want to get my speedo reading right

[blazinzuk]

In the building of my new truck I would like the speedo to have the correct speed, its an 87 truck with the stock speedo, however it has a th 350 with a doubler. Is there a way to figure out what correction I would need. I assume I will need tire size (42s") gear ratio (4.56) and the ratio that came in the t-case. The truck will not be running for a couple weeks and I would like to be able to order the ratio adaptor before so I can get it here.

So basically is there any way to figure it out with out the truck running or moving???

 

[tRustyK5]

Really best to take it for a drive with a GPS unit on board. No sense 'guessing' and having to order stuff twice, or three times.

Rene

 

[blazinzuk]

Really best to take it for a drive with a GPS unit on board. No sense 'guessing' and having to order stuff twice, or three times.

Rene

You are probably right. I have a couple of those speedo adaptor box things kicking around and was kind of hoping one would get me close.