Evolution of the Road Razor

Inspired by the success of my recent conversion from 110 mm cranks to 102 mm cranks on the 28, recent discussions in this forum about weight saving with lighter tubes on Copkers, and a conversation I had with the man in the local bike shop, I am once again toying with the idea of building the Road Razor: a super lightweight, super skinny 700c.

As a gesture of goodwill to the man in the shop who spent some time advising me about rims, even though he clearly thought I will never buy one, I bought a new tyre: a Continental Ultra GatorSkin, 700 x 28c. That’s instead of the 700 x 32c fitted as standard to my Nimbus 28.

I removed the old tyre and made a quick weight comparison using the kitchen scales. I reckon the saving was something in the region of 275 grammes. That’s not a lot when you’re picking the unicycle up, but it’s a lot less when you think that the tyre travels further than any other part of the unicycle, and has to be accelerated and decelerated more - and when you consider the gyroscopic effect on steering.

So, I swapped the tyres.

A scientist should only change one variable at a time, so that the effect of that one change, in isolation, can be assessed. However, I was impatient. As a nod in the direction of scientific analysis, I rode the uni up and down outside my house a little bit and decided it was “obviously loads better”. Ahem!

I then swapped the cranks, down to my old pair of Dotek 89s. I freemounted first time, and realised that the thread in one of the Doteks is damaged and the pedal was at an angle. Clearly, I’d need to change. Off came the 89s, and on went some cheap steel 90s from the bits box.

And then I was ready, so off I go down to the Water Sports Centre.

For the first time in a long time, I am quite nervous about riding. The 28 on 102s can be a bit temperamental, and the 90s are over 11% shorter. (Note to mathematicians: yes, I know there isn’t a unit of shortness, and that statement is therefore meaningless, but you know what it means.)

So, I freemount and step off again within about 2 metres. I stop, made as if to check my shoelaces and adjust the seat (just in case anyone is looking) then I freemount again and set off. So far so good - until 30 metres into the ride, I’m on a patch of ballast, I hit a stone that doesn’t move, and I’m on the floor. Elbow and knee bruised, wrist guards earning their keep. I remount and continue with great caution, until I’m on the tarmac again.

The first slope is a challenge, and I ride it more slowly than I would on 102s or 110s, because I know that I lack the braking power if I spin out of control. Then I’m on the flat lap of the lake. I stop briefly to tighten the crank nuts then continue.

It feels slower than on the 102s. Experimentation shows that it takes me about 10 pedal strokes to slow down to walking pace from somewhere near top speed. Every bump is a challenge. I find myself riding well within the comfort zone. On my first ride on the 102s, I found myself drawn forward as if by magnets, spinning faster and faster. Clearly, at my current level of ability, the 102s represent some sort of optimum, and the 90s are so short that they are counterproductive.

Stopping only once for a phone call (this time, a welcome one from a friend I’ve not seen in months) I do an easy 5 km lap of the lake. It takes virtually no effort. The tyre feels smooth and light, and is almost silent on the tarmac. However, the 90s make complete concentration an absolute necessity.

After the first lap, I decide to see what it can do by riding some of my usual easy cross country sections. Here, the shortness of the cranks is a problem, and it’s made worse by the very skinny tyre. Sometimes you need the confidence of long cranks to get you over some rough ground; sometimes you need the cushion of a soft tyre. The machine in its current set up is pure road, and although I can ride most (but not all) of my regular sections, it is too challenging to be unalloyed pleasure.

Back to the car park, I practise some slow speed stuff and idling. Idling it left foot down is achievable with great care. Right foot down is a bit of a lottery. (For comparison, I can idle my 20 (on 110s) for several minutes at a time, either foot down, or one footed.)

What I do notice is that the unicycle turns really nicely. The narrow tyre has a smoothish surface with a few narrow grooves cut into it for grip. The old 32mm tyre had a moulded tread. The new tyre makes the uni much nicer to turn on the spot, and small figure eights are easy.

Back onto the circuit, I keep to the rougher sections, and find that the uni is very temperamental indeed. The tyre has no cushioning effect if I hit a stone, and the cranks are too short to give me that sudden burst of control I need to recover from a surprise. However, I do manage to ride up and down the zig zag path - that’s no great achievement in itself, but it’s a section that I use as a yardstick because I can never be 100% certain of riding it on any set up.

