obezkirpi

Hi guys, I'm gonna ask this question: since deraiilleurs with different speed also have different shift ratios, what does 9/10 mean?

For example, my bike has Tiagra RD-4600(or 4601?) on it as front derailleur. Sora FD-3500 (triple) front, 9 speed hg53chain, st-3503 brifters (3x9) and a 9 speed cassette (28-11). It is a 3x9 setup as you can see.

totalcycling.com/en/Shimano-Tiagra-4601-910-Speed-Rear-Derailleur/m-20492.aspx Acoording to this page, my tiagra is 9/10 speed. Does it mean 9 speed and 10 speed chains have same chainring size, cable pull ratios etc.? If I get some 3x10 shifters, will those be compatible with this 9/10 derailleur? Or if I get a 10 speed new FD, can I just mount it and will it be OK? Or is there a simple mechanism on deralleur, like OFF=9 speed ON=10 speed?

dsbrantjr

Many Shimano derailleurs have the same pull ratio; this is the case for 6 to 10 speed road derailleurs. Shimano 10 speed mountain and 11 speed (both kinds) are different. This site has a more complete explanation: Art's Cyclery Blog » Science Behind the Magic | Drivetrain Compatibility

SkyDog75

"9/10" means it'll work with either 9 speed or 10 speed. Since Shimano's 9-speed and 10-speed road shifters and derailleurs use the same cable pull ratio, 9-speed and 10-speed derailleurs are interchangeable for practical purposes.

The very latest 10-speed units are an exception. If I remember correctly, Tiagra 4700 shifters and derailleurs use the same cable pull ratio as Shimano's 11-speed drivetrains.

Shimano actually used the same pull ratio from their earliest indexed shifters up through 10-speed for road parts and 9-speed for mountain bike parts, so there's even more interchangeability. There are other factors to keep in mind when mixing and matching, though, like chain width.

3x10 shifters would be compatible with your 9/10 speed rear derailleur's pull ratio, so the shifter would get the derailleur to align with the cogs correctly, but in order for your derailleur to work with a triple drivetrain, it needs to have enough 'wrap capacity' to handle the bike's gearing range. When you shift down from your larger chainrings and cogs to smaller ones, the chain doesn't need to be as long. The chain would hang slack if it wasn't for the spring-loaded pulley cage on the rear derailleur. Triple drivetrains have bigger differences in gearing, so there's more chain slack to take up, and so derailleurs used in triple drivetrains need to have longer cages.

The ability to take up slack is quantified as 'chain wrap capacity', expressed as a number of teeth. It's calculated by adding the difference in your chainring sizes to the difference in your cassette cog sizes. For example, if I've got a 30-40-50 triple chainring and a 12-30 cassette, the wrap capacity I'd need is (50-30)+(30-12)=38 teeth.

obezkirpi

my derailleur has capacity of 39, its fine (28-11)+(48-28)=37, it can handle.

i made an example image for this situation, is this correct then? oi65.tinypic.com/169rurr.jpg If I get a 10 speed shifter, it would operate on all 10 speeds of my RD?

SkyDog75

Derailleurs are dumb devices and don't really have "speeds". They just translate X amount of cable pull to Y amount of lateral movement. It's the shifter that has "speeds" since the shifter is the part with the detents that control how much cable is pulled per click. A 10-speed shifter will shift to every cog of a 10-speed cassette as long as the derailleur is designed for the same cable pull ratio as the shifter.

So to apply that answer to your specific parts... A Tiagra 4600 rear derailleur is designed to use the same cable pull ratio as all of Shimano's 10-speed road shifters except Tiagra 4700, so a Tiagra 4600 derailleur will successfully shift a 10-speed drivetrain so long as you pair it with any Shimano 10-speed shifter other than Tiagra 4700.

Looking at the bigger picture, it's not just 9 and 10 speed shifters and derailleurs that share a cable pull ratio. Shimano used the same pull for almost all of their 6, 7, 8, 9, and 10 speed road derailleurs and shifters. What makes those derailleurs slightly different from one another is that they're designed for slightly different chain widths. As more cogs have been crammed into cassettes, chains have become gradually narrower. But chain width is similar enough from one speed to the next that a given derailleur can usually be bumped up or down a notch. 8 speed derailleur on a 9 speed drivetrain or vice versa? No problem. 10 speed derailleur on a 6 speed drivetrain? Maybe not the best combo.