Gear Ratio Discrepancy

[BrMac901]

Hi Guys,

New to HP Tuners. Just read my stock 2009 Sierra 1500 4.8 and found a discrepancy in gear ratios. Just wondering if anyone has encountered this before. I'm assuming this would affect the trans tuning.

ECM 3.42
Build Sheet 3.42
TCM 3.73
Gear/Tire Wizard 3.73

Gears.jpggear wizard.jpgbuild.jpg

[TheMechanic]

You need to do a more thorough job on the RPO's. It is possible to see the equip group but have an additional RPO that has a gear change and locking diff. I have not had HPT have this error. It has always been spot on. Verify mechanically with rear tire rotation on a jack stand that you actually have 3.42's and not the 3.73's. If you actually have 3.42's then you need to correct that.

[blindsquirrel]

My Envoy was built with RPO GT4 (3.73) and the stock file has
Ratio 3.73
Ratio - Error 3.73
Trans 4.10
Trans - Error 3.42

[2xLS1]

You need to do a more thorough job on the RPO's. It is possible to see the equip group but have an additional RPO that has a gear change and locking diff. I have not had HPT have this error. It has always been spot on. Verify mechanically with rear tire rotation on a jack stand that you actually have 3.42's and not the 3.73's. If you actually have 3.42's then you need to correct that.

Then you haven't looked at very many Gen 4 truck calibrations.

[TheMechanic]

Then you haven't looked at very many Gen 4 truck calibrations.

You regularly find the diff gearing in the wizard does not match the actual diff gearing?

[Alvin]

You regularly find the diff gearing in the wizard does not match the actual diff gearing?

Sometimes the wizard doesn't know (shows a 6 something) and there will be 2 different ratios in the speedo tab.

[TheMechanic]

I will have to pay more attention to that. I rarely change the gear ratio with the wizard unless it happens to have been changed.

[2xLS1]

Never use the wizard on Gen 4 truck calibrations. Do it manually in the speedometer tab. That is where you will find all kinds of discrepancies. Using the wizard is just asking for the Brake and or ABS light to come on.

[Alvin]

I wouldn't say that.. I use it several times a day and do not have any issues outside of guys coming in with absolutely insanely big wheels.

[2xLS1]

And I got this in a PM a few days ago.

"HPT wizard changed all 3 fields for vss tire revs per mile, and changes the
driven tire circ and non driven circ as well as the final drive 3 fields to match gear ratio.
AND it is causing ABS freak out.

07 silverado put on 35s and abs freaks out about 40mph."

[Alvin]

07 silverado is likely one that read 6.51 or whatever in the gear tire change box unless it's a classic OBS.

And 35's are getting into that "insanely big wheels" category.