[Joshua02]

hey guys

thinking of putting 31s muddys on my 96 sierra, it has a 2 inch body lift aswell

what are the pros and cons ??

cheers

[tanshi]

if you dont have transfer gearing there are no pros

[want33s]

Pro's are: It'll be totally awesome.

Con's are: Reduction gearing needed including transfer swap.
No Cr-Mo front axles/CV's available for coily.

[Joshua02]

tanshi wrote:

if you dont have transfer gearing there are no pros

what do you mean by that ??

[tanshi]

i mean it will be such a pig to drive both on and off road that you will wish you hadnt bothered

[Joshua02]

tanshi wrote:

i mean it will be such a pig to drive both on and off road that you will wish you hadnt bothered

right so what would i do to solve this problem

[toastysteve]

Engine conversion, or some performance work on your existing setup (assuming you haven't done any already).
Or change your gearing.

[Joshua02]

toastysteve wrote:

Engine conversion, or some performance work on your existing setup (assuming you haven't done any already).

best engine to swap it with ??

[tanshi]

g16b vitara engine

[Joshua02]

tanshi wrote:

g16b vitara engine

fair enough, so what if i got 31 A/Ts ?

[Gwagensteve]

It's tuesday

more power doesn't offset taller tyres. More torque lower in the rev range will help, but some quick and rough maths tells me a coiler on 31's would be spinning at about 2800rpm @ 100km/h with 31's on it, so you'd need an engine that puts out 20% more torque than a G13B at 3500rpm whilst spinning at 2800 rpm. That's beyond even a G16B. Gearing really is the better option.

OK, you need to fit a Leaf sierra transfer case to you coil car. From memory, this will require a WT jackshaft as well as the coil jackshaft is longer. It will be best to find a WT transfer case as it will have the right flange bolt pattern. You can then fit low range transfer gears which will almost correct the road gearing and will bring offroad awesomeness.

Once you've done this (and this is a circa $1K exercise unless you find a transfer with gears cheap) you might find the coil front CV's and inner axles are a weak link. There's no commercially available fix for this problem, although custom axles and using the stubs from doubletoughs are possible, similar to what 31zook has done for his jimny.

If you are a sympathetic driver and drive mostly mud you might find the front end lives, but it's always going to be borderline.

Likewise if you are into mud mostly, you might *just* get away with a 1.0 "switch light* transfer case, but it's going to be less than ideal and it requires the flanges swapped to WT items to match your driveshafts.

if this all seems like a lot of money/work unfortunately that's just the nature of things. a 31" tyre is 20% increasem that's like putting a 38" tyre on a patrol - it costs money to get the car right with that much tyre.

Steve.

[Matthew]

An engine upgrade is not a substitute for gearing.

You have to gear it.

Edit - Beaten by Steve.

[Joshua02]

Gwagensteve wrote:

It's tuesday

more power doesn't offset taller tyres. More torque lower in the rev range will help, but some quick and rough maths tells me a coiler on 31's would be spinning at about 2800rpm @ 100km/h with 31's on it, so you'd need an engine that puts out 20% more torque than a G13B at 3500rpm whilst spinning at 2800 rpm. That's beyond even a G16B. Gearing really is the better option.

OK, you need to fit a Leaf sierra transfer case to you coil car. From memory, this will require a WT jackshaft as well as the coil jackshaft is longer. It will be best to find a WT transfer case as it will have the right flange bolt pattern. You can then fit low range transfer gears which will almost correct the road gearing and will bring offroad awesomeness.

Once you've done this (and this is a circa $1K exercise unless you find a transfer with gears cheap) you might find the coil front CV's and inner axles are a weak link. There's no commercially available fix for this problem, although custom axles and using the stubs from doubletoughs are possible, similar to what 31zook has done for his jimny.

If you are a sympathetic driver and drive mostly mud you might find the front end lives, but it's always going to be borderline.

Likewise if you are into mud mostly, you might *just* get away with a 1.0 "switch light* transfer case, but it's going to be less than ideal and it requires the flanges swapped to WT items to match your driveshafts.

if this all seems like a lot of money/work unfortunately that's just the nature of things. a 31" tyre is 20% increasem that's like putting a 38" tyre on a patrol - it costs money to get the car right with that much tyre.

Steve.

Im currently running 235/75/15s on it how much bigger are 31s ? i dont know if any previous work has been done to the car?

[Matthew]

31s are about 7% larger, depending on brand.

[Joshua02]

Matthew wrote:

31s are about 7% larger, depending on brand.

so would 7% make that much of a difference on an A/T tyre ?

