tjbmarks

in the last two year i,ve boken 2 different dura ace 7800 non drive side crank arms. last october where pedal screws in to arm (ate pavement). after 5000 miles arm cracked in middle. both were warranty replacements but i'm worried about serious injury. i am a 200lb rider who averages 20-22 mph on mostly flat roads, favorite gear is 53 x 14 & 13. suggestions for options - strength, durability and of course performance

cman

That sucks ....My friend just broke his non Drive Dura Ace on the top end. His is older so probably no warranty.

rmfnla

I've never seen the point of the external bearing set-up; just more marketing jive to get people to buy stuff they don't need.

Glad you weren't seriously hurt.

sideshow_bob

how does a crank arm snapping mid arm relate to inboard vs outboard bearing design?

to the op. so one of the failures was after dropping the bike. i'm actually amazed you managed to get a warranty replacement on that.

the second one, was there any prior crash on that arm before it failed? i've never seen a DA crank fail like that that hadn't suffered previous impact damage.

the other thing that seems a bit odd, is you are riding 53x14/13 and averaging 20-22mph. to manage those kind of speeds in those gears you must have a cadence of like 30rpm. while i'm not going to tell you to lift your cadence up past 100, me thinks you over gear, not that that has anything to do with your crank failing.

tjbmarks

equipment is well maintained, no accidents-just ride hard. frame is litespeed ultimate that came with ultegra group, upgraded to dura ace after ultegra arm snapped in 2001. weld at bootom bracet failed in 2003 and frame was replaced. replaced crank with new style dura ace in 2005.

bronaugh

All this suggests that there's an insane amount of force around the pedals -- so I have to ask, what pedals are you running? And how far out from the crank arms is the point at which you apply most of the force with your feet (if clipless, this'd be where the cleat is; if not, you'll have to eyeball it / think about it)?

RockyMtnMerlin

Good question!

tjbmarks

check out: home.comcast.net~bicyclebill/DACrankset/ these pictures are similar to my 2 breaks.

toolong

what kind of pedals are you using?

dobber

It doesn't. Neither does the fact that the anodization on my Sugino 75 cranks seems to be waering off where my shoes rub.

nadimk

Would narrowing your q factor work? It might place less lateral stress on the crank arm. You must eat through chains!!

Erzulis Boat

Sounds like you need to go with a more robust crankset.

I have never seen so many bike component failures as there has been in the last decade.

You should be running a solid forged crankset. I still run solid forged Record 10 Speed cranks vs. the carbon offerings due to potential durability issues. I also mash some tall gears, and stick to the tried and true.

rmfnla

My impression is the pinch-bolt system that secures the off-side arm is not as robust as the older designs, but to be fair I did not notice the part where the OP had crashed his bike. Also, breaking at the pedal is pretty unusual and is totally unaffected by the BB design.

patentcad

Uh-huh. D.A. 7800. Snapped like a twig on a 10% grade.

xyzzy834

So, if I read this right, you've snapped three crank arms (2 Dura Ace, 1 Ultegra) and broken one frame at the bottom bracket weld.

Don't ask to ride my bike.

HillRider

Uh, this thread is 2-1/2 years old. How did it ger resurected? I'm also impressed that the OP managed to break three high-line cranks and a Ti frame.

mrrabbit 

Me wonders if the OP is straight legging and stiffing the frame when standing up and accelerating. I.e., instead of allowing the bike to weave side to side a little with slack elbows to dissapate some of the input - he instead holds himself and the bike stiff and straight in the centerline - and drives his legs straight down until he is up to speed or done accelerating...no weaving.

That will increase the stresses at the BB and at the pedals....provides a more immediate response and feedback for acceleration purposes but flexes the heck out of the crankarms and bb junction.

=8-)