Cranky conclusions

Unicycles and Equipment
1

Just been out for a blast on the 24 with the teeny weeny 89mm cranks.

Top recorded speed according to the computer was 16mph, and my back of the envelope calculation translates that into 224 rpm. I simply can’t believe that, but the other readings are plausible and consistent, so it must be true - if only for a very brief burst.

After half an hour, I had travelled 3.86 miles which is an average of 7.72mph. Not substantially faster than on the old 102s, and the lack of control meant that certain sections were unrideable (slimy mud in particular).

On the last leg of the trip, I had two or three no-obvious-reason UPDs on level tarmac. I’m pretty sure that these would not have happened with the slightly longer 102s. I was aware that on all difficult sections (inclines, declines, slimy bits, road junctions, kerbs) of the ride, I was slowing down more than I would have with longer cranks. Not the fear factor (at 7mph!) but the caution factor. Less leverage means you need more power i reserve.

Of course, with more practice (I’ve probably done 15 miles on the 89s) there will be improvements, but with the same amount of practice, there would be the same amount of improvement on the 102s, and they would always be that bit easier and more torquey.

So, for anyone who’s followed my ramblings over the weeks, my provisional conclusion is that very short cranks may be challenging and jolly good fun for short bursts on the flat, but a law of diminishing returns operates after a certain point. Higher top speed can translate into lower average speed for a journey on mixed surfaces.

For me, 110mm is probably the most practical size for general use, 102mm for fast ‘n’ furious, and 150 for slow but controlled. And surprisingly, these sizes of cranks seem to work similarly across the range from 20 - 28 inch. I’m as happy on the 28 with 110s as on the 20 with 110s.

Perhaps these numbers would vary for other riders, depending on experience and weight, but the principles will presumably remain the same.

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Re: Cranky conclusions

Mike, it is possible you hit 224 rpm even though it sounds too fast. Really
fast riders have hit speeds well over 224 rpm. Did you feel like you were
floating? When I get up to about 180 rpm and above, the feeling changes from
spinning the wheel to sort of floating - I don’t know quite how to describe
it, but there is a change for me somewhere around 180 at least on the Coker.
It might be different on a 24 though. Was it pretty smooth? I’ve ridden a
28" with 102mm cranks but didn’t ride it enough to get going really fast.

—Nathan

“Mikefule” <Mikefule.g2psz@timelimit.unicyclist.com> wrote in message
news:Mikefule.g2psz@timelimit.unicyclist.com…
>
> Just been out for a blast on the 24 with the teeny weeny 89mm cranks.
>
> Top recorded speed according to the computer was 16mph, and my back of
> the envelope calculation translates that into 224 rpm. I simply can’t
> believe that, but the other readings are plausible and consistent, so it
> must be true - if only for a very brief burst.
[good stuff snipped]

3

Re: Re: Cranky conclusions

On the 24 with 102s, the ride is fast and smooth - it sort of keeps going almost at constant speed over a variety of surfaces. With 89s, it’s less smooth because I know that when things go wrong, it will be very sudden. What tends to happen is that I spin it up to speed and then back off a bit, then do a fast burst again. As I get better and more confident, the bursts of speed get longer. However, with the tiny cranks, there is less margin for error, so I have to slow down two or three wheel revolutions before any obstacle - in fact from fast, it can take more revolutions than that.

On a uni with lower gearing (e.g. the 24 with 125s) it is possible to do almost an ‘emergency stop’ with a movement similar to that part of idling where the uni goes forwards and the rider leans backwards. Try that with 89mm cranks and the rider leans much further backwards (horizontal!), and the uni sets off on a frolic of its own. :astonished:

Generally, a larger wheel is smoother (regardless of crank length).

It seems to me that for high average speed, you want to do this: choose the biggest wheel available, then fit the shortest cranks that will still allow you to idle the uni with reasonable confidence. It’s not that idling is important to travelling fast, but it is a fair guide to the ‘controllability’ of the uni.

Note that given identical crank:wheel ratios, the ease of idling will still vary because of the length of the ‘pendulum’, and the weight of the wheel.

