Hi all,
As several of you might have read, I was waiting for a KH 29 for some time. It finally came and I am in love again.
The KH frame is really beautiful – and of course the “MUC blue” helps.
I was shocked at the weight savings of this set-up. I had a steel frame with a GB4 seat post. I replaced it with the standard KH 29 frame and Kris Holm seat post (without the brake lever. Amazingly, the weight saving was about 40% (3.2 lbs. down to 1.9 lbs.)!!! My entire ride weighs in at just over 10 lbs. (10.2). Of course this is not the KH set-up but my attempt to build a light, effective cross-country ride for my weight (150 lbs.)
KH 29
KH seat post w/o brake bracket
CF seat
Mavic 17mm tandem rim w/ alloy niples, 3X
Nanoraptor tire
Suzue hub with 155 Euro cranks
Oydessy Twisted pedals
This morning I took it out on it’s virgin ride. The frame is wonderfully stiff (yes, I have an air saddle). On the steel frame I often could feel the fork blades give as I torqued laterally. None of that with the KH.
I’m one happy camper. Be for warned, I have my eyes set on a new uni course record for the Tour de Wolf course!
Sounds nice. I must say I really like the look of the new blue KH frames.
Regarding the steel vs aluminium, I hadn’t really thought about it that much in the unicycle context. Coming from a bicycling background (sorry!) it’s certainly cheaper (because of less building skill involved) to build a light aluminium frame than a light steel frame, but aluminium framed bikes feel dead to ride because of the lack of spring in the material (and they tend to crack for the same reason). A good (but relatively expensive) steel frame gives a much livelier and more comfortable ride, but it must be built by a good builder if it is to be both light and stiff enough. Titanium almost gives the best of both worlds, but at a serious cost premium for the materials.
For a unicycle though, the lack of spring of aluminium may well actually be an advantage, as unis don’t rely on the spring in the frame for liveliness like bikes do. Just as long as the frame doesn’t get cracked in a crash (you can bend a bent steel fork back, within reasonable limits).
How much of the overall weight of a unicycle is the frame though? Certainly on my muni (26x3 nimbus 2) I reckon the tyre and saddle probably account for a good proportion of it.
I totally agree with your regarding your observations/ preferences of steel over aluminum for a bike. On my cross country uni, with its 29" wheel, I can build in enough suspension with the construction of the wheel and the tire pressure. However, as I’m trying to torque the frame around a turn or over a root I don’t want to feel the wheel twisting laterally beneath me. Granted, I’ve just started playing with this new ride so I’m still in the honeymoon of my new love affair. Too, we’ll see how it holds up.
You are so right. The bearings on a KH need to be 42mm. I had to buy the bearing shims that UDC sells to bring my bearing size up from 40mm. So far, after only two rides now, all is well. Still smiling!
When I tossed in the Suzue hub the bearings were just a touch narrower than the bearing holders - perhaps just a couple of mm. I did nothing. Perhaps, over time, the bearing will pull a few mm out from the hub but I really doubt it. Thus, to answer your question, it is close enough to call it a fit.
Interesting. It’s lovely to read of someone who’s getting so much pleasure from the riding experience.
I’m no engineer, but I do remember from my scuba diving days that aluminium air cylinders were heavier, size for size, than their steel equivalents. Simplistically: aluminium is lighter (well, less dense) than steel, but you need more of it.
Of course this depends on the steel. There are many sorts. Also, there are different types of strength: resistance to stretching, bending, twisting, or compression. In the same way, there are different sorts of stiffness.
My Pashley MUni is made of “Reynolds tubing” but it doesn’t say whether it’s 453, 501, 531, etc. All I know is it feels like it’s made of scaffolding poles. It’s made of lighteweight material: lots of it. So if I eat 500 low fat doughnuts, will I lose weight?
For a unicycle, the weight of the wheel and tyre combination makes most difference because it affects acceleration and deceleration. The weight of the frame and seat combination should in theory be somewhat less important - especially if you realise that a pound or two in weight saved here can easily be wiped out by the contents of your camelbak, or a big breakfast.
