Short cranks - ZOOM! What gives?

So, the pedal on my 26" Pashley finally broke. I was going to just take the pedals of my stealth torker for a temp fix, but then I decided to get wacky and swap out the cranks from the torker as well. So I had 170mm on the Pashley, now I have 125mm, I think.

It’s very cool - definitely much faster and it wasn’t as hard to get used to as I thought. I do lose a lot of control. I can’t stop on a dime any more. I really have to ease down the speed before stopping, or else I’m bowling.

The one thing that really suprised me, and I still don’t get it, is riding up this super steep hill on the way to work today was actually much easier with the shorter cranks. This doesn’t make sense. Shouldn’t it be harder, since I’ve lost leverage? I did bring the saddle up to compensate for the different cranks, maybe a little more than necessary. Could the ease of hill climbing have something to do with my legs being straighter?

I’ve been thinking about getting a new KH24 - but it comes with 170mm cranks and now I’m starting to wonder if I might like shorter cranks better.

Two things might explain your ease in riding up the hill. First, with the shorter cranks it’s easier to have a smooth pedaling cadence. If you’re approaching the hill with speed, the short cranks will get you farther up before you have to start really cranking. In short, my guess is that hill is not as super steep as you thought.

This is especially true after one returns home from Moab. In Moab, chances are you rode more steep stuff concentrated together than you ever have before. At least for me, I consider it a turning point in my “rough terrain education.” Though you were toting a camera the whole time, hopefully you rode enough that you are simply better at riding hills now.

If the hill is steep enough, you will reach a point where the 170’s are necessary. But if it’s a paved hill, you can get away with quite a lot on short cranks. Remember, I rode with 150s until very recently. They’re great for non-steep stuff, but when the going gets extra rough, or steep, the extra length comes in real handy.

So what length to use? It depends on where you ride, and your personal tastes. Bring your Pashley with 125s to Santa Cruz, for instance, and you’ll be missing your longer cranks. But on some of the Sacramento area trails you’ll be okay, as well as a lot faster.

Hmmm. I wonder how much money changed hands on whether I’d be the first to respond to this thread.:wink:

Firstly, everything I say is only opinion. I don’t count myself as an expert unicyclist, but I have made a point of experimenting with different cranks and trying to understand the various effects.

I would describe 170mm (or 175mm) cranks as extremely long and for specialist applications only. I say that knowing that 170mm is the standard length for bicycle cranks; bicycling and unicycling are very dissimilar.

170mm cranks will tend to produce a slow cadence, and therefore a slow speed for any given wheel size. It is possible to pedal fast, but it requires skill, and it is not what 170s are ‘for’.

170s will give you great control when releasing potential energy gradually - or ‘going down hill’ as the layman might term it. ;0)

Going uphill, 170s will give more torque than shorter cranks at that part of the pedal stroke where torque is being directly applied. For most of us, that’s about 1/3 of the circle for each pedal.

So what can happen is this: you get to a steepish hill. You’re already going slowly (because of those big long cranks) so the unicycle stops or nearly stops. The pedalling action becomes very uneven. As you push the pedal from just past top dead centre to bottom dead centre, the unicycle accelerates. As the pedal hits bottom dead centre, the unicycle decelerates, or even stops. Then you have to work that top pedal past top dead centre.

So progress becomes a series of steps and stops. This means there are more ‘balance events’ or changes in the balance of the rider/unicycle unit. This demands mental and physical effort from the rider, reducing the effectiveness and efficiency of the pedalling action.

And where have we got to now? A series of steps, rather than a smooth flowing circular action. And how big are those steps? 2X 170 mm. Imagine you’re walking up a flight of stairs where each step is 340mm high (13.4 inches.) A typical househld staircase has steps which rise about 6 inches each.

Especially if you are not overtall, this repeated stepping up a 340mm stair case can become tiring and difficult to coordinate smoothly. I speak as one who is not overtall. ;0)

Now try 125mm cranks. You have less torque at that part of the pedal stroke where you are applying most torque (just past top dead centre to bottom dead centre). However, the circle is smaller (250mm = 9.8 inches).

This means you can pedal in a smoother circle. Instead of alternating pulses of massive torque, you are delivering slightly less torque, but at a more constant rate. (Motorcyclists might like to compare a big single, a V twin and an across the frame 4 to see how power/torque can be delivered in very different ways.)