[Gwagensteve]

It doens't matter if it's an AT, a MT or a slick - it's the gearing, not the tread pattern that matters.

You can check transfer gearing by jacking the back wheels up, turning the driveshafts, and counting out the ratios. I'd say your car would already be pretty horrible to drive with 235's and stock gearing, the added weight and height of 31's will really make it suck. I' already have changed the gearing if I had a coiler and was running 235's.

Steve.

[tanshi]

yes. your not listening.

31s without gearing will be terrible

[Joshua02]

Gwagensteve wrote:

It doens't matter if it's an AT, a MT or a slick - it's the gearing, not the tread pattern that matters.

You can check transfer gearing by jacking the back wheels up, turning the driveshafts, and counting out the ratios. I'd say your car would already be pretty horrible to drive with 235's and stock gearing, the added weight and height of 31's will really make it suck. I' already have changed the gearing if I had a coiler and was running 235's.

Steve.

just jacked her up turn the tailshaft from the transfer case to the diff in neutral i turned the tailshaft 4 times for 1 complete rotation of the wheel ?? am i doing this right ?

[tanshi]

coilys run 3.9:1 diff gears so yeah probably close enough

[Gwagensteve]

Yes, but you need to do it with the transfer case.

Put the transfer case in low range, gearbox in neutral, and with the back wheels off the ground, turn the tailshaft once and count how many times the jackshaft turns. The jackshaft is the little shaft between the gearbox and the transfer case. If it's roughly 2 times, everything is standard.

If it's just over 2.5 times, you have a 1.0 transfer case.


Steve.

[Joshua02]

Gwagensteve wrote:

Yes, but you need to do it with the transfer case.

Put the transfer case in low range, gearbox in neutral, and with the back wheels off the ground, turn the tailshaft once and count how many times the jackshaft turns. The jackshaft is the little shaft between the gearbox and the transfer case. If it's roughly 2 times, everything is standard.

If it's just over 2.5 times, you have a 1.0 transfer case.


Steve.

its roughly 2 times :/ so no point in getting 31s then ?

[JrZook]

Joshua02 wrote:

so no point in getting 31s then ?

Re-read all the info and advice already given to you in this thread, then come up with a decision.

[Gwagensteve]

Only you can decide whether it's worth spending the money and getting your gearing right. As I've said, I couldn't live with your car the way it's geared right now, so I would have already gone to a WT transfer case and reduction gears even with 235's, let alone 31's.

for the sake of the exercise, you should try and borrow a set of stock tyres and go for a drive with the car geared back to standard. I bet you'd be amazed how much better it feels with the gearing correct.

Steve.

[Ace]

Zooks have bollocks low range to start with, mine is standard gears and 30's (29'.2 / prob a 235-15 true dia) and its BS. MT, AT, HT... the actual tread dosnt matter its the rollin dia. Work out the cricumference of a circle (your tyre).

divide the circumference of the tyres you want by the circ of you factory rubber and there's the difference.

31 inches x 25.4 gives it to you in metric - 235 75 15... 15' x 25.4 gives the rim in mm, 235 x .75 gives the sidewall height x 2 (top and bottom of rim) plus rim dia in mm = answer

Short ans, get gears

[greenzook89]

I wouldn't go any more than a 235 with standard gears, after having a few Zooks with that tyre size its ok. Not as bad as my stock geared jimny on 30s though.

[Gwagensteve]

It depends on the terrain you're driving greenzook. In my opinion is steep technical terrain 235's are murder on the car. If it's beach/mud then maybe 235's are OK.

Add a locker though and the added traction will just kill the clutch with 235's and stock gearing though.

Steve.

[greenzook89]

Well up here its mostly mud now Haha. Sometimes steep shale climbs. I did notice the difference between standard gearing and 235s when i changed them. No plans for lockers atm.

[Rye_Bread]

You don't have to do an engine swap or get reduction gears! I ran 31x10.5 muddies on my sierra with stock engine and transfer and it ran fine!! It was a bit slower but it was still good off road and on road!! I only did the engine swap because I flooded my ok engine...

[atari4x4]

Rye_Bread wrote:

You don't have to do an engine swap or get reduction gears! I ran 31x10.5 muddies on my sierra with stock engine and transfer and it ran fine!! It was a bit slower but it was still good off road and on road!! I only did the engine swap because I flooded my ok engine...

people that say this have never wheeled a 4wd with reduction gears.

[Matthew]

And drop shackles are awesome