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…
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.
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.
Mikefule, do you have any comment on the road camber experience that peter.bier referred to?
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.
Re: specifically roads only big wheel?
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.
“erectile function trumps public image - David Stone, commenting on the importance of seat comfort”
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.
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.
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.
Re: specifically roads only big wheel?
In message
<e36f1122069d9a6597d604da045c8f18.1zh1s0@NoEmail.Message.Poster.at.Unicyc
list.com>, Mikefule <Mikefule@NoEmail.Message.Poster.at.Unicyclist.com>
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?
Martin E Phillips nb Boden, Splatt Bridge
http://www.g4cio.demon.co.uk martin/at/g4cio/dot/demon/dot/co/dot/uk
Homebrewing, black pudding, boats, morris dancing, ham radio and more!
The Gloucester-Sharpness canal page http://www.glos-sharpness.org.uk
The yellow uni in the middle of this pic has a very skinny tire. I have no idea what size it is. It’s hanging in Darren’s shop. (I inverted the pic.) Any ideas?
The yellow uni in the middle of this pic has a very narrow tire. I have no idea what size it is. It’s hanging in Darren’s shop. (I inverted the pic.) Any ideas?
[QUOTE=Martin Phillips]
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?
QUOTE]
I’m sure about the basic logic of what I am saying about coning. It is a recognised phenomenon. It comes up from time time in motorcycle magazines along with a phenomenon called “white lining” when the motorcycle “squirms” as the tyres catch the edge of the white painted lines in the road. This is because the paint is sometimes quite thick - thick enough to create a coning effect that is noticeable at motorcycling speeds. On my Vespa scooter (modern with 13 inch wheels) the effect can be most unpleasant.
But if you are a relatively inexperienced unicyclist, two things might be happening:
Simply your perception might be wrong because “common sense” would suggest that you would tend to drift down the slope because of gravity. You perceive what you expect to perceive because you’re not yet able to interpet the feedback accurately.
If you are still at the stage where your tyre track is more of a sine wave than a straight line (ahem;) ) then the coning effect might be less obvious than the tendency for the unicycle to roll down the hill on that part of the sine wave, and the slightly increased resistance to pedalling on the part of the wave where you are going back up the slope.
Wow, that’s a beauty. It will say on the side of the tyre if you’re really interested. It’ll say something like 700c x 28, or 700c x 32. (Or an imperial (inches) size like 27 x 1 1/4 .
At a guess, I’d say it’s probably around 28 mm, same as mine. Coul dbe a touch narrower. Nice looking machine. 
Re: specifically roads only big wheel?
On Sat, 3 Dec 2005 22:15:53 +0000, Martin Phillips <martin@nospam.com>
wrote:
>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?
The effect that I described (the tyre partially folding at the contact
point) would move the unicycle downhill. I’m not sure if it would
‘veer’ downhill, in the sense that the heading changes. But I agree,
when I ride on a camber, it feels as if I constantly must attempt to
turn uphill a bit, or else I would drift downhill.
As a remedy, increase your tyre pressure. (As an alternative remedy,
relocate laterally on the road/path/whatever where there is less or no
camber. Watch out for other traffic though.)
“erectile function trumps public image - David Stone, commenting on the importance of seat comfort”
Re: specifically roads only big wheel?
In message <43928b3f.2647725@newszilla.xs4all.nl>, Klaas Bil
<klaasbil_remove_the_spamkiller_@xs4all.nl> writes
>On Sat, 3 Dec 2005 22:15:53 +0000, Martin Phillips <martin@nospam.com>
>wrote:
>
>>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?
>
>The effect that I described (the tyre partially folding at the contact
>point) would move the unicycle downhill. I’m not sure if it would
>‘veer’ downhill, in the sense that the heading changes. But I agree,
>when I ride on a camber, it feels as if I constantly must attempt to
>turn uphill a bit, or else I would drift downhill.
I suspect that the situation isn’t quite as simple as Mike’s geometric
interpretation, and almost certainly complicated by knobbly tires (I’m
riding on a 2.5" x 20" tyre at the moment, until the Nimbus 26" that
I’ve just ordered arrives 
I seem to cycle on cambers with “shoulders
to the mountain”, as ski instructors say, so my hips are twisting round
in the uphill direction.
Will try to find a well-cambered road later and ponder what’s happening
more…
>As a remedy, increase your tyre pressure. (As an alternative remedy,
>relocate laterally on the road/path/whatever where there is less or no
>camber. Watch out for other traffic though.)
More tyre pressure definitely helps. The lanes around here seem to be
cambered randomly!
Martin E Phillips nb Boden, Splatt Bridge
http://www.g4cio.demon.co.uk martin/at/g4cio/dot/demon/dot/co/dot/uk
Homebrewing, black pudding, boats, morris dancing, ham radio and more!
