Sorry I'm kinda reposting the same question, but I didn't want this to get lost in the other post. I did my own calculations and got these figures:

My tranny gears are:
1-4.03
2-2.37
3-1.50
4-1.00
5-0.76

The calculations show that with my 15 inch tires, at 2500 RPM, 3.42 rear gear ratio, and in 5th gear (.76 tranny gear ratio), I should be going about 86 MPH. But when I'm on the freeway in 5th gear going 2500 RPM, my speedo shows that I am going around 75MPH. And at this speed I am keeping pace with the rest of the people in my lane, and if I slow down 10 MPH, people start backing up behind me. So I want to know what's up. Are the calculations off a bit, or is my speedo way off mark? Can wind resistance and weight really drop 10 MPH off the speed? And yes I tried halving my 15 inch wheel radius which is 7.5, and I got some rediculous answer like 45 MPH, so I figured they meant diameter in that area.

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ICQ #: 77308896
AIM: Ezekiel2sc
2.8L MPFI w/ K&N filters & homemade ram air
5 speed manual
3.42 rear axle
180W Clarion CD Deck
Pioneer 4*6 in front
Polk 3 way 6*9 in back