[mika]

now i know the pros and cons for fat and skinny mud tires
ie. fat tires float on deep mud/snow and skinny dig to hard surface in shallow mud/snow plus the weight and stability
because sierra's, even widetrack, aren't the most stable vehicles i'm wondering if sacrificing some grip for a bit more stability by running say a 12.5" wide tire would be a good option. would a sierra with 6.5:1 gears struggle too much too spin a 33x12.5. I'm particularly interested for vic conditions and for people who have run both a 12.5 and say a 10.5 but the more opinions the better
cheers mika

[Damo]

Pizza cutters are the new black

It will be interesting to hear what the Vic boys say. In my experience you need wheel speed in mud, and fat tyres are harder to spin than skinny ones. I think that down there the skinnys would work well.

[mika]

i agree completely but sometimes lack of stability can make an easy obstacle hard and/or mean u can't use as much momentum

[86slowsierra]

10.5 is more than enough to float. trust me. so i see no point in going to 12 and sacrificing power and turning.
i depends on what you like to drive.

[steak_knife]

Damo wrote:

Pizza cutters are the new black

It will be interesting to hear what the Vic boys say. In my experience you need wheel speed in mud, and fat tyres are harder to spin than skinny ones. I think that down there the skinnys would work well.

With ya, wouldn't say new tho.

[11_evl]

i run 12.5s and the extra weight helps me stay on all fours

[joeblow]

the best tyres i've used in mud were skinnies. but, they offer little protection for the vehicle, and stupidly offset rims will kill bearings. the worst tyres i've used were 12.5's, even on rock. 10.5's are a good all-rounder, but at the end of the day i've seen more vehicles struggle in mud because of vehicle weight and not tyres.

[mika]

anyone with a 10.5 or skinnier tire in 32-34" ever feel their rig would be more capable with 33x12.5 due to extra stability?

[jdk81]

I run 32 x 9.5 simex ET "centipedes".

In terms of mean maximum ground force pressure (MMGFP) as used in terramechanics by US, UK and AU military.
Note: this is not nominal ground force pressure.
MMGFP takes into account the mean peaks of pressure which deform the ground (grip and/or get you bogged).

MMGFP - assuming same specs 900 kg vehicle
my zook
33.4 x 9.5 = 95 kPa (14 psi)
33.4 x 12.5 = 75 kPa (11 psi)

40 x 9.5 = 77kPa
40 x 10.5 = 71kPa
40 x 11.5 = 66kPa
40 x 12.5 = 61kPa

A marsh buggy is 35kPa, snow mobiles are around 25kPa.
Trucker snow car is 14.5 kPa
To acheive 35kPa you need much bigger tyres (45" x 20").

The biggest killer is actually tyre deflection. Even at 0psi the tyres dont deflect enough, this greatly affects the ground force pressure.

Larger tyres, also have greater intertia. Turning and stopping these will really test the vehicle.

The pedes, and pede knock offs, self clean very well.

I have only had issues in mud when it is really really deep.

In bog holes with mud at the bottom, and water the rest of the way. The car does fine and often have water/mud 1/2 way up the windscreen.

In bog holes which are like quicksand (no idea how deep), the car just sinks and sinks.

In terms of stability (the offset is 3p), I experience sphincter clinching moments frequently, usually when it drops into a deep rut. Exo is high on the to do list.

Bumped into a fellow zooker with same tyres etc, but he had massive offset on rims.
He got stuck in bog holes, where mine would drive through easily.
I suspect this comes down to track width. Having offset of 3p means the tyres scrub a bit, usually 1 side (passenger or driver) is in the rut, whilst the other grabs onto the sides of the ruts, instead of going all the way in.


A decent little read
http://www.expeditionswest.com/research ... _rev1.html

[mika]

jdk81 wrote:

I run 32 x 9.5 simex ET "centipedes".

I have only had issues in mud when it is really really deep.

In bog holes with mud at the bottom, and water thr rest of the way. The car does fine and often have water/mud 1/2 way up the windscreen.

In bog holes which are like quicksand (no idea how deep), the car just sinks and sinks.

In terms of stability (the offset is 3p), I experience sphincter clinching moments frequently, usually when it drops into a deep rut.

Bumped into a fellow zooker with same tyres etc, but he had massive offset on rims.
He got stuck in bog holes, where mine would drive through easily.
I suspect this comes down to track width. Having offset of 3p means the tyres scrub a bit, usually 1 side (passenger or driver) is in the rut, whilst the other grabs onto the sides of the ruts, instead of going all the way in.


