Question about 3-arm cranksets...
 

Hi Everybody,

I suppose this is kind-of a history question, but is there a technical reason behind the general disappearance of 3-arm cranksets? Or was it just aesthetics? Or maybe production costs? I'm curious to know why they fell out of favor...

Total guess here but I'd wager that manufacturers got a greater strength to weight ratio with more webbing and cutouts. We've seen a reverse trend down to 4 arms spiders and wide arms but there's a lot of contouring and hollowed pieces in these cranks.

Were many of the 3 arm spiders steel?

Blame Campagnolo.

Prior three arm steel was very common for interchangeable rings, then the Simplex adaptors that provided a 6 place attachment for aluminum rings.

Alternately there was the 50.4 mm BCD 5 point attachment to the outer ring. In steel then Aluminum. Tourist bikes ended up with those, some track bikes too way back.

Campagnolo brought out the 5 arm Aluminum cotter less crank in the late 50's. Slow to catch on, it overwhelmed eventually, Surpassing the Stronglight and TA alternatives, TA having a three arm model and a 50.4 BCD.

Williams Made a nice three arm Steel Cottered crank set with nicely machined steel rings, weight was not bad either.

I think it was Racer Worry that three in aluminum was not enough. Many wanted to stick with steel cranks as they were worried about aluminum failing...

At least three mfgs each in Italy and France.

FSA has several 3 arm cranks in production. I've heard that the chainrings can be damaged - it's possible to fold them, I assume from lack of support.

3-armed cranks should be divided up according to the bolt circle size. The largest group is probably the 116 mm family, which includes cottered steel cranks from Stronglight, Nervar, Magistroni, Williams (though only the 1200 model), and many more; and chain rings from Simplex etc; followed by cotterless ones from Stronglight, Nervar, TA, Campagnolo. I don't know why these disappeared, but I'm suspicious it was simply a matter of an industry not seeing the profit in retrocompatibility.

Most Williams and Nicklin 3-armed cottered cranks were a smaller bolt circle that never made the jump to cotterless or aluminum.

There have been several other 3-arm cranks with other bolt circle diameters, including Rene Herse, SR, Shimano; and they have no cross-compatibility, which means they disappear as soon as they are no longer made.

SR Custom-3 is an interesting exception with its 86 mm bcd, since FSA has recently started making compatible cranks, and rings. I like them.

probably greater stiffness in the chainrings with more arms, depending on the design of the rings

For me steel chainwheel designs from the early days were the best. Steel was easy to machine and single chainsets were front and centre adornments to bikes. Doubles and triples and alloy changed many rules. I like so many early rings, like this Paramount. Probably for Pacing, speed attempts, something

http://www.citizenarcane.com/files/2..._paramount.jpg

the thicker sections of aluminum crank arms does make the geometry stiffer than thinner steel, but 3-arm cottered steel 1x cranks are classy.