Wide Vs Skinny Mud Tyres

[Suspension Stuff]

I like the look of the STT Coopers mud tyres. What are the advantages and disadvantages of the 285/75/16 over the 305/70/16. They are both the same diameter within 1mm.

Cheers
Shane

[Zuki]

i think the 285/75/16 is a 33x11.5x16 i think

and 305/70/16 is a 33x12.5x16 i think but yer i think it is just wider i spose some advantages of the 305 would be more tread width

[Beastmavster]

And the benefit of the 285/75/16 is that there's more pressure on the surface of the tyre due to it being spread over less area.

Effectively should be more grip per cm2 of tread... that's the benefit of the skinnier tyre.

[cloughy]

And the benefit of the 285/75/16 is that there's more pressure on the surface of the tyre due to it being spread over less area.

Effectively should be more grip per cm2 of tread... that's the benefit of the skinnier tyre.

So if i put 165/95/16's on my vehicle they'll will grip even better vause they are skinnier , 285's are cheaper but go the 305's cause they sit on 8" rims just nice

[dogbreath_48]

I've always been an advocate for skinny tyres, since my worn 7.50R16 road grippers out-gripped fresher 10.5" all terrains (both lame, i know), but i'm sure there's a limit - a happy ratio of ground pressure versus contact patch size.
I'd go the 285's - probably look better too!

[dieseldude]

I much prefer skinny tyres for grip and surface pressure these days too.

In the past, I have run 14 inch wide Dick Cepek's and compared to my new set of 7.50r16 Super Traction tyres (MRF Brand), I much prefer the skinnies. They steer heaps better too.

I guess it is all a trade off and you could get to the point where the fat tyres just aren't practical anymore.

Each to their own, but i run 285/75/16 BFG AT's on my 105 series for street use. They're a good practical size and don't look to crazy either.

Cheers.

Anthony

[YankeeDave]

the fatter the tyre the more stable you make your car on side slops and the such.

[-Scott-]

How is this so called "surface pressure" NOT directly proportional to your tyre pressure?

Want more "surface pressure" - increase your tyre pressure.

Want less "surface pressure" - decrease your tyre pressure.

The difference between fat and skinny tyres is the shape of the contact patch.

If you want to compare 14" Dick Cepek's against 7.50r16 you'll also need to consider rim offset (you wouldn't use the same rims for both tyres.) This will affect your scrub radius, which will affect your steering feel. But I don't doubt that skinny tyres will steer nicer than fat tyres, everything else being equal.

Fat/skinny, BFG/Cooper, Toyota/Nissan - you'll never get everybody to agree.

Scott

[G_loomis]

How is this so called "surface pressure" NOT directly proportional to your tyre pressure?

Want more "surface pressure" - increase your tyre pressure.

Want less "surface pressure" - decrease your tyre pressure.

The difference between fat and skinny tyres is the shape of the contact patch.

If you want to compare 14" Dick Cepek's against 7.50r16 you'll also need to consider rim offset (you wouldn't use the same rims for both tyres.) This will affect your scrub radius, which will affect your steering feel. But I don't doubt that skinny tyres will steer nicer than fat tyres, everything else being equal.

Fat/skinny, BFG/Cooper, Toyota/Nissan - you'll never get everybody to agree.
Scott

Thats the beauty of opinions....everybody has one!

I have often noticed the skinny tyres always seem to go better on the beach too...or am I dreaming? The theory about tyre pressure and surface area makes sence to me...but so does the increase/decrease tyre pressure thing....Seems I am a fence sitter on this one.

But I would think that skinny tyre filled to say 25psi would have the same pressure on the surface of the tyre, as a wider tyre would filled to the same psi. Granted there maybe more air in the wider tyre to gain that psi, but the surface pressure would be the same....I think.

So did I just jump off the fence then.?

[jeep97tj]

skinny tyres are the go for for clay type surfaces and even wet grass and gravel, fat tyres are the go for sloppy bog holes and rocks.

I have had both fat and skinny tyres and have also wheeld with other people running fat and skinny tyres, that is where i have got my opinion from.

