Transfer case reduction gears

I have a question for the Bigjimny brains trust, people who are smarter than me
I hear you can get reduction gears for transfer case that reduce raitios in the high and low range
Does that mean I can have larger wheel diameter without extra strain on the motor?
Does that theory work in real life?
How big can i go in tyre size and i guess i have to do a body lift
Thanks Neil

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I have never really looked at what gearsets are available but I know trailgear do complete sets. Once you have an idea of what you want there is a gearing calculator called grimmjeeper that will allow you to work out either the tyre size for the gears or the gears for the tyre size. Many people have done this before.

32-33' tyres can be used but you do need H/D shafts and CV's or you will keep blowing them... There are a few options for gear sets up to 6.5-1

sniper

Jimny bits sell a variety of gearset to change the transfer case ratios. You can also fit older Suzuki transfer cases and modify the ratios in them. Then there is a choice of 3 standard diff ratios and over the years the Jimny has used 2 gearboxes with different gearsets.
The maths is fairly simple. Use a website like tiresize.com/calculator/ to calculate in the % increase in tyre circumference and aim to match or exceed this figure with the high range gear reduction. For low range, the lower the better really!
You don't have to go much bigger than standard before you get body clearance issues. The relationship between tyre size and lift required is well documented on this site.
The best approach is to choose a suitable tyre size, then do the sums for the gearing, then look into what sort of lift and trimming you will require. Don't buy stuff until you've done the maths. It soon becomes quite expensive to do it properly!

Hi!
Building a fully off-road Jimny, have got 2004 with M16A nonVVT engine and AT box, manual transfer case.
I will be running 31 or 32" tires, so
1) Do I need gear reducers in t-case, why, what real benefit do they give apart from more controlled descending?
2) What gear reduction would you suggest with the 1.6 engine, AT box, 32" tyres?

ps Did a lot of searching in the forum archive but could not find this answered, if it has - you can direct me to the thread please

Ideally you would need something like the trailgear reduction gear set sold by jimnybits to bring it back to or below standard. At the moment you will be cooking the transmission fluid from both ends with the extra power of the 1.6 and the taller tyres. I would also suggest a separate transmission cooler as well though calculation of the exact size to keep the fluid in working range may be a bit trial and error, it can be too cold.

You really suggest tcase cooling, not auto gearbox cooling?
Btw, would there be an issue with the reduced gearing eg no more top speed or smth?

Transmission cooler not transfer box. You will potentially experience lower top road speed but that would depend on which gear set you went for. The standard ratios for the boxes are in the Jimny information section on the top banner, and a site called grimmjeeper has a calculator to allow you to adjust for different tyre size.

Dured,

Fit VVT 4.3 diffs and you would have the same drivetrain as me bar VVT. 

1600VVT + R7ME gearbox + Manual (stick) transfer box + 4.3 diffs + 30" tyres...... My shafts are standard. 

It goes well for a Jimny, powerband and road speed are well matched and eager in all gears... 70mph @ 4000rpm, could probably handle 31" comfortably......

Start going above 30" tyres and most I know who use them to lane, have needed Longfield shafts and CV's following failures of standard kit. On a road car it might not be such an issue.... but it's why I'm staying at 30" for now. If i go bigger than 30" I will fit H/D shafts and CV's, so £800 before you look at tyres..... Might be on 30" for a while yet lol....

sniper

I got the trailmaster gear set. 1,6 VVT and 235 75 15.
Work well, but there is room for 30" I guess. Without them the car was more or less useless offroad but ok on the highway. A bit high rev now on the highway but ok if I had 1,3.

Edit: mine is a 2005 stick shift 5t manual with a push button transfer. All original except for the gears in the transfer box, 1.6 VVT and 235 tires.

Don't forget this refers to an automatic main box which has different ratios.

 

 

Lambert wrote: Don't forget this refers to an automatic main box which has different ratios.




 

I had missed that Lambert, thank you..... VVT diffs would still be of benefit but you would be looking more to 30" tyres....

There may be some benefit from changing to a manual electronic transfer box but I'm too thick to do the math.....

 

sniper