RPM's vs MPH

[Old Smoky]

Someone told me that 33" tires, 3. 54's, an NV4500, and 3600rpm add up to 135mph. Remember guys, safety first.



Mike

 

[BushWakr - RIP]

All I can say is ... . Mikey' don't be a girl...



I can also attest to the fact that 105 mph I do NOT have any two tires on the ground at one time..... they kinda... take turns...



pb.

 

[Marty1]

At 70MPH with 4. 10 gears & in overdrive my truck is at 1600RPM.

Don't believe me Pastor... Get those mechanics off it & go take her for a ride... you'll see!

 

[Greenleaf]

Yes yes yes..............

... ... ... I know. My tires have thrown the speed o off. 6 MPH to be exact. When I said 55mph, my speed o is showing 61.



I have driven past our local radar trap/sign/wagon enough to know it's off 6 mph. They set it up in town near schools. When it says 35, mine says 41.



When I return from out west... ... . (Indiana ) I'll post my rpm @ 70 mph... ... ... . providing the wife can hold me there long enough to obtain said reading



-S

 

[MMiller]

No girl here! Last night I went to town to fill it with fuel, and checked on the way home. Yep is still runs 95!



Michael -restricter screw still installed-Miller

 

[JFitzgerald]

Originally posted by Daniel John

If your like me and don't have a tach or you want to check the accuracy of your tach here's an easy formula.

RPM = (MPH x Gear Ratio x OverDrive Ratio x 336) / Tire Diameter

Am I right that 5th gear is 0. 77 for the Getrag? If so, mine figures out to 1779 rpm @ 55 mph, and 2264 rpm @ 70 mph. That's with 4. 10s and 32. 8" tires.

 

[Grey Wolf]

JFitzgerald,



You are correct 5th is 0. 77



One of our members had this gear calculator on his site, its set up for the NV4500, NV5600, 47RE and 48RE, but it can be changed to fit your ratio's.



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

 

[JFitzgerald]

Thanks Grey Wolf, I'll see if I can plug the Getrag numbers into that spreadsheet.

 

[MMiller]

Gonna jack this thread a little with a question for the auto guys. With 3. 55's in drive what revs are you turning at 55? What about drive with 4. 10's? Will 4. 10's even run 55 in drive? 518's will be the same in drive as my 727. I'm trying to figure out what to do for gears in my 90. Thanks



Michael

 

[MRickard]

Mine has no power up high - if it downshifts into drive from overdrive, it is like the brakes were put on, and when it upshifts, it is like 'afterburner' - kind of strange, but then again the torque curve (at least if it is the same one banks posts for the power pack on my engine) totally dumps off. It kinda sucks. I would go with tall gears. Only drawback - when I put taller tires on, the transmission just seemed to slip more and I did not get ahead really - so what I would do, is gear it for the rpm you would cruise at to be atleast at the stall of the converter, which feels like around 1800. I would like it to be 1400 (peak torque in my engine). But get the peak torque from your engine, and gear it for that. The stock TC sucks big time, and the better stall (lower) cost so much you do not make any savings with the fuel efficiency, just heat.