OK, So you want to know how what speed you will be going in at different RPM's with different gearing... Well here is how to do it with a simple math equation...

(yes wat we learnded in skool wuz gud 4 sumting)

First thing we need to do is figure out how many times your tire size will rotate per mile.


A simple tool to use...

Tire Size Calculator:


Stock Tire Size (245/45/18) will rotate: 756 Times per mile


Here is the equation...

RPM / Final Drive Gear / Tire RPM x 60 = Speed


Example in 5th Gear on a 6MT (1:1):
Example in 4th Gear on a 5AT (1:1):

3000RPM / 3.538 FD / 756 TRPM x 60 = 67.3 MPH
3000RPM / 3.917 FD / 756 TRPM x 60 = 60.8 MPH
3000RPM / 3.357 FD / 756 TRPM x 60 = 70.9 MPH


If you wanted to see what you would be doing at say 5000 RPM in 2nd gear here is how to figure that:

First you must find the gear raito for 2nd gear: 2.324

Multiply FD size by 2nd gear ratio: 3.538 x 2.324 = 8.22

8.22 is now the overall final drive ratio to the wheels...


Here is an exmaple of 5000 RPM in 2nd Gear with a 6MT trans:

3000RPM / (3.538 FD x 2.324 G = 8.22) / 756 TRPM x 60 = 28.9MPH
3000RPM / (3.917 FD x 2.324 G = 9.10) / 756 TRPM x 60 = 26.2MPH
3000RPM / (3.357 FD x 2.324 G = 7.80) / 756 TRPM x 60 = 30.5MPH


Gear Ratio for 6MT Transmission:

1st: 3.794
2nd: 2.324
3nd: 1.624
4th: 1.271
5th: 1.000
6th: 0.794


So for fun lets do one more:

6th Gear in 6 speed manual car at 7200RPM:

7200RPM / (3.538 FD x 0.794 G = 2.80 FD) / 756 TRPM x 60 = 204.08MPH
7200RPM / (3.917 FD x 0.794 G = 3.11 FD) / 756 TRPM x 60 = 183.73MPH
7200RPM / (3.357 FD x 0.794 G = 2.66 FD) / 756 TRPM x 60 = 214.82MPH


This will work for any combination of RPM / Gear Size / Tire Size...

Enjoy!

 

Woops! My trusty co-worker Eddie Takahashi pointed out to me...

"First thing we need to do is figure out how many times your tire size will rotate per hour."

should be:

"First thing we need to do is figure out how many times your tire size will rotate per MILE"

TYPO!!!!!!!!!!!

 

cool... right now I'm geared for 201.25mph

So theoretically I've got a 200mph car... I think that puts the Z in supercar territory!



Ok ok ok....it may not do it... but it's geared for it.

 

haha...

Its more just to show what the gearing is capable of... aerodynamicaly is what you have to worry about at that speed I would think...

but you can figure the MPH at the top of each gear if you wanted to...

 

Updated original post.

 

haha thanks that makes it make sense now...

 

Should be a sticky

 

http://locost7.info/gearcalc.php