3.25 vs 3.55

If you want better fuel mileage on your rig from a 3.25 ratio lower it by .91 = 2.34 or a 2:36 to get a good fuel saving but you'll be a little slower taking off on first gears and slower on up pulling up hills you will need to lowered shift to bring ur rpm up to climb up the hills but you'll be saving a lot of $$ on fuel yearly or weekly.

 

The engine rpm’s will increase slightly, if the only thing changed is the ratio.

 

I know this topic is super old but I need help I can’t figure out the number I need to put into the computer to gauge my miles correctly. The reason I ask you guys is because you guys are talking about a 3.25 diff with 295/75 22.5. This truck stock came with 11r’s so far we got it down to about 3 miles extra for every 100 but my OCD won’t let me leave it like that. Please help since I charge per mile I don’t want to seem like a thief.

 

Spicer Transmission Ratio RPM Calculator

Diameter should be about 40.7"

 

I really appreciate you answering but the number that goes into the computer is a 5?? Something number right now the mechanic put 513 but it didn’t fix it.

 

Revolutions per mile I bet. You should be able to look that up for the tire brand and size.

There are other road speed calculators that utilize rotations per mile, just Google road speed calculator.

 

Or, you can figure the circumference of the tire (2pieR) and figure the rotation per mile.

Probably around 502 maybe.

 

Thank you bro for taking time out and trying to help and make a big difference in someone’s business. I googled tire revolutions per mile for 295/75 22.5 Toyo tire are 517 only 4 off but still tacked on 11 miles to my 700 driven today. More taxes God Bless

 

Do you think there is something else that causes the truck to read mileage off? No matter what number we changed it to it would always tack on more miles. I remember one time he had it at 533 was still tacking on 3 miles extra per every hundred. Higher the number the less miles right?

 

Other than ton/mile states like Oregon being off won't affect taxes on IFTA. Yes, it will alter your mpg, but that is

only used to calculate how much fuel was actually used in each jurisdiction. You still use the same amount of fuel, and therefore pay the same amount of fuel tax.

That said, I would want it accurate as well. It sounds as if there is another problem in the calculation, like incorrec overdrive ratio for the transmission, or incorrect rear end ratio. I assume your plugging this number into the ecm, correct? Is it possible to adjust any other parameters besides revs per mile? Like 3.25 to 3.36 for rear end ratio, or .79 to .73 for trans overdrive?

 

Yes sir there is one time he got so frustrated he wanted to move the diff rating from 3.25 to something else. He got scared and said that would open another whole can of worms. Call me crazy but I seen with my own eyes the speedometer would change but not the miles it was marking when we would move it. We even had Apple Maps going and another app that records speed and distance. I got frustrated and told him just leave it like that and I’ll try to charge the customer by Apple Maps but sometimes we take truck routes and are further.