splined vs square taper
 

I am considering ordering some new cranks/ BB and was wondering about the differences between splined and square taper. I understand them both in terms of design, but I am curious to know what each type offers in terms of benefits, strengths, flex etc?

I ask because when I purchased my first SS bike (maybe a year and a half ago), the cheap, square tapered cranks I had on kept coming lose and I ended up needing to switch out my cranks. My LBS guy recommended a splined BB as he assumed that me being so tall ( 6'3" 200lbs) I may need a different style BB.

This happened a while back when I was a noobie

Any opinions....?

Well, the reason your square taper cranks kept getting loose was because you probably didn't tighten them enough in the first place, using a torque wrench. Having said that, IME square taper cranks when new need to be re-tightened a few times before they finally get seated, because the bolt loses some of its pretension force as the crank arms creep a small amount along the spindle. So, to that extend I suppose splined cranks are more convenient in that they don't creep and once tightened properly they stay tightened. The problem with splined cranks is that they need to be made very precisely to avoid play between spindle and crank, and cheap crap like FSA often have problems. If you buy something good like Dura Ace you won't have any problems. Myself, I'm a 100% square taper guy from way back, and have never had any problems. As to strength, well if Sugino 75 NJS square taper cranks are good enough for pro keirin, they're certainly good enough for you and me.

Don't hold me to this, but i think it's not so much the crank/bb interface, as much as what the interfaces allow. As long as your cranks are held securely in one place, the degree of performance or flex is going to be attributed way more to the physical properties of the crankarms themselves and bottom bracket spindle.

for anything with standard internal bearings, you're just looking at upgrades to the alloys used in the crankarms or bb spindle.

For outboard bearing bottom brackets, the gains start to compound. Using an outboard bearing bb allows the bearings to be larger, thus allowing the bb spindle to be larger in diameter. This translates into a stiffer bottom bracket/feel to the cranks. (which can of course be used in tandem with stronger alloys)

also, a larger bearing diameter means the bearings themselves will spin slower (yeah, one revolution is one revolution, but with greater circumference, the tangential speed of the bearings themselves will be slower, math, math, math etc) which, iirc, means a little less parasitic drag from the bearings themselves.

i think this is in the ballpark, but if someone could confirm, that'd be great.

yea I had actually bought the bike as a complete, and had the LBS wrench look at the cranks/bb 3 times. Each time they torqued it down and it just kept coming loose. Either way, Im running a Raceface Cadence crankset with an FSA MEGA splined BB. They havent let me down yet, but I am getting ALOT of creaking and a grinding feeling as I ride.

I was in an accident and the drive side was hit head on. I guess I am just worried about their integrity in the long run.

outboard meaning External? sorry...

Have you disassembled your cranks and bb to make sure there was no damage from the collision? If it were me, I'd probably remove the pedals, crank arms, chainrings, and bottom bracket; clean them all up; and give them a close inspection for cracks, etc. Having a crank or pedal fail you can be pretty painful--I watched it happen to a rider crossing in front of me and it was bad news. Good luck!

yea full inspection, and eventually replaced the pedals and chainring. Everything looks good.