My Iroc came thru with a 115mph speedo and 15" rims. I changed to the 140 speedo and put 16" Iroc rims on, with 245/50 tires.

To make the speed correct again, all I must do is change the gear in the side of the tranny, right?

I'm dropping a WC tranny in soon, and I'd like to change to the right gear while it's out. What one do I need?

I have the LB9, WC T5, 3:08 posi rear.

 

If you only changed the entire speedomoter assembly then you don't have to make any changes. The speedo is already geared correctly.

The tires you picked are stock diameter, so again... no change needed.

If you only changed the face of the gauges then you'll need to drive the car next to someone that has a car with a stock/correct speedometer and compare them. Have them cruise at 60 mph (it's the easiest number to do the math with) and see what your speedo reads.

Then go to the home page and use the "Equations" link. There are a few calculators in there that will give you an idea of how far off your speedo is.

Next you'll want to click on the "FAQ" link and read the write-up in there on how to calculate which one you'll need. There's even a list in there of the part numbers.

 

So changing the speedometer (not just the face) will not affect the reading? That's good to know!

I don't know what the configuration of the car that my new T5 came from, that's why I want to change the gear now.

I'll have to look for that link, thanks. Is that something that I can get from the dealer?