Bicycle Mechanics - Road compact size crank with mountain strength?
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01-28-09, 06:00 PM
Hi there. I am building a Bike Friday Pocket Llama, and am wanting to gear it to the tune of 34-50.
The Pocket Llama is a small wheeled mountain bike, and would be used for cross country riding. The small wheels call for the large rings, as does the braze on front derailleur (Shimano R-440)
Are there strength concerns with using standard road compact cranks in cross country applications? I've never given this much thought, any insight would be appreciated. Any manufacturers out there putting out "stronger than average" road cranks for CX use, something like that?
01-28-09, 07:09 PM
Look into Dimension cyclocross arms from QBP. Sturdy and inexpensive.
From my experience most CX racers are using road cranks with chain rings sized for CX racing. Road cranks are plenty strong.
01-28-09, 08:03 PM
I am not sure that MTB cranks are any stronger on average than road cranks. If they have similar cross sectional area in the arms, and are aluminum, the strength will be about the same.
Originally MTB cranks had smaller spiders and were triples. The smaller spider allowed a smaller middle ring than could be fitted to standard 130mm BCD road cranks.
Early MTB cranks were 110/74mm BCD units such as the Sugino triple originally introduced for touring bikes. This format was adopted by Shimano for their early MTB and touring triple cranksets too. In the mid 90s the micro drive cranks with even smalller BCDs were introduced along with casettes with an 11 tooth small sprocket. These saved weight, increased ground clearance to the outer chain ring and still gave about the same overall gearing.
01-28-09, 09:31 PM
I believe that there is no difference in strength between a mountain and road crank, the only thing I would watch out for are ultra light road cranks. Cranks for road that use carbon fiber and titanium may not be fit for mountain riding.
Are there strength concerns with using standard road compact cranks in cross country applications?
I'd have no qualms at all about using road cranks for CX, as even road stuff seems to hold up well for the occasional curb jump, speed bump and similar. I'd might reconsider if I was planning on doing a lot of drops and jumps.
01-29-09, 03:40 AM
Just make sure that the BB spindle length gives you a good chain line.
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