Tire pressure - TV rec vs tire max

[Micah.TX]

I've been reading the forum (and Google) and have not found a definitive answer. My TV placard recommends 30 F and 33 R psi. The tire says 51 psi max. What is right for towing? Should I keep it at TV placard when not towing and inflate when towing? Look low at 35 when towing. What about the TT? Go by what is on the tire (50)? New TT (Passport 2890RL) and it's inflated at 35 psi from dealer. I want safety, but don't want them too soft. Decent mpg would be nice, too. Any thoughts? Thanks.

[buzzcop63]

Large RV show in Portland this last weekend and in talking to Curtis Trailer, my dealer, Curtis said to always run trailer at Max tire pressure as stated on the tire. Tow vehicle when not towing the recommended tire pressure is on the inside of the drivers door on my Tundra, when towing I run the rear tire up to max on the tire to meet the load in the truck, the front tires I run the standard pressure as the weight with the weight transfer hitch stays about the same as with no load. Without the WTH the front end would be light and the back end very heavy.

[Keywestparrothead]

I had a similar question with my new dually. The new 450's come with 19.5 commercial tires rated at 110 psi. I though it would ride too rough so I played with lowering the pressure based on someone's recommendation. I then figured I would have to bring the pressure back up when it came time to tow. Well not wanting to play that game, tire valve stems are not fun on the dually, I called Continental Tire and actually talked to one of their engineers (actually first talked to front line help support and when they realized my question was over their head, they had me craft my question in an email and they forwarded it on to the back line engineering dept.)

A day later an engineer called me and then told me there is an inflation chart to follow based on the weight per tire. He also indicated that running the tires at max pressure, without the weight applied, is actually bad for the tires (at least the G rated 110 psi tires on the 450) What I did was figure my actual weights, when loaded and hooked up to the 5er, and added 5-10 psi as a buffer. So I am running 90 psi in the front and 85 psi in the rears.

Here is the link to the Continental inflation chart, he said it should be the same for Goodyear, Mich, etc.

http://www.continental-truck.com/www...tables_en.html

Good luck, I hope this helps.

[jkohler70]

I suggest max on the RV, but then it might depend on what type of TV you have. The door sticker is considered the best balance of comfort and fuel efficiency. Mine is 32/32, but I inflate to 50/50 for towing. Doing this allows the tire have stiffer sidewalls and better heat dissipation. You cannot harm your tires by inflating them to the max on the sidewall, but heat buildup in the tires certainly will.

[Micah.TX]

All good answers and a big help. Someone smarter than me should create an app that tells you what the inflation should be both towing and not towing. Put in your tires, TV, and TT. FYI - I put a call into my RV dealer on this subject - I hear crickets. Hmmm.

[CWtheMan]

Originally Posted by Micah.TX

I've been reading the forum (and Google) and have not found a definitive answer. My TV placard recommends 30 F and 33 R psi. The tire says 51 psi max. What is right for towing? Should I keep it at TV placard when not towing and inflate when towing? Look low at 35 when towing. What about the TT? Go by what is on the tire (50)? New TT (Passport 2890RL) and it's inflated at 35 psi from dealer. I want safety, but don't want them too soft. Decent mpg would be nice, too. Any thoughts? Thanks.

You’re asking about two different sets of inflation pressure parameters. Automotive tires must have a percentage of load capacity reserves - by inflation pressures - provided by the tire selection of the Original Equipment (OE) tires by the vehicle manufacturer.

It’s important to remember that vehicle manufacturers are solely responsible for setting the recommended tire pressures found on the tire placards. Because light trucks have the ability to often carry heavier loads than normal passenger vehicles they often have another set of recommended tire inflation pressures (especially SWR) described in the truck’s owner’s manual. In any event, the tire inflation pressures must not be less than what is on the tire placard. Tire shops/dealers may say it’s OK. They didn’t make the truck. Tire selection is a collaboration between the tire manufacturer and the vehicle manufacturer with the vehicle manufacturer ending up with total responsibility for the fitments and inflation pressures.