So if you can apply the torque more smoothly, there is less acceleration and deceleration when riding up a hill. If there is less deceleration, there is less need to accelerate. If there is less need to accelerate then you need less peak torque anyway. So up to a point, a slight reduction in cranks can give you a smoother power delivery, so you need less torque.

But sooner or later, you will get to the step, stop, step, stop situation. What then? Well, the steps are smaller. YES, the wheel is travelling just as far, and YES you are raising the combined mass of the unicycle and rider just as far, but within that, the mass of the rider (or rider’s legs, if seated) is oscillating less.

Now ask yourself this: could you give your girlfriend/boyfriend/spouse a piggy back up stairs? Yes. So your legs can produce enough power to propel nearly twice your own weight up stairs. Your unicycle weighs about 10% (or less) as much as you. So it isn’t power you’re lacking when you can’t ride up a hill. It’s delivery of that power.

So back to the stairs analogy, and I’ll make it extreme to illustrate:

Would you rather carry a 100 pound weight up a 50 foot flight of 6 inch steps, or a 50 pound weight up a 50 foot flight of 24 inch steps?

Back to unicycling, I have observed that within certain limits, I find it easier to climb smooth surfaced hills with slightly shorter cranks, especially when it gets to the stage of step, stop, step, stop. It feels like I don’t have to lift my own bodymass so far before I can use it to propel the pedal downwards.

Technique and timing make a big difference. Descending and ascending are very different situations, and very different things are happening.

Leverage does play an important part in controlling a descent. Indeed, there comes a point where the crank is not long enough to reach ‘into the slope’ far enough to reach past the point of contact between the tyre and the ground. Then (barring the small amount of leverage you get from pulling on the seat/handle) you’re past the point of no return.

Going uphill, the ability to keep the wheel turning is more important than the actual amount of peak torque.

There are many variables, and individual riders, wheels, slopes and techniques will produce different results. I have observed that on a 24 with 102mm cranks, I once stormed up a rough surfaced hill which I KNOW I couldn’t have ridden on my 26 with 150s. I regularly ride up short hill son my Coker which stop my 26. In both cases, the 26 has more ‘leverage’.

But I know which one I’d rather ride DOWN the hill… the one with the most leverage.

Well, one thing that makes a big differenc here is, they are actually 140mm - not 125mm. I just measured them. The reason I thought they were 125 was because that’s what unicycle.com has listed under the description for the stealth torker. I’m not usually good with guessing sizes, but I thought 125 seemed small.

Some of the stuff your saying, John, makes good sense - particularly about the smooth cadence. Part of it being easier was that it felt a lot smoother. However, I don’t come at the hill with any speed, since its at the end of a crosswalk where I have to almost come to a stop and then turn a corner before heading up the hill.

After Moab, I definitely had some muscle tone going that I’d never seen before. Unfortunately, for a few different reasons, I couldn’t get any good riding for almost a week afterward and I feel like I’m losing all that great muscle.

I’ll play around more with the shorter cranks. If/when I get the KH24, maybe I’ll throw down for the optional 140mm cranks and try them both.

Wow, thanks, Mikefule also.

This does make sense - even moreso now that we know we’re dealing with 140 rather than 125. Now I want to try the short cranks out on the trails…

the cranks on my Steath Torker are 127mm and they even say so one the inside of the arms.better measure again,from the center of the pedal hole to the center of the crank nut.

Yeah, I guess your right, Jagur. It says 127 B-6 on the crank. When I measure it again, I guess that’s true. Measuring center of hole to center of hole, it looks to be 130mm. I guess I’ll believe 127 - but it really looks like 130 to me. I must have got 140 by being sloppy. These millimeters are so dang small.

This is so complicated - now I can’t decide what size cranks I really want. I know that I really like shorter cranks than the 170’s I’ve been using (you can’t make me go back!). But, a little longer than these 127’s would probably be nice. Plus, I have to think of the difference it would make on a 24" wheel, since I’m thinking about buying that.

Ugh…I wish I could go for a test drive before I buy.

you might already know that im using 145mm Profiles on my 24x3.they work great but i do plan on getting some 160mm in the future to swap back N forth.

if i was planning on getting a KH24 (production model) i wouldnt blink at getting the 140’s aswell.swapping cranks on the 8 splined kh axle is probobly easier than the 48 Profiles to boot.

