Will I need a new tune??

[97xl]

I know I can't adjust the speedo with the programmer, needs to be done by swapping out the VSS gear. Just wondering if I'll need a new tune to make the shift points correct. Last thing I wanna do is go messing with the shifts in the programmer and make things worse. It should be liveable until I can get new tunes. Right now the speedo gear is set for stock tire size of 235/70r16 and since my winters are 255 and summers are 265 it was already off to begin with but that didn't seem to make a difference with the tune(when I had the tune made I put 255s as the tire size on Troyers order form.) Guess I'll just wait till PHP is open again and find out the details.

Thanks for the info.

[Jackpine]

Originally Posted by 97xl

I know I can't adjust the speedo with the programmer, needs to be done by swapping out the VSS gear. Just wondering if I'll need a new tune to make the shift points correct. Last thing I wanna do is go messing with the shifts in the programmer and make things worse. It should be liveable until I can get new tunes. Right now the speedo gear is set for stock tire size of 235/70r16 and since my winters are 255 and summers are 265 it was already off to begin with but that didn't seem to make a difference with the tune(when I had the tune made I put 255s as the tire size on Troyers order form.) Guess I'll just wait till PHP is open again and find out the details.

Thanks for the info.

Thanks for reminding me of the name. If the VSS gear makes your speed correct, then the shift points should also be correct. I'd say install a VSS, with the new gears, that matches the tires you use most of the time and live with the slight error that will be present with the others. Looks to me like you'll have only a 2% error between the 255s and the 265s.

- Jack

[97xl]

Ok just so I have things clear in my head...the shift points are controlled by the speedo...the VSS gear in the truck right now is the stock one so I know the speedo is off but if I change the VSS to match say my 265s that will correct the speedo error and since the shift points are based on the speedo then the truck should shift at the proper point without having to modify the tune??

[Jackpine]

Originally Posted by 97xl

Ok just so I have things clear in my head...the shift points are controlled by the speedo...the VSS gear in the truck right now is the stock one so I know the speedo is off but if I change the VSS to match say my 265s that will correct the speedo error and since the shift points are based on the speedo then the truck should shift at the proper point without having to modify the tune??

Yes, almost. The part throttle shift points are controlled by speed AND throttle position. At a fairly open throttle, the shift is delayed to a higher speed, and vice versa. But yes, having the correct VSS for the tires AND gears will make the shifts occur where they should.

- Jack

[97xl]

Ok thanks for clearing that up. This mod is already costing me big $$ and I was hoping not to have to spend more to get new tunes.

[97xl]

Well the rear end has been installed and my speedo is waayyy off...when I know I'm going close to 60 kph(based on tach rpms) the speedo says 80ish. The trutrac has a whine to it whenever you let off the gas. My mechanic said to bring it back in a week so he can check to make sure its ok. Now to get that VSS gear.

[Power Hungry]

Once the VSS gear is corrected, the shifts will all return to normal, at least based on MPH. However, they may still be a little high RPM-wise since you've now changed your RPM/MPH ratio. This isn't necessarily a bad thing, but might not exactly be what you're looking for... especially if you're looking for fuel economy.

If you can provide old gear/tire combo and new gear/tire combo, I can run it through the calculator and let you know just how much to expect your RPM to change. Of course, you've probably already noticed the difference.