315 80R/22.5 vs. 12R/22.5

[TimSullivan]

My 2000 Magna with a single rear axle came with 12R/22.5 tires on both the steer and drive wheels from the factory. I need to replace all 6 tires due to age and was wondering if it might be a good idea to upgrade the front steer tires to a higher load range like the 315 80R/22.5 rather then just replacing the factory stock 12R/22.5.

Though I haven't yet weighed the motorhome to see what the actual loaded front axles weights are I thought I recently read something about a lawsuit involving CC with the claim being that the factory front tires were to small, load wise, for the weight on the front axle.

Thoughts on going up to the 315 80R/22.5 for the front steer tires rather then the factory specified and lower load limit tire size 12R22.5?

[Peralko]

According to the brochures, the 315 80R/22.5 tires were mounted on 9" wide wheels, the 12R22.5 were mounted on 8.25" wheels. You may want to ask what impact this would have if you mount the bigger tires.

[Steve Ownby]

Originally Posted by Peralko

According to the brochures, the 315 80R/22.5 tires were mounted on 9" wide wheels, the 12R22.5 were mounted on 8.25" wheels. You may want to ask what impact this would have if you mount the bigger tires.

Michelin publishes a specific load/pressure chart for the 315s on 8.25" wheels. It still shows a significantly higher weight capacity than the 12R.

https://www.michelinb2b.com/wps/b2bc...s_Brochure.pdf



Steve Ownby
Full time since '07

[olyshed]

Don't know where you are located....we just went through a tire change ...2001 Affinity..Les Schwab in Juntion City....helpful people....we but 315's on where we could...all but tag....real happy...OLYSHED

[phays]

OLYSHED
Do you know the spacing on your rear wheels? I don't believe I have the required spacing for the 315's on my 2000 Magna.

[olyshed]

Hi Pete....We had 12R's on the drive and tag...315 on the steer....the 315's on the drive had the same clearance as the 12R's on 8.25 wheel but the tag could not handle the 315 because of the wheel layout.. put them to close to the outside fender..but there was no problem between the dual drives.

[B Bob]

Tim I have 315s on the front of my coach but also have different wheels. My front wheels have a pressure max of 130 psi and not the 120 psi of the standard 12R wheels. In my experience the 315 tires cost more.

What did the factory recommend for your coach? If they recommended 12R and you are worried about that call CC and see what they think.

You can tell the difference on my coach wheels by the fact that the air holes in the rims are a bit smaller. Enough so you can see the difference from a few feet a way. As far as I know the problems were more about Toyo tires than size.

[TimSullivan]

Looks like wheel size is the key. I noticed that the Michelin Tire Guide footnotes are very specific as to the maximum tire pressure allowable on the 8.25" wide wheels (120 psi) vs. the 9.00" wide wheels (130 psi maximum).What this means is that I could only run 120 psi on my 8.25" wide wheels if I run the larger size 315/80R 22.5 tires and thus would only get a maximum of 8,000 lbs on the wheels while the 12/R 22.5 tires size on the same 8.25" wide wheel at maximum psi of 120 gets 7,390 lbs.

The larger 315/80R 22.5 tires are significantly more expensive then the 12/R 22.5 tires. When I priced out the tires locally, including balancing, installation and all the various taxes they ran about $535 for the 12R's and $769 for the 315/80R 22.5 for the Hankook AH11/12. So it would cost me around $235 more per tire to gain only about 610 pounds more per tire--not a very good value equation in my eyes. Now if my 8.25" wheels would have allowed for 130 psi, which they won't, I would have been able to get a full 9,090 lbs per wheel and I could see the value of using the more expensive tires. But I'm not willing to risk running my Alcoa 8.25" wheels higher then the factory recommended maximum of 120 psi.

Nope, I'm sticking with the factory recommended 12/R 22.5 tires all around on my rig.