Crankset Life?

[rideon]

OK you experts out there. I have a 4 year old DuraAce crankset that I've had on a couple of different frames. I split mileage between 3 different bikes, probably averaging 75-100 miles per week on this particular crankset. I am a racer (6'2" 175), however I usually do not race w/this bike. My question is... how long can I expect this crankset to last? Now I know chainrings need to be replaced regularly, but I was curious if there was a school of thought on when the crankarms need to be replaced. Also, I can't say I feel any flexing and I do a fair bit of climbing. What do you think?

[bulliedawg]

For ever.

[cs124]

For ever.

Totally agree... unless you've crashed on it.

A few years ago one of my good mates (6'4", 230lb sprinter) had a pretty big crash ... broken down tube, bent h/bars, knackered front wheel, torn saddle, lots of cuts & bruises. Anyway, a few weeks later, everything has been replaced, repaired or had the stitches removed and there's 3 of us out on a shakedown ride. We come to a steep little rise, the big fella gets out of the saddle, cranks down with his left leg and "SNAP". Crank snapped through just above the pedal axle. He tumbles left on to me, I manage to stay upright and hold him off the ground while the gradient brings the speed down a little. A second or so later he slips off my shoulder, hits the deck and my other buddy JT rides right over the top of him.

More cuts & bruises, another bent set of bars and another torn saddle. We reckon the crank must have had a hairline crack in it after the first crash that wasn't spotted by the mechanic when the bike was put back together. Ended up being an expensive and painful few weeks.

Anyway, the point of this ramble was that normal use won't wear out your cranks, they just don't like severe impacts.

[CNote]

The only real potential problem would be reinstalling the crankarms someday without matching up the splines properly. If you're careful with this, they should last forever. The problem with square-tapered cranks was that the square cut-out would eventually wear out over time after multiple reinstallations, thus causing play at the crank/BB interface. The big advantage of splines that I can see is that they eliminate this issue.

[cs124]

... The problem with square-tapered cranks was that the square cut-out would eventually wear out over time after multiple reinstallations, thus causing play at the crank/BB interface...

Very good point CNote, I have seen a square taper crank made pretty much useless this way. As always, there's more than one way to wreck a bike part.

[Peter]

Square taper cranks do have a limited life span, but don't replace one until you experience an actual problem. As CNote pointed out, repeated installation/removal cycles will stretche the tapered hole on the crankarm and they'll begin to creak no matter how much you tighten the bolts. Replace the crank so you don't drive your riding buddies nuts with the incessant noise. My Campy Nuovo Record crank lasted about 40k miles.

The 13 year old Shimano Deore crank on my ATB, which I feel sees the most stress from high torque loads and banging on rocks, is still going strong.

Oddly enough, the replacement Shimano Ultegra Octalink crank, installed this last spring, has developed a chronically loosening left arm which tells me the only way to fix it is to replace the arm itself.

You should occasionally inspect the crankarm around the pedal eye and the spider for cracks.