This calc can be used to find any (one) missing value.
Solve for your MPH.
Solve for your RPM.
Solve for your Differential Ratio.
Solve for your Tire Diameter.
Solve for your Transmission Ratio.
Solve for your Transfer Case Ratio.
Solve for your Crawl Ratio.

If your tires are bigger than stock you probably, like myself, have spend a lot of time trying to WAG (wild ass guess) your actual MPH when going down the road. If you know your gear ratio and tire size you can get a fairly close idea here. Fill in all entries except the one you want an answer to (in green section).

If you'd like to find your overall crawl ratio, enter the Diff/Trans/TransfCase ratios. Remember, the yellow section (crawl ratio) is only for output only, do not type anything in this box.

Clicking on the Transmission or TransferCase links will jump to bottom of this page.

Formulas used


and

These calculators are color coded by function
All fields Required	Leave ONE field blank	Supply ONLY one field	Results Only

Popular Transmission Ratios Manual Transmissions: AMC SR4 (Borg-Warner) Jeep 1st 2nd 3rd 4th 4.07 2.39 1.49 1.00 SM 420 1st 2nd 3rd 4th 7.00 3.60 1.70 1.00 SM 465 (MUNCIE) GM, Chevy 1st 2nd 3rd 4th 6.55 3.58 1.57 1.00 T-176 Jeep 1st 2nd 3rd 4th 3.52 2.27 1.46 1.00 T-177 Jeep 1st 2nd 3rd 4th 3.82 2.29 1.46 1.00 T-178 Jeep 1st 2nd 3rd 4th 3.00 2.08 1.46 1.00 Mazda 5-spd Ford, Mazda? 1st 2nd 3rd 4th 5th 3.40 2.20 1.50 1.00 0.79 NV3500 Chevy 1st 2nd 3rd 4th 5th 4.02 2.32 1.40 1.00 0.73 NV4500 Chevy 1st 2nd 3rd 4th 5th 5.61 3.04 1.67 1.00 0.73 ZF S6-650 Chevy 1st 2nd 3rd 4th 5th 6th 5.79 3.31 2.10 1.31 1.00 0.76 Automatic Transmissions: TH 350 Chevy 1st 2nd 3rd 2.52 1.52 1.00 TH 400 GM, Chevy, Jeep 1st 2nd 3rd 2.48 1.48 1.00 TH 700R4 GM, Chevy 1st 2nd 3rd 4th 3.06 1.62 1.00 0.70 4L80-E Chevy 1st 2nd 3rd 4th 3.10 1.48 1.00 0.75 Allison 1000 Series Chevy 1st 2nd 3rd 4th 5th 3.10 1.81 1.41 1.00 0.71 C-4/C-5/C-6 Ford 1st 2nd 3rd 2.46 1.46 1.00 Ford AOD Ford 1st 2nd 3rd 4th 2.40 1.47 1.00 0.67 TORQUEFLITE 727 Jeep, Dodge 1st 2nd 3rd 2.45 1.45 1.00

Popular Transfer Case Ratios     Dana 300 Jeep Lo Hi 2.62 1.00 Borg Warner 1356 Ford Lo Hi 2.69 1.00 DANA/Spicer 18 Jeep Lo Hi 2.46 1.00 DANA/Spicer 20 Jeep, IH (TC-145), GM, Ford Lo Hi 2.00 1.00 NP 203 Chevy, Ford, Dodge Lo Hi 2.00 1.00 NP 205 Chevy, Ford, Dodge, IH Lo Hi 1.98 1.00 NP 207/208 Jeep, Chevy, Ford, Dodge Lo Hi 2.61 1.00 NP 231 Jeep (YJ) Lo Hi 2.72 1.00 Toyota (67-74) Land Cruiser Lo Hi 2.31 1.00

Formula used

These calculators are color coded by function
All fields Required	Leave ONE field blank	Supply ONLY one field	Results Only

Most of the formulas dealing with gear ratios will want a tire diameter (measured in inches). This formula is a quick way to get the tire diameter of those metric tires that are common on just about everything stock. For example a LT265/75R16 would be around 31.6 inches tall and 10 inches wide. Enter any three of the numbers into this form to solve for the fourth. "LT" means Light Truck and "P" means Passenger tire. The bigger number (on the left) is the Section Width. The number to the right of the slash ("/") is the Aspect Ratio (percent of width). The "R" means Radial tire and the last number, far right, is the rim diameter (in inches!).

Formula used



Width in inches = section width / 25.4

Section Height in inches = Width in inches X Aspect Ratio (%)