Tires: larger tires on a motorhome,?, holiday rambler endeavor, speedometer accuracy

Question
i'm buying a 2001 Holiday Rambler Endeavor 38ft. 30.000 lbs, GVW, deisel pusher, it has 22'5" (steel) wheels(no tag wheel),  but with low profile 235/70 tires, that look too small. they are the orginal tires (with 13,000 miles). I'm thinking 275/80 tires would look much better  I've seen many  motorhomes this size with 275/80 tires. Could i mount these (or another)larger size tire without causing problems?  thank you

Answer
Barry,

Are you sure you have the original tire size correct?  I don't find a listing for that tire size.

I'm going to assume you mean a 255/70R22.5 for the purposes of the discussion below.  This way you'll have an idea of what's involved, because I can tell there are plenty of problems with what you are proposing.

First is the rim width.  A 275/80R22.5 requires a 7.50" or an 8.25".  A 255/70R22.5 also requires a 7.50" and an 8.25"  So if the rim is not one of those, it won't work, because the shape of the tire will be distorted.

The second is the tire diameter vs speedometer accuracy.  A 255/70R22.5 is 36.61" in diameter and a 275/80R22.5 is 39.84" in diameter - a 9% difference!

Third is the amount of room in the fenderwells.  There isn't any way for me to tell how much room you have, but a 275/80R22.5 is going to take 1 1/2" more vertical space and in the front about a half an inch more room on each side of the tire.  Don't forget the worst condition is fully turned / fully compressed.  I don't think you can really  fully compress the suspension without taking the spring out.

Fourth is the spacing of the duals.  A 275/80R22.5 requires a minimum dual spacing of 12.24, where a 255/70R22.5 requires 11.30 - almost an inch wider.  That means that the wheels are likely to need a spacer, which means the studs may need to be longer.  It also means that you need an inch more room on each side of the tire.  Of course in the rear you don't have to worry about clearance when turning, so only the fully compressed condition applies.    

So if I have the tire size right, you see what the problems are.  However, if the size is indeed a 235/70R22.5, then the situation is even worse.

Hope this helps.