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I'm looking at two Devinci bikes. One says "Compact Truativ Rouler GXP 50/36T" The other doesn't say anything.

Now the bikes are the same, and looking further at the 50/36 I assume that means compact cranks. So, what do compact cranks do? Are they just shorter?

Are there any advantages? I know fit is the big issue, but assuming they don't have any in stock, what should I know about the two?

David.
 

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"compact" refers to the bolts where the chainrings bolt on to the cranks. They're a little closer to the BB axle, which allows you to fit smaller chainrings. The smallest possible with the normal Shimano 130mm bolt circle is 39t. The smallest possible with a 110mm bolt circle "compact" is 33t, although those are rare and 34t or 36t is what's normally fitted. The cranks themselves come in the same lengths as normal cranks, its just the bolt circle and thus the gearing that can change. With a 36 and a 50t big ring the rings are the same difference (14t) as a 39/53 setup (although the percentage difference is more).

Many bikes are geared for pro riders or criterium racers but are used by normal humans on long rides that can involve lots of hills. So lower gearing is a good thing. Sometimes bikes are specd with a compact crank and then a tight 11-23 cluster, which sort of blows the lower gearing idea. At least the cluster is an easy thing to change.
 

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Compact bikes, frames and cranks

A "compact" bike or "compact" frame refers to a frame geometry in which the seat tube length is reduced and the top tube slopes downward from the head tube to the seat tube.

A "compact" crank refers to a crank with reduced sized chainrings (which requires that crank spider must be smaller to allow smaller chainrings to be bolted to it).

"Compact" frames and "compact" cranks are independent and unrelated you can mix and match compact or non-compact cranks with compact or non-compact frames. Do a search for either to find the pros and cons of compact frames and compact cranks
 
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