Over to the canoe slalom course, I find it impossible to ride up the smallest of kerbs onto the footbridge - and I attribute this to the very narrow high pressure tyre - and I UPD as I drop down the very small kerb at the other end - this being more to do with the lack of control because of the short cranks. (I’m not making excuses here, just saying that I know my abilities well enough to recognise which of the two new factors was more significant in each case.)

Back to the car, and a bit more slow speed stuff, then home to write this up.


Riding a 28 on 90 mm cranks is easy enough on the flat, but it offers no speed advantage (to me) over 102s. (102s do offer a speed advantage (to me) over 110s.)

On 90 mm cranks, the margin for error is very much reduced, and there are safety considerations on hills, unpredictable surfaces, and near traffic or crowds.

The 28 mm tyre is nice for road riding, and slow speed control and manoeuvrability, but makes the wheel very vulnerable to “tripping up” if it hits something that doesn’t have any “give” in it.

Lightening the tyre (or, presumably, the tube, wheel rim, rim tape and spokes) does make a significant difference to idle-ability and the effort required to ride.

I will stick with the idea of getting a really nice light wheel, but for now, 102s for speed, 110s for control, 90s only for novelty factor and practice.

A good friend of mine came to the same conclusion on 89 mm cranks, i think you could only get the extra speed out of them if you were really good at controlling longer cranks. Been meaning to ask, and it is vaguely related, has anyone tried making a uni using a racing bike wheel? By which i mean somethign with wheels like this: http://www.velotours.co.uk/velotours-racing-bike-france-touring-france-spain.jpg (just a random example) All the road unis i’ve seen still seem to sport relatively wide tyres, nothing like the tyre and rim sets i see on the road and racing bikes of my friends. I’m guessing someone’s going to come back saying either that they’re not strong enough or the hardness of the tyre makes them unrideable but i just thought i’d see

Aah, a story from Mikefule makes my weekend (I think I missed you last weekend, did you write one?)


Riding Through the Glen - last Sunday’s ride
102 Damnations - Tuesday’s ride

For the first time in ages, I rode three days in a row.

I don’t write up every ride, because most of them are very similar - fun to do, but nothing to report. It never fails to surprise me that people ask for the stories, so they’ll keep coming from time to time.

Yes, I read those. Must have been the weekend before that I was thinking about.

Keep riding and writing. I do enjoy them.


No doubt about it, it is far easier to ride on a wide fat tyre than a skinny hard one.

On a bicycle, your weight is supported by your seat and by your handlebars. On a unicycle, as you may have noticed, it is all on the seat. Thus, a nice squidgy tyre makes it less uncomfortable. It is unwise to put any form of suspension between the hub and the seat - such as sprung forks or a shock absorbant seatpost - because it alters the distance between the seat and the pedals.

On a bicycle, you are inherently stable along the direction of travel. On a unicycle, if you hit a bump or obstacle, your weight is thrown forwards and you need to recover your balance. A soft tyre softens the blows and smooths out these sudden changes in wheel speed.

Also, there is an argument that the heavier wider tyre generates a flywheel effect which keeps the unicycle going over uneven ground. The most famous example is the “autopilot” effect you get when riding a standard steel-rimmed Coker.

So there is no practical argument whatsoever for having a hard skinny tyre on a unicycle. It is less comfortable, less forgiving, and requires more concentration.

However, there are few practical arguments for having a unicycle at all. Unicycling is a sport in which we all choose our own levels and styles of challenge. I like the elegance and purity of the 700c. It’s the nearest thing to a “one wheeled bike”. It is light and portable; it covers distance reasonably well 10 - 15 mile rides are easy); it is safe on the roads, and amongst pedestrians; and it is instantly recogniseable to serious bicyclists, as a “proper wheel” and they treat it with more respect and, indeed, with genuine interest.

And I forgot “4 inches of frantic fun”

I tend to think of your stories collectively as ‘Tales from the Riverbank’ although I know not all of them involve water.


Re: Evolution of the Road Razor

On Sat, 30 Jul 2005 13:28:45 -0500, “Mikefule” wrote:

>That’s instead of the 700 x 32c fitted as standard to my Nimbus 28.

Are you sure? ISTR that your Nimbus 28 from UDC came with a 35 mm wide
tyre (as came mine). If so, it sets the Road Razor further apart from
the original Nimbus (if only by 3 mm…).

Seems that you should put the 102’s back on.

