What's the history behind the skip tooth sprocket? Markm and I were talking about them and neither of us could pin down the rationale...
Skip Tooth Sprocket
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ere are some thoughts on the origin of 1” pitch chain, why it was so prevalent on American bicycles in the pre-war and early post war period and the reasons that it was eventually replaced by ½” pitch chain.
The Ordinary (late 1870’s-1890) developed out of optimizing the size of the driven wheel for a 1:1 rotational relationship with the pedal cranks.
During the same time period, the earliest bicycles designed to increase this ratio to permit the use of smaller wheels did so though the use of gears either enmeshed or connected by chain.
The earliest chains were often proprietary and differed greatly in construction and dimension. Early chains were often heavier than modern chain because the metallurgy and designs of the day required the use of more material to achieve satisfactory strength.
The earliest standardized bicycle chain was 1” pitch block chain which became the norm by the mid 1890’s.
A block chain is comprised of metal blocks with a hole drilled through each end for a pin. The blocks are linked by two side plates pivoting off the same pins. Sprockets are cut so that the teeth will align with the cavities created between the blocks and link plates. The skip in skip tooth sprockets is equal to the size of the blocks.
The next major advancement in chain was the inclusion of a friction reducing rollers located around the connecting pin. The rollers allowed the chain to roll over the sprockets during engagement rather than be drug over them. Because the standard design of sprockets for 1” pitch block chain included a gap between the teeth, the earliest roller chain was designed to fit the existing 1” pitch sprockets. This is the reason that 1” pitch chain is constructed with a long link to mesh with the sprocket tooth and a short link sized to replace the block.
It was a short design leap to redesign the chain with equal ½’ pitch links and tool new sprockets to use with the chain. Metallurgy had also improved to allow for thinner sprockets by this time and the new improved ½” pitch design basically superseded 1” pitch in most application by the early teens.....except in America. While many American adult bicycles began to use ½” pitch chain in the teens, the bicycle in America was increasingly becoming a child’s transportation device and the 1” pitch sprockets were less expensive to manufacture (note that most 1” pitch sprockets are a simple flat cut stamping whereas most older ½” sprockets have more forming to maintain lateral strength and often have cut rather than stamped teeth) and stronger (I have never seen a bent 1” pitch balloon sprocket.)
By the thirties the 1” pitch sprocket had become the American standard to the point that there was little reason to change it.
It is probably due to a small growth in the Adult bicycle market in the mid to late thirties that some manufacturers started to offer ½” inch pitch chain and sprockets on their adult models and a few high end balloon bicycles.
After WW2 many American manufacturers were almost starting from scratch to tool up for the anticipated post-war boom. Most manufacturers reentering the bicycle market had made money and upgraded their factories and equipment during the war so retooling was necessary and easier than it would have been during regular production. At this point the shift to ½” pitch chain was probably partially in answer to competition from “higher performance” imports and also due to the fact that American manufacturers found that one avenue to increasing profit was by purchasing components abroad. (We know where this practice led.)
rms37
Posts: 97
Information was donated by RMS37 :mrgreen: :mrgreen: :mrgreen: :mrgreen:
The Ordinary (late 1870’s-1890) developed out of optimizing the size of the driven wheel for a 1:1 rotational relationship with the pedal cranks.
During the same time period, the earliest bicycles designed to increase this ratio to permit the use of smaller wheels did so though the use of gears either enmeshed or connected by chain.
The earliest chains were often proprietary and differed greatly in construction and dimension. Early chains were often heavier than modern chain because the metallurgy and designs of the day required the use of more material to achieve satisfactory strength.
The earliest standardized bicycle chain was 1” pitch block chain which became the norm by the mid 1890’s.
A block chain is comprised of metal blocks with a hole drilled through each end for a pin. The blocks are linked by two side plates pivoting off the same pins. Sprockets are cut so that the teeth will align with the cavities created between the blocks and link plates. The skip in skip tooth sprockets is equal to the size of the blocks.
The next major advancement in chain was the inclusion of a friction reducing rollers located around the connecting pin. The rollers allowed the chain to roll over the sprockets during engagement rather than be drug over them. Because the standard design of sprockets for 1” pitch block chain included a gap between the teeth, the earliest roller chain was designed to fit the existing 1” pitch sprockets. This is the reason that 1” pitch chain is constructed with a long link to mesh with the sprocket tooth and a short link sized to replace the block.
It was a short design leap to redesign the chain with equal ½’ pitch links and tool new sprockets to use with the chain. Metallurgy had also improved to allow for thinner sprockets by this time and the new improved ½” pitch design basically superseded 1” pitch in most application by the early teens.....except in America. While many American adult bicycles began to use ½” pitch chain in the teens, the bicycle in America was increasingly becoming a child’s transportation device and the 1” pitch sprockets were less expensive to manufacture (note that most 1” pitch sprockets are a simple flat cut stamping whereas most older ½” sprockets have more forming to maintain lateral strength and often have cut rather than stamped teeth) and stronger (I have never seen a bent 1” pitch balloon sprocket.)
By the thirties the 1” pitch sprocket had become the American standard to the point that there was little reason to change it.
It is probably due to a small growth in the Adult bicycle market in the mid to late thirties that some manufacturers started to offer ½” inch pitch chain and sprockets on their adult models and a few high end balloon bicycles.
After WW2 many American manufacturers were almost starting from scratch to tool up for the anticipated post-war boom. Most manufacturers reentering the bicycle market had made money and upgraded their factories and equipment during the war so retooling was necessary and easier than it would have been during regular production. At this point the shift to ½” pitch chain was probably partially in answer to competition from “higher performance” imports and also due to the fact that American manufacturers found that one avenue to increasing profit was by purchasing components abroad. (We know where this practice led.)
rms37
Posts: 97
Information was donated by RMS37 :mrgreen: :mrgreen: :mrgreen: :mrgreen:
Thank you so much!!
:!: Wow Uncle Stretch when you wanna answer a question you answer it! I nominate you for ratrodbikes.com's very own Dear Uncle Stretch Column! :mrgreen:
No but sincerly thanks for the info I always kinda wondered bout that.
No but sincerly thanks for the info I always kinda wondered bout that.
Trust me I was not the person that learned all that. RMS37 was the one to thank. If I had to memorize all that I still wouldnt be able to tell it to you. I was doing good to remember where it was :lol: :lol: :lol:
On this subject; Many people think skiptooth on a bike is proof of pre-war status, but that is not always true. I can't say when the parts were made, but manufacturers were shipping these well into the '50's, and some didn't get sold until early '60's. Older kids in my neighborhood had them, and I remember seeing a few in stores. People have also been swapping parts since the very beginning of mass production, and some guys were putting these on speed bikes :shock: in the '70's. :shock:
As for me I think they just look sick!! :mrgreen:
