Under/Overdrive: (bolt-on drive only)
*
Transmission: 1st Enter all values
2nd on this form in
3rd whole or decimal
4th format only -
5th no percentages.
6th
Reverse
*
Transfer Case: High
Low
*
Differential Gear:
Common Transmissions:
SM420
SM465
NP435*
NV4500 (92-94)
NV4500 (95+)
NV4600
T18*
T19*
T4
T5
T90*
T150
T176
SR4*
AX15
46/47Reh
NV3550
T177
Series II
Series IIA A/B
Series IIA C
Series III
TH350
TH400
200-4R
700R4
C4
C6
T904
T999
TF727
reset

Common Transfer Cases:
Dana18
Dana20*
Dana300
NP203
NP205
NP207
NP208
NP231
NP241
NP242
FJ-40
Series II
Series IIA
Series III
Spicer 23
Timken (GM)
reset
note: transmissions and tcases with an asterisk (*) were available with multiple gear sets


  • This program will calculate the engine RPM for tire diameters of 26 through 44 inches in combination with road speeds up to 100 MPH or a redline of 7000 RPM.
  • Do not fill in the "Underdrive/Overdrive" field unless you have a "bolt in" overdrive! Overdrive transmissions are already accounted for.
  • NOTE! Where possible I have included Reverse gear ratio in the 5th gear field so dont let that confuse you :-)
  • WARNING! Depending on your browser and CPU speed, this script may take some time to complete!
  • Finally, I don't know who to give credit for this bit of javascript. I found it as uncopywritten material so I snagged it, modified it, cleaned it up and integrated it into this site. I will continue to update it adding transmissions as I find specs. If you have a trans or tcase you'd like included please send email to florida4x4-@-florida4x4.com (remove the hyphens from my email address before sending). Thanks.