Oh yes...

Based on the great work by JPOP, I was running some numbers for myself based on a 6-speed JK. Basically I wanted to know which gear with a 3.21 ratio would be equivalent to 6th gear at 70mph for a 4.88 or other gear ratio, based on engine rpm only. I know that re-gearing will address acceleration and driveability, but at a set cruise speed, we manual transmission drivers have better control by using our 6 speeds. There are various threads that have talked about getting the JK to sit in a particular power band, so this new chart tries to address that issue. Planman has been very helpful to a lot of people on this thread.



In other words, say I have 3.21 gears right now and 33" tires. If I go to 4.88's, my cruising rpms at 70mph would be 2923. If I shifted to 4th gear with my 3.21, my rpms would be 2862, approximating quite closely the "effect" of having better gearing.

Revs above redline have been deleted.

Anyhow, this could be completely useless to anyone other than me, or open up some discussion. Look forward to any comments.

Cheers!

 

This could be completely fantastic for someone like me as well. I am in the exact same boat as you 3.21 thinkin' of of goin' to 4.88's and 33's maybe 35's. Same province even. Thanks everyone involved in this. I am guessing this again is based on real world dimensions ie. I would have to buy 37" KM2's to get 35" actual diameter tires?

 

I based the rpms on jpop's chart, which is based on real-world tire diameters for 6th gear. Then I used the actual gear ratios for 1st through 6th to calculate the rpm differences.

 

Now I can see how far off my speedo is!

 

so if i had a 4in lift with my 2dr 6spd on 35's and im on the highway a lot should i get 4.56s'??????????????

 

Do you have a Garmin or GPS maps on ya phone, that will give you a very accurate MPH - I checked mine on a Garmin after a Superchips tire size change (measuring the actual size) and it was 'spot on'.

 

Looking at re-gearing Bill? I am hoping my 3:73 6spd will handle 35's for a year as the fund's for both 35's and gearing/rear locker will not happen this spring...it's one or the other.

 

Not at the moment. I was hoping to map out which gear on my 3.21's would equate to running another gear set, so I ended up with this chart.

Basically it says if I want to see what running 32's and 4.88s would feel like in my six speed in 6th gear (3014 rpm), then I could try to zoom along in 4th gear (2951 rpm) and be reasonably close.

Bunch of other expenses for me too - so playing will need to be delayed for a bit.

Are you running 35's now Mike? The chart will tell you that your 33's in 5th gear with 3.73's will feel like your future 35's with 4.88's in sixth, less around 100 rpm.

 

No 35's yet! I am waiting till Spring when all the snow, salt and gravel are off the roads before I put on my nicer rims and that's when I will get 35's not sure if I will head down south across the border for tires yet...but it is looking like I may have a holiday planned in Washington state in April.

I figure I can run around in 5th on the highway with 35's and live with it for awhile. I am sure I will have to drop it into 4th a few times on these mountain passes! But I figure a 100-150RPM difference will not be a deal breaker for 35's and 3:73 gears.

 

Good point. That would be way easy. I have no idea why I haven't done that yet!