specifically roads only big wheel?

well, i was wondering...
you know them b*kes with the really skinny tires made for roads and
roads only?

well... has anyone made a big(ish) wheel like that?
and what is the biggest skinny road tire size that is currently made
today? the largest i've found is a 28...
I've been curious about it... it'd dramatically reduce the wieght for
long distance rides...


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abbabibble wrote:
well, i was wondering...
you know them b*kes with the really skinny tires made for roads and
roads only?

well... has anyone made a big(ish) wheel like that?
and what is the biggest skinny road tire size that is currently made
today?



I put a skinny road tyre on my 28" to see how it would handle. I
didn't like it all. It was incredibly light but the weight savings
were outweighed by some big disadvantages.

The road tyre was significantly harder to balance on, probably because
the contact patch had been substantially reduced. Also when riding I
felt absolutely every bump and road camber was very noticeable. I
spent a lot of time feeling very unstable and the lack of friction was
very noticeable. After losing traction on several corners I gave it up
as a bad idea and wrote off the tyre as lost money.

I have seen people race unicycles with very skinny tyres and that is
probably the only good use for them. I imagine they could confer an
advantage on a smooth level surface while riding in a straight line or
a gentle curve. They are not at all suited for general road riding.


--
peter.bier

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The standard European size for a bicycle road wheel is 700c, which is
what we often refer to as a 28.

Although a few older bicycles had slightly larger wheels, there isn't
much real difference - an inch or so. Above that size, ther is only
the 36 (Coker).

I have a 700c to which I have fitted a 700c x 28mm tyre. I use 102mm
cranks. It is a joy to ride. It's a little tempramental, a little
twitchy, but so light that it accelerates, brakes and idles nicely. I
did a 50 mile ride on it earlier this year.

To be honest, a fatter tyre would be faster and more comfortable, and
easier to ride. But that's not the point. When funds allow, I will
probably get an even skinnier wheel built and take the tyre down to 24
mm, or maybe even less - not for any genuine speed improvement, but for
the purity of the riding experience.


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Mikefule, do you have any comment on the road camber experience that
peter.bier referred to?


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goldenchicken
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Yes.

The road camber problem is less noticeable with a good quality skinny
tyre.

"Road camber problems" are the sort of problems you get when you ride
across a slope, rather than up or down it. Many roads have a "camber"
which means the centre of the road is slightly higher than the edges.
This is for drainage. other roads are deliberately cambered in the
direction of a corner, like a banked race track, to help motor vehicles
travelling at normal traffic speeds.

If you are riding across a slope (e.g. along a cambered road) and you
are trying to keep your unicycle vertical, then the width of the
contact patch is critical.

The theoretically perfect wheel would have no width at all, but this
could never exist in reality. A skinny tyre might have a contact patch
10 mm wide, and a fat tyre might have one 20mm wide. (These are not
accurate figures, but simply to illustrate a point.) The width of the
contact patch will depend on the shape of the tyre, the pressure in the
tyre, and the steepness of the camber.

Along the central axis of the tyre, the rolling circumference is at its
greatest. the further you move to one side, the smaller the rolling
circumference.

Thus, when you are riding across a camber, one edge of your contact
patch (down slope) is where the wheel is largest, and the other side
(up slope) is where the wheel is smallest.

So, instead of riding on a nice round tyre, you are effectively riding
on a truncated cone. You can all visualise what would happen if you
rolled a cone: it would turn one way. So, the tyre that is being
ridden across a slope will tend to turn up the slope. This effect is
sometimes called "coning".

It follows that, all other things being equal, the narrower tyre will
have less coning effect than the wider one.

A secondary effect is that a narrow tyre will tend to be shallower
(lower profile) so you need a higher air pressure to be sure of keeping
the rim from "dinging" if you hit a pebble, kerb, etc. The higher
pressure will contribute further to keeping the contact patch narrow
and reducing the coning effect.

Some of the same factors contribute to making a (good) skinny tyre much
easier to steer. The ideal tyre for steering has a rounded cross
section.

However, the sensitivity to bumps and sudden changes in the rolling
resistance of the surface on which you are riding is more noticeable on
a skinny high pressure tyre. This is partly due to the higher momentum
of the fatter tyre (it can ignore minor variations) and partly due to
the reduced air pressure in the fatter tyre, which can soak up the
small bumps.

So, riding a skinny high pressure tyre is great fun, and feels precise
and controllable when steering, but it can be hard work over a long
ride on uneven ground because it requires much more concentration and
adjustment of speed and pedal-force.

On my 700c X 28mm tyre, with 102 mm cranks, I have done some light
cross country. With 110s, it is surprisingly nimble. The tyre becomes
a limiting factor only when traction is poor, or when the ground is
yielding, or when the ground has sudden changes in contour (e.g. tree
roots etc.).

