Gear/Speed Calculator

[klenger]

I worked up an Excel spreadsheet to calculate vehicle speed based on tire size, axle ratio, and transmission type. All you need to do is input the tire size specs and final axle ratio, and the spreadsheet will calculate vehicle speed for all three Dodge transmissions (6 speed, 5 speed, auto). You can also override the Revs/Mile calculation with a number from the tire manufacturer to get more accurate results. It appears that Revs/Mile are not an exact mathematical result of tire size, but varies with speed. Let me know what you think of it.



Ken



http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls

 

[TGaines]

awesome calculator. I was just about to ask someone if they knew what a 3. 73 was like in a 96 auto. Thanks

Travis

 

[Hutchew]

Different results with these calculators:

http://www.f-body.org/gears/

http://www.fbody.com/calc.htm

http://www.dirtroad.com/gears.htm



Using 315/75/R16 (34. 8" diameter per BFG), 3. 54 ratio, nv4500 transmission(0. 74 OD Ratio), about a 10 mph difference at 1900.



I have only paced my truck against a new Ford, but plan on doing the GPS thing to see how far off it really is. Right now it appears my truck is within 1-2 mph of correct. I do run about 74-75 mph @ 1900-1950, BTW. Maybe you have a little glitch in your data. Or maybe my Isspro tach isn't right. Lot's of variables

 

[klenger]

I'll have to recheck the formulas. I was in kind of a hurry and have been known to make mistakes.

 

[Chris Bethurum]

It's probably your tac and or a slight difference in actual circumference of the tires as opposed to just using the listed diamteter from the manufacturer.



I notice . 75 listed in the chart for 5th ration in a NV4500.



I have seen . 74 listed on the Gear Vendor site. I have also seen . 73 listed on a site that deals with NV4500 conversions etc. My guess is the . 74 is correct. ?





Nice chart, I've had some fun playing with it. I am used to doing it the long way or relative to some tire/rear gear/rpm stuff I have memorized. The chart is more better.



Chris

 

[klenger]

Thanks for the nice comments. Keep in mind that there are two ways to enter the tire specs.



1) is to enter the tire size and let the calculator figure out the revs/mile



2) is to enter the revs/mile directly, which overrides any tire specs entered. If you can get the revs/mile from the tire manufacturer, you should get more accurate results.



I might play with the worksheet a bit to make this a bit more obvious. You can also enter different transmission gear ratios by unprotecting the worksheet, and therefore use it for non-Dodge CTD vehicles.



enjoy

 

[klenger]

I reworked the worksheet to make it more obvious how to override tire size information and also added detailed instructions. I checked the results against an example on Fritz's webiste at http://dodgeram.org/tech/specs/axle/5sp_vs_6sp.htm and the numbers seemed to match, so I think the math is OK. If you downloaded the previous version, you may want to download the new one at http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls.

 

[TN farmer]

When you go to 4LO what is the reduction in the transfer case?

 

[klenger]

2. 72



See http://dodgeram.org/tech/specs/tranfer_case.htm