Outer Limits 4x4 Board

i have looked at this thread from the bible ( http://www.outerlimits4x4.com/PHP_Modul ... 236#584236 ) and if i have worked it out right 5.12 ratios would be about right for 33" tyres. Am i correct in assuming this? if this is correct does anyone have a spare set of 5.12 diff gears they dont want (i already have one set)

You're about right for the road.

Off road 33's will need more gearing than 5.12's alone due to the added traction, weight and drag of the bigger tyre.

Steve.

ive got a 1lt t/case would that be ok offroad or would i need still more gearing

I think you'd want more gearing.

Steve.

would 32" mongrels be ok with this gearing

A good compromise would be some transfer case gears and diff gears.

You'll ned up wanting transfer gears eventually.

Crawl ratio you're proposing:

3.65X2.55X5.12= 47.6

Unless you're running mud only and a 1.6EFI or something, that's going to suck on 33's. IMHO even 60:1 is marginal for 33's in my book.

with NT diff gears and a 4:1 case:'

3.65X4.1X3.9=58.3

With 5.12's

3.65X4.1X5.12=76.6 - sweet unless your into the super technical stuff

with a 6:1

3.65X6.4X3.9=91.1

with a 5.12's

3.65X6.4X5.12=119.6

with a 33 or so, that 91:1 figure will be pretty good and NT diffs are much cheaper/easier to get than 5.12's (and stronger)

With 33's, you'll run about 3300rpm with this setup @ 100kph in 5th. MArginal for a 1.3 but easy for something with more torque. That's with a TT gearset, with something with a shorter high range, (like the series 4 RH) you'll be pretty close to stock at 100kph in 5th.

I run 5.12's but I don't think they are any substitute for transfer gears for a car that's used offroad.

Steve.

Don't you use the front diff gears out of a vitara?

you will need two front sets to do the job

Yes that's correct. 5.12 fronts are pretty easy to find, most 4 Cylinder vitaras ran them.

Steve.

waiting for joeblow.....


i cant add anything to this conversation, steve has pretty much said it all.

flyinwall wrote:i have looked at this thread from the bible ( http://www.outerlimits4x4.com/PHP_Modul ... 236#584236 ) and if i have worked it out right 5.12 ratios would be about right for 33" tyres. Am i correct in assuming this? if this is correct does anyone have a spare set of 5.12 diff gears they dont want (i already have one set)

you'll love em and you'll have enough gearing for 33's, even better if you had an auto. our group all run diff gears and 33's, some with stock engines too, and they perform ace offroad. 99.5% of the time we use normal low range ( lots of our trucks have twins ). go for it, you'll find them RELIABLE.( oh and the other 0.5% is for showing off). pm me if you want more details and pics of some of these rigs.

Joe and I disagree over this. Joe doesn't like transfer gears because they had a poor reliability record, generally when there was only one supplier to the australian market. I've seen lots let go years ago but it's been a long time since we've had any fail in the club here in vic - about three years since a failure and that was warrantied. (eventually)

We're now all using US supplied gears and haven't had a failure. They're quiet, install easily and they're cheap.

Lets work some numbers out:

Joe likes 5.12's, and it is true that they do offset about a 33' tyre, pushing cruise RPM up to 3900 rpm on the highway with a 33" tyre on an otherwise stock car.

However, the big gain in road gearing doesn't translate into off road gearing. Stock crawl ratio is 29:1 for a WT, and goes to 41:1 with 5.12's in the car, which looks good, but you have to add in the effect of the bigger tyre:

Divide that by tyre diameter:

29/26= 1.11
41/33= 1.24

Your low range is actually only 12% lower than stock. That's not enough. Yes, you can add in a 1.0 transfer case, and now it's another 14% lower than stock, but your road revs rise another 12%, making for 4300rpm at 100kph.

from now on I'll assume a best case of a 1.0 transfer with it's lower gearing.

To counter this lack of low range, Joe (and others - even I was going to do it once) likes to run dual transfer cases. This is a very major modification, as you could imagine. The problem is, vitaras have a very tall low range of 1.81:1

So, for the work of dual transfers, you have 4300 road RPM, a 2.55 low range, a 2.87:1 low range, and a 4.6:1 compound low range. That 4.6 compound low range adds up to a crawl ratio of 86.2 Which is sweet, but possibly the most amount of work ever to gear a 33 on a sierra.

Of course you could use a 4.6 or something in the diffs to lower cruise revs, but then the crawl goes to 77:1 and cruise revs drop to 3900 rpm or so. Again, a lot of work for less gearing than a 4.9 transfer set.

The major selling point of the duals is that your stock 2.55 low range is retained for easy driving. That's fine, and sometimes i'd like an intermediate step, but I'm much lower overall (6.51 transfer) so I don't get much speed out of low range at all - about 20kph. do I think it's worth all the work of duals? If I had a 4.7 low range, I'd never need an intermediate, taller step.

Joe already knows all this though, which is why he likes AW-4 autos. These have a taller 4th gear to lower those cruise revs, and the 2.4:1 converter ratio means the 4.7 low range is absolutely all you ever need. this adds even more work and $$$ to the solution. Thing is, there's no need for the second transfer once you have the AW-4 - with 5.12's and a 1.0 transfer, the effective crawl ratio is 94:1 anyway.

Of course, if you're convinced transfer case gears will keep failing, then duals look feasible; but it's not really the case any more.

Steve.

don't worry bout the duals..just mentioned that so people won't go "oh, but he has duals". try diff gears you'll like em!

try t-case gears, you'll love them

Would the stongest option still not be a little of both?

ok i guess i should have said this before but i have a toyota 4k and 5sp (3.789 1st gear) 1lt case and 4.1 diff gears at the moment but i am considering putting the 5.12 diff gears in just to regain the drivability

and this would be the cheapest option by far (i love it when mechanics are mates)

flyinwall wrote:ok i guess i should have said this before but i have a toyota 4k and 5sp (3.789 1st gear) 1lt case and 4.1 diff gears at the moment but i am considering putting the 5.12 diff gears in just to regain the drivability

and this would be the cheapest option by far (i love it when mechanics are mates)

4.1's would be 1 litre diffs from memory .. 5.13s wont fit in them as they are larger.

i have nt 1.3lt diffs and they have 4.11 ratios (acording to markil who i purchased them off) so the 5.12 ratios will fit

go on low range n order 6.5 rockhopper for $475 plus $50 fraight plus about $25 for difference in the dollar n all your gearing problems r fix it will be the best $550 u ever spent on the zook

the best $500 i spent was for the 4AGE sitting under the house

Go the 6.5's! i just ordered mine and they cost me AUS $577 delivered. which consists of $475US for the gears and $60US shipping, which worked out as $577 AUS.
Mitch

flyinwall wrote:the best $500 i spent was for the 4AGE sitting under the house

How is that helping ?

flyinwall wrote:the best $500 i spent was for the 4AGE sitting under the house

and if i recall correctly, its been sitting there for a very long time...

gears gears gears gears:)