Thread: Skinny Tyres Vs Fat Tyres

Originally Posted by PAT303

You missed my point,a long tread is better than a short one.You have to keep things in perspective,a 35x12.5 is wide compared to a tractor tyre or track,it would be 10 feet across if made the same dia.I asked my local tyre bloke about this and he said the bigger the tyre the lower the pressure,lower pressure also gives more bite.I ran 40psi in my 7.50's,I now only run 34 in the 33's and that gives an advantage on it's own.One last thing I have noticed that the ball bearing gravel over here eats wide AT tyres yet narrower aggressive tyres aren't worried as much. Pat

I understood your point. You missed mine.

I don't think anyone is saying that small and fat is better than long and skinny - I certainly am not. A larger diameter tyre will certainly roll much better over uneven ground - so running a larger diameter is definitely better (in almost all cases).

However - you can only go so big (regardless if you are talking legal sizes or not). So my point is, that for a given diameter, a wider tyre will give you more traction in DIFFICULT offroad situations.

I agree with you that (touring) on WA pea gravel is probably better with narrow tyres.

Some interesting stuff guys...I'm going to be in the market for new tyres in the next few months and am hoping to get something a little higher than the 7.5 R16's I've got on the Defender atm...am leaning toward 255/85/R16 so far.

By the way, I came across an interesting article from some guy in the States who fitted 255/85/R16's BFG MT's and gives an interesting insight into his reasons for liking narrow tyres over wide:

Expeditions West: Tire Selection for Expedition Travel
Expeditions West: BFG 255/85 R16 MT KM, 33 x 10.5

Originally Posted by isuzurover

True, but if it gave a real competitive advantage to run skinnys then I'm sure someone would try them.
e.g. - steer tyres on 2wd offroad buggys are VERY skinny - it obviously gives them lighter weight and more precise cornering.
As I said above - ice tyres in the WRC are skinny - 145s!!! Since the car is actually riding on the studs, the total contact patch is the size of a postage stamp!!!

And what about events like the Dakar? The 4x4s run pretty wide tyres, and the trucks run SERIOUSLY wide tyres (see pic below) - but in the heavy truck field, you can't argue that serious R&D hasn't gone into skinny tyres.

The small slits that the manufactures put in the lugs of tyres add 13% more grip than when their left out, something to do with the nature of rubber under a shearing force. Racing slicks do not have them as they use a soft compound that would not have an acceptable life outside of the race track.

This is just one of the known tyre features that is being phased out by fashion.

Youtube has lots of video where big tyres spread the load to thin to get good traction.

YouTube - Defender vs Unimog (part 2)

Those small slit are called sips and they are to aid wet weather traction. The tread evacuates the bulk of the water and the sips mop up as much as possible of what wetness remains under the tyre.

WRT slicks, it has nothing to do with tread life, a slick pattern is all about performance. Actually, introducing sips will cause reduced tyre performance and increased heat due to tread block squirm. F1 slicks are grooved due to FIA regulations and the goal is to slow the cars (which narrowing the tyre failed to do due to aerodynamics), and cutting tyres is also done in some catagories to get a slightly different shape onto the tyre or to remove some edge to fix problems - eg prod cars on soft tyres. Slicks do have holes in them though, these are purely tread depth indicators.

For 4WDing, it isn't uncommon for people running rock crawling tyres etc to add additional tread cuts into the tyre also, but this is usually to make a stiff thick tyre more able to flex and mould to the surface it is on. These are full cuts though, not sips. The other thing that sips can do when used on open pattern tyres, is to increase the susceptability for them to fracture the tread blocks. This is notable on the Cooper ST.

Originally Posted by samuelclarke

Some interesting stuff guys...I'm going to be in the market for new tyres in the next few months and am hoping to get something a little higher than the 7.5 R16's I've got on the Defender atm...am leaning toward 255/85/R16 so far.

By the way, I came across an interesting article from some guy in the States who fitted 255/85/R16's BFG MT's and gives an interesting insight into his reasons for liking narrow tyres over wide:

Expeditions West: Tire Selection for Expedition Travel
Expeditions West: BFG 255/85 R16 MT KM, 33 x 10.5

I agree with that guy that a tall skinny tyre is best on a touring vehicle. Most of his science is OK, however he has one fundamental flaw - his "mechanical locking" theory assumes that more pressure is better... This implies that a heavier 4x4 is more capable (all other things being equal) - but this is not the case...

I also have my doubts about someone who is sponsored by a tyre seller...

Slunnie - I agree - however the word is "sipe", names after John Sipe, who in 1920ish foundf that small cuts in his shoe soles improved grip in the wet.

Snow tyres have thousands of sipes, but they handle like crap on dry roads.

Originally Posted by isuzurover

Slunnie - I agree - however the word is "sipe", names after John Sipe, who in 1920ish foundf that small cuts in his shoe soles improved grip in the wet.

Oops.

Oh wow, talk about innovation from.... oh well.

Love to see those skinnies in Black Soil

Dig down to this.....


BTW, Anything sub 255 is skinny... Even my bike has a wider tyre

Since PAT303 mentioned tractors...

Yes - the tractor manufacturers know what they are doing - and they have obviously come to the conclusion that skinnys are better - hence modern tractor designs that look like this:




As you can see - VERY skinny