Seat post height vs optimum leg position

Hi all,
I’ve got new seat post for my unicycle as the current was way too short. I need to cut the new one down to fit as it’s too long.
Question is, what is the best height to set it to for my leg position to offer optimum leg positioning? The unicycle will be for road only use so I want maximum power without my hips rolling.
For example, on my road bike the rule i use is to set the saddle to a height when sitting, your knee is at slightly bend position when crank is inline with seat tube (roughly when pedal further point from seat).
Ordinarily I’d use this same rule but thought to check with others as the geometry on a standard unicycle is different to a cycle.

Comments appreciated.

Speaking as a newb here, what I find works best is about 1" or 2.5cm lower than the height you would use on a bicycle. You want it a little lower than on a bike so that you can still use your legs to absorb bumps even at the bottom of your pedal stroke. Also, a lower seat makes freemounting easier.

Just make sure you cut it in such a way that you can switch between too high and too low. That’ll give you enough room to adjust it whenever you feel like it.
So take your bike height, add 1-2cm and then cut it to the minimum insertation. This way you have maximum play to lower it whenever you want to learn certain techniques…

If you’re riding exclusively on roads on a road unicycle then the recommendation would be the same for optimum efficiency, but generally people will ride with the seat an inch or so lower as it makes mounting and things like handling bumps/curbs etc easier.

If you’re riding Muni then you might want to go another inch lower than that.

What size unicycle?

I think I’d add about 5 cm myself just in case I decided to switch to shorter cranks in the future. Unless he’s already riding on short cranks or will never be switching them.

Good point, I ignored the crank length, so shortest cranks you’ll ride + 1-2cm would be safe :wink:

Many frames are don’t accommodate a large range of seat post adjustment. @mrmortar, sorry, I don’t recall what frame you’re using.

Like @mark.vogels said, consider the possibility of moving to shorter cranks in the future, which means having spare seat post length equal to the difference in crank length.

Since you can remove length but you can’t add it, and if you’re dealing with a limited possible range between low and high, maybe you should experiment with cutting off less than you think, then taking a spin around the block. Also, at first, get the bottom of the seat post as close to the tire as possible. If that setup is too high, that is obviously unsafe, but you might start out by challenging yourself with a higher than normal setup. Also, keep in mind that the minimum suggested insertion is 1.5 inches.

Slightly off topic, but I was using the Shadow seat post on my 26" Oracle. When I went from 165mm cranks to 150mm (briefly), I ran out of seat post. It had never been cut. To my knowledge, the Shadow seat post comes in one length. I am tall and ride with the saddle high. I fudged on the minimum insertion, bringing it closer to an inch. No problems, but probably not safe.

On the Qu-Ax #RGB frame it’s almost 10cm, so that might be something to look up first on the frame specs.

10 cm. Wow! Thanks for the info. I thought the recommendations were roughly the same for all frames, but I guess not.

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It’s a 26”, a Huni-Rex. The stock seat posts it comes with are way too small for me (I’m 5ft11) so had to get a longer one.

I doubt I’ll ever need to adjust the crank lengths.

Plus i notice I can’t get the post to go beyond the top of the arch due to welds so I’m limited to keeping it within the boundaries of the seat tube (if that makes sense) which is a shame because there is about 1.5 inches gap to the tyres.

Someone needs to invent dropper posts for unicycles :crazy_face:

Everyone keeps saying that dropper posts wouldn’t hold up on a unicycle (which is probably true), but I’ve not actually seen anyone try it yet.
Also people say you can’t pull up on them - is that because it pulls the hydraulic fluid valve open?

If so, you presumably just need a valve that seals both sides, and a stronger mechanism against twisting.
Something like Fox’s designs with apparently locked ball bearings for different heights could presumably work, but be limiting in positional adjustment.

Maybe the inside of the tube could be filed/gently grinded away so the post could drop further

Ideally you’d use a reamer as the tube has probably ovalised a bit - your LBS or local framebuilder might have one of a suitable size.
It’s a little disappointing that it wasn’t reamed after welding to be honest, but it is a Huni-Rex.