Someone on here had a calculator for our trucks to calculate what RPM, MPH and so forth......that you would achieve with a certain gear and trans ratio that you are running. I would love for someone to help me find where to download this site to go to and download this calculator!!

Thanks Fellows!!!!!

James

 

http://www.classictruckshop.com/garage/shopmathrpm1.asp

 

I always just do it myself with a calculator. I came up with this a while back...

You can determine engine RPM from some calculations.

R = Engine RPM
S = Speed in MPH
G = Rear End Gear Ratio
T1 = Transmission 1st Gear Ratio
T2 = Transmission 2nd Gear Ratio
T3 = Transmission 3rd Gear Ratio
T4 = Transmission 4th Gear Ratio (OD)
V = Tire RPM at 1MPH
-------------------------------------------------------
4L60E Ratios 4L80E Ratios
T1 = 3.059 T1 = 2.482
T2 = 1.625 T2 = 1.482
T3 = 1.000 T3 = 1.000
T4 = 0.696 T4 = 0.075
-------------------------------------------------------
Find the RPM at a known Speed using the following:

R = V (S (G * T))

Find the Speed at a known RPM using this:

S = (((R / V) / T) / G)

-------------------------------------------------------
Finding V is a little more complicated.

D = Tire Diameter in inches
W = Wheel Diameter in inches
C = Tire Circumference in feet
M = Tread Width in millimeters
I = Tread Width in inches
A = Sidewall Aspect Ratio
V = Axle RPM at 1MPH
L = Distance covered in one minute at 1 MPH. (88 feet)
pi = 3.14

To find the Axle RPM at 1 mile per hour use:

V = (L / C)
V = (88 / C)

Find C in several ways - if tire diameter is known, use:

C = (pi * D) / 12
C = (3.14 * D) / 12

If Diameter is unknown, use Tire Specifications:
First convert Tread Width from Millimeter to Inches

I = M / 25.3886

Then find Diameter in inches.

D = W + (2 (I (A / 100)))

or

D = W + (2 ((M / 25.3886) * (A / 100)))

-------------------------------------------------------
For example, To find the engine RPM of a 3/4 ton Suburban
going 80mph in overdrive with a 4.10 rear, 4L80E and
245/75 R16 Tires, use the following:

R = (88 / ((3.14 (W + (2 ((M / 25.3886) * (A / 100)) )) /12)) * (S (G * T))

R = (88 / ((3.14 (16 + (2 ((245 / 25.3886) * (75 / 100)) )) / 12)) * (80 (4.10 * 0.75))

R = (88 / ((3.14 (16 + (2 (9.65 * .75))) / 12)) * (80 * 3.075)

R = (88 / ((3.14 (16 + (2 * 7.2375)) / 12)) * 246

R = (88 / ((3.14 (16 + 14.475)) /12)) * 246

R = (88 / ((3.14 * 30.475) /12)) * 246

R = (88 / (95.6915 / 12)) * 246

R = (88 / 7.9743) * 246

R = 11.0355 * 246

R = 2714 engine RPM (with torque converter locked)

 

Thank you very much sirrrrrrrrzzzz!!!! This will help greatly!!!

 

There is also a calculator on bowtieoverdrives.com

http://www.700r4.com/speedoCalc/rpmcalc.shtml

Mike

 

Or try http://www.tciauto.com/tech_info/calculators.htm#9

 

Thank ya'll for all of your help!!!!! This info has been very helpful!!!

Thanks

James

 

So with the calcs I've done so far, with a 4:56 gear, 4L60E and a 285 tire(31.46) traveling @ 80mph, my rpm's will be approx. 2730???? What is ya'lls opinion??

 

Correct.
I run 4.56:1 gears also, and with 30.4" tires (formerly 29.4") but I get away with it because of the extra overdrive. That's a lot of RPM to be spinning to just cruise. Try sustaining 2700RPM in third gear and see if you're comfortable making that much RPM on the long haul.

(I can't tell if you have the 4.56:1 gears already, hopefully this helps.)

 

No. I don't have the 456's yet. I was just trying to plan ahead and do my homework. What do you mean by the extra OD??? You must have a gear venders or something like this....???....My calcs were with the a 4L60E trans. Why do you suggest I do a calc in third gear??? I kinda don't understand this question cuz I won't be in third gear in a long haul situation. I will be in OD. If my rpm's are somewhat low @ highway speeds, it shouldn't matter what they are in thrid gear cuz this will be @ the track anyways. I want to try to keep my rpm's below atleast 3000rpm @ lets say 80mph in OD. This was my goal. I can live with this. Yes...all of this info that you guys are suggesting is helping very much!!!