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Compact crank?


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norm, it has to do with the length of the crank. I think a standard crank is 175mm and a compact is 172.5mm It allows for faster revolutions apparently so it suits climbing.

 

However I am here to learn so rather try google sheldon brown - he has some nice info

 

But I am sure loads of other informed people will correct me, point out flaws and your simple question will become a discussion in physics, torque, ego and who goes faster.

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A standard crank has chainrings with 52 and 39 teeth - a compact crank nornmally has two combinations - 50 and 36 or 50 and 34.

It has absolutely nothing to do with the crankarm length

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A standard crank has chainrings with 52 and 39 teeth - a compact crank nornmally has three combinations - 50 and 36 or 50 and 34.

It has absolutely nothing to do with the crankarm length

see I told you someone would correct me ! :)

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The PCD of the crank chainring bolts are also different to that of a normal crank as far as I can remember....

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Correct Owen. And you can not simply put compact blades on a normal crank (or visa versa) as the bolt diameter is also different.

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taken from wiki (googled compact crank)

 

Compact crankset

In the context of mountain biking the term compact crankset refers to smaller triple cranksets, giving a small benefit in weight at the expense of increased wear and also giving the bike better clearance over obstacles. Typical ratios would be 22/32/44 teeth as opposed to 28/38/48 or 24/36/46 teeth. These would be used with smaller cassettes (Generally cassettes are available with 11 tooth minimum gear sizes for compact chainsets while standard chainsets were designed for cassettes with a 13 or 14 tooth top gear), giving the same overall ratio. Compact chainrings are the dominant standard for mountain bike cranks for the past decade or so.

 

In the context of road cycling, compact drivetrain typically refers to double cranksets with a smaller (usually 110mm) bolt circle diameter than the standard 130mm or Campagnolo's 135mm. As of 2006, all of the major component manufacturers such as Shimano and Campagnolo offer compact cranks in their midrange and high-end product lines. The compact crankset provides a compromise between the standard road double crankset (with 39/52 or 39/53 tooth chainrings) and the road triple (with 30/42/52 or 30/39/53 tooth chainrings). The compact crankset has two chainrings and typical ratios are 34/48, 34/50 and 36/50. This provides nearly the same lower gear ratios as a triple but without the need for a third chainring, a triple front derailleur and a long cage rear derailleur. Note that both Shimano and Campagnolo recommend and sell front derailleurs specifically designed for compact cranksets, claiming better shifting.

 

Compact gearing is not necessarily lower than standard gearing if cassettes with smaller sprockets (such as 11–23) are used. A high gear of 50×11 on a compact drivechain is actually slightly higher than the 53×12 of a standard set.

 

Compact gearing usually has a large percentage jump between the two chainrings. In balance, it may also allow small jumps in the rear by allowing a closer ratio cassette to be used, except for the 9% jump at the high end between the 11 and 12 tooth sprockets.

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"But I am sure loads of other informed people will correct me, point out flaws and your simple question will become a discussion in physics, torque, ego and who goes faster."

 

 

Beautifully said :lol: :lol: :lol: , thanks for the afternoon free laughter !!

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mmmmm could you have the same number of teeth, but shorten the crank arm ?

 

Most cranks, compact or normal, comes in an array of lengths from 165mm-180mm.

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