Today we had a dry spell in a rainy season and I went out for a spin.
Lots of mud and skidding around (that’s also an answer to Andrew C’s
question - be it that my skidding was not on purpose). On a few
downhills the wheel slipped away from under me - splash!
I have a Contra Identiti 24 x 3.0 tyre which has a quite agressive
profile <www.xs4all.nl/~klaasbil/tyres.jpg> but at the time it was
full of mud. Do even more aggressively profiled MUni tyres exist and
would that be useful? Or maybe the would be for these mud
circumstances but not overall?
(I reckon aggressiveness is some combination of knobblies’ numbers,
pattern, width and height. More precise definition welcome.)
I’ve got the same tyre; the only time I can remember skidding was on a wet, smooth metal surface, so that’s not entirely unsurprising. It always strikes me that while the knobbles may be quite big there don’t seem to be very many of them…
The way I see it, the tread pattern for a road tyre consists of grooves cut into the rubber. The grooves allow water to disperse, leaving the road surface as dry as can be achieved, so that the big blocks of rubber can grip it. The grip is created by the size of the contact patch (rubber to tarmac) and the friction coefficients of the rubber and tarmac.
On the other hand, an off road tyre is ‘the other way round’. Instead of smooth rubber with grooves cut in it, it is smooth rubber with lumps stuck on it - it’s a question of emphasis. The grip comes from the knobs digging in, not the ‘stickiness’ of the rubber.
The closer the knobbles, the easier it is for the gaps to become clogged with mud. The further apart they are, the less rubber there is touching the ground, so the less friction there is.
So a few knobbles to dig into the mud might work in the mud but would be counterproductive on the dry rocky sections of the same ride. So it’s a compromise.
I did see an interesting tyre the other day when I was looking for one for my MUni, and the tread consisted simple of two rows of blocks. each block was about 1cm wide (in the direction of travel) and half the tread width across. The gaps between the blocks were identically sized, and the left row was in the opposite phase to the right row. The following diagram may be clearer:
/ / / / /
\ \ \ \ \
I almost bought it, but thought it would make my teeth rattle on the tarmac sections. If it helps, I will go to the shop and see what it’s called. (The tyre, not the shop, fool! )
I’ve found that tires with a relatively smooth tread or microtread do better in mud for me. The smooth tread allows the tire to shed the mud easier so you always get tire onto the mud instead of mud onto the mud. It also helps keep your uni from waying 2 tonnes from all the mud in the tire. I run a 2.1 by 26 IRC mythos front on my pashley. I have found that the mythos rear (with a micro tread down the middle) has worked very well for me in all conditions and wears out relatively slowly on the road. These tires are also really cheap. Although I have never used hutchinson tires, they are also recomended for wet conditions with mountain B*kes.
-gauss
>I did see an interesting tyre the other day when I was looking for one
>for my MUni, and the tread consisted simple of two rows of blocks. each
>block was about 1cm wide (in the direction of travel) and half the tread
>width across. The gaps between the blocks were identically sized, and
>the left row was in the opposite phase to the right row. The following
>diagram may be clearer:
>
>/ / / / /
>\ \ \ \
>
>I almost bought it, but thought it would make my teeth rattle on the
>tarmac sections. If it helps, I will go to the shop and see what it’s
>called. (The tyre, not the shop, fool! )
I’ve seen a similar tread pattern on very large tractor tyres. If the
spacing and the obliquity (SP?) of the blocks work together well, then
one block (pair of blocks really) takes over the support when the
other is about to “let go”. So it would be teeth-rattle safe.
>It
>always strikes me that while the knobbles may be quite big there don’t
>seem to be very many of them…
My guess is that just because there are few knobbles, each one presses
firmly into the mud and thus is in a position to enhance traction. If
you increase the number of knobbles (keeping their size constant) they
would sink less into the mud; eventually the tyre would be knobbles
only - that would definitely not grip well. My gut feel tells me that
the usual knobbles / non-knobbles ratio is about optimal.
)