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Folding Bikes Discuss the unique features and issues of folding bikes. Also a great place to learn what folding bike will work best for your needs.

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Old 08-28-17, 02:11 PM   #26
Hisamatsu
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Originally Posted by Rick Imby View Post
It is a problem since you are focusing on it. Human bodies are very good at adapting. If she did not have the option of a 130 and you had not pointed it out that she should have a smaller crank arm she would never have thought of it.

Do you redesign buildings with shorter or taller stairs? Does she have a problem walking up stairs?

The standard stair in the US is 7" which equals 177.8 mm.

I believe it can make a difference it performance and it is great that you are spending the energy and money to build it for her.

Have fun and report back---
There is a reason why kids bikes don't come with adult 170mm cranks, because they are smaller and shorter. My SO is basically kids dimensions, she had issues while riding regular adult size bikes, knee pain, discomfort etc, we didn't know why, just assumed it was how it is. Took a couple years for us to find islabike which has shorter cranks, they are basically bikes designed for kids. She was happier with it, less discomfort and complaining means more willingness to ride. Got a brompton for travel and knee issue again. All the effort is worth it as I hear less complaining from her while riding =]
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Old 08-28-17, 07:09 PM   #27
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Good to read it worked out. Did you end up using the standard Brompton BB with your new cranks?

I'm running 165 mm cranks on our Bromptons. My SO was not a "dedicated" cyclist and I wanted to address any possible sources of discomfort BEFORE we started touring.

I've gone from 175 -> 170 -> 165 and my knees thank me for it!

I am considering shorter cranks for my SO as her inseam is 10 cm shorter than mine.
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Old 08-28-17, 07:17 PM   #28
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Good to read it worked out. Did you end up using the standard Brompton BB with your new cranks?

I'm running 165 mm cranks on our Bromptons. My SO was not a "dedicated" cyclist and I wanted to address any possible sources of discomfort BEFORE we started touring.

I've gone from 175 -> 170 -> 165 and my knees thank me for it!

I am considering shorter cranks for my SO as her inseam is 10 cm shorter than mine.
I haven't installed it yet, still awaiting for the crank on order to arrive.

But my SO does have another bike with shorter crank from Islabike. I find the formula (inseam with shoes)/5 pretty close to the optimal crank length. My inseam is 864mm so I fit the average crank length 170-172. My SO on the other hand has inseam of 700 which needs shorter crank around 140.
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Old 09-09-17, 05:35 PM   #29
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Update:

I installed the Promax SQ1 135mm crank on and everything is working great with a few quirks.

Brompton uses 119mm spindle but the SQ1 is designed for 113mm. Had to use 3mm spacers with longer chainbolts to get the chainline back to 43mm.


The folding pedals wouldn't fold, got caught by the bottom edge of the arm, I just filed it down a little.
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Old 09-10-17, 06:39 AM   #30
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That's fantastic that you got everything to work. I hope she is happy with her new ride.
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Old 09-10-17, 11:31 AM   #31
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With a shorter crank you will be raising the saddle, (35mm) to keep the saddle to pedal distance consistent..

As is, the pedals are low due to BB height in frame design,

So stopping at stop-signs, will now require getting off the saddle, to put a foot down.

which is not a big deal ... I have to do this with my Bike Friday Pocket Llama, due to its higher BB, in the frame design.






.....

Last edited by fietsbob; 09-10-17 at 11:35 AM.
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Old 09-10-17, 12:41 PM   #32
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Mark Stonich in Minnesota has shortened a few cranks for me:

BikeSmith Design and Fabrication

Not all cranks can be shortened. Tip: Save yourself a few bucks and remove the chainrings before you send your crank in. I seem to remember that he charged an extra $5 if you left the chainrings on.
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