what gear ratio do i have?

Discussion in 'Fox 5.0 Mustang Tech' started by txgunrunner, May 10, 2005.

  1. does anyone know a way to tell what gear i'm running without taking the cover off the pumpkin. a buddy said to count the wheel turn versus the driveshaft but couldnt quite remember how to do it. thanks for the help.
  2. Do a search.
  3. count the amount of times the driveshaft rotates (mark with chalk) for one tire revolution.
  4. Yep.
  5. Double yep
  6. A.) Measure your tire diameter from the ground to the top.
    B.) Go out on the road and drive a steady 60 mph in 4th gear. Note the RPM you are turning at that speed.

    Ok with those two bits of info calculate the following....

    C.) Multiply your tire height times the RPM. Write that down.

    D.) Now multiply your speed you noted that RPM at (60 in my example) by 336 (336 is a mathmatical constant). Write that down.

    Now divide the answer from C by the answer from D. That's you gear ratio. If you get like 3.30 it's a 3.27 gear. It's not perfectly accurate due to human error, tach error, maybe speedo error. But will get you close.

    This is good if you don't want to jack the car up and count drive shaft and tire revolutions.

    Here's the formula with my car as an example.

    (26" Tall Tire X 2900 rpm) / (60 mph X 336) = 3.74

    I run 3.73 gears.
  7. :stupid:
  8. i think its a little easier just to mark the driveshaft and spin the tires once.
  9. if his gears are factory cant he just check his door tag?
    91 lx
    that would take no work...other than opening the door...?? :shrug: i dunno maybe im wrong...
  10. I dont think he knows if his gears are factory or not.Lotta people change them out then sell the car.It happened to me.When I bought my 98 I didnt know what gears where in it.Turns out it has 4.56s. :nice:
  11. ahhh i see.....duh! :doh: