Author Topic: Can 12R22.5 Tires for 8.25" rim be replaced with 315/80R22.5 for a 9-9.75" rim?  (Read 6741 times)

Doug Till

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I cut a tire when turning into a campground yesterday on the rear outside dual-my bad. While backing into the campsite, the tire was flat and is now loose on the rim. I have a 40’ 2003 Beaver Marquis-Ruby with a tag axle and a Cat C-12 Engine. I have Toyo 12R22.5 tires on all three axles with 2011 date codes and the style of the tires is M111z. The local Toyo dealer can’t find the M111z style, not sure if Toyo even makes this style any longer. I will purchase two new tires and take one of the tires I replace to use for the outside rear tire that I ruined since they have the same mileage and wear.

The local dealer does have two M144 in a 315/80R22.5 that I could put on the front axle or tag axle. I looked on vin plate and the tires shown were the 12R22.5 with 8.25” rim width. Looking on Toyo’s specification for the 315/80R22.5 tires shows a recommended rim width of 9 to 9.75”. What problems do you think I may encounter if I purchase the 315/80R22.5 tires and install them on the 8.25” wide rims-or would the 315/80R22.5 tires even fit on the 8.25” rims? If the 315/80R22.5 tires fit on the 8.25” rims, would I be better to install the 315/80R22.5 tires on the front axle or tag axle?

If I can’t get the 12R22.5 tires, do you think I could remove both tag tires, and use one to replace the cut tire on the dual and then drive home? I am about 1000 miles from home. The vin plate shows 47,000 lbs. and I had just weighed my coach a couple of days ago. It weighed 40,700 lbs with a full tank of fuel, ½ full (50 gallons) on the fresh water, ¼ full (12 gallons) on the gray tank and ½ full (25 gallons) on the black tank. I do pull a trailer with my coach and it weighs 9,900 lbs.with 960 lbs. tongue weight.

Thanks for any advice.
Doug & Sarah Till
40' 2003 Marquis-Ruby, C12 505 HP

Edward Buker

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I think the tire you may want to study for your fronts are Toyo M-144, 295/80R-22.5 tires. I am running these in all positions on a 2002 Marquis non tag axle. That allows you to do the rears eventually in the same tire. I think the 315s may be too large but I am not sure. Some info from others in this link...

http://beaveramb.org/forum/index.php?topic=3891.0

Later Ed

David T. Richelderfer

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I cannot find verification of my opinion online, but this is what I remember from a year ago.

About one year ago I replaced the 295/80R22.5 Michelin tires on my steering axle with 315/80R22.5 Dunlops.  At that time I found a chart that indicated the single versus duel load ratings for the 315 tires depending upon not only inflation pressures, but also rim sizes.  What I remember is the load rating for the 315 tires when placed on the narrower rim (8.25" versus 9") will be reduced.  Fortunately, all my coach's rims are 9".  The new Dunlop 315s I had installed are 22 ply and have a load rating of 9,090 lbs at their max cold inflation pressure of 130 lbs.

Thus, yes you can place 315/80R22.5 tires on 8.25" width rims, but you will lose some load rating.  It is very important that you check the clearances as we did - as noted in the following link.

http://beaveramb.org/forum/index.php/topic,3891.msg29980.html#msg29980
« Last Edit: September 03, 2015, 04:00:00 PM by David T. Richelderfer »
2004 Beaver Marquis Sapphire

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Doug Till

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Thanks everyone for your replies and much needed help. I tried for several days to locate Michelin 12R22.5 tires but the local dealers did not have any and said the Michelin tires were on backorder. So I call the Advantage hotline and Ed said there were two 12R22.5 tires in Michigan. When I asked the larger local dealer to check out what it would cost to ship the tires from Michigan to Nashville, they were reluctant to get me a price. I called several days in a row and could never get a price, so I gave up on the local Michelin dealer. The local Toyo dealer couldn't get any tires shipped in to Nashville within the week. The only tires I could find in the Nashville area were the Dunlop 12R22.5 150L SP348 RSS H (16 Ply), so I purchased two and had them installed on the front axle. The front axle tires were the same brand and model as the tire that I cut on the back axle (Toyo M111z 12R22.5). The tire serviceman didn't think much of measuring the circumference of the inside dual tire and the replacement from the front. He said since the tires were the same size and model, you should only measure the thread depth. There was only 1/32" difference in the thread depth between the inside dual and the replacement tire from the front axle, so he went ahead and installed it. I now have one Toyo spare tire in case I may need it. The downside is the Dunlop tires are rated for 9” wide rims, so I’ll have to find out what the de-rating of the Dunlop tires would be for the 8.25” rims. I plan to get my corners weighed as soon as I can so I know how soon I should replace the Dunlop tires. All the rear tires have manufacture dates in 2011, so if I don’t have to replace the Dunlop tires immediately, I plan to move the Dunlop tires to the tag axle and purchase new tires for the front and rear axle, in a year or two. Again, thanks for the advice.
Doug & Sarah Till
40' 2003 Marquis-Ruby, C12 505 HP