But if you count your legs as the “springs” because they support the biggest part of the mass of the rider/uni combination, then any savings on the weight of the uni are savings to “unsprung weight” which will make the uni easier to ride over roots and bumps.
But at bottom, it’s just much nicer to ride a nice piece of kit, and I’ve noticed that even a couple of hundred grammes saved on a tyre have made my own 700c more fun to ride.
I echo what you said about the meaningful weight of the wheel/tire/cranks/pedals as opposed to the weight of the frame. I would LOVE to figure out how to save 1 pound of weight off my wheel - rather than the frame as I did by going to the KH 29. I’m shaving weight off where ever I can these days. In fact, last night I had a dream that rode the Tour de Wolf trail (our local cross-country racing course) on a 700X38 tire. That would be a REAL and meaningful weight savings that, I’m sure, would produce some amazing performance enhancements. However, should I bend the wheel or bust my butt I won’t have nearly as much fun. But in my dream I was FLYING! Ahhhh, the dances we do.
You can lightweight rim tape, lightweight tubes, and choose the lightest tyre. Tyres are the biggest problem, because you need the grip and the section if you’re riding off road.
However, have you thought of double-butted spokes? In my bicycling days, enthusiastic bicyclists paid extra for spokes that were thick at the ends, and thin in the middle (the opposite of a dinosaur). 36 spokes must weight quite a bit, so 10% or so of that might be worhwhile.
Yes. I did used D/B spokes on this wheel - and aluminum nipples. The genesis of this unicycle was to build the lightest, yet strongest, most performance oriented 29" for my weight and for a slightly technical cross-country course. I beleve that I’ve done this with this set-up.
You are totally right about the difference in performance between that weight flying around verses that weight sitting static.
I want to bring back this thread because I am curious about the performance of steel vs. aluminum in terms other than weight.
Like Rob said above, in the biking world an aluminum frame does much less to dampen the bumps than a steel or carbon frame does. A lot of riders swear by steel frames.
Has anyone noticed that a steel frame is better on bumps when riding muni, xc, or road?
The way a unicyclist and a bicyclist use frames are very different. The amount of weight that you put on a frame, particularly when riding muni is very little - most of it is on the pedals and transferred to the tyre. All of a bike riders weight is supported by some part of the frame/forks.
I have only had one aluminium frame, which was the Schlumpf frame. I didn’t swear by it, I swore at it! So, maybe I’m not the best person to answer your question, but the thing I noticed with the ali frame was that it would twist under torque, particularly going up a hill. My new frame, however, is titanium, which I guess is more steel-like but without the weight overhead. That doesn’t flex at all. It is very very rigid, and that translates to a much more precise ride with no twisting under torque.
All of my other unicycles have steel frames, but, to be honest, I’ve not noticed any issues with regard to flex, weight, bump absorption or anything else - but that’s probably because I don’t treat them too hard.
I am sure Semach’s comments are accurate. I just wanted to note one of Ti’s weakness’s, as a material, is it’s lack of resistance to twisting. Despite being gram for gram stronger then steel in other respects, Ti lacks torsional rigidity.
Because of this unfortunate fact, heavy parts on unlimited budget factory race motorcycles, such as the crank shaft and transmission shafts, are always made from steel. In these applications, resistance to twisting is vital, and gram for gram, normal steel is stronger then Ti in torsional rigidity.
That’s probably not to do with the frame material, that’s to do with the poorly designed frame - that frame is super twisty because it’s made out of such lightweight parts. It’s massively under-built for unicycling. Which I guess is why it is quite light, but does mean it has several problems that a £20 nimbus frame doesn’t have.
You can see it flex by pulling the brakes and watching how much the frame flexes - which isn’t the case on a KH frame, or even my hacked together nimbus brake mounts.
Joe
ps. I dunno how you know about torque going up hill anyway?!!
I read about it in a book once and thought it sounded cool!
As I was typing that, though, I meant to imply that it was more to do with the poor frame design, but actually that didn’t really come across. But as that is the only Ali frame I’ve owned, I can’t honestly compare it to other ones.