[Dyna Beast]

Hello
The old school argument about wide verses skiny tyres was.Fat tyre tend to float over bog holes,mus etc were skiny tyres will cut trough the crap till hopefully the will grip.AS jeep97tj note skinny`s are good on clay cause the will cut into the surface more.I run 750`s on my truck,thought I would have to get a set of wider tyres.Now I reckon the are not to bad for grip.Will probaly get a set of 750/16 Simex pedes.
Cheers

[Gwagensteve]

I am a big fan of skinny tyres. No, you are not imagining it, narrow tyres do work better in the sand. It is a matter of the shape of the footprint not just the size.

Unfortunately, it is hard to get genuinely skinny and aggressive tyres over 34" which is why I ended up on q78's.

I wish there were more 9.00x16's on the market.

Skinnier tyres are also easier on the car and easier to fit.

I guess the dream sizes for me would be 35 9.5, 36 10.5, 37 10.5 in a straight swamper. The 42 12.5 Irok has a nice ratio but is a bit tall for most of us.

Steve.

[Suspension Stuff]

Will the 285/75/16's go good on a 8 inch rim, like is it perfect for them?

[Gwagensteve]

I believe that 255 85 16's are available in some cooper patterns? These are a very nice size and go on a 7" rim.

the 285 is still a bit chubby for me, but is fine on an 8" rim.

Steve.

[Shadow]

How can a skinny tyre work better on sand?

A 7.50inch tyre bagged would be a max contact patch of about 14" (and its not a flat contact patch). A 14" bogger has that without bagging, and sand driving is all about surface area!. The tread pattern is also important but we arent talking tread pattern, were talking width (assume a 7.5" bogger aswell)

I also dont understand the surface pressures argument. If a tyre is inflated to 32PSI (POUNDS PER SQUARE INCH) it has exactly the same pressure over every square inch. Thats what 32PSI means.

The fact is, A wider tyre has more grip because it has more surface area with which to engage the friction coefficient of the surface it is on.

The only time I can think a narrower tyre will produce more grip is when the narrow tyre cuts through the slop and hits firm ground. Otherwise the fatter tyre wins.

[sudso]

BFG and Simex make a skinny mud tyre 33-34" dia. and 9.5" wide

Agree, skinnier muddies cut through the slop down to the harder stuff a bit quicker than a wide one on the same truck/weight etc.

[Gwagensteve]

Skinny tyres work better in sand for a couple of reasons. In any surface with yield, part oft he battle of moving the car is pushing the terrain in front of the tyre and compressing it. On sand, the car has to push a wave of sand in front of each tyre. This has two effects. One is that it absorbs power. secondly, it is like the car is constantly having to climb a small hill constantly.

Let's not talk width, lets talk contact patch. Fact is, on anything other than a sand rail, the power absorbtion of trying to turn the bogger in sand will mean that the nice elegant 7.50 will kill it everytime.

A narrower tyre has less sand to push ahead of it, so it is a more efficient way of moving the car.

Paris/Dakar and rallying are two areas where you will see very narrow tyres used on surfaces with yield (sand, snow)

Lancia experimented with wider and wider tyres back in the early 80's with their 037 rally car, and ended up reducing width and increasing diameter. It gave better drivability for the same ground pressure.

sure, in sand, lower ground pressure is better, but this is the only surface where this is true. On firmer surfaces, there is always a need for some ground pressure. this is part of the reason why on some (dry) surfaces, a car with a small all terrain will outdrive a car with big swamper. (Mate, I have been there, and I was the one with the swampers )

Lowering tyre pressure is not all about lowering ground pressure. It also increases traction due to getting the tyre to conform to obstacles and introduce more edges (which have very high ground pressure) to grab with.

Steve.

[redzook]

Skinny tyres work better in sand for a couple of reasons. In any surface with yield, part oft he battle of moving the car is pushing the terrain in front of the tyre and compressing it. On sand, the car has to push a wave of sand in front of each tyre. This has two effects. One is that it absorbs power. secondly, it is like the car is constantly having to climb a small hill constantly.