Re: Short cranks - ZOOM! What gives?

You can buy the 140mm KH cranks as well and swap between the two. Splined cranks make it really easy to take your cranks off- you just need an allen key.

It’s fairly steep here but I find myself using my 29’er with 150mm for just about everything. I think the smoother pedaling cadence you get with shorter cranks really help.

Oh fiddledee…thanks Jagur you ruined my wonderful insight :angry: . I guess I’ll need to wake up a bit earlier.

Re: Short cranks - ZOOM! What gives?

On Thu, 17 Apr 2003 12:02:30 -0500, Mikefule
<Mikefule.m1hr1@timelimit.unicyclist.com> wrote:

>Hmmm. I wonder how much money changed hands on whether I’d be the first
>to respond to this thread.:wink:
I still have all my money but when I saw the subject line I
immediately scanned the respondent names for yours (my newsreader
screen layout is different from the forum).

I know you are a big fan of short cranks (generally) and I know you
talk from experience, but I don’t buy the explanation.

>Going uphill, 170s will give more torque than shorter cranks at that
>part of the pedal stroke where torque is being directly applied. For
>most of us, that’s about 1/3 of the circle for each pedal.
So, 2/3 of the 360 degrees for the two pedals combined? That’s not too
bad.

>However, the circle is smaller (250mm = 9.8
>inches).
>This means you can pedal in a smoother circle.
This statement is essential in your explanation. John Foss mentioned
it too. But why would a smaller circle allow smoother pedaling? I
mean, it may FEEL smoother, my 125’s feel smoother than my 170’s too
but that I think is caused by the fact that the leverage is smaller
and hence variations in force exerted have a smaller effect (in
absolute sense) on torque. But I think the RELATIVE variations will be
just as large.

>Indeed,
>there comes a point where the crank is not long enough to reach ‘into
>the slope’ far enough to reach past the point of contact between the
>tyre and the ground. Then (barring the small amount of leverage you get
>from pulling on the seat/handle) you’re past the point of no return.
Small amount of leverage? I think I sometimes yank with half my body
weight on the seat.

>Going uphill, the ability to keep the wheel turning is more important
>than the actual amount of peak torque.
Ummm. It is exerted torque that keeps the wheel turning. I’m
disregarding ‘peak’ because I think that the relative variation in
exerted torque along one revolution is about the same for short and
long cranks (very roughly sinusoidal).

>But I know which one I’d rather ride DOWN the hill… the one with the
>most leverage.
I’m not sure that up and down are that different in their requirement
for crank length. I love my 170’s. But I agree, it’s personal.

All of this is not meant as criticism but as a contribution to trying
to unearth ‘truths’ about crank lengths.

Klaas Bil - Newsgroup Addict

Nearly 85% of the people killed by lightning are male.

Re: Short cranks - ZOOM! What gives?

On Thu, 17 Apr 2003 11:22:24 -0500, nbrazzi
<nbrazzi.m1fwa@timelimit.unicyclist.com> wrote:

>The one thing that really suprised me, and I still don’t get it, is
>riding up this super steep hill on the way to work today was actually
>much easier with the shorter cranks. This doesn’t make sense.
>Shouldn’t it be harder, since I’ve lost leverage?

Maybe you still have that MOAB muscle tone?

I am used to riding my 24" Muni with 170 mm cranks on the local
trails. The slopes are sometimes quite steep, they are shortish but
not short enough to overcome with kinetic energy (speed, as the laymen
say).

This week I took the 24" Semcycle with 125 mm cranks out for a spin on
a 6 mile roundtrip on pavement. At the end of it, I made a small
detour through the park with its steep trails. Well, I couldn’t climb
NEARLY as well as on the MUni.

To me it makes sense, but with your experience, and Mikefule’s and
John Foss’s explanations it seems that I am on my own. Well, so be it.

Klaas Bil - Newsgroup Addict

Nearly 85% of the people killed by lightning are male.

Re: Re: Short cranks - ZOOM! What gives?