My fastest ground coverer is the 28 with 110s. I can idle it confidently, but with care. I can just about idle the Coker with 150mm cranks, and I reckon it covers distance better with 150s than with 125s, even though it is faster on the flat with 125s. There is little difference in the recorded top speeds of my 24, 28 and Coker, but average speeds seem to favour the 28.

4

Re: Cranky conclusions

Thanks for the update, Mikefule.

On Sun, 22 Dec 2002 11:31:31 -0600, Mikefule
<Mikefule.g2psz@timelimit.unicyclist.com> wrote:

>Top recorded speed according to the computer was 16mph, and my back of
>the envelope calculation translates that into 224 rpm. I simply can’t
>believe that, but the other readings are plausible and consistent, so it
>must be true - if only for a very brief burst.
I saved the numbers of your earlier reports in a spreadsheet, and 224
rpm on these cranks works out as a footspeed of 2.09 m/s which is
exactly what you reached earlier with 102 mm cranks on the 24" (posted
11 Nov). CFSH holds!

>So, for anyone who’s followed my ramblings over the weeks, my
>provisional conclusion is that very short cranks may be challenging and
>jolly good fun for short bursts on the flat, but a law of diminishing
>returns operates after a certain point. Higher top speed can translate
>into lower average speed for a journey on mixed surfaces.
I think from what you wrote the answer is ‘no’ but I still ask: is the
ride with 89 mm possibly more relaxed than with 102 mm? The question
comes forth from my observation that on a bicycle riding easily on
flat tarmac, a higher gear feels more relaxed.

>And
>surprisingly, these sizes of cranks seem to work similarly across the
>range from 20 - 28 inch. I’m as happy on the 28 with 110s as on the 20
>with 110s.
Somewhat surprising indeed. The gear ratio of the 110/28 combo is
quite a bit lower than on 110/20 so one would expect less control from
the former.

>Perhaps these numbers would vary for other riders, depending on
>experience and weight, but the principles will presumably remain the
>same.
I plan to purchase 110, 102 and 89 (in addition to the 125, 150 and
170 I have) when the weather is mmore amenable to fast road rides
(read: spring). Not that I’m nearly as fast as you though but that’s
good: it brings in variety.

Klaas Bil

The average length of film titles in English is 17 letters.

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Re: Re: Cranky conclusions

I’ve snipped your post considerably and will address the points above.

  1. :astonished: I didn’t realise I was being taken so seriously. Very flattered!:o

  2. Definitely the ride with the 89s is NOT more relaxed than the 102s or 110s. The comparison with a bicycle is misleading. On a bicycle, a high gear ratio can produce a higher wheel speed from the same pedalling cadence. On a bicycle, you can pedal harder at the same rpm. On a unicycle, you need to pedal at a higher cadence, but the shorter cranks make this easier. I think the most relaxed feel is when you could manage cranks one size smaller than you have! That is, the gearing is fairly high, but not so high that you are near the limits of your ability.

  3. Yes, the 28 OUGHT to be harder to ride than the 24, given identical 110mm cranks, but I’m not sure that it is. i think this is because the bigger wheel tends to smooth out the pedalling action, and because there isn’t the same pressure to pedal fast to go fast. The 28 inch wheel is 17% bigger than the 24, so you’re going 17% faster at the same rpm - or you can pedal a little bit slower, but still go a little bit faster. In an out and out speed attempt, control of the 28 at maximum rpm would be harder than control of the 24, but for average speed over a journey, the 28 wins.

  4. Flattered :o but I’m not claiming to be particularly good or particularly fast. I’m just interested in the possibilities and have the time and facilities to play these games. I’m keen, but not an expert.

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Re: Re: Cranky conclusions

That’s right. My top recorded speed on a 24" unicycle is 17.5 mph, back when I had both a good computer on there and good training. That was with 125mm cranks, the legal limit for racing. So with shorter cranks it would not be too hard to reach 224 rpm at all.

I just don’t like the lack of control with really short cranks. If I’m going to ride varied terrain, I prefer more crank so I don’t have the constant worry of sudden dismounts, plus more comfort going both up, and down, the hills.

Even with 6.5" cranks on my 45" big wheel, I was still slowed to a relative crawl on the one big hill in the UNICON marathon race (the turnaround). Being in shape would have helped, but I definitely lost a lot of time there.