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Superollicks

Hello,

Does anyone know what these numbers mean? (see image, below) It’s a small piece of paper, about half by three quarters of an inch, and it was taped to the top of the handlebar stem of the 1971 TdF I bought a couple of months ago.

Thanks,

James

scozim

Looks possibly like gear inch ratios and probably for a half-step gearing set up. Although, a low gear of 60's is pretty big.

Gtane

James,

I agree, the numbers look to be ratios. Outside ring ratios on the left, inside on the right.

60 is a high low but perhaps the bike is running a close ratio / straight through block.

Do post shots of the bike when you have a moment.

Tim

Christophe

Hi ! I guess it's a 52 / 42 crank as the division af any number on the left by it's counterpart on the right column gives 1. 23 ie 52/42.
If you divide a line by the previous one, right or left column, it gives you 1.07, 1.07 etc.. then 1.12 etc ....These should be the ratios for the cassette sprockets. I assume it jumps from one tooth to two teeth in the end thus 1.07 to 1.12. Starting with a 14 teeth on the upper line , it gives 14.89 then 15.91, 16.87 and 18.92 so roughly 14-15-16-17-19 teeth. Starting with 15,16,17 or 18 teeth doesn't match better than with 14.

But do these numbers exactly stand for ? Not a pedaling cadence as it would decrease from the upper to the lower one. Not a development distance , as it doesn't match either in feet nor metric.

Please check out the number of teeth of both cranks and cassette so i can think further on ...

scozim

Running through Sheldon Brown's gear calculator these are the gear inches for a bike with 27" wheels, 170 mm crank arms, 52-42 chainrings and 14, 15, 16, 17, 19 freewheel.

52 42
14 100.3 81.0

15 93.6 75.6

16 87.8 70.9

17 82.6 66.7

19 73.9 59.7

Sorry, about the spacing - can't seem to get it to work correctly.

verktyg

That paper was something that all good "gear freaks" had.

One of the puproses of multiple speed derailleur gearing was to be able to maintain a constant cadence over varying terrain not just to have the high and low gear combinations at the extremes.

So called Alpine Gearing became popualr at the beginning the US bike boom of the early 70s. Most entry level bikes from that era came with a 14-28T 5 speed freewheel and 52-42 chainrings - sometimes 52-40 or 52-36 rings. Sporting models came with 14-24 or even closer ratio freewheels.

A 42-28 combination gave you ~40" low gearing while 52-14 resulted in the 100" magic number for high gears. Later many bikes especially Japanese models came equipped with 14-30, 14-32 or 14-34T freewheels with long arm derailleurs that could wrap up the extra chain needed for those larger freewheels.

Chainrings with 52-42T sprockets never provided more than about 7 gears because there was a lot of overlapping ratios with alpine gearing. Add to that the rule that you shouldn't use the large - large and small - small combinations because of chain line distortion and you were lucky to 7 distinct gears.

That "gear chart" was probably made to use with a 14-19T frewheel and a 52-42 chainrings. Since the bike most likely had a "corn cob" or "straight block" freewheel the rider could get 4 easy to shift into ratios on on one chain ring and 4 on the other.

I used to use Half Step gearing where there was a 4 to 5 tooth difference between chainring sprockets. A 49-45 combination on the front with a 5 speed 13-26T freewheel gave me a high of 101' and a low of ~47".

With a single shift I got about a 10% change in raitio, shifting both front and back it was about a 5% change.