"Upsizing" tires

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waldo

waldo

Active member
Joined
Apr 16, 2010
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27
Location
Southern California
I just got my motorhome back from the shop and was advised the tires are in desperate need of replacement.. not worn out, rotted.

The coach is currently equipped with 225/75-16 Firestones.  I'm a little concerned over using such a small tire on a 31' Class C, so I thought perhaps going up to a 245/75-16 would provide me with a little better margin when it comes to tire loading.

I'm a little worried however, that the increased width of the tires, might cause the rear duals to come in contact at the bottom and create a wear issue or overheating due to the friction of contact. 

Can anyone offer any advice or guidance on this... the last thing I want to do is create a safety hazard.

Thanks for any thoughts...
 
The 245's will be .8"(or just over 3/4") wider which will put your duels that same distance closer together. That shouldn't be an issue if you have plenty of clearance now. You'll have to pull out the trusty tape measure. They will also be about 1.18" (or just under 1 1/4") taller. You could just go up to the next load range (if they are available in your size tire) if you don't want to change tire sizes.

You definitely do not want duels coming in contact with each other.
 
Thanks for your reply... after I posted this question, I came across a topic on the internet, discussing what was described as "kissing duals".  The pictures of the results weren't pretty.

This afternoon, I crawled underneath my MH and checked the clearances between the rear tires.  Its look to be about an inch, so it would appear that the additional width would cause them to be in contact, at the bottom, where they bulge.

On Monday, I taking the MH in to replace the tires, so it looks like it's gonna be another set of the 225/75-16's.  The "best" load range I've seen so far, for that size, is "E"... I'm assuming they'll be sufficient.

Again, thanks for the input... 
 
You don't have to assume that LR E is sufficient - there is a max weight rating in lbs right on the tire sidewall. Or in the tire specs that the dealer should have or you can view online ahead of time. The tire ratings for all the tires on the axle should at least equal the axle max load rating and preferably exceed it by about 10%. You want to exceed the axle limit because the weight may not be balanced equally and one tire typically carries more than half the total load.

If you get more Firestones, their RV inflation table says a 225/75R16 carries 2680 lbs single or 2470 as a dual (max, at 80 psi). That would be 9880 lbs on the rear dual axle and 5,360 lbs on the front.
 
This is probably the best information that can be found on the internet that correctly lays out the entire procedure for plus sizing tires. Starting on page 19 all the way to the appendixes and beyond you will find all the information necessary to insure proper fitment and documentation of the new plus sized tires.

This document fulfills all DOT requirements and follows industry standards. Its easy to understand and follows a logical path through the entire process.

http://www.tiresafety.com/images/Tire%20Replacement%20Manual.pdf

Highly recommended.

FastEagle
 
Gary RV Roamer said:
You don't have to assume that LR E is sufficient - there is a max weight rating in lbs right on the tire sidewall. Or in the tire specs that the dealer should have or you can view online ahead of time. The tire ratings for all the tires on the axle should at least equal the axle max load rating and preferably exceed it by about 10%. You want to exceed the axle limit because the weight may not be balanced equally and one tire typically carries more than half the total load.

If you get more Firestones, their RV inflation table says a 225/75R16 carries 2680 lbs single or 2470 as a dual (max, at 80 psi). That would be 9880 lbs on the rear dual axle and 5,360 lbs on the front.
Click to expand...

Thanks for the info... having never been in the position to purchase tires for a motorhome before, I'm finding the process anything but simple.  There are so many considerations to take into account, not to mention so many differing opinions on different tire manufactures... even different tire models within the same makers.

My singular goal is to replace what I have with a tire that will serve me well.  Of course, initial cost is always a consideration, but not at the sacrifice of safety.

Sometimes, I feel like putting all the makers names on cards, pinning them to the wall and tossing a dart while blindfolded... whichever one gets poked is the tire that gets installed.
 
It's really no different than car tires, except for considerations for duals and larger pick-up trucks share that factor as well. It's just that most people simply replace the OEM tire with another one exactly like it (same size and load range) and never have to worry about it. Presumably the vehicle manufacturer sized the tire right initially, so buying more like it is the right thing to do. If you changed the size when purchasing a new car tire,  the concerns would be the same.

You started out with the assumption that your OEM tires are too small and need to be up-sized (you said "I'm a little concerned over using such a small tire on a 31' Class C"). You may or may not be right.  When you say that, it implies you have evaluated the tire specs and doubt that the RV manufacturer sized the tires properly to begin with.  Making that judgement requires that you understand what all those specifications mean and then determining which ones need to be improved. 
 
Gary RV Roamer said:
...You started out with the assumption that your OEM tires are too small and need to be up-sized (you said "I'm a little concerned over using such a small tire on a 31' Class C"). You may or may not be right.  When you say that, it implies you have evaluated the tire specs and doubt that the RV manufacturer sized the tires properly to begin with.  Making that judgement requires that you understand what all those specifications mean and then determining which ones need to be improved.
Click to expand...

I guess you're right, I did assume the tires were a bit undersized for the stresses they're subjected to... I'd thought the upsized tires might provide a little bit greater margin of safety.

However, with what I've learned through this discussion and other sources, tire maintainence plays just as big, if not bigger, part in tire performance... assuming the tire is designed for the application.

Once again, thanks for the information you and everyone else passed on...
 
Well, I replaced the tires today... ended up installing a set of Michelin RV specific tires, 225/75-16's.  Of all the tires I checked into, these were the one with the highest number of recommendations and fewest complaints.  Paid a bit more, but I'm thinking the quality and safety is worth it.

The manager of the shop installing them did a great job of explaining the problems associated with using over sized tires, particularly the issue of the tires contacting each other.  He showed me the results of that very thing, it was a tire on which the sidewall was completely shredded... I could clearly see the "strip" on the sidewall where it had rubbed against the other tire.

I'm glad I came here to do some research, the information saved me from a dangerous mistake... 
 
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