[CR]gear question, second request

(Example: Component Manufacturers)

Date: Fri, 07 May 2004 18:37:57 -0400
From: "HM & SS Sachs" <sachs@erols.com>
To: classicrendezvous@bikelist.org, marcus.e.helman@gm.com
Subject: [CR]gear question, second request


Marcus Helman wrote:

Oh wise ones,

A little while ago I posted asking about gearing theory. No one answered. I know you were all at Cirque, but I could have just dug a hole and whispered my question into it. Here goes again.

I get the concept of setting things up so that there is not much duplication, but I have questions.

MH: How much difference is noticeable? Harvey: I think I can notice small changes (like one tooth in back, at least for smaller cogs, where it approaches 5%. I just don't think it matters in most applications.

MH: I can imagine setting it up so that the steps are good, but I have to shift both front and rear each time. Can this be avoided? Harvey: Yes, pretty easily. Two examples: classic half-step, when you would change both half the time. Long ago, I went to the other extreme, with a 28/48 front, and a close 5-speed block, so I had 5 speeds with the 28, and an additional 4 with the large cog (28x14 was very close to 48x whatever).

MH: Does it make sense to set up a reasonable progression for the big ring, and the small ring, and not get hung up on avoiding duplication? Harvey: It only has to make sense to you, and be available with the cogs you can use on that bike with that derailleur and cranks. Do you get gears that are low enough, high enough, and close enough?

MH: What is half-step gearing? Harvey: A system in which each step in back has about the same per cent change as the others; and the change between the large and middle (ignoring the granny) is half of that change. For example, a 14-16-18-21-24 has about 14% steps. A 47-50 or similar front set has about a 6% range, so you can get very nice, closely spaced gears with a rather wide range. On my wife's bike, we have used a 13-16-20-25-31 Regina Oro with 40-45 Stronglights for 20 years or so. that gives changes in back that are about 25%, and a front split of 12.5%. Top is 93, low is 35, so you have a pretty remarkable range for a 10-speed. This is very nice in situations in which you want fine tuning capability, as when riding long distances with fairly long but constant effort levels. Long hills, etc. When it is rolling, or very steep, half-step is not as useful, but no penalty: you just do "full" shifts across the back when you get to the top of the hill. Or the bottom.

MH: Is there such a thing as whole-step gearing? Harvey: In the old days, the Schwinns were so afflicted, something like a 39-50, if I recall correctly.

MH: Is there a written source on all this? Harvey: Senior moment, don't remember, but I'd expect it in DeLong and similar books.

harvey sachs
mcLean va