Confusing tire sizes

[crazyoffroader]

I've been looking at cheap ways to gain more ground clearance, and for now I've settled on a 32/9.5 r16. for a spare I rwas going to carry a 32/9.5 r15 I have, but when I compared the two the r16 was a good 1.5" taller than the r15. Now, I was under the impression that the 32 was total tire height, and after further inspection of all tires in my possession(too many) I found the following:

Goodyear LT235/75/r15 = 29"
Michelin LT235/75/r15 = 29.25"
Bridgestone LT235/75/r15 = 29.5
Sears LT235/75/r15 = 29.5"

Goodyear P235/75/r15 = 28.75"
Michelin P235/75/r15 = 28.75"

Michelin 31"/11.5"/r15 = 30.25"
Michelin 31"/10.5"/r15 = 30" *
Goodyear 31"/10.5"/r15 = 30"
(Unknown) 31"/11.5"/r15 = 29.75" *

Michelin 32"/10.5"/r15 = 30.75" *

Michelin 245/85/r16= 31.5"
Goodyear 245/85/r16= 31.5"

All tire sizes are the average size for the number of tires I have. Tires with astriks are of illegal tire depth(too shallow).
Can tire wear account for the 32's I have that are 30.75" tall?

I currently have 4 different new tires on 4 different unballenced rims (have a friend with a machine) and all are 28.5" (+-.5") even though they are all LT235/75/r15's, so, how inacurate are tire sizes?(and why don't I have an alignment problem, or a wobble, or any problem for that matter?)

 

[JLane99XJ]

...
... how inacurate are tire sizes?(and why don't I have an alignment problem, or a wobble, or any problem for that matter?)

each tire manufacturer and each product line within each maker varies as much as 1/2" from the denoted size, example some 31" tires are only 30.5" tall whereas others are 31.5" Its a common thing..

in reference to mis-allignment or wobble being caused by the tires being slightly different heights is a farce..

only a really large difference like 2 or 3"s would make a difference in allignment

and so long as the tires are properly balanced (not out-of-round) then the effects of wobble shouldn't be present, or if the tires aren't balanced then the tightness of the steering components and the accuracy of the allignment can be combating any wobble effects

**NOTE: a slight amount of TOE-IN can resolve fairly severe death wobble caused by worn or slack steering tie-rod ends, about 1/8" to 1/4" toe-in instead of the 0-degree toe in setting (yes this will cause slightly premature and slightly un-even tire wear, but to me the bennefit of being able to drive from point a to point b without having to constantly fight the steering wheel and brake at every bump in the road is worth it.)

 

[Root Moose]

The other pattern I've noticed is that tires that are targeted at the "street tire" crowd tend to be smaller than comparable off-road biased tires.

An example, the 265/75R16 Michelin LTXs I have for my tent trailer are visually noticably smaller than the 265/75R16 Truxus MTs I have for the Cherokee.

I've also noticed that BFG tends to be smallish regardless of AT, MT, Long Trail, etc.

Interco tends to be pretty close to marked until you get some of the larger tires.

Never owned a GY so can't comment.

 

[Eagle]

In the floatation sizes (such as 31-10.50/15) the first number is the nominal diameter ... of a new tire. A very few brands are actually close to the nominal diameter, but if you look at the catalogs and web sites, you'll find that most tires run about 1/2" smaller than the nominal diameter.

Tread depth for new LT type tires runs from 13/32" to 16/32". If I remember 5th grade fractions rightly, 16/32 is sort of the same thing as 1/2, so a tire worn down to the wear indicators would indeed have lost at least 3/4 of an inch of overall diameter.

 

[Yucca-Man]

Keep in mind that the tire will also be a different nominal height with different rim width and tire pressure. For an idea if how small some tires run compared to the sidewall 'height' check out BFG's website:
BFG AT - http://www.bfgoodrichtires.com/assets/pdf/all_terrain_ta_kd.pdf etc