Why don't 33's measure 33"

89_Sahara · 02-13-2006, 04:08 PM

On the side of the tire it says 33x13.5 but when I measure it I end up with about 31.5. Whats up with that?

**Matt Gertsch** · 02-13-2006, 04:25 PM

How wide are your wheels?

lupinsea · 02-13-2006, 04:34 PM

I can't remember the exact reason but I thought I recall it having to do with manufacturing process or where different manufacturers measure from.

Do you measure an inflated tire where a level is placed on the outer most portion of the tread face where it bluges out slightly? Or to the edge of the shoulder lugs? And then do you measure horizonally or vertically (if a tire is mounted on a vehicle sitting on the ground compressing things a bit). Is the measurement taken to the tire carcass or the outer limits of the tread blocks. I don't think there's a hard set industry standard on this.

Same thing for the tire ware ratings. Those are guid lines set by the manufacturers and not industry standard. For instance. The OEM tires on my miata had a rating of ware 160 where as the aftermarket tires by a different maker I got had a ware rating of 200. And yet the OEM tires lasted longer than the aftermarket tires (something I was expecting).

Coils Rule · 02-13-2006, 05:00 PM

Yeah some do some don't. I know Swampers are prety close but my 35 MTR's are closer to 34 than 35.

mr_user · 02-13-2006, 07:04 PM

Tire rack has a chart on their website with the advertised v.s actual tire ratings.

For instance, my "31x10.5" BFG AT's measure only 30.7 inches in diameter.

Matt

FlaJeepin · 02-13-2006, 07:18 PM

My 30's measure 28.5".

**Awshux** · 02-13-2006, 07:21 PM

Some brands are more off than others. My BFG A/T's were off by less than a quarter of an inch, but I had a set of Dunlop's that were over an inch different.

godsowndrnk · 02-13-2006, 07:33 PM

Quote:

Originally Posted by Awshux

Some brands are more off than others. My BFG A/T's were off by less than a quarter of an inch, but I had a set of Dunlop's that were over an inch different.

An inch larger, or smaller?

got_4_lo · 02-13-2006, 07:34 PM

notice how they are never biger than adverised size?

kinda like crt computer screens...

**Awshux** · 02-13-2006, 07:38 PM

Quote:

Originally Posted by godsowndrnk

An inch larger, or smaller?

Smaller, in both cases.

(Story of my life...

)

xjrrrdx · 02-13-2006, 07:41 PM

My 31" BFG ATs measured 28.5" but my 34" Trxus measure 33.5"

**Texas ZJ1** · 02-13-2006, 09:42 PM

You must have bought some MT/Rs.

Hunter

**War Eagle** · 02-13-2006, 09:44 PM

Who knows? I've been calling this <---------------------> nine inches for the last 30 years.

**Texas ZJ1** · 02-13-2006, 10:27 PM

She hasn't!

Hunter

**Matt Gertsch** · 02-14-2006, 11:02 AM

Quote:

Originally Posted by War Eagle

Who knows? I've been calling this <---------------------> nine inches for the last 30 years.

Yeah, it causes problems when you tell your wife to get you 3 feet of something and she comes back with a foot of it.

02-13-2006, 07:04 PM	#5
mr_user Registered User Join Date: Sep 2004 Location: Fairfield, CT and Oxford, OH Posts: 2,070 Profile Gallery Classifieds My Jeeps	Tire rack has a chart on their website with the advertised v.s actual tire ratings. For instance, my "31x10.5" BFG AT's measure only 30.7 inches in diameter. Matt __________________ Old: '96 ZJ 4.0, 32" MT/R's, 4.5" Lift, Mickey Thompsons, JKS Disco's New: '02 WJ Limited 4.7L, Stock for now

02-13-2006, 07:21 PM	#7
Awshux Cynical Bastard Join Date: Jul 2004 Location: The desert Posts: 1,744 Profile Gallery Classifieds My Jeeps	Some brands are more off than others. My BFG A/T's were off by less than a quarter of an inch, but I had a set of Dunlop's that were over an inch different. __________________ You live and learn. At any rate, you live. -Douglas Adams

02-13-2006, 07:41 PM	#11
xjrrrdx Registered User Join Date: Oct 2004 Location: Denver, Colorado Posts: 1,616 Profile Gallery Classifieds My Jeeps	My 31" BFG ATs measured 28.5" but my 34" Trxus measure 33.5" __________________ 96 XJ 159k RE ZJ 3.5" coils with 1.75" spacer, DPG 5" springs, JKS 1" shackle/ Black Steelies 4" BS/ 34" Trxus MT / RK 3-link LA / Rock Monitor Front Bumper / RE XD Trackbar w/ mount / C-Rok Rear Bumper / Aussie Front Locker / AJs Sliders, RE H&T www.rocklizardfabrications.com