Wheel width vs. tire width

Brad12 · Post by **Brad12** » Wed Jan 25, 2012 8:36 pm

So Costco refused to mount my 35x12.50 tires on my stock 7.5 in. wide alcoas because they stated my wheels needed to be a minimum of 8.5 inches wide to meet manufacturer specifications. Now, I know plenty of people here are successfully running this combo. For those that do, are you running at a lower psi to decrease wear in the middle of the tire? Have your vehicle's handling characteristics, especially around corners, changed? If so, how? Is it a safety issue to run this combo?

Silverslk · Post by **Silverslk** » Wed Jan 25, 2012 9:32 pm

I'm running 35x12.50's on stock Alcoas......no problems.

Wood · Post by **Wood** » Wed Jan 25, 2012 9:34 pm

Bead taper is designed for probably 8-10" wide wheel. Narrower wheel will put sidewall of tire and bead at sharper angle than it is designed for. Obviously you could mount them on a 7" wheel and do fine, I'm sure plenty of people here could tell you they've done it for thousands of on and off road miles without incident. Costco is just stricter than most tire stores for litigious reasons I'm sure...I am surprised they would mount them on any wheel...last I knew they would only mount OE tire sizes. I wanted to buy some 31 tires online and I had to enter my vehicle as a 1989 montero or something just to check cost!

If you want to run that combo I'm sure your local llanteria will mount them up no problem.

hobbyturnedobsession · Wed Jan 25, 2012 10:27 pm

I'm running 315marks 75 r16 (35 12.5) on 8the wides and no issues either.

philofab · Post by **philofab** » Wed Jan 25, 2012 11:09 pm

I ran 35x13.50x15 tires on 15x7 wheels. No issues. A wide tire on a narrow rim will sway more.

Brad12 · Post by **Brad12** » Wed Jan 25, 2012 11:29 pm

Wood wrote: Costco is just stricter than most tire stores for litigious reasons I'm sure...I am surprised they would mount them on any wheel...last I knew they would only mount OE tire sizes. I wanted to buy some 31 tires online and I had to enter my vehicle as a 1989 montero or something just to check cost!

Costco told me they won't even touch anything 1 inch over OE tire sizes anymore... the only reason they fixed a nail in my tire and replaced the valve stem is because I bought my tires from them back before their current policy.

Shouldn't a wider tire on a narrower wheel hold a bead better, especially at low PSI? I'm trying to understand what safety risks, if any, there are in running a 12.5 inch tire on a 7.5 inch wheel. Is there potentially too much sidewall flex? Does 6 or 10 ply increase/decrease these stresses?

And for those of you who are using this setup, are there noticeably and/or significantly different handling characteristics due to the tire flexing on the wheel at all? Or no?

I guess I could always call the tire manufacturer to get these questions answered, I just trust the knowledge of the people on this board a great deal more.

johncharlesb · Post by **johncharlesb** » Thu Jan 26, 2012 12:46 am

I run 33x12.5 on 15x7.5 Alcoas. No issues on the street or aired down in the sand. Tire wear is normal. My local Discount Tire mounted them right up.

kahuna bill · Post by **kahuna bill** » Thu Jan 26, 2012 1:36 am

i'm running 35" x 12.5" KM2 class C on my 7.5" stock alcoas. max psi is 35 cold. great wear on all 4 tires, no issues with the bead ever coming off. i typically run them at 10 psi on the trails and rocks, 12-15 in the sand, 35 on the road. but for road manners they do feel like marshmellows. i don't feel it's a safety issue once you know how the truck is going to react on the freeway.
walmart mounted mine for cheap.

Copykat · Post by **Copykat** » Thu Jan 26, 2012 7:17 am

Like said Costco is just sticky for legal reasons. Take the tires and rims to a real tire shop.

Here in canada you cant take a wheel and tire into them alone. It has to come with the vehicle it's to be mounted on.

If your truck is 4x4 you can't go in and buy 2 new tires for the back. They require you to buy 4 new matching tires. Same with an AWD car.

I'd just never go to costco period for tires. They may be cheaper but the extra hassle doesn't make up for it.