A low speed, there’s not much difference. But as the speed goes up, the difference becomes more and more obvious. At racing speeds (200 rpm or so), you are acutely aware of the size circle your feet are making. Not only are your feet going round and round, but your entire legs are making the motions they’re making, and constantly changing direction. Namely your thighs. Up down up down. The longer the cranks, the further the thighs move, and the more momentum they develop with each pedal stroke. This means you need more energy to keep switching them to the opposite direction.

So, as explained in non-technical, non-physics terms, low speed, not much difference. High speed, huge difference!

That’s only true for me if the trail is stupid steep. Otherwise, give me the ability to pedal faster, and I’ll have fun rolling down!

But yes, if it’s steep or nasty, you will definitely feel and be safer with more leverage available.

For Nick: it’s not the muscle, it’s the skill. It is highly unlikely that one day of hard riding followed by half a day of hiking added any muscle mass onto you. Or me. But I remember how much I learned by experiencing the slickrock. I know I came out a better rider, and have had those additional skills since my trip there in 2001. I’m sure you picked up some skills as well.

Re: Re: Re: Short cranks - ZOOM! What gives?

OK, I can see that point at 200 rpm. It is the reason that short cranks allow higher rpm in the first place. But we were talking going up steep grades. You’re not revving them up at 200 rpm right? Maybe you would gain speed before the slope so that momentum carries you up to some extent. That indeed would work better with short cranks. But I was assuming that the argument is about sustained climbing. And for that I’m still not convinced.

Klaas Bil

Why is pedalling in a smaller circle smoother?

Let’s take a comparison with bicycling. Going up a steep hill on a bicycle, you can stand up on the pedals, secure in your balance because the cycle has two wheels, and you have handlebars to hold onto. This permits a style of hill climbing which we used to call ‘honking’: you step up onto the top pedal, and as you straighten your leg, your whole weight is allowed to fall onto the pedal. You’re not simply pushing down with muscle strength, but with your bodyweight.

OK, so if you’re pushing down with your bodyweight, this means that your centre of mass is falling - even if it’s only by a few inches.

And that means that to get ready for the next pedal stroke, you have to raise your body mass relative to the cycle - in fact, relative to the bottom bracket spindle. So, effectively, you have to step UP onto the new top pedal.

So honking up a hill becomes a series of steps up. The average movement of the centre of mass of the bicycle/rider unit is exactly parallel to the road surface. However, the centre of mass of the rider alone moves up and down relative to the road surface.

So if the bicycle had 170 mm cranks, the centre of mass of the rider would be moving up and down by up to 340 mm. Because of the bending of the legs, I guesstimate that the centre of mass of the rider would actually only move up and down by rather less than 170 mm. The rider would use that injection of extra power (from his or her bodymass) to give the initial thrust to the pedal stroke.

And it follows that if the cranks were only 125mm long, then the rider’s centre of mass would move up and down somewhat less. Simply: the rider would be ‘walking up’ a flight of smaller steps. His or her movement would be less violent, less reciprocating, smoother.

Now apply this to the unicyclist. the unicyclist has only one wheel on which to balance. The handle (if fitted) offers less control and balance than bicycle handlebars. Therefore, any element of oscillation in the rider’s movement is more critical. Balance is that bit harder. Smoothness is more important, because smoothness results in fewer ‘balance events’ (sudden changes in the dynamic balance of the rider/unicycle unit).

This is at least part of the reason why I am perfectly happy riding a bicycle with 170mm cranks, but I find them intolerable on a unicycle.

So, smaller cranks = smaller circle = less vertical oscillation of the rider’s body mass when up out of the saddle to climb a steep hill.

So the rider has less peak torque, but a smoother action. And even when the smooth action eventually breaks down into a series of steps and stops, the steps become smaller, so the balance events are less significant.

But I stress, it is all a question of degree. I have ridden with cranks from 89mm to 170 mm, and I have found that each extreme produces different benefits and disadvantages. So much can be achieved with cranks between about 110 mm and 150mm. Above 150, I find the cranks too long for comfort and smoothness. Much below 110 mm and I find control is reduced, but with no significant increase in speed.

I do know that I am now routinely riding stuff on 110s or 125s which I found unrideable on 150s a few months ago. That’s technique, experience and confidence. And I’m not claiming to be particularly good, because any quick reading of posts in this forum suggests to me that my skill level is in the bottom quartile of posters here.

