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Cranks, Groupsets and how the link together?


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Hi guys,


I am fairly new to cycling. I have a MTB and Roadie bike.


Recently, I managed to destroy my entry-level Tiagra Crank. Now having to replace it, I have reaslied how little I know about Group Sets etc.


Would any of you chaps be nice enough to explain the different types of threads / cranks and their compatibility?


My frame's a Scott Speedster 3 (I believe they are all almost the same throughout the Speedster series?).


Thank you Gents!!


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I can think of 4 or 5 recent formats, I'm sure if you ask Johan Bornman he will be able to name 20..  I'm not going to bother with non-cassette BBs (i.e. BB axle with loose bearings), these are all sealed bearing, cassette type BBs.


Primarily there is an older set of BB formats which had the BB and the crankset separate (BB bolts into frame; Crankset bolts onto BB axle using 2 axial crank bolts), and then a newer set with external BB bearings (2 BB bearing cups bolt onto frame, crankset is manufactured in one piece including the axle piece, which you then tap through the BB bearings)


Separate BB and crankset -

1. Early BB's had a square tapered axle

2. Octalink was an 8-splined BB format developed by Shimano

3. ISIS drive (10 splines?) was used by Raceface and Truvativ for a while, still used by some I think


For these 3 formats the BB (bearings + axle) threads into the BB shell on the frame - there are 2 thread patterns available, being Italian or English threads, but only one BB shell diameter.  All 3 are/were available in differnt widths to suit the frame and crank chosen - best to get some specific advice here if you're going to change widths. (the BB shell width may vary from bike to bike, and depending on the crankset you may need a wider BB to avoid it bottoming out on the frame - I remember using a 108mm BB for a double crankset and then a 118mm for a triple on a 68mm(i think?) BB shell).


External bearing BB

4. EBB Shimano/Race Face, which is BB cup and crankset combination that fits the same thread sizes on the BB shell that Octalink and ISIS drive used (I'm sure it has a formal trade name, can't think of it now).  These BB cups are mostly interchangeable between Race Face/Shimano, an Shimano has redesigned their cups in 2009/2010 to provide a much tighter fit and hopefully much longer life.


Width issues for EBB cranksets are dealt with by using plastic spacers to fill out the frame to a standard shell size.


5. BB30 - a larger diameter (30mm) external BB that fits directly into an integrated bearing race on very new frames (or into oversize bearing cups on some italian frames). The Crankset axle is the same size as the previous format, but the bearings are bigger.




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..and if you're looking to buy I'm selling a Shimano 105 crank, BB and deraileurs for R1000 Wink

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I honestly did not think that anyone would take THAT much time in responding! Thank you boet!!


I am rather strapped for $$ atm - saving up for a trip - so the whole set is out of the question :/


If you're keen to sell just the crank, let me know? :)


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