BTW 12.5" tires are required to have a 8-10" wide wheel, as per manufacture spec.

I ran 33's on a 7" rim and had to air them down to about 20-22 PSI over normal 28-30, just to keep the centers from wearing. Lower PSI would have been better but then the tire becomes too soft and the chance of rolling a bead with a tall sidewall like that is likely.

Silverslk · Post by **Silverslk** » Thu Jan 26, 2012 7:18 am

I'm running BFG Bajas (the old mud terrain looking ones) and those sidewalls are stiffer than lots of street car stuff I've had. hahaha Seriously, I can't tell a difference in any of the tires I have had on the Alcoas (31" Dunlop, 33" Baja, 35" Baja) heck, I notice more roll and handling issues since I put on the lift that when I was running stock height with sway bar removed.

philofab · Post by **philofab** » Thu Jan 26, 2012 8:22 am

I ran my Toyos at 5psi in the sand and never lost a bead.

Post by **SteveG** » Thu Jan 26, 2012 9:26 am

Brad12 wrote:And for those of you who are using this setup, are there noticeably and/or significantly different handling characteristics due to the tire flexing on the wheel at all?

Yup. You get used to it, but it's there. Any time the wheel is narrower than the tire, you're going to get some movement of the wheel inside the tire. No one would run a tire this way on a car that was meant to go around corners fast... it's a save your wheels in the rocks kind of thing.

Running slightly lower pressure in the front can help this a bit. My wagon has a pretty tall tire for the wheel. For long trips with the car fully loaded I run the rear tires just above their max and the front a couple pounds below... drives great.

On the Bronco, the tires wear more in the center because of the ballooning effect.

PaulW · Post by **PaulW** » Thu Jan 26, 2012 10:22 am

My 12.5" Bajas on stock 7.5" alloys show even wear across the tread. They are very worn now and will be changed soon. The only thing different is the right front is more worn than the left front.Narrow rims are great for saving them from the rocks.
Wide rims are for the street for improved cornering.
One of my rigs has 13.5" on 10" rims and the rims show lots of damage due to scrapes with the rocks. To expensive to change rims, but if I did I would use 9".
The aftermarket tire stores always push rims that are to wide even for street vehicles. Some dont even stock correct rims - just the wide ones.
PaulW

ogre20012001 · Post by **ogre20012001** » Thu Jan 26, 2012 7:16 pm

one thing to keep in mind when choosing a wheel is that your 12.5" tires usualy only have a tread width of around 9"-10" and the 12.5" comes from the section width that is side wall to side wall. so with a narrower rim you can bring your side wall in and your bead in where they are a little more protected. and you will find it harder to pop a bead cuz you will have to move the bead that much more and it is pressing its self on the rim.

Brad12 · Post by **Brad12** » Thu Jan 26, 2012 8:17 pm

Well I really appreciate all of the information and feel much better about running some 12.50 inch wide BFG A/Ts on my stock alcoas

denhabr · Post by **denhabr** » Sat Jan 28, 2012 3:29 pm

I have 35x12.50-15 Goodyear Silent-Armors on 10-hole Ford 15 x7.5" aluminum 'rivet' wheels (Hollander 1701).

No issues whatsoever. Running stock PSI's front & rear, with only slight wear on the fronts...mostly due to the camber changes.

Go for it.

robertcrav · Post by **robertcrav** » Sun Jan 29, 2012 9:01 am

Where did you get the Silent Armors in that size? Good years site doesn't list them????

philofab · Post by **philofab** » Sun Jan 29, 2012 10:27 am

After 60k miles on 9" wide rims. 37x13.50x17 tires.

denhabr · Post by **denhabr** » Sun Jan 29, 2012 10:35 am

robertcrav wrote:Where did you get the Silent Armors in that size? Good years site doesn't list them????

I bought them in 2009, and they were officially discontinued in ~2010. I even tried to buy one as a spare, but had to switch over to a 35" off-brand sold at my local Les Schwab.

I bought the Silent-Armors specifically for their tread design and square shoulders. Been working great on my Bronco...but I wish someday that Mickey Thompson would bring back their 36" Baja Kings in radial design. Oh well...

Sorry about that...