big tyres

[muddy80s]

hi just wondering if anyone knows the true diameter of bfg 315/75/16 tyres i have been on the bfg website and they state 884mm (just under 35 inches) but i also have a set of 285/75/16 mud tyres myself and they are about 810mm or about 32 inches .mathematically they should be about 33 inches and bfg say they are .i want to buy bigger for my 80series but im not gonna if they are much smaller than 35 inch.a mate had wrangler mudders in 315/75/16 size and his are only 33 inch. any details would be appreciated

[Slunnie]

What exactly are you asking?

315/75-16 are 35's
305/70-16 are 33's
285/75-16 are 33's.

[RV80]

Any tyre is going to be smaller when measured on the car.

[muddy80s]

my question is why are these a different size on the car than advertised. 285/75/16 are not 33 inches across

[Toy80Diesel]

Ummm would these calculations be correct?

a 285/75 16 tyres for example.

to work out the height, 285 X 75% = 213.75 (height of one side of the tyre)

Multipy by two for the two sides, 427.5, add the rim (16") 406.4 gives you 833.9mm, in inches 32 7/8 inches, (almost 33")

Maybe when you put the tyre on a wide rim, say 8", the tyre expands to the beads and loses a little height? Or flattens out to the 810mm you mentioned.

315/75/16 totals up to 878.9mm or 34 5/8" (closer to 34 and a half!!!)
305/75/16 totals up to 863.9mm or 34"

[muddy80s]

thanks id already calculated the size correctly but your probably right ihave 8 inch wide rims this could be the problem. but also bfg website says 315/75/16 are 886 mm,still doesnt calculate properly. but anyway thanks for input.

[just cruizin']

Go to a decent tyre shop who stocks them and measure them, don't forget the sizes quoted on the tyres are pretty nominal.

If you're after big rubber like that go something a bit more aggressive then the BFGs, for the same dollars you'll get a better tyre

[[WANAPLAY]]

Go Here, works most stuff out for ya quickly and easily;

http://www.miata.net/garage/tirecalcold.html

Cheers Ryan