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Old 2017-12-01, 10:00 PM   #1
Vogelfrei80
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Bigger wheel or smaller cranks?

I don't really know the difference in climbing using different cranks so I wish someone could help me to understand the mathematics about the torque. I could use a 26" geared at 150% with 125mm cranks or I could swap to 29" geared atll 150% with 150mm cranks... I read somewhere that climbing with 150 cranks is doable even on 36"... So I'd better use the longest cranks solution?

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Old 2017-12-01, 10:35 PM   #2
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Lots of questions there!

I have spent a lot of time and money experimenting with crank lengths and I posted my findings many years ago.

The outcome is I ride my 36 on 150s, sacrificing a small amount of top speed for a lot more control. On 150s, I can climb our biggest local hill, which on a bike is several minutes of riding, with the last half standing on the pedals.

Choose the wheel size for the riding you want to do, then make "tuning adjustments" with the crank length.

The ideal crank length for safe road riding and controlled off roading is the length at which you can mount, start, stop and idle.

The ideal crank length for just going fast is shorter than that.

Extra long cranks (bigger than 150) give you more torque but at the expense of comfort and speed. On my 24, I replaced my 165s (?) with 150s and it instantly became more enjoyable to ride.

Yes, you can do the maths, work out ratios and "development" and so on. It's all fairly simple division and multiplication, but the fact is, the results are only accurate within a narrow range, and the exact range varies from rider to rider.

Compare a 4 inch wheel with 1 inch cranks, a 20 inch wheel with 5 inch cranks, and a 36 inch wheel with 9 inch cranks and you will soon see what I mean.
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Old 2017-12-02, 06:57 AM   #3
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The outcome is I ride my 36 on 150s, sacrificing a small amount of top speed for a lot more control. On 150s, I can climb our biggest local hill
I found that a 26" x 3.5" x 125 solve the pedal stroke issue, but I cannot increase only crank lenght due to that problem. That is why I'm comparing 26x125 to 29x150: no way to use a 26x150!
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Old 2017-12-02, 07:33 AM   #4
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If you are comfortable on 125s, then 125s on a 26 or 29 will be pretty much the same. I know that the wheel sizes are only nominal, but if you take them as accurate, 29 is only 11% more than 26. That's equivalent to 1 tooth different (a change of one step) on a derailleur on a road bike.
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Old 2017-12-02, 09:44 AM   #5
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This chart was orignially posted by saskatchewanian. Crank lengths on the left side and wheel sizes on top. G=geared.
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Old 2017-12-02, 06:21 PM   #6
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Great!!!! It answers a lot of questions! When I'll be fine with 29 ungeared I'll go 29 geared!
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Old 2017-12-02, 10:33 PM   #7
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Quote:
Originally Posted by Vogelfrei80 View Post
I found that a 26" x 3.5" x 125 solve the pedal stroke issue, but I cannot increase only crank lenght due to that problem. That is why I'm comparing 26x125 to 29x150: no way to use a 26x150!
Please clarify. Are you talking about a normal unicycle? On a normal 26" unicycle, you could go longer than 125mm without worrying about pedal strike. I do muni on my 26" with 170mm cranks, and I rarely have pedal strike. Did I miss something from a previous thread?
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Old 2017-12-02, 11:15 PM   #8
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I suppose those wanting to go to 27.5" or 32" wheels can guestimate from this handy chart.
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Old 2017-12-03, 03:01 AM   #9
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Vogelfrei If I'm wrong please correct me if I'm wrong but I'm guessing you have a Huni-rex with the crank pivot lower than the wheel axle. Hence the comments about pedal strike.

There is a version of that chart with 32 and G32 included somewhere, but it's really just a rough guide to give people some reference on similar torque requirements/gain ratios. The categories were based on my experience at the time and also a bit of fun, It does break down at the extremes.

If you want to figure out your gain ratio just divide your wheel radius by your crank length then multiply by any gearing.


Personally I was commuting with a geared 26 (Schlumpf) last year. 137mm was a good length for me in winter while I preferred 125 with my summer tire. I rode mostly in high gear but might have gone slightly longer if I didn't have the option to downshift for the lumpy areas.
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Old 2017-12-03, 03:56 AM   #10
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Here is the chart with a 32:
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Old 2017-12-03, 08:16 PM   #11
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Originally Posted by saskatchewanian View Post
Vogelfrei If I'm wrong please correct me if I'm wrong but I'm guessing you have a Huni-rex with the crank pivot lower than the wheel axle. Hence the comments about pedal strike.

There is a version of that chart with 32 and G32 included somewhere, but it's really just a rough guide to give people some reference on similar torque requirements/gain ratios. The categories were based on my experience at the time and also a bit of fun, It does break down at the extremes.

If you want to figure out your gain ratio just divide your wheel radius by your crank length then multiply by any gearing.


Personally I was commuting with a geared 26 (Schlumpf) last year. 137mm was a good length for me in winter while I preferred 125 with my summer tire. I rode mostly in high gear but might have gone slightly longer if I didn't have the option to downshift for the lumpy areas.
You are right with everything. Huni-rex, cannot downshift, cannot go longer than 125 on G26 (maybe can go longer, but don't want to be careful on sharp turns). That is why I was wondering about 150 on G29. Can you climb small hills in high gear G26?
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Old 2017-12-03, 09:51 PM   #12
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Originally Posted by Vogelfrei80 View Post
You are right with everything. Huni-rex, cannot downshift, cannot go longer than 125 on G26 (maybe can go longer, but don't want to be careful on sharp turns). That is why I was wondering about 150 on G29. Can you climb small hills in high gear G26?
Everyone is different but assuming summer conditions and good pavement I don't think I would have a problem with hills geared up with 137mm cranks on a G26. 150mm on a 29 is pretty close to 137 on a 26 as far as gain ratio is concerned.

Another anecdotal point of reference: I also have a geared 32 that I was using with 140mm cranks. Haven't used it in a while but I would not want to be stuck in high gear on that one for going up-hill.

How much room is there over the tire in the fame? I have never owned one so don't know how big of a wheel you can fit in there. If it fits, 29 with 150mm cranks seems like a reasonable choice.
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Old 2017-12-04, 06:29 AM   #13
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[QUOTE=saskatchewanian;1691026]How much room is there over the tire in the fame? I have never owned one so don't know how big of a wheel you can fit in there. If it fits, 29 with 150mm cranks seems like a reasonable choice.[/QUOTE I'm using a 3.5 tire which leave no room. But I could manage to mod the frame
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Old 2017-12-04, 02:59 PM   #14
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mmm. a 26x3.5 tire will make your wheel as tall as a regular 29".

Would you have pedal strike issues if you put 150mm cranks on your current setup? If so then switching to a 29" wheel won't help much in that regard. Where it would help is you end up with a lighter, faster rolling, and more responsive wheel. A faster rolling tire can make a difference (my crank length change for winter has more to do with tire choice rather than riding through snow.)

Is there any way to simply swap out the sprockets for a lower gear?
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Old 2017-12-04, 08:28 PM   #15
Vogelfrei80
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I never thought about changing the sprockets.. :mad that could really help me! I'll have to solve the related chains tension, but probably that's the way to go! I could try! Thank you for all your help! Hope someday I'll post a video review of my uni and its pros and cons

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