Custom 07 Tahoe, Speedometer Issues

[smmperformance]

Hey Guys. We are working with a unique project and would like to resolve our speedometer issues. The vehicle is a 2007 Tahoe LTZ SUV with a GM LS7 7.0L engine and GM 4L80E transmission.

First of all, see our most recent attached tune file...

We have had the OEM 07 Tahoe PCM & TCM flashed with a new VIN for a vehicle with a 4L80E transmission, for proper operation.

Our issue is that the speedometer is off because of a gear change size. We attempted to use the automatic calculator by typing in the tire size and gear ratio, but they are not clickable and are shaded out. Why is this happening? Our speedometer is clearly off calibration...

I appreciate everyone's help... Please advise.

[5_Liter_Eater]

This is a dumb question but if you have another cal open as a compare file and you have the editor viewing the compare file the fields will be greyed out because you can't change the compare file. Are you sure you're not viewing the compare file instead of the main file? What about all the fields under the calculator? Are they greyed out too or just the calc?

[smmperformance]

There are no other files opened or being compared, no... We are viewing the main file, yes. Just the calculator fields are grayed out.

[Russ K]

For some reason the commit button is grayed out. What gear ratio did you install. Would you list the current & stock tire sizes?

Russ Kemp

[smmperformance]

Hi Russ. The gear ratio is 3.73, factory ratio.
OEM Tires: 275/55/20, 31.8" Diameter
New Tires: 275/60/20, 33" Diameter

[Bill@HPTuners]

This is because GM has several different ways they calculate gear ratio/tire size in their calibrations, some of which even they fudged some of the numbers to get things to work out right. Our software can only calculate gear ratio/tire size 1 way for a specific calibration which we've tried to calculate the most common one, in the cases where the auto calculate funtion is not available you would need to manually scale the parameters & use the manual scale feature to rescale your shift points & TCC parameters.

[Russ K]

This is the best I could come up with. But I don't understand what to do with the VSS Tire Revs per > Dist - Trans field. the help file says this is the tire revs per mile. Yet on some vehicles, this value is the same as the field above it.

Note that you have to manually scale the shift tables & TCC tables by 1.0377 as shown.

Russ Kemp

[DBCKSSR]

This is because GM has several different ways they calculate gear ratio/tire size in their calibrations, some of which even they fudged some of the numbers to get things to work out right. Our software can only calculate gear ratio/tire size 1 way for a specific calibration which we've tried to calculate the most common one, in the cases where the auto calculate funtion is not available you would need to manually scale the parameters & use the manual scale feature to rescale your shift points & TCC parameters.

Bill, On a related subject: Were you guys able to find the 'missing' or 'behind the scenes' parameter for SSRs that is needed to adjust the speedos after a gear change? Maybe it is a combination of parameters?

ZC

[Bill@HPTuners]

We've added one in the recent weeks & are looking into adding some others that may be needed as well.