Outer Limits 4x4 Board

i would have thought running a 15"tsl
@same psi as 10.5" i wouldnt of had the
same problem on the beach/dunes of bogging down
its always been a big controversy fat/skinny size tires
Imo i found wider was better on my truck all round

you would think a wider tyre would sit on top of the sand better and not bog down as much as a narrower tyre. then again less to push through with a narrower tyre

I'm going to try and explain this as simply as possible.

It's not the width of the tyre that's important, it's the shape of the footprint.

The wider the footprint gets relative to it's length, the more it sucks. Why? because for the car to move forward, the tyre has to conform, compact, or displace more material. That consumes more power, and hurts directional stability. ( that's why rudders are longer than they are wide on ships, as an example)

Add to that that most tyres are now radial, and are therefore very stiff across the tread, even if no though the sidewall, and a short, wide tyre starts looking like a poor proposition than a taller, narrower tyre.

I've proved it over and over again - many years ago with two identical hiluxes, both on fresh BFG mud terrains (one on 31 10.5, the other on 235 85 16) and last year with suzuki sierras, one on 34 10.5 LTB swampers, and the other on flogged old 9/34 swampers) The narrower tyres, in the same tread pattern, on the same car, always provide better drivability - more ability to steer, more lateral stability, and a sweeter car to drive.

The thing is, the theory of the construction of traction tyres was well sorted 70 or so years ago. By the time of WWII, it was less established - a height to width ratio of around 4.5:1, sidewall height about the same as overall width, and something like 40% void ratio, and a bar tread design for multidirectional tyres, or a 23˚ chevron pattern for unidirectional tyres (ie tractors). That holds true for a 7.50 16, 9.00 16... even a Q78 16 Swamper.

Have a look at the "cutting edge" competition tyres a 40X12.5 17 creepy crawler or 39" Krawler- roughly a 3.2:1 height to width ratio, almost the same sidewall height as width, and a modified bar tread design - in fact, the Krawler even comes as a "blank", ungrooved, that looks a lot like a bar tread. Bear in mind these tyres a more focussed on rock than terrain with yield, but them seem to work very well everywhere. Funny that... so does a 9/34 or a 7.50, assuming it's the right size for the weight of the car.

Now look at a 33 12.5 15 - the sidewall is about 80% of the width, the height is only 2.6 times the width and the footprint is wide and short. They look grouse, if that's your thing, but they're never the best tyre for any condition.

Notice that the most capable off highway vehicles ever, (tracked vehicles) have the longest possible footprint - it's normally as long as the vehicle. Relative to its length though, it's generally quite narrow.

Just some thoughts and theories, that I've always found backed up by performance.

Steve

guys,

have a read of the following writeup that uses the same sort of mathematics that gwagensteve used to explain why and how a tall narrow tyre beats a wide tyre offroad.....

its a great read.....

http://www.expeditionswest.com/research ... _rev1.html

Gwagensteve wrote:I'm going to try and explain this as simply as possible.

It's not the width of the tyre that's important, it's the shape of the footprint.

The wider the footprint gets relative to it's length, the more it sucks. Why? because for the car to move forward, the tyre has to conform, compact, or displace more material. That consumes more power, and hurts directional stability. ( that's why rudders are longer than they are wide on ships, as an example)

Add to that that most tyres are now radial, and are therefore very stiff across the tread, even if no though the sidewall, and a short, wide tyre starts looking like a poor proposition than a taller, narrower tyre.

I've proved it over and over again - many years ago with two identical hiluxes, both on fresh BFG mud terrains (one on 31 10.5, the other on 235 85 16) and last year with suzuki sierras, one on 34 10.5 LTB swampers, and the other on flogged old 9/34 swampers) The narrower tyres, in the same tread pattern, on the same car, always provide better drivability - more ability to steer, more lateral stability, and a sweeter car to drive.

The thing is, the theory of the construction of traction tyres was well sorted 70 or so years ago. By the time of WWII, it was less established - a height to width ratio of around 4.5:1, sidewall height about the same as overall width, and something like 40% void ratio, and a bar tread design for multidirectional tyres, or a 23˚ chevron pattern for unidirectional tyres (ie tractors). That holds true for a 7.50 16, 9.00 16... even a Q78 16 Swamper.

