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Old 2012-01-04, 09:28 PM   #1
Twente Muni
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Why am I not faster with shorter cranks? (Oh no, not crank length again...)

The last months I rode my 29er a lot again, for faster XC/muni.
I have dual hole cranks, and mostly I ride with the 165 mm holes, it gives me the best control.

The last five rides I gave the 137 holes a try. After getting used to the shorter crank length it felt smooth, and easy xc in the mud wasn't a big problem. I am really confident with this length now.

I was getting very curious about the speed, so I put a cycle computer on the T-bar. To my surprise my top speed is 21 km/h (for mph divide by 1.6 ). The cruising speed is 16 km/h, 10 mph.

Today I wanted to find out how fast I can go with 165 cranklength. I gave it a short try in the neighbourhood and I found out that the speed difference is very small.
I got a top speed of 20 km/h, I only did a few tries. The cruising speed is 16 km/h, so no change. It is more work to spin the bigger circles however.

I was expecting more speed difference. The cranklength difference is 17%, and I get 5% more topspeed. Difference is cruising speed is even less.

What could be the reason:
1) going 21 km/h means that I spin 150 rpm. I know from my singlespeed MTB period that my topspeed was also at 150 rpm, with 175 mm cranks of course.
Could it be that my legs can't go faster, at any crank length?
2) 5 rides of 1,5 hours is not enough to benefit from a short crank length?
3) I am 6'3" and have long legs, maybe it is easy for me to spin big cranks fast. (I suppose 150rpm is fast???)
4) I rode MTB for far to long?

Can you think of any other reasons?

I leave the pedals in the 165 holes for now. It gives me more control offroad, at almost the same speed.

I am very curious about your comments.
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Old 2012-01-04, 09:48 PM   #2
nordicnoel
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I've been riding a KH29 with 165 mm cranks since last spring, but I put the 125 mm cranks that it came with on a week ago hoping to get faster. I've only ridden with the shorter cranks for almost 4 hours. I've noticed that the shorter cranks make it even easier to out-spin my comfort level: in the 125--165 mm range my limit isn't how fast I can spin, but how fast I feel comfortable riding. So my top speed isn't really any better with the shorter cranks, it is just slightly easier to hold it for longer. Then my speed freaks me out and I UPD...

Oh, and there is the extra saddle height affecting balance too. 40 mm shorter cranks mean 40 mm higher seat.

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Old 2012-01-04, 10:03 PM   #3
From the Woods
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I think it has a lot to do with practice. But also how you can deal with higher speeds is important. You are used to riding about 20km/h so if you go faster you will feel out of control at first. Mostly because you are reaching speeds where running out of an UPD isn't that easy any more. Moreover everyone is different. So maybe you are just someone who likes longer cranks more.
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Old 2012-01-04, 10:20 PM   #4
Twente Muni
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Quote:
Originally Posted by From the Woods View Post
I think it has a lot to do with practice. But also how you can deal with higher speeds is important. You are used to riding about 20km/h so if you go faster you will feel out of control at first. Mostly because you are reaching speeds where running out of an UPD isn't that easy any more. Moreover everyone is different. So maybe you are just someone who likes longer cranks more.
Maybe you are right, there might be some fear involved. At speeds over 20 km/h, the control is getting worse because op high rpm, and an UPD might be very bad.
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Old 2012-01-05, 01:29 AM   #5
mbalmer
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I never was able to go any faster with shorter cranks though they are a smoother ride. I also don't go any faster than I can run out of a UPD (no more than about 16 km/h). I prefer shorter cranks (125s) on my wheels up to 29", but prefer the 150s on my 36" and MUnis. I like the 137s on my Schlumpf.
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Old 2012-01-05, 03:15 PM   #6
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longer cranks = more control (up to a point- obviously 250mm cranks aren't going to be much use )

I find that with 150s- my preferred length on my 24x3, I'm very happy to occasionally go full spurt and feel safe doing so.

If I switch to a 'faster' setup, eg 29-er with 125s- theoretically I would then be on a faster machine- however, I would not feel happy or safe to go full spurt, due to the lesser amount of control.

This applies across the board- for example, some Coker riders have noticed that using shorter cranks on their 36-ers results in a ride taking longer, because they find they have to dismount/remount more often (for example if the ride involves several sets of traffic lights), whereas, with a longer crank, they don't have to dismount as often, so it's actually quicker.

I think shorter cranks are best when you're riding very regualrly/consistently and therefore aquire the necessary skill to get the most out of them.
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Old 2012-01-05, 06:06 PM   #7
Twente Muni
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@ mbalmer: you say you ride 16 km/h maximum. On your guni and 36er also ?
Do you have them just for the comfort of slower pedaling instead of speed ?


