pics of 39's on stock M715

[porkchop]

You may want to think about changing out the tubes and flaps. You need to make sure you are running radial tubes and flaps with radial tires. If not heat can become a big problem for you. What PSI are you running?

[Treepusher]

Green with a J-cab, same as mine. I have Buckshot's on stock rims. Do the taller tires make much differance in gearing (rpm) at highway speeds (50mph)?

[FSJ Super Swamper]

The 0nly way thoughs tires are coming off thoughs stock rims is if I finally get a 1 piece rim.

And we put 12 psi in each to start and I'm going to drive it around town tomorrow and adjust from there...

[brute4c]

Point of reference for gear ratio effect due to tire height....

A stock 34 inch tire with a swap to 4.56 gears = a 44.5 inch tire with the stock 5.87 gears.

So if you keep the stock gears and put 44.5 inch tires on, its like changing the stock truck to a 4.56 gear ratio....

This combo, 39's, is roughly halfway between...

[2ndA]

Except, of course, these are no longer 39.5 The arch across the tread from the narrow rims has added an inch or more to the center height(and reduced the contact patch accordingly). Still, it looks GOOD!

[FSJ Super Swamper]

they measure 38" tall with 12 psi

[2ndA]

That's with the weight of the truck on them, right?

[vrod02]

Porky ,There Bias not radials.

[boondockster]

The effect of the larger tires can be calculated like this:

old diameter / new diameter * gear ratio = effective ratio

So:

34 / 38 * 5.87 = 5.25

[boondockster]

I should have also mentioned that you can apply this directly to engine RPM at a given speed:

old diameter / new diameter * old RPM = new RPM

So if we calculate for change in RPM at 50 MPH:

34 / 38 * 2900 = 2595 RPM