Need help understanding tire sizing and if I can change

[Phil Hendrix]

Hey everyone,

I am interested in knowing if I can change the tire size on the coach now. I contacted the chassis manufacturer and they told me the vehicle left with the following:
Goodyear G159  11R22.5 tires and 22.5 x 8.25 rims

The coach now has:
Michelins  295/80R 22.5  (which need to be replaced)

I have come across a man selling new take offs but does not presently have the same size but does have alot of bus tires 315/80R 22.5.

My questions are:

1. How do the original 11R compare in size to the 295/80?

2. How much bigger are the 315/80 than the 295/80 and will the 315's fit on my coach?

3. Are "new take offs" basically new tires and does anyone know of other places where these tires are sold?

When I contacted Spartan they told me I would need to ask the coach builder this question or just take the coach to a tire center and let them measure for fit.  I am planning to contact American Coach tomorrow and ask them if the 315's will fit.

I guess I am going to try to learn and understand tire sizing. Thanks for your help.

Phil

 

[Ron]

Personally I do not recommend buying any used tires even take offs.  Tire life is seven years from date of manufacture.  A tire older than 7 years since manufacture is just trouble waiting to happen.  IMHO tires that have been installed and removed for what ever reason are used.

We had more than 90,000 miles on our G159 Goodyears when we replaced them when they were six and a half years old, not because of wear but because of age.  Oh we had new Goodyear G670s installed.
I agree it is a good idea to call American Coach to confirm what size they recommend installing and have NEW tires of the same size installed.

 

[Ned]

There are a few considerations when changing tire size, especially to a larger tire.  One, the odometer may read low if the new tires are larger in circumference than the original tires, and two, you have to be sure you have sufficient spacing between the duals so the new tires won't rub, if the new tires are wider through the sidewall.

 

[scottydl]

That first number in the tire size (295 and 315) is millimeters.  So the 315's are 20mm wider than the 295's.  Maybe not a big deal, but you would DEFINITELY want the coach wheelwells etc. measured to assure there would be no tire rubbing or other interference while moving.

The other problem is wheel/tire height.  That needs to always remain the same, to keep your speedometer accurate and in some cases protect the transmission from possible damage.  The second number in tire sizing (80 in your case) is the sidewall height % of your width.  So for a 315mm wide tire, an 80% sidewall is 252mm.  With your current 295mm wide tires, the 80% sidewall is 236mm.  So the 315/80R22.5 tires will be TALLER than your current tires in addition to WIDER.  Again that could cause clearance and gauge inaccuracy problems.  And that's not considering the age of the used tires (regardless of the tread remaining), as Ron pointed out.

 

[ArdraF]

I think what the others have said is this may not be the bargain it appears to be.  If you end up with not enough space between the two tires you may end up with a blowout going down the road and that could seriously damage your undercarriage.  Moreover, old tires are more likely to have problems than new and also could cause serious damage, either as an accident or to the undercarriage.

ArdraF

 

[Karl]

Phil,
Are you talking about duals or singles? The 295 has a loaded width of 11.6"; same as what was originally on it, and a loaded radius of 17.6", giving a total height of 35.2". The 315 you're thinking about has a loaded width of 12.4", so in a dual mounting situation, you're reducing the tire spacing by 1.6"! I Don't think you can get away with that. Don't know what the loaded radius is, but as Ned mentioned, it could throw your speedo/odo off. I wouldn't have a problem with take-offs if they're new, at a good price, and they fit.

 

[Phil Hendrix]

Yes I was talking about duals on the rear....and I see your point. I would be closing up the gap to much.

I guess I kind of thought it was not going to work....but that's why I wanted to ask. Thanks everyone for the imput. I think I will just stay with the same size. He did say he would probably be getting more of the size I need at some point. He did say these were new take offs, very little age on them. I love to save money but then again I don't want to get tires that will be trouble right after I get them.

I do have a couple months before I need to do anything, the tires are holding the coach up out of the snow for now.

I see Ron suggested the Goodyears G670....anybody else want to cast a vote? I did price them and they were about 550.00 each installed. The Michelins were about 750.00 each if I remember correctly.

I was reading somewhere yesterday that somebody suggested Kelly Springfield???

Thanks, Phil

 

[Ned]

We bought 6 G670 RV 275/75R22.5 tires a year ago for just under $400/each.  With mounting, balancing, and a front end alignment, the total was about $3300.  This was at Purcell Tire in Phoenix.  We have had nothing but Goodyear tires on the motorhome for over 10 years and have been satisfied with the performance and life.  We did wear the steer tires out prematurely because of an alignment problem.

These tires are formulated for RV use and should give a better ride than standard truck tires.  They should also be less susceptible to UV damage.

 

[Lowell]

The attached link provides a way of comparing tire sizes:

http://www.miata.net/garage/tirecalc.html

 

[Karl]

Lowell,
Interesting tool, but it doesn't come even close to what Goodyear publishes for their own tires.

 

[Alaskansnowbirds]

We put 6 255/70R22.5 G670 RV tires on in July of '05, $2229 out the door. That included mounting and balancing with Equal and all taxes and misc charges. We have been very happy with them.

Don't know where you're located but we bought them at Ziegler Tire in Canton, Ohio.