It’s been around 15 years since I’ve been here last time but now I got back at least a little bit into unicycling and XC in particular. I used to have a 24" Qu-ax back then and now borrowed this uni back from the friend that I sold it to some years ago for trying it out again myself. For this I put the shorter 145mm (or was it 140mm?) cranks from my trials on and that works pretty well even in steep uphills.
Now I’m considering a new own one and since I would like to be a bit faster when cycling with my son (he on his bike) a larger uni could be cool. But because we don’t only go downhills I wonder how much I’d lose in uphill performance with a 27.5 muni? My Qu-ax used to be pretty heavy with its Duro Leopard tyre and some enforcements where things broke or were to weak. How much do I gain with a lightweight uni and especially with a lighter tyre? What’s your experience especially if you use both regularly?
I’m not so great at uphill, but I noticed my 27.5 muni gets me up the early parts of some uphills with momentum, whereas I don’t get that same feeling on my 24” muni.
But, it might be different with different crank lengths etc.
This is based on having the 24” on 137mm length cranks and 27.5 on 129mm. I also end up dismounting my 27.5”on many uphills I feel I should be able to ride up on that setting. I can also put the 27.5” muni on a longer crank setting, but I feel the 148mm length is rather long.
I’d say weight does matter, but tire and cranks are probably the biggest factor for the uni. I have a lightweight 29 (500g rim, sapim laser, 569g tire, UL tube) and it climbs like a dream because it is easy to accelerate it due to less weight. My 27.5 had a heavy 1.2kg tire with deep tread and climbing it was hard with 140s. Longer cranks and a lighter and possibly thinner tire will make it easier to accelerate but the amount of overall weight your pushing up has a big effect too. Ie if you carry lots on a muni trip or could lose 10lb of body weight it would be more noticeable.
You can play around with performance and the feel of your uni and this is probably 1/3 of the puzzle with cranks and tire being the biggest factor. You and your kit are the heaviest component of this though.
I don’t think weight is as important a factor as crank length, tire diameter and tire cross section.
The best climbing combination I’ve used so far is 148mm cranks on a 24" uni with a 2.6 tire. It seems that so long as I can keep upright and my tire doesn’t slip that I can just keep grinding uphill on that thing. The tire is the weak link in this combo and often slips when climbing over roots or on loose ground. I think the lower center of gravity helps however as well as the smaller diameter being easier to maneuver. My experience is that 1/2 of climbing offroad is being able to choose the right line while you’re standing on the pedals and pulling up hard on the handle and the 24" excels at this.
My 27.5 with 145mm cranks and a 3" tire rolls over the obstacles better and doesn’t slip as much, but otherwise it’s a weaker climber. It’s been several months now, but for awhile I had 170mm cranks on it. When I switched from 170mm to 145mm I think it actually improved my climbing ability. The 170mm cranks just felt too slow and awkward whereas with the 145s it seemed like I could maintain my speed better. Now I wonder if that was just me as an inexperienced rider being unable to maintain my balance and effectively use the 170mm cranks.
One thing for certain, there is a huge difference in tire selection between 24" and 26 or 27.5". With 24" you’re limited to around 5 tires for muni and you might have to hunt to find them. With either 26 or 27.5 the selection is massive.
I’m 6’3" and love climbing our local mountain on my stock KH29. (usually on 127mm but due to knees that are awaiting a knee replacement, I’m using the 150mm holes for the last year)
A 29" is barely fast enough to keep up (comfortably) to a general cross country ride with a mountain bike.
On a downhill, even a 29" isn’t fast enough and your son will be waiting (or going a lot slower than normal) for you an a regular basis. 27 1/2" would cause even more of a spread.
On an uphill, the 29" shines and fits in well with mountain bike speed.
So I’m gonna say that for cross country, I wouldn’t ride anything but 29" or bigger unless I had no other choice. (my 29 and 36" would have to be broken)
The other big factor is how in shape you are.
Thanks for all your responses so far. I’m 6’ tall with rather long legs and used to high cadances. So that shouldn’t be an issue. My son doesn’t have a real MTB, rather a multi purpose bike that he likes to use offroad from time to time, and he enjoys to have at least one sport where he can easily beat daddy
So the main focus isn’t speed, it’s not only XC but also a little bit of muni. Therefore I have the feeling that the maneuverability of a 27.5er would fit better.
But it’s good to read that even on a 29er uphill isn’t an issue with relatively short cranks.
In general I’d agree, but in particular maybe not always: If I pedal up a steep hill on a uni I do this in half wheel revolutions with each pedal stroke. So the wheel is accelerated and decelerated over and over again. As a rule of thumb wheel mass counts twice, so a lightweight tyre could be an advantage - at least that’s my theory.
For the body weight I’m not exactly the candidate with much tuning potential there…
I think it all depends on how steep and how technical the climb is. I can’t imagine doing some of the climbs I have difficulty with on a 24" on a 29er with short cranks. I know from experience it would be more difficult.
Of course the main factor is always going to be the rider and there are probably a few guys out there who can climb like beasts on short cranked 36ers.
I agree more in line with Sexy’s advice. The tire weight is a large factor. But not only that. The whole wheel including the rim and tube when it comes to climbing. Having light weight outer perimeter parts of the wheel are going to make the biggest difference when it comes to climbing. I have experimented with lightweight carbon rims and light weight tires and tubes. The difference is astounding. It also enabled me to use shorter cranks on hills.
I have that heavy 24" from Qu-Ax myself. But despite my 27.5 is nearly the same weight (due to Schlumpf hub) my uphill performance on the 27.5 is far better. I tried lighter 27.5ers ant that is another big improvement over mine when it comes to uphills.
That’s interesting. I rode my 27.5 for around 1.5 hours on Saturday and my 24 for about 40 minutes off-road on Sunday and it was surprising how much better the 24” climbed. The cranks on the 24” are 5mm longer, but I think a certain amount of it is also the lower center of gravity and the quicker turning.
As with anything where cycling is involved it is not just one thing. Weight does make a difference, there was a good GCN+ video looking in to this and the biggest thing was riders weight. Although I will say that a major factor is if you are comfortable riding the unicycle on the terrain you are riding - if you are struggling to control it then you will not be able to apply lots of load on the cranks. Some experimentation has shown that too long cranks stops the riders flow and makes it harder to go up some hills. Being able to spin and flow is important to unicyclists. Unicycles do not normally run out of power with our crank ratios.
Thanks for all the replies, that was really interesting to read. In the meantime I was able to borrow a KH 27.5er which is definitely lighter than the good old Qu-ax in more or less all parts. And I’m quite surprised about the climbing ability which basically confirms some of your experiences! Although the KH has 137 mm cranks (shorter than what the 24" Qu-ax has) I had the impression that on one of my steepest hills it climbs even better. The difference gets smaller the more bumpy the path is. There I think the longer cranks on the heavy muni pay off because it’s more the control that is challenging than the pure power required to push the uni up the hill.