Klaas Bil - Newsgroup Addict

I ride like a princess. - john_childs

Re: Evolution of the Road Razor

On Sat, 30 Jul 2005 15:56:53 -0500, “kington99” wrote:

>has anyone tried making a uni using a racing bike

In addition to Mikefule’s reply: A skinny tyre has less aerodynamical
drag. On a racing bike this is a significant factor. On a unicycle,
with its generally lower speed, this advantage is practically

And the rolling resistance of a wide tyre is even LOWER than that of a
narrow tyre (profile and pressure being the same).

Klaas Bil - Newsgroup Addict

I ride like a princess. - john_childs

Re: Re: Evolution of the Road Razor

Ooops! yes, you’re right. I wrote from memory, rather than checking. The original tyre was indeed 700 x 35C.

“Only” 3mm - this is a case where the percentages are more important than the numbers. There is a comparison here with cranks or wheel size. When you get to very small numbers, a “small” difference is a bigger perceentage difference.

Thus, the 12 mm drop from 102s to 90s is quite significant (12%) but a 12 mm drop from 152s to 140s is minor (8%). (Note that 12% is 50% more than 8%!)

And with wheels, a 24 is 2 inches (10%) bigger than a 20. A 26 is 2 inches (8.3%) bigger than a 24, and a 28 is 2 inches (7.7%) bigger than a 26.

So the 28 mm tyre is only 7 mm narrower than the 35, but that is a difference of 20%.

I have, of course, put the 102s back on. Whether the elegance, smoothness and pose value of the new tyre is worth the extra fidgetiness on rough ground is something that only time will tell.

about light tires - if you laced one of those super-light road bike wheels up into a 28’er (700c?), wouldn’t it control really well? Would it rival a 20, or perhaps a 24 for general maneuverability on hard smooth surfaces (thinking road here)?

I’d be really interested in that. Also, my friend has a red nimbus 29’er with a big apple on it - is that the same frame/rim as yours, mikefule? Just trying to get a feel for what you’re riding here.


The uni started life as a Nimbus 1, 28.

It has the standard Nimbus 700c rim which is clearly designed for a standard 700c x 35 tyre. I’ve never tried to fit anything fatter.

As for comparisons to a 20: think of the 28 as a big 24, not a small Coker.

With long cranks (here, I’m thinking 125 or possibly 150) it is more or less as easy to ride as a 24. When I bought it, it had 110s, and I was able to idle it easily on a perfectly smooth gym floor.

Where you do lose out on manoeuvreability is that your weight is a bit higher, so idling is a slower “pendulum swing”, and the larger radius of the curve of the wheel means that tight turns are a little less tight.

On a perfectly smooth surface, with the skinny tyre, it is a beautiful feeling to ride a 28. On a rougher surface, it is an entertaining challenge.

What I like about unicycling is that there are so few variables (wheel size, crank length, tyre section) and you need to choose a set up optimised for a certain type of riding. Nothing is perfect for everything. Me being me, I tend to avoid the obvious, which is why I’ve been riding cross country on a 28 (rather than a 29) and I’ve been known to do long distances (20 + miles) on a 24 when I have the Coker available. It’s all good fun.

That’s really interesting. My friend has a Nimbus 29’er, and it feels like a small coker, ‘autopilot effect’ and everything. I can’t idle on it at all! It’s amazing the difference rotating mass out at the rim can make, I guess. Hers is still fun to ride though - it’s so smooth! Very slick.

To demonstrate the rotating mass at the rim effect, take a household broom.

Hold it so the handle is vertical. Now, with a single twist of the wrist, start it spinning, then stop it by tightening your grip.


Now, using the same broom, find the balance point and hold the broom horizontally with one hand at the balance point. Now, with a single twist of the wrist… much harder, isn’t it?

Exactly the same mass, but it’s further from the centre of rotation, so it’s harder to start, and harder to stop.

Ice dancers control their speed of rotation by moving their arms in and out slightly, using the same principle.

As for idling a 29, it should be possible, but you have to be less aggressive, and more thoughtful. Idling a 20 can be done with brute force, and you can do it fast or slowly. On a bigger uni, you need to work with the unicycle’s natural period of oscillation. That means a gentle prod of the pedal to start it moving, and leave plenty of time to slow it down, or it will kick straight past you and spit you off.

Idling is moving from one position to another and back again, at exactly the right speed.