hey guys;

sorry if this has been discussed already

I'm wondering what the differences are in the crank-arms of the Ultegra and the Dura-ace cranks (mainly weight wise ). I've spent a bit of time searching but I've only been able to find the differences of the complete crankset, I'm interested in just the crank-arms. Any info appreciated, I really have

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Apparently my bikes were talking the other day & are undecided whether to upgrade the current rider or get a new one...

one of the schemers...

Yep, weight. Stiffness is roughly equal. I believe only the 105 cranks are stiffer. But also heavier, which is of course more important

the 6600 cranks are stiffer and a bit heavier no more than 50 grams.

I was under the impression that the 5600 crank arms (without rings) were lighter than the 6600 crank arms, but the 5600 chainrings are much heavier so 6600 crankset (with rings) ends up lighter. My 5600 bare crank arms (172.5 mm) weigh 580 g. Does anyone have bare 6600 crank arms to compare?

Visually, the 5600 and 6600 arms look the same, but the 5600 uses a thicker, but lighter aluminum axle while the 6600 uses a stiffer steel axle, although I did see one 6603 crank with an aluminum axle so there may be more out there. Hence the bare 5600 arms are lighter and the 6600 arms are supposedly stiffer, but frankly I cannot discern the difference between 5600, 7800, or indeed any other 24 mm axle crank that I have ever ridden.

The 7800 versus 5600 arms appear rather different. The 5600 arms are taller and beefier, while the 7800 arms appear more svelte and have different contours. From the side view, the 7800 arms taper from the axle to the pedal hole whlie the 5600 arms are pretty straight. The pinch bolts for the 7800 cranks are slightly shorter and thread into blind holes, while the 5600 crank uses through holes.

The q- and u- factors are consistant at 147 mm and 137 mm, respectively.

for the record, a set of Ultegra 6600 cranks, they weigh 736g with chainrings and chain bolts (170mm).

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Apparently my bikes were talking the other day & are undecided whether to upgrade the current rider or get a new one...

one of the schemers...

I'd say most of the extra weight on the Ultegras is due to the thicker-walled axle.
Try scewing a 7800 'end cap' on a 6600 axle like I did. Not even close.