I haven't ridden much recently, mainly due to old age, bad weather and
other commitments. However, writing about it is making me miss the
700c - it is the purest form of unicycling that I have tried, because
the tyre has no built in margin for error on uneven ground.

Also, it is good for drops of up to about 5 feet.

Too keep the interest of the reader, I have included one factual
statement in this post that is not actually strictly true.


--
Mikefule

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On Sat, 3 Dec 2005 10:00:51 -0600, Mikefule wrote:

(snipped)

That was one interesting read Mikefule, and most of it was strictly
true. My Nimbus II 700c was delivered with a 35 mm tyre, and now has a
Big Apple. The BA is much better for general road riding.

I'd like to add two points:

Surprisingly, the rolling resistance of a wide tyre is SMALLER than
that of a narrow tyre, if tread pattern and pressure are the same.

There is one more thing than 'coning' that contributes to adverse
camber effects. The following is my theory. The tyre starts hitting
the road while it is relaxed and located in the symmetry plane of the
wheel. In the middle of the contact patch however, the tyre is
load-bearing and since you're on a cross-slope, this will cause it to
'fold' somewhat. That makes the wheel travel in a direction that is
different from the plane in which it is rotating.

1. The effect is larger when tyre pressure is low.
2. The effect is larger with a wider tyre which has more height to
fold.
(1 and 2 often -but not necessarily- go together.)
3. And obviously, the effect is larger with more camber.

Klaas Bil - Newsgroup Addict
--
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Interesting, Mikefule. The cone theory was new to me but I had no
problem swallowing it. However, we all know that a 700c wheel can be
dropped at least 10 feet. Actually, I think you can even throw it out
from an airplane.


--
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Klaas Bil wrote:

My Nimbus II 700c was delivered with a 35 mm tyre, and now has a
Big Apple. The BA is much better for general road riding.



An experienced road unicyclist here in Sweden was appalled by the
effect that BA had on his riding after buying a 29er. The wide contact
path made him very sensitive to the slightest angle of the road. He
quickly sold the 29er and went back to his old 28 frame with a narrow
tyre.

But! some months later he bought a Coker and almost went lyrical about
it. Now, why doesn't that fat monster tyre pull him into 'coning'?

This is also my own experience, on the Coker I seldom have any 'camber
problems'. Only wind & ass problems.


--
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goldenchicken wrote:

But! some months later he bought a Coker and almost went lyrical about
it. Now, why doesn't that fat monster tyre pull him into 'coning'?

This is also my own experience, on the Coker I seldom have any 'camber
problems'. Only wind & ass problems.




Given a similar tyre section and profile, the Coker will cone less than
a 29.

The difference in radius between each side of the contact patch will be
the same in millimetres - but as a proportion, it will be different.

To illustrate, assume that the radius of the upslope edge of the
contact patch is 5 mm less than the radius of the downslope edge of the
contact patch.

Now, to take an extreme (and physically impossible) example: a 10mm
diameter wheel would become a perfect cone, rather than a truncated
cone. On the other hand, a 5mm difference would be completely lost on
a 10 metre wheel.

A Coker is 36/29 as big as a 29. That's almost a quarter bigger. That
is enough for the proportional effect of the coning to be significantly
reduced.

Moving back to Klaas Bil's points:

Yes, the rolling resistance of a fatter tyre should be less - at the
same pressure. The contact patch will be a bit wider, and therefore a
bit "shorter" (front to rear along the direction of travel). Therefore
the angle of the front edge of the deformation of the tyre, relative to
the vertical, will be nearer to 90 degrees. With no deformation of the
tyre at all, along the direction of travel, and given a perfectly
smooth surface there would be no energy lost to the rolling resistance
of the tyre.

In practice, I suspect most fat tyres are run at lower pressure than
most thin tyres. Most fat tyres have a knobblier tread. These two
things would tend to reduce the effect Klaas Bil describes.

Also, the offset thing: given a hard tyre with no deformation at all,
when riding across a slope (or along a cambered road) then the central
plane of the tyre would be out of contact with the road altogether and
that would introduce some interesting handling quirks.


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In message
essage.Poster.at.Unicyc
list.com, Mikefule
writes
Thus, when you are riding across a camber, one edge of your contact
patch (down slope) is where the wheel is largest, and the other side
(up slope) is where the wheel is smallest.

So, instead of riding on a nice round tyre, you are effectively riding
on a truncated cone. You can all visualise what would happen if you
rolled a cone: it would turn one way. So, the tyre that is being
ridden across a slope will tend to turn up the slope. This effect is
sometimes called "coning".

I wouldn't dispute your logic, and I'm a rather inexperienced uni rider,
but my impression is that my cycle wants to veer downhill when riding on
a camber. Is this others' experience or have I interpreted what's
happening wrong?

Wassail!
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