Gear Ratio

[fitpony]

Sorry I'm brand new to all this so hopefully you can direct me. I've already searched for a black and white answer to this.

Should or can you adjust the gear ratio without actually changing the gears? I have 35" tires on my F150 and I've already done the 91 tune. I've read that a 4.10+ ratio is ideal for tire size but I want to make sure I don't screw anything up.

Thanks

[mikel]

No, the gear adjust setting in the tuner is there to program the pcm to correct the speedo only IF you change the gears.
Adjusting this without changing the gears will simply lead to poor shifting and a speedo out of whack.

[fitpony]

Thanks. Appreciate the quick response.

[BuzzBait]

I’m having a problem trying to set up my speedometer after gear swap... my truck (08GMC Sierra) has 4:88 gears with 35” tires, all was fine Before the gear swap i had the tires set at 35” on tuner and speedometer was correct, when I installed the gears I went in adjustable parameters and set the gears to 4:88 tires to 35”, Went for test drive and gps speed was 56 my speedometer was reading 80-80 mph, then tried to set my gears back to stock, test drive same thing, next I tried returning tire size to factory spec and same thing. What should I have my settings on to fix this problem.
Ps I’m not having problems finding the area in the tune to adjust tire size and gears like everyone else I’ve read about. Lol.

[06MonteSS]

set the gear ratio to the correct setting for the gears you have installed in the truck... then just adjust the tire size setting until you get the speedo within 1-3 mph of a gps, and then you're good to go...