Have a look at the "cutting edge" competition tyres a 40X12.5 17 creepy crawler or 39" Krawler- roughly a 3.2:1 height to width ratio, almost the same sidewall height as width, and a modified bar tread design - in fact, the Krawler even comes as a "blank", ungrooved, that looks a lot like a bar tread. Bear in mind these tyres a more focussed on rock than terrain with yield, but them seem to work very well everywhere. Funny that... so does a 9/34 or a 7.50, assuming it's the right size for the weight of the car.

Now look at a 33 12.5 15 - the sidewall is about 80% of the width, the height is only 2.6 times the width and the footprint is wide and short. They look grouse, if that's your thing, but they're never the best tyre for any condition.

Notice that the most capable off highway vehicles ever, (tracked vehicles) have the longest possible footprint - it's normally as long as the vehicle. Relative to its length though, it's generally quite narrow.

Just some thoughts and theories, that I've always found backed up by performance.

Steve

Geez mate, you have such an eloquent way of explaining things,, my thoughts and experiences exactly though and for the reasons you have stated i think a 9.00/16 is the perfect tyre for a Patrol driven hard in varied terrain.

My tyres are actually 255/100r16, so sidewall is 100% of the tread width

Yet with all the comments this still comes up


The flotation tire provides three benefits. Greater high speed handling safety and improved lateral traction on constructed roads (concrete, asphalts, etc.), greater section width for support of the heavy vehicle on soft terrain, and appearance. The engineering concept behind the flotation tire can be found in its name. These tires were designed to provide flotation on loose surfaces like sand. Flotation only comes at the cost of contact pressure. Flotation is achieved by minimizing the surface pressure per square inch exhibited by the vehicle. These features are important for heavy, full size trucks and SUV's, but not most trail vehicles

I dont know i could be wrong but Im prety sure there hasent been alight small 4wd since the bundera

Jeep Wrangler, Suzuki Vitara, Suzuki Jimny to name a few

sorry should of said real ones

flame suit on

sorry will pay the uki ones

my point is that a 10.5 is wide on a small wagon like those

I found that really skinny tyres handled on the road alot better than the 10.5's did and was better again on the gravel. On an 80 series that is.

steel wrote:
This has been the topic around many a camp fire, along with the " which tread pattern is best in sand " discussion, and its been proven again and again on beaches and dunes all over WA that narrow tyres are better in sand.
sometimes the exception to this rule is if you are running at road pressures.
driving in sand with narrow heavily treaded tyres may require a change in driving technique, with a little more finesse with the clutch and more restraint with the right pedal, for example, this tosser im unfortunate to know would dig himm self into holes quite regularly on the beach, but after fitting a 350 chev and 35/12.5/15's he's buried alot quicker and alot more often now.
The moral is you've got to learn to adjust your driving style to suit more than just your mood and doug's useless behind the wheel -- there its been said --

Shhhhhhh Don't tell 'em the truth... then we'll have nobody left to save when they're bogged up to their axles and the tides coming in and the mozzies are biting and the sun's going down.... and we save 'em and tell 'em that the skinny ghay lookin' highway terrain tyres are KING on sand.

beinthemud wrote:my point is that a 10.5 is wide on a small wagon like those

iu run 10.5s on a sierra and have found they are awesome on the sand if u can turn/spin them.
thou on road esp in wet they act like floaties and may as well grease the tyres up before i go out.

chimpboy wrote:

THICKNICK wrote:can someone also explain the benefits of a narrower tyre to a wider one.

I can't explain it but I've seen narrower tyres go well in mud even when wider tyres with better tread struggled in the same spot.

The theory I heard was that the narrow ones sink through the soft stuff and bite into the hard stuff underneath it, while the wide ones "float" more. True or not? I don't know.

This is my experience and the tale of my associates. 31x10.50 are called flotation tyres. Probally cause they rely on width to float on top.
7.50x16 is still a great all round tyre if you have suitable rim. I'm stuck with 31x10.5 and suffer the pro and con of this.