A decent little read
http://www.expeditionswest.com/research ... _rev1.html

great article

regarding ur wheeloffset, what's 3p i've always heard wheeloffset and backspacing measurements in inches?

thanks to all for the replies

[jdk81]

added more, I forgot to actually answer your question and instead I put in the MMGFP.

EDIT: answering the question.. yes it is unstable, and no way in hell would i go wider.

usually people run 25N (25mm negative offset) I believe, where mine is positive 3mm.

The 25N offset makes the wheels stick out further and puts greater load on the bearings.

The tyres with 3p offset were on it when i bought it, so i didnt choose them. Bar the loss of turning circle i actually prefer it.

wheel offset info
http://www.speedywheels.com.au/wheel-tech.htm

[mika]

jdk81 wrote:

added more, I forgot to actually answer your question and instead I put in the MMGFP.

EDIT: answering the question.. yes it is unstable, and no way in hell would i go wider.

usually people run 25N (25mm negative offset) I believe, where mine is positive 3mm.

The 25N offset makes the wheels stick out further and puts greater load on the bearings.

The tyres with 3p offset were on it when i bought it, so i didnt choose them. Bar the loss of turning circle i actually prefer it.

wheel offset info
http://www.speedywheels.com.au/wheel-tech.htm

cheers mate
some great info there
in general do u think ur narrower track(less offset wheels) is an advantage or would u like to go for more offset like most run?

[v.w.dave]

I have 33 12.50 15s Micky T. Baja Claws and the only advantage I have found between myself and the next zook is having tires that big it lowers my center of gravity because of the weight of them. I have fallowed a sierra with exactly the same as mine less the 2"shackles. He was running the exact same tire but 31 10.50 and I was able to handle the really deep thick mud better but in every other aspect he ran circles around me.

[jdk81]

mika wrote:

cheers mate
some great info there
in general do u think ur narrower track(less offset wheels) is an advantage or would u like to go for more offset like most run?

If i was to run wider tyres, I would still opt for narrow offset. Being able to bite into the sides of the ruts instead of ploughing in them is a huge benefit.

But side angles will still be a bit of a problem.

I would actually like to whack it on a tilt tray and test it to find the CoG.
Then I would know exactly what sort of difference the offsets and wider tyres make.

[jdk81]

v.w.dave wrote:

I have 33 12.50 15s Micky T. Baja Claws and the only advantage I have found between myself and the next zook is having tires that big it lowers my center of gravity because of the weight of them. I have fallowed a sierra with exactly the same as mine less the 2"shackles. He was running the exact same tire but 31 10.50 and I was able to handle the really deep thick mud better but in every other aspect he ran circles around me.

+1 which is to be expected.

Knowing the difference between 12.5s and 10.5s would you try narrower on yours next time? Or maybe even borrow his muddies and see if you like it?

How do you find your alround capability? Is it worth sacrificing alround ability for the really deep thick mud ability?

[303zuke]

I am utterly gobsmacked that you consider 10.5's as "Skinny" tyres on a Suzuki!

The choice between Wide and Skinny tyres used to be between 30x9.5-15 as Wide, and 7.00-16 (30" dia) as Skinny.

7.00-16 were very attractive in that you could go for all sorts of articulation and wheel lock and not rub on the body or chassis. However, as they tended to be crossply construction and in S***house tread patterns, on-road performance and traction tended to suffer something chronic.



30x9.5-16 offered absolutely massively superior traction and stability, but you had to be careful with body and chassis clearance.


Sometimes, 30x9.5 or 235/75-15s were absolutely essential for stability such as an LJ50 with a 4" Lift SPOA conversion. Any sort of crossply in that case would see you roll quicker than you could say "FAAAARK".

[MacDaddy]

Wow that is some really good info on tyre selection...

I am even more happy with my tyre selection after reading that, i went with KUMHO Road Venture 215 x 75 R15 AT's, they handle very well on the road, and on the sand, yet to take them on mud or rocks, but going on the info, they should do ok...

I went to the Overlander magazine website and checked their tyre tests first before i bought them, i think i will do a new thread with the tyre test info...

[zukenutter]

303zuke wrote:

Shit that's a clean looking "50"

[Highway-Star]

mika wrote:

anyone with a 10.5 or skinnier tire in 32-34" ever feel their rig would be more capable with 33x12.5 due to extra stability?

I run 31x10.5

Personally I find my Sierra so ridiculously stable, anyone who says Sierras are unstable as a broad general statement is either ill informed or speaking out the wrong end. I'm sure they can be built unstable though

[BlueSuzy]

I run Nankang 33x12.5 but i dont like mud for bearing and brake issues..

If i was unhappy i would of changed them by now. Had them for prob 1 1/2 years now..

I run rock mostly.