Significance of frame and unicycle mass?

I’ve just been to visit the man who’s building my frame for me and talking to him made me think about the importance of little variations in the mass of a unicycle. I’ve changed the flat bit of my crown in the design from 10mm thick to about 6mm thick or so (what he had in the workshop). A few people have told me that the 10mm bit would be far too heavy and excessively strong. I agree about it not needing that sort of strength in that part of the unicycle but how much of a difference in weight would it really make? Steve Howard said that the difference between a 6mm piece like this and a 3mm piece is about 90g. I don’t see how this is enough of a difference to worry about.

I think that there are other factors that so many people (like me until now) don’t think about such as the clothes you’re wearing particularly shoes and pants, whether or not you’re wearing a helmet (let’s hope you are), and even how much you’ve just eaten. Surely when you consider all these things, these little changes in frames don’t make any real difference. Please correct me if I’m wrong. Also, the wheel is by far the heaviest part of the unicycle so the frame won’t really make too much of a difference.

I’ve got one more question. If one person weighs a lot more than another person and has been that heavy for a long time, would he/she be disadvantaged at all with regards to hopping and gapping? I was thinking that if the muscles in the heavier person’s legs have been carrying them around for long enough they would just get stronger anyway and cancel out the extra weight. I therefore thought that there would only be a difference if one person had just very recently gained a lot of weight and the muscles hadn’t yet caught up. Does this make any sense?

Andrew Carter

Re: Significance of frame and unicycle mass?

Correct. Not to say that you can’t necessarily feel the difference, but a rider who can do a set of skills can probalby do them about the same with a frame that’s a little heavier.

In bicycling, it’s always important to consider rotating mass vs. non-rotating mass. It takes more work to speed up and slow down the weight in your wheels, so you try to take weight from there first. On unicycles this is less of a factor.

I’d say that for a unicycle, weight gains are more noticeable as they move further from the center of the wheel. A fork crown, for example, is just outside the wheel and goes everywhere the wheel does. Not a big change. But a big heavy gel insert in your seat instead of a lightweight innertube could be a much bigger difference.

Of course. Bigger mass takes more energy to move, and it takes especially more energy to make continual, sudden changes in direction (like hopping)

What you left out of your scenario is the fitness level of the two riders, which means everything. Even though the heavier rider is used to carrying his weight, if he rides up a mountain every day before breakfast and the light guy doesn’t, the light guy is going to lose the competition.

The power of “the engine” is more important than any changes you can make to your equipment. It’s just that the equipment changes are more fun to play with and show off.

You weigh several times as much as your unicycle. A litre of water in your hydration pack (or ‘bottle’ as we say where I live) weighs about 10% of the weight of a MUni. Saving a few grammes here and there on the uni will make very little difference… until you have to carry it up a hill, or over a stile, or push it home with a puncture.

The weight in the wheel matters a lot, because the wheel moves further than the rest of the unicycle. If a kilogram of wheel has to move further than a kilogram of frame, then it needs more energy to move it. And more energy to stop it. There are also gyroscopic forces to consider. A heavier wheel will be less responsive to steering input.

And the centre of mass of the tyre moves about twice as far as the centre of mass of the spokes, so the tyre/rim weight is important, even if the spokes are heavy. (Different thread refers.)

And for big people and fat people? If two people are the same shape but different sizes/weights, then the cube/square law applies. If person B is twice as tall as person A, then he weighs 8 times as much, but his muscles have only four times as much cross sectional area. So generally, bigger people can jump less than smaller people, all other things being equal.

But take a formerly fat person and shave some weight off him, and, yes, perhaps his legs will still be strong from carrying all that fat. Seems like a lot of trouble to go to, though! :roll_eyes:

I thought the same thing. I feel, for trials riding, that when doing seat out in front, it would be an advantage to have a lighter frame. This way, you can torque the uni around easier, where ever you want it to go. I think that you c’ant skimp on the wheelset (more weight) but that a light frame wouldn’t hinder your performance, wouldn’t break, and you could do trials problems slightly easier. I agree with all those things about weight, however, there is a trade-off. If you’re fairly tall, i think you would be able to hop higher, because you have more lag compression, but most important for hopping height, i think is technique and a person’s vertical Jump.

just my thoughts,


Saving 90 grams by itself won’t make a lot of difference. But save 100 grams or so in the frame, 100 grams in the wheel, 100 grams in the pedals, and 100 grams in the seatpost and seat, and then you’re talking about a weight difference that is noticeable.

Less weight in the uni is nice when you’re jumping. Jump around on a heavy unicycle and then switch to a lighter one and you definitely notice the difference. But weight isn’t the only thing to worry about. I ride a KH24 and a Vortex 26x3. Both unicycles are a little on the heavy side. If I was a true weight weenie I would be riding a Wilder.

Thanks everyone. You’ve definately answered my questions.