I recently installed a 3.40 locking rear differential in my chev p/u. before it had 3.08 gears in it, My question is, the higher the gear ratio, the slower your going compared to your spedometer? I'm asking this because i looked on the tech board and i did that calculation from 3.8 to 3.40 and it showed up as 91%? So does that mean when im going 65mph im actually going like 59?

 

Come on guys, i need some input*

 

That's sounds about right to me.
I went from 2.73 to 3.73.
What i did was have a friend with an accurate speedo drive next to me at a certain mph. Then we did it again at another speed. I used 35 and 70mph.
At 35, i read 45, and at 70 i read 90.
Then i devided 35 by 45 and got like .777, and the same for 70 by 90=.777.
They should come out to the same. Then you have your accuracy percentage and can find out your actual speed for any mph.
This is just how i did it, i'm sure there are simpler ways- like the tech board.

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'88 RS (originally 2.8)
New 350, .040 over, ported vette L98s, ported stock tpi.
Old 305 injectors & chip
TES headers, 3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
(Damn the 2.8!)

 

thabks alot, i thought i was going really slow on the highway when everyone was passing me