Big T

Well I got the smarty installed and adjusted the tires to 35", because i have 35-12.5-18 on it. The ? is the tires are not 35" tall when I measure from the ground up it is about 33.75 is this the measurement I should use or how are you guys doing it?

Boz007

Use the measured height.

dodgezilla04

measured height is the correct way.

JohnInNH

Front or rear... Loaded or unloaded? My front tires are "lower" than my rears even at higher pressure when unloaded or even with a light to moderate load. Pressure?

Height vs circumference ....

I suspect the height of the tire OFF the truck would be the most accurate. Or am I all wet?

The circumference is the same regardless of the height when loaded or unloaded (which may be an 1" or so off)

What is the best way to measure to get the most accurate Speedo?

N.Johnson

"What is the best way to measure to get the most accurate Speedo?"

You asked so I'll answer. I took a 2 foot level and measured from the top of the rear tire to the ground on the truck. Guessing the rolling dia. height doesn't change much on the truck. Maybe a heavy load would lower the height as the front tires are lower but the same pressure. Anyway I Input that into Smarty. I figure that the speed sensor thingo is in the rear diff so.....Am I Right?

tbarbee1

I measured the front for my superchips and its dead on

Danderson

What's wrong with using the manufacturer's data supplied by their website? I do wish Smarty let you input the revs. per mile. My 285-70-17's are supposed to roll 636 rpm's. I supplied 32.7" to Smarty. I will check it on my GPS on an upcoming trip.

PhilR

I used trial and error with a few GPS aided freeway runs to get my speedo within 0.5mph accurate. My final number into the Smarty was 34.65" for a 35" Toyo M/T.

RamWheelsBy4

Well the manufacturer usually has fairly accurate actual diameter measurements on each tire size. They also provide revs per mile that is also fairly accurate. I used the BFG 285 32.7" diameter for my Smarty programming and the BFG 285 636 revs per mile for the DRBIII tool to reprogram. They both are fairly close to accurate according to GPS.

Raspy

Exactly the tires and number I used in my Smarty. My tires are about 2/3 gone now and they test out 1/10 mile extra on the odometer over 5 miles.

The "height" seems like a weird way to do it to me. As I don't think the flat spot on the bottom changes the revs per mile much but it does change the height. Best to go with the factory listed tire height. Then tune it as needed.

Wetspirit

tbarbee1

I used maesured tire height and checked with my GPS its within a mile on the speedo. This is what worked for me good luck