RPM's @ 75MPH with 3.73's and 315's?

[Devil Black Diesel]

Can someone tell me what your RPM's are at 65mph and 75mph with 3. 73's and 315's? I have an '01 auto with 4. 10's and 315's and I'm running approx 2200rpms at 75mph with GPS (my speedo actually reads about 70mph). I'm looking to put 3. 73's in my truck and I'm thinking my RPM's might drop approx 200 at that speed which would be perfect. If nobody knows, can someone do me a favor and record your RPM's with a GPS at 65mph and 75mph? I usually drive about 80mph out here on the Freeways and I want to lower my RPM's.



Is there any reashon why my '01 with 3. 73's wouldn't have the exact same rpm's with a 3rd gen running 3. 73's and 315's?



I know there are RPM calculators but I want some hard numbers from another truck.



Thanks.

 

[klenger]

If you have Excel, you can play with the numbers till the cows come home with the worksheet I have on my website at http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls



If you can't run Excel, I'll try to run the numbers when I get a few spare minutes.

 

[JCleary]

Is there any reashon why my '01 with 3. 73's wouldn't have the exact same rpm's with a 3rd gen running 3. 73's and 315's?

Only if your transmission has different ratios. So a G56 is different than a NV4500 or NV5600.



On edit:



Oops, I see you have an auto. I think they're the same.

 

[bpenrod]

How much does swapping to 3. 73's run? I have 3. 73's and a Gear Vendor and that is great for buzzing down the freeway. 1800 rpm at 80 mph and 20 to 21 mpg. The gear vendor can go from truck to truck pretty easy if you decide to sell. I had a new driveshaft made when mine was installed so I can swap back if I sell. Just another idea for you to think about!

 

[Devil Black Diesel]

If you have Excel, you can play with the numbers till the cows come home with the worksheet I have on my website at http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls



If you can't run Excel, I'll try to run the numbers when I get a few spare minutes.

Klenger,



I've seen these calculators but the numbers are not matching up with the numbers I get in my truck. I'm 100% sure I'm not doing 80mph at 2200, it's more like 77mph. That's why I want someone else with 3. 73's and 315's to take a look with a GPS and let me know.



Thanks again.

 

[Devil Black Diesel]

How much does swapping to 3. 73's run? I have 3. 73's and a Gear Vendor and that is great for buzzing down the freeway. 1800 rpm at 80 mph and 20 to 21 mpg. The gear vendor can go from truck to truck pretty easy if you decide to sell. I had a new driveshaft made when mine was installed so I can swap back if I sell. Just another idea for you to think about!

I received a quote today for $1000 an axle (parts and labor). I haven't shopped around yet and this was the first quote I received. How much is the gearvendor bpenrod?



I know, I know, I'm sure someone will chime in and tell me it's not worth the 2K to swap gears because it will take me X amount of months/years to recover my investment but I don't care... plus, I want more gear on the top end at the dragstrip too.



One last question for everyone... can I swap gears with a 3rd gen or are the axle's different? If yes, anyone in SoCal want to swap their 3. 73's for my 4. 10's?



Thanks

 

[lawdog]

My truck has 3. 73 and 315's with a 48RE auto. . 70 on speedo is right about 2000 rpm 75 about 2100 rpm That is Speedo speed not GPS speed. Tire calculator said add 8. 6 or 8. 7% to speedo speed for actual...

 

[JApol]

PLug these into the gear ratio on the spread sheet and everything should come out right, its what I had to do for my spreadsheet as the numbers were not coming out right.

Description Automatic 48RE Gear Ratios



1st 2. 45



2nd 1. 45



3rd 1. 0



4th0. 69

 

[bzingre]

315 with NV5600 and 3.73s

2000 RPM = about 75. 5 mph

1730 RPM = About 65 mph

calculations equal gage readings after speedo calibration for big tires withing 1 MPH.

 

[klenger]

For what's it worth, here's the numbers I come up with using the Excel worksheet. Note that the calculations assume 31575R16 tires for a 2nd gen.



http://www.klenger.net/misc/315-tires-47re.gif



If anyone sees any flaws in the calculations, please let me know and I'll look into it.

