A question about gear ratios through the ages.

[HTupolev]

Originally Posted by carpediemracing

The bigger cog jumps forced the chain to twist/bend more.

How? I'm having a hard time visualizing what you're talking about.

With old-school squareish tooth profiles, any shift basically involved ripping the chain off of a cog before it could clap down on the next one.
With modern shift gates, bigger shifts simply use longer paths. They don't require sharper angles.

This was critical to indexed shifting because

It was useful to some sorts of indexed drivetrains (including what Shimano was selling in 1984), but it was not critical to indexed shifting in general.

The reality is that a large fraction of modern indexed drivetrains - including both extremely low end models and extremely high end models - do not use slanted parallelograms. For example, SRAM's lineup of modern rear derailleurs for 1x drivetrains is generally non-slanted, including the top-end stuff. And I think that this is a very deliberate design choice on SRAM's part.

Slanted parallelograms are not the only way to achieve a consistent chain gap. It was how SunTour did it in 1964, and it was how Shimano did it in 1984 with Dura Ace 7400, and it remains a very good way of doing it if your drivetrain needs to tolerate multiple chainrings.
However.
In some situations, you can also use things like the offset between the cage pivot and the jockey wheel to control chain gap. For example, if the jockey wheel sits behind the cage pivot, then it will naturally swing away from the cogs as the derailleur wraps more chain as it goes onto larger cogs. This approach doesn't work as well in multi-chainring drivetrains (because front shifting also affects the position of the jockey wheel), but it can operate very well on its own in 1x arrangements, or for drivetrains with small front ranges (which is part of how Campagnolo's mid-century geometry remained somewhat-passable for so many years, despite the parallelogram being opposite to ideal).

[marciero]

Originally Posted by HTupolev

Derailleurs largely did start from a "more compact" place. Their early development was largely driven by touring and randonneuring crowds, and those crowds have always included folks demanding wide gearing range.
For instance, check out this Cyclo catalog from 1936. Customizable 2, 3, and 4-speed freewheels with cogs ranging from 13 to 28 teeth. Double and triple cranks with chainrings available from 24 to 52 teeth. And to handle it, a rear derailleur with nearly as much wrap as current-generation road parts.

Most of what people know as the "history of gear ratios" is really the history of road-racing gears, which has been very conservative.

If you are going to go back that far it is worth noting that derailleurs were not even allowed in the Tour de France until the thirties or maybe even forties, if I recall- long after they were in standard use by cyclotourists and randonneurs. Henri de Grange thought they were for sissies and women, and TDF mostly avoided epic climbs that were no problem for tourists.

[HTupolev]

Originally Posted by marciero

If you are going to go back that far it is worth noting that derailleurs were not even allowed in the Tour de France until the thirties or maybe even forties, if I recall- long after they were in standard use by cyclotourists and randonneurs.

1937. The first year that Goddet - not Desgrange - organized the race.

[Mark McM]

Originally Posted by carpediemracing

This was critical to indexed shifting because you couldn't have too much lateral chain flex because such flex would slow down shifting, and make indexing impossible.

By having a slant parallelogram shifter, you could keep the distance from the upper derailleur pulley to the cog at less than one pair of links (the b-screw would fine tune this - my preference was to have it such that it was a touch more than the pulley hitting the cogs, so way less than a pair of links). Any more than that and the chain, even with hardened pins, would flex too much, which would make. the clicks not line up with the shifts. The slant was for that, not for any other reason. Earlier derailleurs could do everything except be precise enough for index shifting.

Well, a certain amount of chain flex is necessary for quick shifting. Quick shifting relies on the chain being angled from one sprocket to the next, so that the next sprocket, so the next sprocket can grab the chain. One big difference between earlier chains is that modern chains use a bushingless design, which is more flexible than a bush type chain. Today's ultra-narrow chains are more flexible still.

Originally Posted by carpediemracing

(The worst was the old Campy Nuovo Record design. It worked backwards - as you shifting into the lower gears, the pulleys swung up and got *closer* to the cogs. As you shifted into the small cogs, the pulley would get further away. That's why there was the "Campy flick" when you shifted - basically you flicked the shifter about two shifts and pulled it back one. This forced the chain onto the next cog, but you brought the derailleur back in place before it could try to shift that second shift. Getting into the small cog was just slamming the heel of your hand onto the shifter, to make it move quickly. To get it into the big cog was pretty smooth since that's where the pulley was closest to the cog and therefore shifted better. The Super Record cage helped correct it a bit (and allowed use of a larger cog, I think a 28T?), and the plates were angled forward a bit more, but really it wasn't enough, so eventually they, too, had to go with a slant parallelogram rear derailleur.)

There were several reasons that derailleur bikes had horizontal dropouts back in the day. One of the reasons was to fine tune the chain gap, to improve shifting with those older derailleurs. Depending on freewheel size, one could move the wheel forward or back to vary the chain gap.

Originally Posted by carpediemracing

So, from the shifter to the cassette, both Shimano (the first to do it) and Suntour (the second) attacked it in similar fashion.

They had an indexed / clicking shifter.

Actually, Suntour introduced an index shifting in 1969, which was a few years before Shimano's Positron system. Suntour's system made even less of a splash than did Positron.

[Gummee]

I'll take 'things you had to learn when you first started riding for $200, Alex' back before Hyperglide: what is easing up on the pedals for a split second as you shifted your downtube shifters?

Even afterwards, if you were racing with DT shifters, you needed to estimate what gear you'd need to be in in the sprint BEFORE the final corner or you were hosed. AMHIK

Getting somewhat sidetracked: I really liked the placement of Zap's 'go faster' button under my index finger for sprints. I could finally start small and shift as I sprinted. The 'go slower' shifter button was in a spot I could reach from the hoods as I was climbing. Good stuff. ...except for the battery issues, but they were rare and I carried an extra in my bar end plug

M

[Tandem Rider]

Originally Posted by Gummee

Even afterwards, if you were racing with DT shifters, you needed to estimate what gear you'd need to be in in the sprint BEFORE the final corner or you were hosed. AMHIK
M

I remember seeing guys hit their DT shifter intentionally with their knee to go from the 13 to the 12 in a sprint. Riding in the pack fill seat it seemed to help a lot, they smoked me, but then again, I was never a good enough sprinter for this to make a difference. I would think this was something that needed practice though.