Jessie The Jeep

Just wondering what gearing would be best for my 4cyl TJ for turning 33 inch tires? I still want to be able to cruise at 110km/h if thats possible.
Any info will help thanks

kelownaluke

Differential Gear Ratio Chart - Tire Size to Gear Ratio

Here is a chart to help you out. As you can see nothing is set in stone, there is not a standard or mandatory ratio for a specific tire size. The only thing i would suggest is that you probably want to lean towards the higher end of the range since you have the 4cyl. A bit more gear will help make up for the lower power output.

Da_Bear

X2 on that

In my experience the 4.56 keeps you close to stock ratios with the 4 cyl. Your speedo will be very close. But I too lean to the deep side on the gearing and almost always recommend going 1 ratio deeper on the mod. It wont be too bad on the hiway and on the trail that one step will pay off in the power transfer for them 4 squirrels under the hood.

4.10 stock trim in 1:1 the engine should be about 3000rpm ish
4.56 with 33's engine should be around the same 3000rpm or so in 1:1
4.88 with the 33's the squirrels will be runnin around 3200rpm ish in 1:1

now add the overdrive into the equation lets say a .85 from an AX-5 and the rpms are much better

4.10 at 60 mph = 2550ish
4.56 at 60mph = 2550ish
4.88 at 60mph = 2720ish

The 4.88's don't look to bad now plus the benefit of the lower crawl ratio off road is a bonus!!

My2centz

Bear

RiponredTJ

Having seen pics elsewhere on this side of the axles Da_Bear is building, I would take that advice seriously.

swamper

x2 on that one its some sweet axles hes buildding with i could put in my zj

Da_Bear

Thanx for the props guyz!!

I can make a set that will feel quite at home in your XJ.......LOL


But back to topic...I hope that you can find a gear ratio that will make you and your Tj happy Jessie The Jeep....any Q's juat ask and I will answer them the best I can!!

Jessie The Jeep

Thanks for all the help i'll let ya know how it turns out

Jessie The Jeep

What is all involved in installing a different ratio?

Da_Bear

Well just a gear change involves a new ring and pinion pinion install set and a good supply of shims. That is providing all else is solid and in good shape in the diffs. Add a New Locker or LSD and the parts/labour list grows with it.

then the fun begins....drain oil....remove axles,check the seals and bearings, unit bearings in the front, replace if needed.....remove carrier.....inspect carrier bearings and side gears/clutches(if limited slip) and repair and or replace as necessary....take baseline reading on original pinion(pinion depth guage) ...remove pinion...inspect pinion bearing races and replace if needed....remove shims from original pinion and install on new pinion then bearings and install...check pinion depth and compare to original baseline and adjust the shim stack to get the same reading....remove ring gear and replace with new one on the carrier.....now the fun begins start with the original shim packs and put them back in where they came from then adjust carrier back and forth to attain a good gear pattern using gear marking compound....once a good pattern is acheived then you have to check for the appropriate amount of back lash....if too tight or too loose adjust side shim pack to get the back lash where it belongs.When perfect(ish) slide the axles in put the pan on after sealant and fill it up with oil. Road test it and listen carefully for any "Bad" noises or howling. If all is good break in the gear set as per manufacturers recommendation then git out and enjoy the mod!!

Dana 35 pinion preload with new bearings: 12-14 IN. LBS Ring gear Backlash .006-.010 Ring Gear bolts 55FT. LBS Side Bearing Caps 55FT. LBS
Dana 30 pinion preload with new bearings 12-15 IN. LBS Ring gear Backlash .006-.010 Ring Gear Bolts 55FT LBS Side Bearing Caps 60FT LBS

Of course there is more to it that that and this is definately abreviated. There is always monkeying around to do in between the steps mentioned.....also I have prolly left some stuff out of that list.....it is different doing it than writing it down......when the wrenches are flying you just know what to do...........writing it down...well stuff gets lost on the paper!!!

On a TJ we charge out about 5.5 hours for the front and 4.5 hours for the back on average...I have a club member in another club that has been struggling with his Ford Ranger for over a month....he has the rear done now and is wrestling with the TTB's gear set. He has learned alot through his ordeal....not sure if he will tackle another set but with some guidance he will pull it off and have the satisfaction of doing it himself(once the frustration fades).

This is not a job that should be taken lightly nor attempted without the help of someone who has done it before(more than once)....It can be very frustrating and tedious work and some people like to look at the pattern charts and hit it bang on......rare, very rare, but there are acceptable patterns outside of the "Handbooks" and that is where the experience comes in......

Bottom line take no shortcuts here...this is your opportunity to catch all the little parts in your diffs that may well be questionable and repair/replace them.
If done correctly you will have reliable diffs that will last you as long as the Jeep(taken care of anyways).

Hope that wasn't too long winded for you and helps you make the right descision for you and your Jeep

Bear