Trans tuning and Tire Revs per Mile

Rubenk · #1 (**permalink**) 09-12-2009, 12:20 PM

Ok, so I've been running Cale's 140 tune since May and I've loved it.

But I'd upgraded from 33" tires to 35's and bumped my tire rev's per mile down closer to what they should "mathematically" be...I had never measured my actual tire circumference, until today!

So, I thought my trans was getting worse on the shifting and actually just bought a spare used one for when it goes. I decided to measure out my tire's rolling circumference now that I was working on the truck and had spare time...

I put a piece of masking tape on the ground and a piece on the outside of the tire. I rolled forward watching my side spotter mirror until it was close, got out and checked it and it was one full rotation, marked spot on the pavement. I measured between the 2 peices of tape on the pavement and came up with 104" or 105" depending on which side of the tape I went to...Divided 63,360(thank god for google on the phone) by both and came up with 604.xx and 609.xx. So you can see that 1 inch does make a bit of difference. I went with the 610 on my tuner as thats what others have used with 35's and took it for a spin to the hardware store for a few things.

All I can say is that EVERYONE should do this when custom tuning regardless of stock tires or not, it made it shift 10x better and I was only off by 15 originally(595, then 590 as experiment) and it made if shift a lot better. Now I'm thinking my trans is probably fine after all, no shift flares and it even down shifts in non-tow/haul mode when it should!

According to a circle circumference formula I should be around 580 rev's per mile, but we can see that the measured 610 is much different...

chuckles · #2 (**permalink**) 09-12-2009, 05:00 PM

good to know, I'll check mine.

dukcaln · #3 (**permalink**) 09-12-2009, 05:37 PM

so even with custom tunes from cale, you can still go into to the sct and adjust the rev per mile? Can you adjust shift firmness to still. I thought all that was done when cale makes the tunes for you.

Rubenk · #4 (**permalink**) 09-12-2009, 05:44 PM

Quote:

Originally Posted by dukcaln

so even with custom tunes from cale, you can still go into to the sct and adjust the rev per mile? Can you adjust shift firmness to still. I thought all that was done when cale makes the tunes for you.

Yup I can adjust all of that. He mentioned when he was building mine with me standing next to the PC with him that he would "leave the adjustable tables in there" or something like that. So it might be an option he puts in there, not sure how that all works...

But yes, I can change rear gear ratio, speed limiter, tire revs per mile, idle rpm, governor rpm, the shift points, and the shift firmness for each shift. Only thing i've actually changed is the tire RPM...

dukcaln · #5 (**permalink**) 09-12-2009, 05:47 PM

Do you drive with the 140hp tune daily? I have it but the shifting was crazy hard.......

Rubenk · #6 (**permalink**) 09-12-2009, 05:59 PM

yep, been driving it every day since April! I tried the 65hp tow tune with turbo brake for a while, and it was really nice but the mpg of the 140 tune is a lot better...I actually drive in tow/haul a lot b/c the speed limits on base are 25mph and a stretch of 40mph for a few miles, it is a lot easier to drive in traffic like that...

Mine doesnt shift what I would call insanely hard, but I havent tried any other tunes to compare to...