From the posts above I conclude that short cranks are only for the people who are really in control with them. Otherwise the potential speed gain is lost by the worse control.
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Old 2012-01-05, 06:59 PM   #8
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I've found the same. I am not noticeably faster with 125mm on the 29" than I was with the 150mm, in top speed, or on short distances. I do notice the average speed is higher on longer rides (able to go faster, longer with shorter cranks).
Changing tire, from a slick Big Apple to a XC type tire, actually made a much bigger difference on my commute. I was noticeably faster with the XC type tire, due to the increased confidence on the gravel trail.
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Old 2012-01-05, 09:14 PM   #9
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Just for information: As far as I can remember, my max speed difference between 165s and 137s was about 2-4km/h BUT the speed difference between ungeared and geared was 2-4km/h too. So for me it's the high speeds I am not comfortable with. Everything over 24km/h scares me and everything over 28km/h lets me feel totally out of control. Even if I could go faster I would not be able to because I am not confident enough.
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Old 2012-01-06, 02:26 AM   #10
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Our side by side testing of different configurations for Ride The Lobster had one clear conclusion: People are fastest on the configuration they're accustomed to.

I really don't think momentary top speed is affected all that much by crank length, but the sustainability of that speed is, and the amount of effort required to maintain it.
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Old 2012-01-06, 05:15 AM   #11
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"Why am I not faster with shorter cranks?"

Apparently because you aren't pedaling any faster. And the reasons are many. I think there's a tendency among riders of all experience levels to not allow enough time to get used to changes in setup. In familiarity is comfort, and in comfort is confidence. For example, it has been a gradual process for me to get comfortable riding fast in high gear on my 36". Many years earlier, it was also scary putting 125s on an ungeared Coker, though today I consider those to be too long for road riding.

Changing crank lengths requires changing seat height, so the cycle rides a little differently as well. Until you get comfortable with the ride quality of shorter cranks, you won't have the confidence you had with longer ones, due to a reduced amount of torque for quick corrections. But you get used to things.

Crank length doesn't make much difference on short rides or sprints. But the longer the ride, the more you'll notice the difference. If conditions are not too difficult for the shorter cranks (steep or bumpy), you'll be able to feel the savings in energy.

29" for road riding? Use 102s unless you're doing big hills. On dirt? It very much depends on the terrain, and how much torque you like. I kind of like the 140s I have on mine right now, but they're only appropriate for the faster, less-technical trails I like that cycle on.
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Old 2012-01-06, 02:12 PM   #12
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Certainly another item affecting crank length could be the size of the unicyclist, couldn't it? I haven't been riding that long (only about a year), but I'm using 110s on a 20", 125s on a 24", 170s on a 26" muni, and 150s on a 29". I am 6'4" and couldn't imagine using anything smaller than 125s on a 29" or a 36". I just think it is a lot more difficult for someone like me to spin in smaller circles than someone with a leg about 15% shorter. ...just curious.

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Old 2012-01-06, 07:10 PM   #13
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Quote:
Originally Posted by tholub View Post
Our side by side testing of different configurations for Ride The Lobster had one clear conclusion: People are fastest on the configuration they're accustomed to.
I think tholub hit it spot-on. Five rides isn't that much practice to get used to a new set-up.

For me (and I only ride 36, so not a direct comparison) both cruising speed and peak speed have consistently increased as I shorten my cranks, although the peak speed takes longer to increase than cruising speed. I've ridden over 1000km on all of 150s, 125s, 110s, and my current 100s.

It usually takes about 7-15 hours of riding on a better set-up for me to start actually benefiting from it, and maybe 15-25 hours before I can really get comfortable and feel "normal".

Also, I haven't found my long legs to be a problem. My inseam is 36" (and I'm "only" 6' tall... there are some huge people on here). I love my 100mm cranks and am starting to get anxious to go smaller! Might need to get a brake to use it in town though... and a longer seat-post.
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Old 2012-01-06, 08:00 PM   #14
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I have been riding a N26 with 165s and I rode this week with 140s and i am going no faster
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Old 2012-01-06, 08:11 PM   #15
Twente Muni
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Thanks for the comments guys,

So to benefit from short cranks I have to:
1) Keep at it for much longer.
My problem is that I like to experiment and change between wheelsizes at lot, depending on what type of riding I want to do. The most fun for me is on the local MTB trail with my 24x3 and 170 mm cranks. At the moment the trail is a complete swamp, so then I take out the 29er on easier trails. I like the speed of the 29er, so I still have a lot of fun.
When I get better, I will be able to do the local MTB trail with the 29er.

2) Longer distances on not too difficult terrain
I don't do long distance, usually 1.5 hours offroad, don't really care about the distance, for now anyway.

So here is my plan for 2012:
Ride the local MTB trails with the 29er with 165 mm cranks.
If I can do that with only a few UPD's I will go to shorter cranks.
The main goal is to do everything I could do with the MTB, and that with increasing speed. Now with 24x3 / 170 mm, upgrading from there.
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