Speedometer Calibration (3.90 was 3.42)

[gatbr]

Today I pick up the truck from the local shop. I had an eaton posi unit, moser heavy duty axles and richmond 3:90 gears installed. I have an 97 c-1500 truck (5.7). a few months ago I installed a magnacharger that comes with superchips programer.

Here's my problem the superchips only has option for 3:08, 3:42, 3:73 and 4:10's. I currennly run a 28.9 inch tire.(275/55r17). What combine of ration selection and tire size should I choose. The programer only can go form 25"-33" tire tires. I currently have it set to 25" tires. The MPH is about 5-8 to fast. I had it at 33" it was 20-25 miles off. I'm trying to avoid sending the superchips back them to be fixed. Is there an gear ratio/tire combination that will work????

Thanks
Brian

[airdeano]

you should program your handheld to:
a 30.50 tire and a 4.10 gear. or
a 27.75 tire and a 3.73 gear.
this is the same roll out as your 28.90 with a 3.90 gear.
airdeano