A couple of general points:
(1) Small changes in crank length matter less with long cranks. 160mm cranks are 10 mm shorter than 170mm cranks. That’s a reduction of 6%
90 mm cranks would be 10 mm shorter than 100mm cranks, but that would be a reduction of 10%.

(2) We should look at the rider, crank, wheel combination as a complete unit. In a motor vehicle, the engine is designed to produce power/torque most efficiently and effectively within a certain part of the rev range. The gears are then used to match the engine’s best performance against the desired speed and the road conditions. If you put a car in the wrong gear, it won’t be happy. If you put cranks on your unicylce which don’t match the performance characteristics of the engine (your legs) then the unicycle won’t perform as desired.

So 170s don’t suit me. They might suit someone taller, or someone more skilled. So, I find 110s on a 28 the lower limit of sensible control. Someone else might find 102s easy. I find 89s on a 24 challenging; Roger found 50s on a Coker, er… smoooooth.

There are no final answers. Only tendencies and principles, judgements and preferences, ideas and experiences. That’s why I find it interesting as a subject as well as a fun activity.

I find ‘honking’ on a unicycle a useful technique for getting up really steep hills and for using different muscle groups rather than sitting all the time. The first time I did this I found myself grinding up something much steeper than anything I’d ridden before. But you have to shift your weight forward onto the seat handle just as a bicyclist will shift some more of their weight onto the handlebar.

Ken

BMXers have a term called ‘torquing’. It is really a combination of two things that combine to make it easier to climb a hill.

What you do is pull on the opposite handlebar from the foot currently pushing down. This allows you to add a little upper body strength into the mix, and it changes the angle of attack.

This means the hill is no longer as steep, you are zig-zagging up the hill.

I have done the same thing on a unicycle, that is the zig-zag, and it seems to help going up steep hills.

Using a handle makes it harder to zig-zag, and for me, right now I think it is easier to climb a hill without using the handle.

I would guess that shorter cranks would make it easier to zig and zag, but haven’t really noticed it much. But the zig-zag could be an effective way of downshifting on a uni.

Hmmm. So you’re saying I just wasted £30 and two drill bits on a handle? Aaaagh!:frowning: :wink:

I think you’re right about the zig zagging. You know, for all the nonsense I write about it, I bet I don’t spend 5% of my riding time going up hills steep enough to matter. But when I do, yes, I do a little zig zag, making a zig (or zag, as appropriate) with every pedal stroke. I think that’s what I meant when i was waffling on about timing and stuff.

And this leads me on to another idea, which may or may not be true:

For hills up to a certain length and steepness (which will vary with the rider’s ability etc.) a bigger wheel is better, because bigger wheels are smoother, even if the ‘leverage ratio’ isn’t as ‘good’. This is why a Coker or 28 can sometimes ‘rush’ a hill that would stop a 24.

For hills beyond that point of steepness and length (the ones where the uni actually comes to a halt or a near halt) a smaller wheel is better.

So when you need a high crank:wheel ratio (lots of torque) I think it’s better to obtain that by moving down a wheel size, rather than up a crank size.

All within reasonably limits, and subject to a number of variables, of course. I just know that on a 24 with 150s, I storm up long steep hills (measured by my low standards) which are a major trauma on a 26 with 170s, even though the 26/170 has a ‘better’ leverage ratio. (51.4% as opposed to 50%)

So the answer is simple: wheels manufactured like iris valves which can expand or contract according to the demands of the terrain. Greg… get to work on it. ;0)

Crank length vs wheelsize

Something maybe no one mentioned is the advantage shorter cranks have in that they don’t scrape the ground as much when you turn sharply. This does not affect steep hill climbs too much but it comes in handy when doing other stuff. I quite like short cranks especially for on the road or pavement. I put cranks off a 20" unicycle on my 24" when I rejuventated it after a double broken axle (I hijacked my little brothers 20" unicycle), and I enjoy the extra speed the shorter cranks give. Without going into a scientific explantion I think just do whatever feels good to you and be happy with that. I reluctantly got 170mm cranks for my mountain unicycle but they seem to do the job reasonably well. It seems that you can not have the best of all aspects combined into one unicycle and that must be why they come in so many shapes and sizes (and prices).