[Scoobert]

I seen several post with people asking what RPM they would have with certain tires and rear axles. Since all the links we give out our normally for a 1:1 Ratio (ie a 5 speed in 4'th or a 6 speed in 5'th) I thought it would be handy to to make up a couple spread sheets with both tranny's listed at final ratio (ie .78 on the 5sp and .84 on the 6sp).
I hope this can help some people

*NOTE* Both transmissions in highest gear and at 65 MPH






*Information and Ideas gather from http://www.4lo.com/ a nice site with lots of calculators *

[orangetj05]

not to be rude but your chart isn't very acurtate for the 6 speed with 31 my runs about 2500 at 65.

[Dogman]

I think it's something like:

mph = Miles Per Hour
x = Overdrive Ratio
y = Gear Ratio
z = Tire Diameter

((mph * y * 336) / z) * x = RPMs

[Scoobert]

Originally Posted by 04TJ

not to be rude but your chart isn't very acurtate for the 6 speed with 31 my runs about 2500 at 65.

Is that with your speedo having the correct gear in it to compensate for the 31's?

by this fomula


you should have



? X 31
------------------= 65
3.73X.84X1X336

Which would be the same (I think, any math majors here?) as saying

3.73 X .84 X 1 X 336 X 65 (68429.08) / 31 = 2207 RPM

[35sUnlimited]

The chart may assume a 31 inch tires is actually 31", when in reality it is probably more like 30". Every tire brand varies slightly. Even the same brand will vary depending on the size rim it is on.

I think the charts are pretty/cool useful. Just have to measure your own tire to see actual diameter.

This link to a calculator on Randy's site is cool beacause you can put in exact numbers. http://www.ringpinion.com/content/calculators/RPM.asp

Use the second one down.

[k8ysv]

For a 31 inch tire and 4.56 gears (which is what I looked at because that's what I'm running)...

How is it that @65 MPH in top gear for a 5-speed, the listed RPM is 2506, but in top gear on the 6-speed it's HIGHER (2699 RPM)? This doesn't make much sense.

Or is it just me?

[Scoobert]

Originally Posted by k8ysv

For a 31 inch tire and 4.56 gears (which is what I looked at because that's what I'm running)...

How is it that @65 MPH in top gear for a 5-speed, the listed RPM is 2506, but in top gear on the 6-speed it's HIGHER (2699 RPM)? This doesn't make much sense.

Or is it just me?

Nope its not you. The 6 Speed actually has a lower ratio @ .84 (higher #) in high gear then the 5 speed which is a .78.

[airduds]

here's a good calculator

http://intercotire.com/site58.php

[coorsmgood]

so where do you find your tc and tranny ratios?

[coorsmgood]

I like your idea of making ONE good chart scoob...let me know when you get this all worked out!

[JeepJohnson]

NSG370(6 speed) 1:4.46, 2:2.61, 3:1.72, 4:1.25, 5:1, 6:0.84, R:4.06

NP231 HR:1, LR:2.72

NP242 HR:1, LR:4

[iismet]

2005 SE 2.4L
4.56 Gears
Corrected Speedo Gear
32" Mud Rovers @ 25 psi

6th gear:

2600 rpm =>60 mph
2800 rpm =>65 mph
3000 rpm =>70 mph

[JeepJohnson]

Better recheck to make sure you have the right speedo gear, with 4.56s and 32s you should be turning 2600 at 65.

[hvac59]

2100 rpm's @65 (per GPS) with 3.73's/33 BFG MT @22 psi
hvac59

[JeepJohnson]

Originally Posted by hvac59

2100 rpm's @65 (per GPS) with 3.73's/33 BFG MT @22 psi
hvac59

When your speedo is off I'm assuming it throws your tach off too right? I just went from the stock 27s to 29" MT/Rs and my tach is reading the same RPMs as it was before. BTW, 2100 is right on the money, so my math ain't off.