Passenger tires for light trucks are de-rated automatically by the vehicle manufacturer. To determine their load capacity for truck service divide the maximum allowed load capacity found on the tire sidewall by 1.1 (example 3000# divided by 1.1 = 2727# maximum load capacity).

RV trailer tires (any design) are not mandated to have any reserve load capacity above the trailer’s total GAWR. Keystone has been known to set trailer GAWRs to 5084# and then install tires with 2540# of load capacity on both ends if the axle.

ST tires are designed to be aired to their full sidewall pressures - ALL THE TIME - and more than 95% of the time that’s what’s going to be on the trailers certification label. The responsibility for OE tires for RV trailers is the same as automotive tires.

CW

p.s. There isn’t any industry standards that discourages the use of tire inflation pressures above the recommended inflation pressures found on the vehicle tire placard or in the owner‘s manual, provided the maximum psi rating of the tire isn’t exceeded. If the tires are OE, the rims will have the ability to withstand the inflation pressures needed for maximum load capacity including the effects of thermal equilibrium.

[C130]

Originally Posted by Keywestparrothead

I had a similar question with my new dually. The new 450's come with 19.5 commercial tires rated at 110 psi. I though it would ride too rough so I played with lowering the pressure based on someone's recommendation. I then figured I would have to bring the pressure back up when it came time to tow. Well not wanting to play that game, tire valve stems are not fun on the dually, I called Continental Tire and actually talked to one of their engineers (actually first talked to front line help support and when they realized my question was over their head, they had me craft my question in an email and they forwarded it on to the back line engineering dept.)

A day later an engineer called me and then told me there is an inflation chart to follow based on the weight per tire. He also indicated that running the tires at max pressure, without the weight applied, is actually bad for the tires (at least the G rated 110 psi tires on the 450) What I did was figure my actual weights, when loaded and hooked up to the 5er, and added 5-10 psi as a buffer. So I am running 90 psi in the front and 85 psi in the rears.

Here is the link to the Continental inflation chart, he said it should be the same for Goodyear, Mich, etc.

http://www.continental-truck.com/www...tables_en.html

Good luck, I hope this helps.

Thanks for the chart!

[CWtheMan]

What B&F are saying in this reference comes from overall tire industry standards. Read carefully (not out of context).

http://www.trucktires.com/bridgeston.../WeighForm.pdf

CW


On Edit: Like most PDF files about tires this one is flawed. I don’t know how to correct it other than pointing out the flaw.

The statement about inflating the tires to a psi that will provide enough load capacity to support the load on the tires is the flaw for tires on motorized vehicles when installed in compliance with FMVSS 571.110 & 571.120 - light trucks, SUVs, RV motor homes, vans cars ….etc.. It is not flawed for RV trailer tires installed in compliance with the same FMVSS (s).

Why is it a flaw? Because all of those motorized vehicles are fitted with tires that MUST have a percentage of inflation pressure in reserve to provide load capacity reserves at all times.

Here is a quote from Toyo Tires.

"Toyo Tire does not recommend an “inflate-to-the-load” policy for RV tires. Tires that are inflated to accommodate the vehicle’s actual loads do not have any inflation safety margin. Consequently, even a minor loss of air pressure will cause the tires to be under-inflated and overloaded. Toyo Tire’s policy is to observe (as a minimum) the tire pressure established by the vehicle manufacturer as indicated on the tire information placard. There are multiple reasons why a safety margin (by inflation) makes sense:"

• All tires lose about 1-1.5 PSI per month due to natural permeation of the tire’s internal
air pressure through the tire’s rubber membrane.

• In the event of slow air leaks from punctures, an inflation “reserve” may allow detection
and repair of the leak prior to reaching a dangerously low inflation level.

• A safety margin is prudent for users who are apathetic regarding tire inflation maintenance.

CW