stmar

I would like to double check my calculations. What are some settings EVO owners are using? Please include tire size, mine are LT265/R70/17 and I am using 2522. Does this seem right??

ford4wd08

The number you are plugging into the evo is the circumference of the tire. To check your calculation, 17" = 431.8 mm. So 265/70/17 is (265*.7)*2+431.8=802.8. Circumference is pi*d which is pi*802.8=2522.07. Looks like your number checked out. Sorry for the math lesson lol. Anyhow what's your squish factor you're using? Depending on sidewall and psi in tires it can be anywhere from 3 to 5%. I would use 4 and verify your speedo and go from there.

stmar

I am not familiar with the term squish factor. I run about 45 psi. I will verify speedo and I assume trip meter would also be effected which would effect AMPG.

ford4wd08

Your tires are not their true diameter or circumference for that matter because they are under load. You adjust according with a percentage. So a 4% squish factor for 2522 would be entering 2421 into you're evo. And yes it affects all of the settings for mileage and odometer.

stmar

Interesting. So what would a lower setting, the 2421, do to mileage and odo readings? I had it set on 2550 for a while so am wondering what that did as far as speedo and odo?? Like you said, the speedometer has to be checked to see if it is correct and I assume this would be true no matter what setting you used. Now to find one of those speed check signs, we have one here just have to see where they set it, and will check odo on the interstate between some mile markers.

ford4wd08

Theoretically it would makes your odometer register more miles. Smaller tires make more revolutions than a larger one per mile. That's why you speedo reads fast when you go up a size in tires.

ford4wd08

Also, a speedometer app on a smart phone is pretty accurate for checking against your truck speedo. It's uses GPS. Best method to figure it out.

stmar

I am confused a bit here so bear with me. Smaller tires rotate more so would the speedo read slower with larger tires since there would be less revolutions? I am going to play with that setting some and see what it does but I am trying to understand the theory so I know what I am looking for. Thanks for your help.

stmar

P.S. Smart phone is on my to do list, I don't even text!!!

ford4wd08

Actually I believe I have it backwards. Your speedo will read slow with larger tires. Ha it's been a while since I've given it that much thought lol. Easiest way is start with the speedo set to theoretical circumference and adjust one it down until you get the correct speed.