Truck tire size question - PeachParts Mercedes-Benz Forum

kerry · #1 10-24-2009, 06:09 PM

Found a Foretravel motorhome in Denver for an out of state friend. It needs tires before he can drive it home. I has 9r 22.5 tires. Anyone know if a metric equivalent will fit? Found some Goodyaer G149 RSA 265/75 R22.5, load range G, truck or RV tires on Craigslist at a good price but I can't find a tire size calculator which will tell me if a metric will fit that rim.

Wodnek · #2 10-24-2009, 06:34 PM

You are limited to that size only for the rear.
The dual rims are very narrow, and metric sizes are wider to the point that under load the tires will touch and destroy each other.

The fronts, others have had mixed results with modern tire sizes, but still the issue remains that the rims are narrower then modern rims.

kerry · #3 10-24-2009, 06:39 PM

Thanks. I finally found a tire size/rim comparison on the Goodyear site and it showed exactly what you describe. The 9r rim is 6" wide and the metric rims are at least 7.5" wide.

kerry · #4 10-25-2009, 11:50 AM

More questions. This chart:
http://www.goodyear.com/cfmx/web/truck/line.cfm?prodline=160553

Shows the rims to be only 3/4" difference in width (6.75 vs 7.5) and the tires only 1" wider than the 9r. Would a 1" reduction in the space between the duals, mean the tires would hit? I don't know what is the standard spacing between tires on a duals.

Wodnek · #5 10-25-2009, 09:41 PM

Quote:

Originally Posted by kerry

More questions. This chart:
http://www.goodyear.com/cfmx/web/truck/line.cfm?prodline=160553

Shows the rims to be only 3/4" difference in width (6.75 vs 7.5) and the tires only 1" wider than the 9r. Would a 1" reduction in the space between the duals, mean the tires would hit? I don't know what is the standard spacing between tires on a duals.

The 1 inch figure; unfortunately is missleading. The gap between the two tires gets closed by that inch, plus the buldge where the weighted tire meets the ground. They are radial tires, which mean they are meant to float from side to side, rather then simply flex like a bias tire. The float, buldge, and gap narrowing all work together to conspire against there being a modern replacement tire size. The 9R, 8 R, 10R type tires are mostly obsolete sizes that do not translate to anything modern. They are all very tall and narrow, and their rims are not offset the same as their modern equivilents.

Nate · #6 10-26-2009, 11:27 PM

What about sourcing other dually rims that could possibly fit?
IE Dodge ram series, Chevy 3500 series, or Ford F-HUGETRUCK/VAN series? School bus's too... I dont know. Ambulances? Fedex box trucks? Something has to work...

Theres gotta be other options. This HAS to be why the thing's for sale.

Mabey a custom 1" spacer if the lugs are long enough. For the love of all that's holy dont use a spacer if the lugs arent long enough.

~Nate

kerry · #7 10-26-2009, 11:47 PM

Well, after talking to my friend, who went to a Goodyear truck tire dealership and talked to them, I bought the tires. Goodyear says they will fit and are as close a match to the 9R's as any metric tire made. The 9R's are radials so I don't think the bulge at the bottom should make a difference. We'll see what happens. They were a good deal, $3000 worth of tires for $500 so it was an attractive experiment. I don't know how wide the existing rims are. could be anywhere from 6.75-7.50. They are aluminum Alcoa's.
So now I'm driving around catching glimpses of all kinds of distances between tires on duals. I've seen some at around 5-6 inches but I saw one truck today with less than an inch between the tires.
Worse comes to worse, if the tires are too close, he can put two of these metrics on the front and put the existing front 9r's on the back with 2 more 9r's.
The motorhome was for sale by the guy who's owned it for 24 yrs because he's in his 80's his wife has had cancer, he recently had a heart attack so his RV'ing days are behind him.
By the way, who would have thought that 6 22.5 inch truck tires would fit inside a 300TD? MM's to spare. Those are heavy tires--100lbs apiece.

Nate · #8 10-27-2009, 12:24 AM

What load range rating? JW. To be that heavy I'd expect 8 or 10 ply, mabey even thicker (I dont work at a retailer that sells that heavy of tire)

Talk about a tough time seating the beads on some motorhome tires, HOLY CRAP!!! 10gallon tank w/2" pipe quick release valve (called a cheetah), with a big huge ratchet strap wrapped tight around it.

The manager said if the insurance would let us, he'd set some of them out back and use starting fluid like "back in the day"

I miss summer...

~Nate

kerry · #9 10-27-2009, 12:28 AM

Load range G. Don't know how many plys. A lot.

AdvisorGuy · #10 10-27-2009, 12:48 AM

Quote:

Originally Posted by kerry

Load range G. Don't know how many plys. A lot.

Load Range G is a 14 ply.. From my work at a Goodyear store way back when, and at least with Jersey laws, we used to install Load Range E (10 ply) on the rear and Load Range D on the front of ambulances. 18 passenger vans and "short buses". 265/75R225 would be much too wide..

kerry · #11 10-27-2009, 12:55 AM

Quote:

Originally Posted by AdvisorGuy

265/75R225 would be much too wide..

For what?

AdvisorGuy · #12 10-27-2009, 01:09 AM

Quote:

Originally Posted by kerry

For what?

It's been a while but I think they're gonna be too wide for the rear in a dualie situation. I'm still in contact with my former boss. He's the truck tire guru. Still does lots of work with NJ Transit, UMD-NJ and many a municipality. He's lived & breathed this stuff since we was in puberty. I'll check with him in the am & let u know.

From what I recall, 75-series and lower in medium/heavy duty applications are actually considered "low profile". A 225/75R24.5 would be a lower profile than a 12/R24.5, for example.. Same as an LR-78-15 would be the equivalent but slightly taller than a 235/75R15...

kerry · #13 10-27-2009, 09:58 AM

Quote:

Originally Posted by AdvisorGuy

It's been a while but I think they're gonna be too wide for the rear in a dualie situation. I'm still in contact with my former boss. He's the truck tire guru. Still does lots of work with NJ Transit, UMD-NJ and many a municipality. He's lived & breathed this stuff since we was in puberty. I'll check with him in the am & let u know.

From what I recall, 75-series and lower in medium/heavy duty applications are actually considered "low profile". A 225/75R24.5 would be a lower profile than a 12/R24.5, for example.. Same as an LR-78-15 would be the equivalent but slightly taller than a 235/75R15...

I think you are correct that they are a lower profile. The overall diameter of the 9r and the 265/75 are virtually identical (.1" difference) but the 265 is 1" wider. The gamble is that the 1" is not a dually deal breaker. Part of the issue is the width of the rim on which the inflated tire is measured. Both tires can fit on a range of different rim widths.

kerry · #14 11-01-2009, 01:33 PM

To bring this to a conclusion; I was able to measure the existing 9r 22.5 tires on the Foretravel today. The metric tires will replace them and work on the duals. The metrics require 11.6" of clearance for duals and there is 12.5" of clearance on the Foretravel.