Forum Discussion

goufgators's avatar
goufgators
Explorer
Sep 16, 2015

Confused...?)

O.K., now I'm confused regarding tire psi. Every post (most every) ends up recommending that the coach be weighed, preferably all four corners and then, based on the mfg.'s psi chart, air up to the chart psi for the weight carried. Makes sense! And, although I could only weigh the front and rear axles, I followed those instructions and based on the Goodyear chart and based on my actual weights, aired my 240/70R/19.6 H to 80 psi.

Now to the crux, steering has become a pain. Constantly adjusting the steering wheel to try to keep it going straight. This is a new development. Prior to having new tires put on and new Monroe shocks installed a few months ago, steering was not a problem. The tires being replaced were F rated and ( found out after the fact) the dealer installed H rated tires. Now, in my uneducated (psi) mind, I thought the new H tires might be the cause of the problem.

I called the RV repair shop I do business with and the mechanic advised to first have the front end checked for alignment. I did that this morning at a highly respected alignment, brake, tire shop. This is where the confusion takes place. The mechanic and the shop owner checked the tire pressure and said that my tires are under inflated. They pointed out on the sidewall the psi of 110 psi and said I should be running that amount or no less that 5 to 10 psi less. At running 80 psi, according to them, the sidewalls were allowed to flex too much contributing to the steering problem.

I tried to explain the reason I aired to 80 by weighing and using the Goodyear chart and, to my surprise, they didn't seem to know what I was talking about. So, I dropped the subject and told them to air up to their recommended 100 psi knowing that I could change it later if I wanted to.

They then did the alignment check and it did need some adjustment.

Driving home, steering was markedly better. Not perfect, but better and livable.

This alignment shop has been in business locally for over 50 years and has a superb record for quality service so I don't want to just discount their advice.

What they said about the tires sidewalls being allowed to flex more with lower psi makes sense. But, the Goodyear chart recommends that lower psi. Confused...yes.

Does the shop mechanic and owner have a valid point? Or, do I stay with the lower chart number?

Sorry about the wordy length.

Larry

27 Replies

  • Larry, now you have ME confused....easy to do that, especially in the AM...:)

    You indicated you have H rated tires, 240/70R/19.5. Goodyear does not make that size tire, so I'm assuming you have SOB tires. (Some Other Brand) That said, your opening statement is correct. To get the most out of your tires, and the smoothest ride, they should be inflated properly. Four corner weights are the optimal way to do so, but next best is axle weights as you have done. Also, be sure to have the same PSI across each axle if you finally do the corner weights.

    Newman Fulltimer is correct on checking your tire with the mfg to ensure they are steer tires. Steer tires have a little different tread design because of the cornering aspect. Because of the compounds used in the mfg of tires, each mfg has their own recommendations. Michelin, for instance is different than Goodyears. Not much, but they are different. I run Michelins as steer tires and Goodyears on the drive and tag. The Michelins seem to wear a little better than the GY.

    As long as you don't exceed the mfg or the rim's maximum PSI you will be ok. Running PSI by weight is designed to give you the most comfortable ride and handling. Increasing the PSI will give you a harsher ride. Only you can decide which is best for you and your coach. Perhaps meeting in the middle is the solution for you. Air them all at 90PSI and see how it drives. Good luck...Dennis
  • goufgators wrote:
    rgatijnet1 wrote:
    To carry the exact same load, the same air pressure is needed whether you use load range F, G, or H tires.
    Using a higher load range tire allows you to carry a heavier load if you use a higher tire pressure that DOES NOT exceed the PSI rating of your wheels.
    I am assuming that you installed truck tires, instead of RV specific tires, which is why the tire store installed "H" rated tires. These are what they had in stock. Unless the truck tire is a "steer" tire, it could be the reason for the harder steering issues.


    Appears these are RV tires since the sidewall number is 245/70R. The "R" meaning RV (I suppose).


    The R means radial tire.
  • rgatijnet1 wrote:
    To carry the exact same load, the same air pressure is needed whether you use load range F, G, or H tires.
    Using a higher load range tire allows you to carry a heavier load if you use a higher tire pressure that DOES NOT exceed the PSI rating of your wheels.
    I am assuming that you installed truck tires, instead of RV specific tires, which is why the tire store installed "H" rated tires. These are what they had in stock. Unless the truck tire is a "steer" tire, it could be the reason for the harder steering issues.


    Appears these are RV tires since the sidewall number is 245/70R. The "R" meaning RV (I suppose).
  • newman fulltimer wrote:
    If I see your tire size right it shows load range h set at 100psi load range f at 80 psi:h


    I was running 80 on the previous 'f's and on the new 'H's per GY chart. 100 is recommended by the alignment shop.
  • To carry the exact same load, the same air pressure is needed whether you use load range F, G, or H tires.
    Using a higher load range tire allows you to carry a heavier load if you use a higher tire pressure that DOES NOT exceed the PSI rating of your wheels.
    I am assuming that you installed truck tires, instead of RV specific tires, which is why the tire store installed "H" rated tires. These are what they had in stock. Unless the truck tire is a "steer" tire, it could be the reason for the harder steering issues.
  • If I see your tire size right it shows load range h set at 100psi load range f at 80 psi:h
  • Easy - try it both ways and see what way it drives better.

    The Goodyear chart gives you the minimum recommended air pressure to carry the load, thats all. The point the alignment shop makes does indeed somewhat make sense.

    I'd try it at the lower recommended pressure from the chart, then try it with the air pressure up as recommended by the service guys. Neither one will be unsafe, for sure.

    Also keep in mind new tires do sometimes need a little "break-in" period. I've often found it takes 500-1000 miles for a tire to settle in to the way it's actually going to drive. And with 7 vehicles in our house, we buy a lot of tires.