Jimny Final Drive and Transfer Box Ratios

Hi Guys,

I am new to the Jimny game and I have been doing alot of research. I plan to run 235/75R15 and I have been reading varying ideas about the issues a Jimny would have with gearing. I have also read that people are installing the automatic transfer box to help with the gearing issue with big tyres. The websit below has the various ratios for the transfer boxes and they all seem to be the same.

Jimny Ratios

My question is why don't people just change the front and rear final drives to the late model automatic ratio which is 4.3

This is a spread sheet with the stock tyres and stock 99 final drive of 3.416

Gear Mph per 1000 RPM Mph @6000 RPM Mph @6000 RPM

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1 5.18 31 31
2 9.94 60 60
3 13.68 82 82
4 19.25 115 115
5 22.90 137 137


This is the stock 99 final drive with 235/75 R15 tyres

Gear Mph per 1000 RPM Mph @6000 RPM Mph @6000 RPM

---

1 5.68 34 34
2 10.92 65 65
3 15.02 90 90
4 21.14 127 127
5 25.15 151 151



This is with the 99 auto final drive of 4.09 with 235/75 R15 tyres

Gear Mph per 1000 RPM Mph @6000 RPM Mph @6000 RPM

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1 4.75 28 28
2 9.12 55 55
3 12.55 75 75
4 17.65 106 106
5 21.01 126 126


This is a the auto VVT final drive of 4.3 with 235/75 R15 tyres

Gear Mph per 1000 RPM Mph @6000 RPM Mph @6000 RPM

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1 4.52 27 27
2 8.67 52 52
3 11.94 72 72
4 16.79 101 101
5 19.98 120 120

Sorry, the original information was not formatted properly so I created a word document and attached it here










There are obviously advantages for running the 4.09 or the 4.3. The overall gearing would be better than stock with stock tyres and if someone can post the conventional conversion for a 31x10.5 tyre, I could input it into the calculator and find out the speeds per gear, but from looking at the above values I am sure you would be pretty close to the stock values with the 4.09 final drive and 31s.

Let me know what you guys think.

See my previous reply:

www.bigjimny.com/index.php/forum?view=topic&catid=6&id=54912

SJ transfer boxes are stronger, far less problematic and a Rocklobster gives you much better ratios for all occasions than any standard Jimny box.

Kirkynut

I thought manual early jimny final drive was 3.909? Not the 3.416 you mention? I once bought a jimny with one auto axle one manual and the above ratios were correct when I found out what was wrong.

I have a pair of 2005 on diffs that are 4.3 that I plan to build into axles but will still keep my rock lobster but up my tyre size.

Thanks for the replies. If you go from a 3.9 to a 4.3 the wheel speeds are exactly the same if you have 235/75 R15 fitted. I would Imagine the Rocklobster would be suited for certain vehicles but the final driver or complete axles would be a much cheaper option

the link you have is to the 2014 jimny (what i'm running). Also some of the figures you quoted are wrong.

Manual non VVT = 3.416
manual VVT= 4.3
auto = 4.09

as the guys stated the only way to improve the vvt manual would be a trans box upgrade or after market diff.

for myself I could change the diff.

I run 235/75/15 tires with no issues on my current set up,.

I used a site like this to do all the calculations
www.grimmjeeper.com/gears.html

You are correct Brave.

Anyone with a Manual non VVT can upgrade to the manual VVT diffs without spending lots on a transfer box. I was just curious as to why noone opts for that option.