I've been trying to read as much as i can about everything and anything Jeep related and have been learning a lot from this forum more than any other or internet site. The one thing I cant wrap my head around is how do you know what the actual tire height will be before purchase? I've read where one name brand 33" measure 31.5" while another will measure 32.5". I know there is a lot to consider on this like PSI, weight of vehicle(mods) and so on but being actual almost 2 " off sometimes seems crazy to me when trying to figure out gear ratios and so forth.

Are there any brand names like Toyo, BFG, Nitto, ect... That tent to run closer to specified diameter?

I have a 2010 JK 2d 6 speed manual(typical heavy bumper, winch, and tire carrier--XRC Gen 1's) and wanting to find a AT tire(one of the ones mentioned) close to a 34" when all said a done and mounted.

I'd hate to buy 5 35" tires and after mounting them find out they are closer to 33".

Thanks in advance

Smokey

 

Pick the tire with good ratings/reviews and be done with it. A single inch in size isn’t going to make a difference for anything. You won’t see a difference between a 34 and a 33 inch tire, so if it’s for looks then it’s a wash. If it’s for off road ground clearance, then you’re only gaining minimum clearance advantage as well.

 

Yea, I'm overthinking it. I'm not worried about the looks. I was thinking in the lines of gears. Trying to find the right size tire for the the gear ration. I'm just swapped 3.21 to 4.1 with 305/55/20 (bought it used, thats what it came with). I'm wanting to go to a 17" wheel that would measure about an 1" to 1.5" taller than what I got now.

I'm running 2800-2900 RPM at 60mph now and trying to find a tire that will help put me more to the 2500-2600 range @ 60.

I say 60mph because thats how fast I've only driven it since the recent gear swap (trying to baby to break it in).

My tires now measure little over 31.5 now with 30-ish PSI

Thanks for your input

 

The only real way is to get the tire circumference from the manufacture.(or measure it yourself). Tire circumference/3.14159=diameter. I use this method with my Flashpaq to calibrate the speedometer and then double check with GPS ground speed.

 

+100

You are really overthinking it. That little bit of difference isn't going to matter with gearing either. There are tires that run a bit more true to size (Nitto and Toyo come to mind), but even that is misleading cuz different sizes of the same tires will come in different load ratings. For example, a Nitto Trail Grappler in 35 or 37 will be E rated with a stiffer sidewall, move up to 40" tire and that is C rated. There are a lot of variables (load ratings, inflation PSI, weight of jeep, etc.). Pick a tire that you really like, pay attention to what load rating it is and determine that is what you want or not, everything else will fall in place.

 

The only accurate way to measure tire size for the Jeeps computer is to measure from the ground to the center of the hub, then double that number. Since the weight of the Jeep will compress the bottom of the tire, the bottom half is shorter than the upper half. The difference may be negligible, but, that’s still the only accurate way.

 

Interesting

 

I think both you guys are right to some degree, just talking about different things. Nothing wrong with jkrubcon explanation in general as it is still a measure of true tire size vs what is stamped on the sidewall, just not the same as installed and under load which is how we typically think about true tire size when it comes to gearing.

 

Allow me to jump in and add.. Jscan shows measuring the height of the tire with proper air pressure that you run (chalk test) and use that for the tire diameter.. You measure from the top to the pavement.. Actual numbers real numbers.. Toyo 35 11.50 x 17 OC ATIII mounted on 8.5" wide wheels measured at 33.50 inches in height with 27 psi Cold. Also have Toyo 35 12.50 17s on 17x9 wheels that measure 34" height at 28 psi cold. Both Jeeps are set with the Jscan for these numbers and the speedo is accurate +/_ a mph. As for width 11.50s I called Toyo and was told that they measure with the tires fully mounted fully inflated to the PSI on the sidewall laying flat on the surface.

 

Good information
Thanks