Can someone please give me a run-down on bottom bracket/cranks. How many options are there? What is ISIS? Is there a difference between shimano doubles/triples? Tapered square vs. splined? How do c(K?)ompact cranks come?
Dave
There are lots and lots of alternatives. Can you narrow it down a little? What are you trying to do?
Okay here goes
Shimano brand cranks, ONLY Octalink
Most other brands (FSA, Truevativ, Race Face (MTB), and I think probably ritchey) are usually available in Square taper, Octalink, or ISIS.
Splined BB’s is just a generic term for Octalink or ISIS
Tapered Square is old school Shimano, and Current Campy
Depending on who you get your Compact cranks from they may be available (or atleast made but good luck finding them) in all 3 styles, or atleast FSA is considering they kind of lead the market on Compact Cranks
Shimano Triple and doubles are different, they both require a different Front derailler, and the BB spacing will be different
I have a road bike with 2003 Shimano Ultegra BB with triple front rings so I assume this is octalink. I am getting a new tri-bike - parts of yet to be picked. I have PC’s (triple) that I can put on my road bike (so must be octalink too). I’d like to get compact cranks on my tri-bike so I assume I could get octalink but I also assume that the BB may not fit the PC’s as the PC’s are designed for a triple so the compact BB would be too narrow? I also assume that if I get ISIS compatible caompact cranks (what is ISIS?) - that the PC’S would not fit on my tri bike.
Dave
The issue with bottom brackets with regards to triples is two fold…
ISIS an OCTALINK are two different systems of connecting the crank to teh bottom bracket. both of these systems are splined meaning that the axle of the bottom bracket is a tube with identations cut out of it these two systems have different patterns for identations
Shimano cranks only come in octalink (unless they are several years old in case they would be square taper)
All other cranks will either come in octalink, isis, or square.
the only thing that matters is that your bottom bracket(BB) is the same system as your cranks.
Now a BB for a triple (3 rings on the crank) is not compatible with the 2 ringed crank. this is because of the length that the axle sticks out from the bottom bracket is different. so you would need a double PC to fit on your bike.
Hello,
Cranks and BB are specified by spindle length and crank/bb interface. Currently their are tapered (campy), octalink (shimano, except newest dura ace and newest mountainbike groups), and isis (similar in looks to octalink, but not compatible). Double and triple cranks are available in all styles, typically double bb are shorter.
So you currently have octalink, nothing wrong with that. You will pretty much have to stick with Shimano cranks and BB. As far as mixing doubles and triples the answer is maybe. Putting a double crank on a triple BB will work but the derailleur may have to be adjusted. Also width between the pedals may be wider. Ptting a triple crank on a double bb may work or the chainring and/or crank may hit frame. If this occurs you need a new bb (makes sure nothing hits while riding, flex under load may cause it). If this works the pedals may be narrower and the front derrailleur may need adjusting.