98Blubrd

iTrader: (13)

I know that to correct the speedometer in HP Tuners for 98 F-Bodies is a bit different than the 99+ since you have to do the whole Tire Diameter divided by Gear ratio. Then punch that number in the speedometer settings. The only thing is that I have looked at about 5 bins from stock 98 f-bodies and everyone has had a slightly different ratio from the factory (based on stock tire size/stock gear ratio). So it seems like from the factory there was really no set ratio.

I currently have 275-40-17's in back which roughly calculates to a 25.661 tire diameter and I have just a 12 bolt with 3.73's in the car. Should I just punch in 6.879 (25.661 divided by 3.73) on my Hp Tuners or is there a more exact correction factor to use.

Thanks.

2xLS1

iTrader: (25)

GM uses 24.9x for the stock tire sizes on all year f-bodies so that's what I use. I use these values on 98s.
Gears Value
2.73 9.11
3.23 7.71
3.42 7.29
3.73 6.68
4.10 6.08

98Blubrd

iTrader: (13)

Does A4 or M6 Matter(I wouldnt think so but thought to ask)? This should be in a sticky somewhere since you only need to do this for the 98's. I guess it really doesnt seem to come up that much as I couldnt find it anywhere the search. Dont you just have to put the gear ratio in 99+'s? Thanks for the help.

2xLS1

iTrader: (25)

The 2.73, 3.23 and 3.42 values I posted are straight from stock 98 GM calibrations.

98Blubrd

iTrader: (13)

Thanks again.