Tyre Sizes -Are they what they are supposed to be

[awright]

OK to get the ball rolling...

I have got some 285 /75 (or 33x 11.5s) BFG All terrains that measure around 32 inches and have nearly full tread.

I have some simex JT2s in a 34 inch that also have plenty of tread that measure about 15mm bigger than the 32's which are supposed to be 33's.

Then I have had 31's that measured 30 odd inches when new.

I was thinking about getting some new JT's in a 33's (because that is what my car is now certified as having) but odds are they will be 32 or less despite what they say on their website. Has anyone got 33 inch JT's and what size are they. (Or do I stick with the 34's that measure 33?)

[Slunnie]

My Simex JT2 34x11.5-16 were 35.2" x 300mm on 8" rims. My 33x10.5 JT2's were 260 wide on 7" rims and I don't recall the diameter.

[bogged]

this has been done before, only few mths ago...

[Gwagensteve]

and really, who cares? do you measure your pencil from the top or the bottom? If your tyres aren't rubbing, they're too small - nothing else is important.

Steve.

[lukethedork]

and really, who cares? do you measure your pencil from the top or the bottom? If your tyres aren't rubbing, they're too small - nothing else is important.

Steve.

AHAH, I love it.

If the weight of the vehicle is on the tires then measure on a horizontal plane, not vertical.

[MUD EMPIRE]

and really, who cares? do you measure your pencil from the top or the bottom? If your tyres aren't rubbing, they're too small - nothing else is important.

Steve.

AHAH, I love it.

If the weight of the vehicle is on the tires then measure on a horizontal plane, not vertical.

I'd be pissed if my 54 inch Claws were only 53.5

This guys tyres don't rub..!!

[Gwagensteve]

I'd be pissed if my 54 inch Claws were only 53.5

I think the trick is to find a girlfriend with smaller hands.

Seriously, it's not hard to find the "real" diameter of any tyre. It either fits or it doesn't based on its real size, not the fantasy written on the sidewall+ what rim width you have them on+what pressure you have them at.

allegedly, when the 37 bias claw came out, they sized them at about 35.9 or something. One suggestion was that this was deliberate, so that jeep owners with 35's wouldn't have too much work to do to "run 37's"

If this is actually a marketing decision (and not a mistake), then I'm even more embarassed to be a 4WDer than normal.

Oh, as an aside, tyres shouldn't ever be larger than quoted - for speedo and fitment reasons (hence, a larger than advertised tyre would be a legal liability for the manufacturer)

Steve.

[ISUZUROVER]

Oh, as an aside, tyres shouldn't ever be larger than quoted - for speedo and fitment reasons (hence, a larger than advertised tyre would be a legal liability for the manufacturer)

Steve.

Plenty of tyres are l arger than they should be mathematically. The original MT117 (280/85-16) are about 36" diameter.

Offroad pattern 7.50x16s are usually 32" or thereabouts
900x16s are usually 35-36"

BFG 255/85-16 MTs are 33.3" (manufacturer spec)

[Slunnie]

about every Simex is way larger than marked on the sidewall. Thats so you can run a 35" which is 36".

[Gwagensteve]

I did say "shouldn't"

[MUD EMPIRE]

allegedly, when the 37 bias claw came out, they sized them at about 35.9 or something. One suggestion was that this was deliberate, so that jeep owners with 35's wouldn't have too much work to do to "run 37's"

All sorts of marketing decisions get made behind closed doors. This sounds like an urban myth but these people are Americans...!!!




One other thing that i have noticed......(all tyres are different) but some tend to grow as they get used for the first few times.

ie. I fitted a set of 38.5 11 15 Boggers on 8 inch beadlocks. The book says OD is 38. We measured them new at 37 (30 psi). After 5 or 6 day trips they now measure 37.75 (30 psi) with a bit of tread wear. and, Yes, that was the same tyre measured each time, off the car.
Other radial tyres won't grow that much but it can happen.