Let's not talk width, lets talk contact patch. Fact is, on anything other than a sand rail, the power absorbtion of trying to turn the bogger in sand will mean that the nice elegant 7.50 will kill it everytime.

A narrower tyre has less sand to push ahead of it, so it is a more efficient way of moving the car.

Paris/Dakar and rallying are two areas where you will see very narrow tyres used on surfaces with yield (sand, snow)

Lancia experimented with wider and wider tyres back in the early 80's with their 037 rally car, and ended up reducing width and increasing diameter. It gave better drivability for the same ground pressure.

sure, in sand, lower ground pressure is better, but this is the only surface where this is true. On firmer surfaces, there is always a need for some ground pressure. this is part of the reason why on some (dry) surfaces, a car with a small all terrain will outdrive a car with big swamper. (Mate, I have been there, and I was the one with the swampers )

Lowering tyre pressure is not all about lowering ground pressure. It also increases traction due to getting the tyre to conform to obstacles and introduce more edges (which have very high ground pressure) to grab with.

Steve.

after living right on stockton beach i would have to dissagree there is no way a narrower tire is betta for sand

take it to the extremes imagine trying to drive on bike tires you would sink straight to the axles then imaginge a 20" wide tire there is no comparison

also have a look at most dune buggys wide tires at the rear to get good traction,drive and flotation
with skinnys on the front to dig in and really help it turn

just my opinion

[christover1]

narrower tire of same diameter as a widey is not good.

But a taller narrow tire better than short wide one.

For the same contact area, long narrow works better than short fat.

I bet bald tyres would probably work good on sand

christover

[Gwagensteve]

Hmm, interesting idea there Tim, I know how hard it is to ride a bike on sand, but the ground pressure on a bike is sky high. Lets compare the same size contact patch (about the size of a 50c piece on bitumen) with a 26" diameter mountain bike tyre, but make the tyre, say, 5" diameter and 3.5" wide. I can guarantee that this will be harder to ride in the sand.

My argument is that for the same size footprint, a narrower tyre is better. This is because is provides a longer footprint, which is more efficient to move, just like getting the front and rear tyres to follow each other where the rears are driving on the compacted sand of the front tyres.

In any case, in the scheme of things, you run tall narrow tyres - a 12.5" wide 37 has quite a high height to width ratio. If you ran a 31 15.5 on the sand, it might have the same contact patch, (and therefore ground pressure) but it woudn'y work as well, because it would be a lot harder to puch in the sand.

Sorry if it sounds like I am moving the goalposts, but height is far more important than width for drivability in all terrains IMHO.

Steve.

[HotFourOk]

To a certain extent, a taller (skinnier) tyre will go better on sand due to less 'bow wave' in front of the tyre. This results in less rolling resistance.

Although, at the same time, a wider footprint causes the tyre to float more on top of the surface and not dig into the sand. This is why you use lower pressures.

I've always thought : more rubber on the ground = more grip

And it looks phatter bro LOL

[christover1]

I've always thought : more rubber on the ground = more grip

yes, exactly.
But the same amount of rubber area in a longer skinny shape, rather than a short fatter shape, works better.


but yep, fat iz kewl

[Gwagensteve]

To a certain extent, a taller (skinnier) tyre will go better on sand due to less 'bow wave' in front of the tyre. This results in less rolling resistance.

Although, at the same time, a wider footprint causes the tyre to float more on top of the surface and not dig into the sand. This is why you use lower pressures.

I've always thought : more rubber on the ground = more grip

And it looks phatter bro LOL

Indeed, except that it is not necessarily a wider footprint that adds floatation, it can be a longer footprint too. On sand, it is all about the footprint size AND shape not size regardless of shape.

More rubber on the ground frequently does not equal more grip. that's why highway tyres (with a very low void ratio=lots of rubber on the ground for the same tyre size) don't work in lots off offroad situations. More void will increase the contact pressure for the same size, and generate more grip. This is why 235 85 16 mud terrains on slick mud have good bite but 35 12.5 muddies are not much chop in the sma conditions - once you increase the size of the tyre for the same vehicle weight you have to increase void to keep the ground pressure to maintain the bite.

