I have built up pretty much my dream 700c with a 700x28 schwalbe one and 100mm cranks. The rotational weight including disc and pedals comes to just shy of 2.4kg. The total build weighs in at around 5. While that might seem heavy, that includes a t-bar, computer, lights and disc brake and is designed as a light commuter and tarmac muncher rather than a racing monster.
The problem I am having is that I cannot build up to a high cadence. I currently cruise at 120-140rpm but max out at 150rpm. Usually I would expect to be able to reach 180-200rpm flat out and can do on a 20" with 100mm cranks (which is actually heavier).
I suspect the issue is lack of feedback and stability due to the light weight of the wheel as the unicycle is now pretty dialled in to my size and preferences.
Is there anything else I should think about or do when trying to build speed or should I just try lots of speed runs on smooth tarmac to break the wall.
I don’t think you should expect to get the same cadence you can on a 20" wheel. Even if the pedal circles are the same, the feeling is a lot different, and you’re also dealing with fear factors and wind resistance. A cadence of 200rpm on a 28" equates to a speed of about 27kph, compared to 19kph on a 20". That’s fast enough to be scary and definitely fast enough to run into wind resistance issues.
And personally, I think a 700cx28 unicycle is going to be noticeably slower than a 29x2.0"; they’re very twitchy and subject to pavement imperfections. You spend a lot of extra energy correcting for bumps and wobbles that a fatter tire absorbs.
The technique I would think about on that setup is to try to float your feet; don’t think about pressing down on the pedals, think about keeping as light a touch as you can.
Im not necessarily hoping for the top end of the cadence range, just a little miffed that I am unable to even reach cadences that I have pulled off with both a 29er and a 36er with longer cranks. I believe the uni has 15-16mph in her on an ideal surface.
As much as 36ers are great fun, my knees do not like them one bit.
There is no doubt about that. My 29er is a flying sofa in comparison. I think the fun of 700c is how much handling it requires and its twitchiness. Like unicycling in general, by being harder to get right, it is more rewarding when done right.
Given that I am riding clipless my pedal strokes are already pretty light but I will try to push that further.
Hello Dave , I think that with the bigger wheel you have more tyre to road surface contact per revolution resulting in more friction. You are driving a bigger tyre circumference which may result in a lower cadence. Each revolution will require more energy output from your legs just like riding with a bigger gear.
Increasing your tyre pressure should decrease tyre friction on the road and help you to spin your cranks faster.
I wasn’t referring to the width of the tyre. I was referring to the circumference of the tyre. A larger/longer circumference will result in more tyre to road contact per crank revolution because with each crank revolution a longer section of tyre will have made contact with the road.
Higher psi means a smaller and less spongy point of contact between tyre and road resulting in better wheel spin.
Using longer cranks will help increase cadence but will reduce overall flat surface speed and will usually be more twitchy. Shorter cranks help reduce wheel twitch resulting in increased forward momentum.
Im riding at 80-90psi which seems to be the optimum pressure. Any higher and general crappy surface riding would be too awkward. It definitely is a lighter wheel after the first few pedal strokes than a 20 though.
I started off trying spare 114s. 100s are much smoother even though I have more experience with 114s.
Twitchy as in snaky. If you ride on sand or with a wet tire on a dry surface, you’ll notice that the path your wheel leaves behind is not a straight line. Although an absolute perfect line impossible to achieve, shorter cranks help getting close to it.
As the unicyclist rides forward, the downward pressure on each pedal pushes the wheel off centre to one side and then to the other side causing a continues twitching of the wheel.
Longer cranks generate more leverage on each pedal stroke which in turn exaggerates that twitching movement. So the longer the cranks the more the wheel will twitch off centre causing the rider to lose forward momentum.
A very twitchy wheel may cause lot of your energy to be wasted. For example, if you were to travel 10 miles on a straight road with a very twitchy wheel, the left and right twitching could mean that you would in fact have cycled up to 12+ miles by the time you’ve reached the end of the road.
150mm cranks on a 24" uni are fine. I use 150s on my 24" muni for downhill technically challenging riding. But if you want a combination of speed and stability then you might consider using shorter cranks with a zero Q factor (i.e. straight cranks that don’t curve outwards).
I consider crank selection to be a very important factor in my setup so I’ve experimented a lot with different cranks. So I’d suggest that you try using shorter cranks 125mm and see how they work for you.
Hope this helps
Pierrox’s description of wheel twitching is very well put.
With a skinny tire it’s generally impossible not to run high pressure. The skinnier the tire, the less range of pressures you have to work with. Like in the early days of Muni, when we were on 1.75" tires and rocks. You had to run them at 60 psi or better, or get lots of pinch flats. To keep a skinny tire off the ground, high pressure is needed. This lowers friction, but at the same time takes away some of the friction that keeps you from wobbling (referred to as ‘twitching’ in this thread).
As to developing a faster spin, you might be hitting a place where your body develops some form of resonance. Some people reach a certain RPM where their body bounces up and down, and have trouble getting past that speed. Like a car that needs the wheels balanced. One thing you can try, to “break through” this, is spinning as fast as you can on other wheel sizes. Smaller ones. Put short cranks on a 24" or 20" uni and you may find it easier to hit higher cadences. Once your body gets comfortable with that pedaling speed, it should be easier to get it going on the larger wheel.
I think I have to do some “small wheel” therapy myself. Most of my riding is on a 36" with a Schlumpf hub, which means I’m not pedaling very fast by unicycling standards. My other main ride is my Muni, on which I’m usually not trying to go real fast. I think I need to do some spin therapy on my old 24" Track uni or similar, to get comfortable pedaling fast again. On the 36" I get scared going downhill, and end up going even slower than on the flats. A lot slower, because I’m worried about the thing rolling out beyond my ability to control it. I didn’t used to have that problem. With practice, you should be able to spin RPMs in the high 100s. In sprint racing, people go well past 200. No reason you can’t learn to do that on a 700c as well.
Interesting thought about a resonance. I know what you mean and have worked through several on my hockey uni before.
The 700 is much closer related to a track uni than a 29. In fact I would hazard a guess that the rim/tyre weight is very similar to that of a race uni. When we think of crank length vs wheel size, i don’t think we realise just how much wheel weight is also a factor.
Well, you used to be a lot younger, too. The older I get, the more I fear a high speed UPD. It is getting so that I lose races to my 3 Teenage sons (not because they are faster…even though they are) but because I am afraid to push it to the max.
I cam probably hold 12 for a while now. That was what I was initially irritated at, the fact I could hold almost my max speed. As for cadence, I am using a wired cateye computer with a crank mounted cadence sensor as well as knowing the wheel size inputted.
The cadence sensor is unfortunately a ‘feature’ rather than something truly useful. Cable routing is a nightmare given the wire lengths assume that the cadence sensor is nearer to the computer than the speed sensor. Unfortunately the old small wired cateye without cadence seems to have gone and I didn’t feel like trying a different brand.