7upedition

Whats up guys? I have 3.73 gears in my 1990 5.0 HO Automatic, it has a 8 tooth drive gear, and I installed a 23 tooth speedo gear. It should be accurate based on all the charts I found in the stickies and elsewhere. However when I am in fourth gear (OD) at 2000 rpms, my speedo reads 62mph, but people are passing my like crazy and I feel like I'm going slower, more like 55mph. My question is, does anybody have a calculator or a link to calculate rpms at mph based on gears and tiresize? My tires measure 24 3/4" tall and their size is 245/45/R17. Thanks in advance guys.

luckythirteen13

my speedo reads 60mph-ish at 2000rpms so that sounds about right. maybe you just have a lot of speeder where you live lol

grabbem88

+1...they prob. see a stang and think cool i'm passing it....now i have a .68 o.d. and at 80mph i'm right at 2500rpm.

PX429

Clicky Clicky

samseed101

The above calculator will work fine as long as you know which gear is your 1:1 gear in your trannyl if you don't know, then You can use this link and enter your info and get exactly what you're looking for.

7upedition

Thanks a lot for the links, i thought i was going crazy but it seems to all add up right, anyways i think im gonna tail the wife at a set speed and see how accurate i am to her truck just for a lil reassurance. Thanks again

AdderMk2

a 245/45/17 tire should actually measure 25.6" i think you botched your measurment alittle bit