The maximum possible amount of rubber on the ground for a given tyre size would be a slick. These are rarely much chop on a 4X4, but might be cool in sand

Steve.

[redzook]

narrower tire of same diameter as a widey is not good.

But a taller narrow tire better than short wide one.

100 percent true

but the question was width, so they are the only variables not height.

all things equal other then width the wider tire will do better

[toughnut]

I have run the silverstone M117 extremes now for the last 2 years. They are awsome in the mud and most surfaces. If you run the right rims they are also good in the rocks. The only thing that lets them down is the sand. The tread is a little too aggresive for soft sand and they just dig dig dig. Once you learn to drive with this they are awsome. The only other thing I'd prefer is if they were for a 15inch rim instead of 16. It'd give a bit more tire between your rims and rocks.

[GQ Toy]

I have noticed in the sand here, my mates simexes (35 x 10.5/16's) at 18psi are easier to drive than my claws (35 x 13.5/16's) at the same pressure, comes back to the bow wave and constantly climbing issue. I would find it easier to make my own tracks rather than follow his ruts

[Suspension Stuff]

The debate is hotting up.

It appears there might be an ideal width to height ratio for a specific surface in the sand, it would depend how soft I suppose.

Would 285/75/16 which is (20mm taller then most 33 inch tyres) be a good balance and what do you think is ideal for the 35 inch tyre and 31's to for the Zuk guys.

Cheers
Shane

[Beastmavster]

I also dont understand the surface pressures argument. If a tyre is inflated to 32PSI (POUNDS PER SQUARE INCH) it has exactly the same pressure over every square inch. Thats what 32PSI means.

The fact is, A wider tyre has more grip because it has more surface area with which to engage the friction coefficient of the surface it is on.

For those who dont understand the pressure/surface area thing I was talking about it has NOTHING to do with tyre pressure.

It's to do with the amount of weight the tyre is supporting, which is the weight of your 4wd. Whether you're on 305/70/16 or 285/75/16 the car basically will weigh the same.


Say you have a 3 tonne 4wd. On a level surface, each wheel has 750kg weight being carried on it (assuming 50/50 weight distribution front to rear for simplicity).


The 285 is 11.2" wide and the 305 is 12.0" wide. Both are the same construction and thus have a very similar length in footprint - the only difference is the width of the footprint, which is 7% wider on the 305.


So the 305 has 7% wider contact patch, and the 285 is putting 7% more pressure on the contact patch it has. This is how the thinner tyre digs into the mud or through the loose gravel easier - there is proportionally more weight on the contact area of the tyre.


Obviously in some circumstances, one tyre is better than the other.
On the road, wider tyres work better in the dry and skinnier tyres better in the wet for instance.



Changing tyre pressure is similar but different - it's do do with expanding the contact patch area, but to do so you reduce the pressure being exerted on each inch of tread touching the ground.

[Beastmavster]

The debate is hotting up.

It appears there might be an ideal width to height ratio for a specific surface in the sand, it would depend how soft I suppose.

Would 285/75/16 which is (20mm taller then most 33 inch tyres) be a good balance and what do you think is ideal for the 35 inch tyre and 31's to for the Zuk guys.

Cheers
Shane

When I wanted to buy some 33"s for the Patrol, I went for 285's over 33"s for these reasons.

Larger height - more clearance (about 15mm or more over a 33x12.5x15)
Tyre and rim combo is lighter - less strain on brakes, axles etc.
Shorter sidewall so less sidewall flex onroad = better handling, braking.


The downside for offroad I can see is the reduced sidewall flex and the greater likelihood of scratching my rims over a 12.5" wide tyre


Would I go to a 255/85/16 for the same reasons? If they were more common and cheaper, maybe. After all it's still as big or bigger a contact patch for onroad as the stock tyres, just much taller for offroad.

[Suspension Stuff]

So the 305 has 7% wider contact patch, and the 285 is putting 7% more pressure on the contact patch it has.

Nearly but not quite because of the extra weight per Square inch on the skinnier tyre it is likely to bag it out a bit more giving a slightly more contact patch then 1st thought. Still probably 5-6% more pressure per square inch than the larger tyre so it does not change what you have said.