OldBeaver Report post Posted October 30, 2019 I am looking at putting new tires in my motorhome. Unfortunately the tires I was originally going to have installed are on backorder with no ETA. The other choice I have are Firestone FS561. The issue is that they do not come in my size (265/75R 22.5). The tire shop can order 275/70R 22.5 which is very close but Firestone specifies 8.25" rims. Mine are 7.5". I saw Copper specifies a range of 7.5"'-8.25" for their time of the same size. I phoned and asked the tire shop manager about it and he supposedly called the Firestone rap who said it spuld be fine....because it's on an RV and not a truck thst will be going through scales, port of entry and inspections. Does anyone know if I would be OK with getting these Firestone tires installed? (one thing I like about them is that in this size there is an over 1000lbs capacity increase per tire. I think the original size is borderline with regard to that). Share this post Link to post Share on other sites
hermanmullins Report post Posted October 30, 2019 IMHO, I would go with the tire size the manufacturer of your coach put on when it was built. Them there should be no issue as to the rims width. Herman Share this post Link to post Share on other sites
richard5933 Report post Posted October 30, 2019 I don't like it when a tire guy (or tire company) says something "should" be okay. If they can't say with certainty, then the answer should be "no". When you install a tire on a rim narrower than the specified/recommended rim, you usually reduce the weight capacity of the tire. For example, my 315s are recommended to be on 9" rims. If they were mounted on that rim, the max weight capacity is reached at max cold inflation of 130psi. I've got them mounted on 8.25" rims. According to Firestone, it's acceptable but results in a max cold inflation pressure of 120psi. This results in lowering the weight capacity to what's in the chart for 120psi. Switching to a wider rim won't necessarily help either, unless you can guarantee that the extra width can be accommodated by your coach at both extremes of your suspension travel, on all four corners. Lot's of engineering involved. I agree with Herman 100%. Get the proper size tire. They're out there. Share this post Link to post Share on other sites
manholt Report post Posted October 30, 2019 1,000 lbs per tire over original, does not mean that you can increase your load. Share this post Link to post Share on other sites
OldBeaver Report post Posted October 30, 2019 3 hours ago, manholt said: 1,000 lbs per tire over original, does not mean that you can increase your load. I did not mean that. From reading various articles I know that many coaches are either pushing their limit or are actually over it when it comes to tires. My problem is that the motorhome is sitting at Commercial Tire in Oregon, about 6 hours away from my house. I know what size tires are mounted on it, but have no idea what the actual size was when it was new. There is always the possibility that one of the previous owners changed them. I don't dare to drive it anywhere beyond a few miles. The tires are old. When I bought the RV 3 years ago I did not know how to read DOT codes. The tires looked great and the seller said they replaces them maybe 2 or 3 years earlier. Well, I just leared that its more like 15 years for the fronts and 16 for the back. Scarry to learn that. Share this post Link to post Share on other sites
OldBeaver Report post Posted October 30, 2019 Herman, thanks. I wanted those Firestones but I guess I better stick with the size that is on it now. Share this post Link to post Share on other sites
wolfe10 Report post Posted October 30, 2019 OldBeaver, The original tire size will be noted on a plaque usually located near the driver's area. If they have access to your coach, should be an easy confirmation. OR, you could include exactly what coach you have (in your signature would be great and help with answers to any of your questions) and perhaps another owner could look it up for you. If the OE tires have limited safety reserve (they are loaded near capacity) getting tires with a higher load range is a good thing. No, it will not raise you carrying capacity, but will give you a safety reserve on your tires. And, this part of the answer you posted above sure scares me: " .....the Firestone rap who said it spuld be fine....because it's on an RV and not a truck thst will be going through scales, port of entry and inspections. " Does that mean it would not be deemed legal by DOT inspectors, but the rep "Feels" it should be fine. WOW. Share this post Link to post Share on other sites
OldBeaver Report post Posted October 30, 2019 Wolfe, that was the part that raised my caution level. Some manufacturers' websites show a range of 7.5"-8.25" for this tire size (Cooper is one), while others just list 8.25". Share this post Link to post Share on other sites
tireman9 Report post Posted November 6, 2019 I would stick with what is printed in the tire company literature for an approved rim for that companies tires.rather than a phone call. Share this post Link to post Share on other sites
OldBeaver Report post Posted November 13, 2019 I ended up buying the same size tires as those that were already on the coach. It is now wearing a set of 6 new Toyos, which was not my first choice but what I wanted was backordered without an ETA. Lots of people seem to be running on Toyos and are pleaeed so I expect that I will be happy with them as well. I am curious if there will be an improvement in fuel mileage. I went with steer/all position on all wheels. The old tires had the traction tires on the back. Also the Toyos are supposed to be an improved fuel usage tire. I shall see. Share this post Link to post Share on other sites
bm02tj Report post Posted November 13, 2019 The average RV does not need traction tires unless they will be in snow or slimy mud I have three peak rated tires as I have been in the snow save travels Share this post Link to post Share on other sites