The Gloucester-Sharpness canal page http://www.glos-sharpness.org.uk
[QUOTE=Martin Phillips]
I suspect that the situation isn’t quite as simple as Mike’s geometric
interpretation, and almost certainly complicated by knobbly tires (I’m
riding on a 2.5" x 20" tyre at the moment, until the Nimbus 26" that
I’ve just ordered arrives I seem to cycle on cambers with “shoulders
to the mountain”, as ski instructors say, so my hips are twisting round
in the uphill direction.
QUOTE]
I agree. There are many variables. Introducing too many of them into my earlier explanation would have made a complex post even more so.
The tread of the tyre is indeed critical, as is the profile of the ttre.
On my 26 Pashley MUni, the original tyre was almost unrideable on a hard surface. It had a central row of knobbles in a soft compound. These would “smear” randomly, but once the direction of smear had been established, it would stick until a change of camber overcame it. the tyre therefore had a constant drag one way or the other.
I replaced it with a slightly better tyre (Michelin Wildgripper) and later replaced that with a Gazzaloddi 2.3". the Gazz was virtually unrideable on hard surfaces and across slopes, and it steered like a pig on ice skates.
I now have Maxxis Holy Roller which has the right combination of profile (very rounded) and knobbles to make steering predictable, and it hardly cones.
As for the upper body thing: you’re right. There’s a lower body thing too. Most people are lopsided when they stand still, never mind when they’re unicycling. My dad went to one of those back specialists, who made him stand with one foot on one set of scales and his other foot on another set. (Fortunately the two sets of scales were near to each other.) One set of scales read about 10 pounds higher than the other because even when he waas trying to stand straight, he wasn’t.
The effect that I described (the tyre partially folding at the contact
point) would move the unicycle downhill.
A soft tyre ridden along a sloped road would be compressed so that most of it (looking at a cross section) would reside on the up slope side of the rim. I can’t see how this can affect the direction you are going unless you count in the cone effect.
Mikefule, you have convinced me that the size of the wheel to some degree lessens the coning effect. I wish there was a 20 mm wide tyre for the airfoil rim so I could really try the theory.
I wrote earlier that I hardly ever have problems on sloped roads. I should have written I can hardly remember having this problem. My memory is very short you see. Today was an exception. Making my regular Coker ride I discovered that a portion of it comprises a sloped bike lane. I guess looking from behind you would see the Coker pointing at eleven o’clock while my upper body aims for one o’clock. Must look silly. Makes it impossible to tell whether it is tea time or not. And it is bloody uncomfortable.
Thanks to this enlightening discussion I now remember my suffering.
Re: specifically roads only big wheel?
On Sun, 4 Dec 2005 05:45:40 -0600, goldenchicken wrote:
>A soft tyre ridden along a sloped road would be compressed so that most
>of it (looking at a cross section) would reside on the up slope side of
>the rim. I can’t see how this can affect the direction you are going
>unless you count in the cone effect.
Let’s assume a wheel rolls across (perpendicular to) a slope, with the
downhill side to the right. (I don’t mean that the wheel is
off-vertical, just that the direction of maximum downslope is exactly
to the right of the rider.) Let’s further assume that the plane of the
wheel is in the same direction as its movement. Now take a point A
along the circumference of the rim, being somewhere in mid-air. There
is a point on the outer circumference of the tyre corresponding to A,
let’s call it B. Now at some point in time while the wheel rolls
forward, B hits the road. At that moment, the tyre sits in first
approximation symmetrically on the rim at that point. (For sake of
simplicity, I forget that the tyre will hit the road first with a
point somewhat beside the centre line of the tyre due to the cross
slope. I also forget that the tyre has some elasticity and will ‘feel’
the road coming even though it hasn’t touched it yet.) Let the point
on the road where B hits it be called C.
Now consider the wheel rolling further forward so much that that A and
B are at the bottom of the wheel, i.e. in the longitudinal centre of
the contact patch. The cross section of the tyre at A and B will be
deformed by now. The tyre has folded such that most of the tyre
contact patch will reside on the up slope side of the rim. I assume
that the tyre has not slipped along the road surface. Therefore, B is
still touching C. However, A has moved to the right of B (i.e.
downslope) because of the deformation of the tyre. Assuming that the
plane of the wheel still is perpendicular to the slope, that means
that the wheel has undergone a lateral translation, in the downslope
direction.
And this process is ongoing continuously, so that the direction in
which the wheel travels is not perpendicular to the slope, but
somewhat more downhill. To counteract this tendency, you need to
constantly steer upslope.
QED.
But could probably have been done less wordy.
“erectile function trumps public image - David Stone, commenting on the importance of seat comfort”
Soft tyre wants to go down slope (deformation)
Hard tyre wants to go up slope (coning)
With the ideal pressure the wheel would go straight?