In the edge manual it says use figure X for H2 tire size. I then get a corrected speed on my attitude. When I divide my corrected speed by my displayed speed on truck I get 15% difference.

Some time back I saw a post that said H2 tires were 12% bigger.

What am I doing wrong?

What size did u put in?


The tires are 34.5" high.


Stock 245 are 30.6 and 680 rev/ mile


H2 315 are 34.5 and 601 rev/mile


so if u do the math it comes to 11.6% difference.

I run 285/75/16 on my truck. I came up with a 9% difference comparied to the stock size on the speedo. But then again I suck at math.


According to the Attitude at 60 mph my stock speedo says 55mph. My math was:


55mph x 1.09= 55.95mph


Thus being 9% difference.


Am I going about this the right way?


Jesse

55x1.09=59.95

Just curious here, but what number do you guys have in for th H2/315 combo?

Oopps, I meant 59.95. Thanks.


Jesse

The difference is almost exactly 12.8% with the H2's.

What Number Are You Entering In To The Attitude For The H2/315 Combo? ...is what he was saying.

I entered the number size on the side of the tire and compared to the book (edge) dont remember now what it was.

But 315/70-17 wasnt in the book http://www.dieselplace.com/forum/smileys/Confused.gif

To get the exact measurement of your tires you have to draw a chalk line on your tire and on the ground at the same spot. Then drive forward until the chalk mark has rotated 360 deg. Then mark the ground again at that spot. Measure in between and use that number to program your edge. I think they use mm or cm. Thats how you know your speedo in the edge is perfect.


Jesse

K

sounds like a plan, thats what Ill do...

The tire settings on the Attitude is the tire diameter in mm. To figure the diameter of a tire in mm, do the following. If you work through my example you'll see it is really a simple equation. BTW, i am not a math guy. Algebra was as far as I went.


((width x aspect ratio x 2) + (wheel diameter in inches x 25.4)) x pi = diamter in mm.


Applying this to my tire size (285/75s):


285 x .75 x 2 = 427.5


16 x 25.4 = 406.4


427.5 + 406.4 = 833.9


833.8 x 3.14159 = 2619.77


I then select the setting on the Attitude that most closely corresponds to that size.

Ok, I'll use 2741.97 for my H2 315s. Thanks http://www.dieselplace.com/forum/smileys/Approve.gif

Sounds right! For those intersted, 315/70R 17s are nominally 34.36" tall.