LSX rear gear question

[Clyde65]

I have the 4.8/4l60e in my truck, was told I had 3.08 gears in my 12bolt truck 3series rear end.

I put a tack in the truck recently and when Im driving down the highway at 70, it shows 2250rpm, which, if you use one of those rear gear calculators show I have a 3.73, am I reading this right or is the tune wrong because I have 27.1" tires ( 255/60r15) and the (?) 3.08 gears with .70 final drive ration on the 4speed auto.

Can yall help me out some?

Thanks,

[Super73]

Jack up the rear, mark the bottom of the tire and drive shaft with chalk.

3.73 turns of the drive shaf to 1 of the tires means 3.73's.

3.08 turns of the drive shaft to 1 of the tire equals 3.08 gears

[TR65]

Clyde,

The numbers you give work out to 3.7 (3.73) rear ratio. (as the calculator says)

The engine speed read by the tach should be independent of the tune or the transmission etc. other than maybe setting the ECM to 4 cylinder if the tach doesn't have a switch for that.

The speedometer could be off, just check it with a GPS. It would have to be reading 15 mph slow to give 3.08!!

Best to just check it like super73 says. But if you don't have a posi there is a factor of two involved.

TR

[Clyde65]

I am going to check it on Monday, 1st day off I have had in 2 months. Ill probably just do the wheel turn thing in the drive.

My tach does have one of those switches, I had it set to 4 cyl as the tuner said to, but it is wrong, have to set it to 8cyl. Why do I listen to those people, why?

[68GMCCustom]

have 3.73's in mine and your rpm looks close to me. My speedo is off tho...and I don't remember what my phone gps reads.