I am trying to reprogram my tire size with HP tuners. When I punch in new tire size and gear ratio it changes the Trans - Final Drive ratio from 4.10 to 3.73. My truck has 3.73 from the factory but the factory program says 4.10. Now the Ratio - Final Drive says 3.73.


Should I leave as 3.73 or should I change it back to 4.10 like the factory?

Also should I auto scale transmission tables?

HELP! What is the difference between the normal Revs per mile and Revs per mile - Trans? Should I change trans also?

Bump

It doesn't say 'revs per mile - trans', it says 'revs per 'dist-trans'. For me it works out to the transmission revs per kilometer. It also worked that way with a file from Dashman. Multiply what you have calculated for 'revs per mile' by 0.621388 to get the number that goes in here. I don't know why but it seems to work. I haven't done any speedo calibrations yet on the allison and I'm not sure if changing stuff on this page will do it properly but it should. I think I would only change the VSS pulses and the 'dist-trans' items and see what happens. Mine also reads 3.73 ratio and 4.10 trans on 2 allison reads.

Let me know if this helps.

Silly me, I just discovered why I got the number that was for a kilometer. I had the HP editor set to metric !!! doh!! Forget what I said about the metric multiplier.

i just did this but i onlyt changed revs per mile nothing else and i am not slow by 3mph

I am also having issues with the speedometer no matter what I do I can't seem to get it right... I can change the vss tire revs per mile all day and it is still 5mph slow according to gps... Now I was reading something in the efi section that says when you install a tune with a different os than your original one it causes issues.. Could this be the issue? Any help will be appreciated

wreedLBZ did you ever investigate this further? How about changing your shift point's? I found the same thing with my truck's factory calibration (the ratio for Final Drive Ratio Axle was correct at 3.73 but for Trans was 4.10) but it's a 8.1 gasser so I have a much wider range of RPM to be shifting from. Well I had a heck of a time getting my Allison to shift when I wanted it to and the RPM to MPH ratio in gears is off compared to speedo calculators like this one http://www.f-body.org/gears/ which didn't help me set my shift speeds or RPM's. I'm beginning to think that the axle ratio and VSS sets the speedo but the tire size and trans ratio set the shift points and my Allison is confused as to how fast it's actually going because it thinks it's twisting a 4.10 gear.

I want to set the "Trans Ratio" right but I'm afraid I'll throw everything off in my entire shift tables now that I've at least got it shifting about where I want it too at WOT, then I'll have to start all over again or do a bunch of math and "convert" entire tables at once to get it back to right even though it will actually be numerically correct at that point.

Do you or anyone else at this point know what I'm talking about here or I am the only one who's dealing with this? If any one found this in their calibration and set thier trans ratio scaler to match the actual gear ratio, what happened? Did the shift tables change themselves or did it start shifting wrong? How did you deal with it?

I want to install my 4.56's but need to figure out what's going on here first.

Thanks,
Vernon

P.S. If anyone goes to that F-body site Gear Ratio/MPH Calculator and wants to start playing with it here's the Allison ratios:
1st-3.1,
2nd-1.81,
3rd-1.41,
4th-1.0,
5th-0.71,
6th-0.61.

Manic, I have never been able to get the auto-scale functions to work with the 8.1L trucks. But the following info may still be helpful to you.
Here is what I have found to work best for me:
First start by opening your stock tune file, and save a new copy to mess with.

Now, open your speedo table and change both gear ratios to the correct number. If you have 3.73's, both boxes (final drive and trans) should read 3.73. Click Save.
Now, enter your new tire size and gear ratio into the auto-scaling function boxes. Example: 265/70/16 is about 31 inches. Click "yes" to auto-scale transmission tables. Apply the changes, and save them.
Load the tune, and see how it drives without making any other changes. Remember it will take the TCM a little while to re-learn the shifts just like any time you re-flash it.
You will notice the truck shifts and drives perfectly; possibly better than stock.
For you 8.1L guys, you will have to manually enter your VSS revs per mile to get your speedo correct, and manually scale the other tables as well. Major PITA but it can be done.

Have fun!

Hey thanks for answering, I was just convinced that nobody was reading the forum. Good to have you and the others to share 8.1 information with. That's what I needed to know, I didn't know why I didn't have an auto scaling option and thought it was due to the "Tuning School" template or configuration or whatever it's called I applied to the Tuners software.

Vernon

Here is my experience with this calibration stuff. I have my odometer reading very very close to deadly. This software has different tables depending on OS of the truck. At least that is what appears to be the case. That explains why there are different tables for adjusting the various years of trucks I have calibrated. I have done a '99 with 4.8l/3.73, '01 w/8.1l/3.73, '05 w/4.8l/4.10, '05 lly and '07 lbz. There are differences in the tables for every one. The '01 and '05 do not even have any thing on the tire/gear calc tab. You should only change the tire revs per dist boxes. The '99 and '07 both have the tire size change tab with the auto adjust button for the trans tables. I will NOT ever use that option again. I used it once with my '07 and the shift points went way out to lunch and I am not sure how fast I would have had to go to get 6th gear. For most people just making the change for a minor tire size adjustment, less than 4%, I doubt the shift tables matter that much anyway. If that option works for you then it must be before the beta version as I think it worked on my '99 with no ill effects.

I would be very interested in knowing whether EFILive has the same different options based on the OS. If they have the same tables available for all years, it means that the programmers for HPT are creating tables they think we need and I wouldn't trust the auto calc tranny shift points option, at least not on the beta. Like I said, ONLY change the revs per mile box and when you have an accurate odometer, your speedometer will also be deadly.