intended for vehicles governed by different regulations. If your MHs federal certification label has recommended cold inflation pressures on it, the standards for maintaining them will come from FMVSS standards. Under FMVSS standards tire manufacturers do not set vehicle tire inflation pressures, vehicle manufacturers do. It's a standards requirement.

In chapter 4 provided below you will find the correct procedures. Read the whole thing. Reading til you find what you're looking for may be out of context and you'll be right back where you started from.

http://www.mcgeecompany.com/wp-content/uploads/2010/12/complete-manual.pdf

 

For those that won't take the time to read the document I'll add this. It's an industry wide standard to NEVER use less tire inflation pressure than what has been recommended on the vehicle's certification label, tire placard or in the vehicle owner's manual.

[Ray,IN]

Tire Hobby, I was boo'ed off the FMCA MH forum for saying exactly what you stated, and I included hot links to backup my statements. In addition to that RMA document in your link, I included what Goodyear stated about MH owners mistakenly running lower pressure in search of a softer ride.

Yes everyone should know the weight of their RV, ideally 4-corner weights. It does not negate the fact no major tire manufacturer recommends running less pressure than what is stated on the Federal tire placard in/on the vehicle.