ACTUAL Tire sizes

[Matt]

Thought of this today after measuring my duratracs... they're measuring quite a bit under what I expected. Figured it would be interesting to see what other tires actually measure (not just what the manufacturer spec says).

Post up the following format:

Goodyear Duratrac
245/75/17 = 31.4
GY website says = 31.7
Actually measure = 30.5 (6 months old, <5k miles, 35 PSI)




(Side Note: this could also be a reason for people reporting variations in MPG. If i programmed my XK for the 31.7" diameter my MPG reading would be about .6 higher than actual because it would think i was traveling further for each rotation)

[07JeepXK]

Isnt the chalk method a more accurate way to measure actual tire size?

[Matt]

Isnt the chalk method a more accurate way to measure actual tire size?

Just looking for installed diameters- how tall the tire is on the vehicle. Tape measure as posted is sufficient (as long as you're reading it properly, make sure you're looking level and not at an angle)

Chalk method is commonly used to find inflation pressure for even wear.

[Sal-XK]

Maxxis Big horns MT

265-70-17 = 31.7
website says = 31.7
Actually measure = 30.5 (24 months old, 20K+ miles, 35 PSI)

I think this right I'm on my phone and 700 miles from my jeep so I can't give a percentage of tread left. The tread is more then enough for street legal driving but pretty low for useful off roading IMHO



Sent from my iPhone using Tapatalk

[NeilSmith]

you will also have some variations depending on tire pressure. does goodyear specify at what pressure they do the measuring ? max air pressure on my duratracs is 80psi, im sure the tire will measure a little taller than it will at 35psi.

[Matt]

Not sure what psi they measure at.

Some brands/models run big or small... for example bfg at's are known to run on the small side and Mickey Thompson's generally run on the big side.

We used to have similar threads like this on other forums I've been on so people know what to expect when their tires show up. I'm not sure if the sizing trends for my full size trucks hold true for the tire sizes we run on our XKs & WKs.

[criket]

The tire size posted on the manufacture's website is probably the spec size. For example whenever they made the tire initially, they probably measured it and that's waht they use as a guide when making more and posted up that size on the website (i.e. 31.7). How they measure that I'm not sure.

I need to measure my tires.

IMO, the best way to measure the actual tire size, is to take the tire off of your jeep, lay on one side on the ground, and place 2 framing squares on opposite ends of tire, and measure the distance between the 2. This should help eliminate room for error when measuring. But then again, that's a lot of work.

[Matt]

Lol yeah... seriously just throw a tape measure up there and see what it looks like. Not trying to land on mars here or anything. Our vehicles are all close enough in weight and the widths/pressures are close enough to draw some qualitative conclusions from what members post. (Ie: hmm the duratracs tend to measure on the "small" side)

[criket]

LOL, I hear ya. I get it in a few.

[criket]

Criket (Toby)

Nitto Terra Grapplers

265/70/17
Website says - 31.57
Actual size - 30.50 (~18 months old, ~12K miles, 35 psi)

Now I KNOW that I haven't worn a full inch off of my tires. If it was a street car, then yea maybe. I like my burnouts