Imo generally as vehicle increases there ground pressure
they decrease there offroad preformance
a vehicle with lower vci (lbs/sq inch)
should out preform vehicle with higher one.
tracked vehicles have low lbs/sq inch, because
the weight is spread out more,so bigger tires
on a 4x4 will give more traction in sand/soft terrain
because more weight displaced
by deflating tires gives you less lbs/sq inch
so a fatter tire would have lower lbs/sq inch
to start of with before you deflate them
that just my personal opinion

285/75 16r is approx 32.8 x 11

food for thought

You'll notice I didn't add "floatation" to my comments anywhere. There's only two terrains where a reduction in ground pressure always means an increase in capability, and that's snow and sand. Outside of those areas, often, inadequate ground pressure is a reason why cars don't perform on mud, and that's why my narrow 34's work so well- they provide high ground pressure for a tall tyre on a light car.

However, for the same ground pressure, a longer narrower footprint will give greater gains in snow and sand than a wider shorter footprint, and that's true in every other terrain too.

Tracked vehicles actually have the best of both words. The cross bars (grouser plates?) on the tracks provide very high ground pressure on hard surfaces, and the enormous surface area of the tracks provides very low ground pressure on surfaces with yield. Either way, the end result is a long, narrow footprint.



Steve.

beinthemud wrote:I dont know i could be wrong but Im prety sure there hasent been alight small 4wd since the bundera

2 Tonnes is light?

And why is it so "light"? Its a cut down cruiser, without real cruiser running gear... and a leaf blower motor???

beinthemud wrote:
I dont know i could be wrong but Im prety sure there hasent been alight small 4wd since the bundera


2 Tonnes is light?

And why is it so "light"? Its a cut down cruiser, without real cruiser running gear... and a leaf blower motor???

I wasn't going to mention anything about that but glad someone did

and you have apic of a uki
and your laughing at me

Id rather have a leaf blower than an undersize go kart with a winch motor

would a 33x12.5 not be able to be aired down
to produce the same length foot print as a
33x10.5.?
would think its more to do with how tall a
tire is that gains more length when aired down.
tracked vehicles increase widths of tracks too.
swamp tracks for dozers are wider for mud/sand.

tread lightly!!
what is recommended optimum lb's/sq"
for ground pressure offroad?

beinthemud wrote:Id rather have a leaf blower than an undersize go kart with a winch motor

Hehe i also have a 100 series, with a 4.2... the smallest engine a 100 came out with

Suzuki put the winch motor under the bonnet of the Sierra, because they knew it would never be needed on the front bar. But some Sierra owners realise they actually do require a winch, to pull their mates in Bunderas out!

I have 33/12.5/15 muddies on my Cruiser and have never needed to aired down on the beach . I put it down to clearence if you are high enough you don't get stuck.

frp88 wrote:I have 33/12.5/15 muddies on my Cruiser and have never needed to aired down on the beach . I put it down to clearence if you are high enough you don't get stuck.

Haahaahaaa Haahaa, very funny!

frp88 wrote:I have 33/12.5/15 muddies on my Cruiser and have never needed to aired down on the beach . I put it down to clearence if you are high enough you don't get stuck.

aaah... suspension clearance, or diff clearance?

33s dont put you that high in a cruiser...

I ran 33x10.5 BFG ATs for years on my TJ and only just recently put 33x12.5 MTRs on.

One point which may or may not matter to you is the weight.

On my old bathroom scales (which are probably out), a 33x10.5 BFG AT on an American Racing 15x7 alloy rim weighed about 26kgs from memory.
A 33x12.5 MTR on a somewhat similar but wider 15x8 American Racing alloy rim was 33kg or so. Even if the scales are way out, it is still a useful comparison on how much extra (or less) weight you have spinning away at the end of each axle.

I love tyre threads. Always full of great content and helpful advice.

T_Diesel wrote:I love tyre threads. Always full of great content and helpful advice.

... and 20 posts "THIS TYRE IS AWESOME", and 20 "THAT TYRE IS SHIT I HAD EM AND ....."

T_Diesel wrote:I love tyre threads. Always full of great content and helpful advice.

Like most decent tech threads (this on actually has some very good tech in it) you always wind up with someone wanting to justify their pruchase based on nothing more than what looks good.

A wide tyre needs to compress much more ground as it is rolling than a narrower tyre. To compress this area it needs to push off something solid remember it is rolling not being placed on top (more like a tracked vehicle is another reason for their excellent abiltiy)
This leads to a much higher "rolling resistance"

My next lot of rubber will be in the tall narrow range (750x16 style) easier to fit in the guard as well