Ive been looking at a few different tires for my next set. Have been checking all the manufacturers websites as well. I know the stock Goodyears are advertised as 33" tall but have seen alot of guys measure them at 31" tall. This got me thinking. I just wanted to make sure my theory makes sense.

The reason guys are measuring them at 31" is because Goodyear has the tire listed as measured on an 8.5" wheel. Since the stock 20 is a 9" wheel, the tire is spreading out more and causing the diameter to drop a little.

It looks like most manufacturers measure a 275 tire on an 8.5 inch wheel. So all of the 33" tires are actually going to be around 31" on a 9" wheel?

It also appears most manufacturers measure a 305 tire on a 9.5" wheel. The ones that meausre out to be 33" on a 9.5" wheel would actually come out a little taller on a 9" wheel because the tire is being squeezed together more?

So basically a 275 33" tire is going to be shorter on a 9" wheel and a 305 33" tire is going to be taller on a 9" wheel.

This all make sense?

Oh and I finally saw a Cooper Zeon LTZ in person today and they are very impressive. I think those is a 305 55 20 would look good.

 

Tire measuring seems to be more of a science than I would like to deal with lol... I got 35's on mine but they measured 34" new and only about 33" now (I've chewed through some tread)

 

While this all sounds good and is accurate, I think a big part of it is they just plain lie. I've probably had 20 sets of aftermarket tires on my trucks over the years and not a one has ever measured to their advertised dimensions.

My current "35 inch" tires are on the 17x9 wheels the manufacturer recommends and were "measured" on . With 80% of the maximum PSI air in them, mounted on my truck they measure slightly UNDER 34 1/4"...

 

Hammer, id say thats highly likely that they arent telling the truth. I guess how much psi you run would play into it as well. I run 35 in the stock goodyears since that's what the door says. What do most guys run in their various aftermatkets for mostly highway driving?

 

tires, across the board, for dang near every application are mysteriously un-standardized for a industry that is 'sposed to be standardized. gotta love it.. one thing to keep in mind: It seems discrepancies in advertised vs. actual are ALWAYS in the manufacturers favor.. for instance, if you are buying over-sized tires, the advertised will always be bigger than the actual.. if you're buying for tread width low profile to take lateral motion away for cornering, they won't be as wide nor the profile as low as advertised..

the width of the rim shouldn't make that big of a difference.. the casing is the measurement for width, not the profile.. Wider rims will give you a more squared profile, where narrow will give you more of a balloon profile.. square gives you a good biting edge which is all tread, balloon gives you more of a contouring contact patch..

I understand how makers who advertise in inches get by with it.. the more precise measurement of millimeters something I don't get... at all..

my dick cepek FCII 35"x12.5" are actually 34.5"x12.25".. they are mounted on a 10" rim, meaning- they are mounted as intended- and still don't measure up..

 

Well YOUR Dick Cepeks are 1/4" taller and the same width as mine measure, LOL.

I have a good buddy with a set of 33" BFG A/Ts that measure just a smidge (and I'm talking like 1/8th) over 31". He AIN'T a happy camper.

Now my Nitto Terra Grapplers on the Grand Cherokee are a LOT closer to advertised specs. They are advertised at 31.57" x 10.79" and actually measure 31 1/2" x 10 1/2" and are mounted on the stock 17x7 wheels with 32 PSI air in them (tire max is 35 PSI)...

 

ha!!! it was most likely 34.25" on mine too.. I was pulling from memory, and just recalled they were slightly smaller than advertised... but then again, you run 17" rims, right? I'm on 20" until the next tire change.. then I'll be joining you!

 

Yep, running 17s...