>In days of yore many crank spiders were
>3-armed(F.B.,Magistroni,Simplex.Campagnolo
>GS,Chater Lea,Bianchi Paris -Roubaix model,Canondale Coda,Schwinn
>Paramount and
>Superior) yet one sees almost exclusively 5 -arm Spiders today. Is
>this because
>the old steel ones were stronger than modern alloys and simply didn't break
>under stress or is it a modern "fashion" preference.I like the look of
>the 3-arm spider and they might actually save weight. Were any 3-arm
>alloy spiders
>known to break(i.e.Campy GS) ? Art Link,San Antonio,TX,USA
Campagnolo used five spider arms, and so others felt the need to do the same - I think that explains why most cranks have 5 spider arms.
Three-spider arm aluminum cranks have been ridden by many strong riders. For example, Genevieve Gambillon won the women's world championships twice, in 1972 and 1974, on a bike equipped with 3-spider arm Rene Herse cranks. She was a sprinter, and when you look at the photos, you realize that her legs could put out more power than most of us!
Current mountain bike cranks have gone to 4 spider arms, and those don't seem to fail much, either.
Over the years, there has been a lot of concern with sideways chainring deflection under load. However, when you look at the load path of the chain pulling on the chainring, you see it's almost exactly in line with the ring - even when you cross-chain a bit. What many interpret as chainring flex in fact is BB/seat tube flex... as explained in the article on TA/Stronglight 49D cranks in the current Bicycle Quarterly. It's easy to check - if your chainring moves only on the left downstroke (when the lever of the pedal on the chain is greatest), then it's the BB that flexes. If the chainring did flex, it would flex the same during right and left strokes. I have yet to get my rings to deflect sideways on the right stroke, even with TA Pro 5 vis (Cyclotourist) rings that are said to be flexible. They move considerably on the left stroke...
Some French tinkerer once made a 2-spider arm crankset (with the crankarm forming one spider arm like the Campagnolo C-Record decades later), and rode Paris-Brest-Paris on it. There was a Rebour drawing in one of the very first Bicycle Quarterly issues.
However, with 180 degrees of chainring unsupported, you need to worry about it against collapsing (in the plane of the chainring). So you'll have to beef up the chainring, and may loose more weight than you initially gained.
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com