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Short cranks

GaryGknGaryGkn Posts: 1,199
edited February 2008 in Road general
I need some short crankss for a Raleigh 20 fixed project.

http://www.sheldonbrown.com/harris/cran ... ingle.html

Bulletproof cranks are a reasonable price in the US does anyone know if they are available in the UK? I think 150 would be a possibility after reading Sheldons thoughts.


http://www.sheldonbrown.com/cranks.html

Below is what he says:

Crank Length

Different cyclists have different leg lengths. It seems obvious that crank length should be proportional, so long legged cyclists should have long cranks, short-legged cyclists should have short cranks....and yet, 99.9% of adult bicycles have crank lengths between 165 and 175 mm. Have the bicycle manufacturers joined in a great conspiracy to force everybody to ride the same length cranks, regardless of their needs?

This is a common misunderstanding. The "leverage" of a bicycle drive train, also known as "gain ratio" depends on the crank length, wheel diameter and the sizes of both sprockets.

Yes, if you go to longer cranks without changing any of the other variables, you will have more "leverage", which is another way of saying you'll have a lower effective gear...but on a multi-speed bike, you can change gears at will!

Ay, there's the rub! Assuming you adjust your gearing appropriately, crank length has no effect on leverage, it just has to do with the range of motion of the knee and hip joints.

Too long cranks cause excessive knee flex, and can cause pain/injury if it causes your knee to flex more than it is used to.

I learned this the hard way when I bought a used mountain bike that came with 180 mm cranks. I found that it made my knees hurt every time I rode it.

On the other hand, there doesn't seem to be any deleterious effect from shorter cranks.

I've been experimenting with this a bit myself lately. For my fixed gear, I commonly ride 165 mm cranks with a 42/15 ratio on 700c or 27 inch wheels, when I'm riding fixed. This gives a gain ratio of 5.8.

My latest experiment is taking place on plastic Trek frame I picked up in a barter deal. I had a pair of TA 150 cranks that used to be on my kids' Cinelli BMX bike, so I've put these on the Trek. I'm running a 45/17, which gives a gain ratio of 5.9, just a bit higher.

When I first get on the bike after riding with longer cranks, it feels a bit funny at first, but within a very short distance it's just fine. I go just as fast, climb just as well. For a given speed, my pedal rpm is higher (though my pedal speed is the same) but the short cranks make it easy to spin much faster than I normally would.

After riding this bike for a few miles, when I get back on "normal" cranks, they feel a bit weird and long at first, then I get used to them after riding a couple of minutes.

I think people really obsess too much about crank length. After all, we all use the same staircases, whether we have long or short legs. Short legged people acclimate their knees to a greater angle of flex to climb stairways, and can also handle proportionally longer cranks than taller people normally use.

Posts

  • DickieDickie Posts: 1,489
    Gary, just spoken to Rich at custom riders the bmx shop.

    2 451 rims.for you.

    Sun IC1 28 hole black eyeletted machined brake face. £29.99ea, I am lusting after these.

    Ciari all black 28 hole not sure if it has eyelets. £24.99ea

    This would mean you could use "normal" cranks as clearence not such an issue.
  • GaryGknGaryGkn Posts: 1,199
    Ah... I wish I could I have had the 406 wheels built onto fixed hubs and to make it worse a box of 12 Sun new rims went for £20 on ebay a couple of weeks back I was at work waiting to bid but alas somebody broke my concentration with a load of nonsense and I missed it by 30 seconds any way it looks like I am stuck with 406 . At least I can get tyres and perhaps the mental clowns cranks will be ok?

    This Raleigh Twenty is a poison chalice.

    Whish I had held off now.
  • GaryGknGaryGkn Posts: 1,199
    Just had a browse BMX stuff looks like big business . Looks like the 150 cranks are my only option as the wheels have set me back £130 already. I guess I will have to order something from the US or bide my time.
  • 4candles4candles Posts: 240
    http://www.highpath.co.uk/cycles/index.html

    go here he can shorten cranks.... !
  • GaryGknGaryGkn Posts: 1,199
    Thanks for that 4candles it may be a last resort.
  • 4candles4candles Posts: 240
    GaryGkn wrote:
    Thanks for that 4candles it may be a last resort.

    No worries... i have a couple of his 1/8 chainrings and they're pukka.
  • GaryGknGaryGkn Posts: 1,199
    What are his prices like?
  • 4candles4candles Posts: 240
    On the steep side, however the 1/8 rings i have been used for 15 years in Track leagues and they'll easy do 15 more.
  • GaryGknGaryGkn Posts: 1,199
    Many thanks for that link and all your help.
    Very much appreciated.
  • Mike Burrows shortens cranks for about 30 quid
  • scherritscherrit Posts: 360
    I've had bulletproof cranks send here to the UK from the US.. no problem and at around 25 quid, what a bargain! My missus uses a set of 150's on the track (with a single ring) and a set on the road as a double..... bolt circle is 130 I think...... harris cyclery used to carry a slightly odd looking ring that was cheap as chips that was drilled for (I think...) 110mm bolt AND 130mm bolt circle.

    If you need a triple, though, or a compact road set-up, it's down to the likes of TA (much money....)
    Good luck..
    S.
    If you're as fat as me, all bikes are bendy.
  • GaryGknGaryGkn Posts: 1,199
    I think the BCD is 110. Although I would love to be wrong and discover that 130 is the exact size. I think I will have to go for these cranks as the price is very good. Thanks for the information. Scherrit and everyone else who has contributed.

    All info and views have been very useful.

    Much appreciated G
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