 

[Devil Black Diesel]

Thanks Everyone... can I swap gears with a 3rd gen or are the axle's different? If yes, anyone in SoCal want to swap their 3. 73's for my 4. 10's?

 

[JVolpe]

My "Pinion Factor" has been reprogrammed for 315s and GPS checked at 70mph and is very close to exact. With 3. 73 gear my rpm / mph.



1800 rpm = 70mph

1900 rpm = 74mph

2000 rpm = 78mph

 

[steved]

Thanks Everyone... can I swap gears with a 3rd gen or are the axle's different? If yes, anyone in SoCal want to swap their 3. 73's for my 4. 10's?

Your 01 will have a Dana 60F front axle with a Dana 70 rear axle (since it is an auto and assuming 2500) or Dana 80 (assuming a 3500). The new 3rd gens use American Axle Manufacturer (AAM) axles and they are different.



IMO, since you have the Dana axles, I would step back to 3. 55s skipping the 3. 73. most guys I have read about prefer the 3. 55s to even 4. 10s except when towing or running really big tires.



steved

 

[Devil Black Diesel]

Thanks everyone, I guess I'm going to start shopping around for some 3. 73's. JVolpe's RPM's are exactly what I'm looking for.

 

[daytripper63]

If you have Excel, you can play with the numbers till the cows come home with the worksheet I have on my website at http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls



If you can't run Excel, I'll try to run the numbers when I get a few spare minutes.

I know this is an old thread but I was doing a search on RPM vs MPH and came across this calculator of Klenger's and with all the post I see about people changing tires and wanting to know what the end result is going to be I thought it was worth bringing back to life... I dont know if Klenger has this posted somewhere that is easier to find than a search but maybe the moderators can sticky it or put the Gear/wheel calculator in a more accessable spot on this site, if thats ok with Klenger

P. S. Thanks Klenger it was exactly what I was looking to find out

 

[CBrahs]

I have an auto, 3. 73's and 37in tires and I am at about 1700 RPM going down the freeway. I don't know actual speed because they can't calibrate for that size of tire (at the dealer anyway) and I don't have GPS yet.

 

[daytripper63]

I have an auto, 3. 73's and 37in tires and I am at about 1700 RPM going down the freeway. I don't know actual speed because they can't calibrate for that size of tire (at the dealer anyway) and I don't have GPS yet.

Did you check the Gear/wheel calculator? here http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls

If your tires are really 37" tall with a 48re automatic and 3. 73 gears at 1700 RPM you are driving 73MPH if in 4th/overdrive



Axle Ratio 3. 73 Enter the axle ratio here

Tire Specs

Dia 37. 00 Optionally enter to manually override with Mfg tire specs

Cir 116. 24 Calculated circumference in inches

Revs/Mi 545. 08 Optionally enter to manually override with Mfg tire specs

K 0. 030 Calculated Mi / Drive Shaft Rev. * 60

47RE/48RE 4 Speed Automatic

Gear 1 2 3 4

RPM 2. 450 1. 450 1. 000 0. 690

1000 12 20 30 43

1100 13 22 32 47

1200 14 24 35 51

1300 16 26 38 56

1400 17 28 41 60

1500 18 31 44 64

1600 19 33 47 68

1700 20 35 50 73

1800 22 37 53 77

1900 23 39 56 81

2000 24 41 59 86

2100 25 43 62 90

2200 26 45 65 94

2300 28 47 68 98

2400 29 49 71 103

2500 30 51 74 107

2600 31 53 77 111

2700 33 55 80 115

2800 34 57 83 120

2900 35 59 86 124

3000 36 61 89 128

3100 37 63 91 133

3200 39 65 94 137

3300 40 67 97 141

 

[CBrahs]

I have not had a chance to play with it. I downloaded it but I have been to dang busy. Will play with it this weekend. I will measure actual height of the tires and see what kind of speed I am traveling. Should borrow my buddies GPS and compare the chart vs GPS .

 

[gsbrockman]

If you have Excel, you can play with the numbers till the cows come home

:-laf :-laf :-laf



I'm glad that this showed up with a minimal amount of GOOGLE effort. :-laf



Thanks, klenger..... I remember this from a few years ago and I have a friend that is into pulling trucks and he will play with it 'til the cows come home. :-laf