Daft Derailleur Question!

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VinceLedge
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Daft Derailleur Question!

Post by VinceLedge »

I was just going to look for a replacement for a new derailleur to replace the one on my indoor 8sp turbo bike when I wondered the following..

If dérailleurs are not themselves indexed does it matter whether you buy an 8, 9 or 10 speed one? I know some makes have different pull ratios, but if I stick with shimano will any one work?
peetee
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Re: Daft Derailleur Question!

Post by peetee »

No, because Shimano mechs have different pull ratios. There are compatibility charts available online and every mech has the model number stamped on it, usually on the back of the inside cage plate.
The older I get the more I’m inclined to act my shoe size, not my age.
TheBomber
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Re: Daft Derailleur Question!

Post by TheBomber »

VinceLedge wrote: 19 Jan 2022, 9:25am If dérailleurs are not themselves indexed does it matter whether you buy an 8, 9 or 10 speed one?
Yes to this bit.
VinceLedge wrote: 19 Jan 2022, 9:25am I know some makes have different pull ratios, but if I stick with shimano will any one work?
No to this bit.

But as there is lots of compatibility between the speeds either check a chart (as peetee suggested) or add some detail on the shifters (preferably the model number, but a model name and/or photo will probably cover it) you are using and someone here can probably advise.
PH
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Re: Daft Derailleur Question!

Post by PH »

Shimano 8 & 9 speed and road 10 speed rear derailleurs all have the same ratio (1.7) so are all interchangeable, possibly 6&7 as well, though I haven't used those. MTB 10 speed gets complicated.
VinceLedge
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Re: Daft Derailleur Question!

Post by VinceLedge »

PH wrote: 19 Jan 2022, 4:23pm Shimano 8 & 9 speed and road 10 speed rear derailleurs all have the same ratio (1.7) so are all interchangeable, possibly 6&7 as well, though I haven't used those. MTB 10 speed gets complicated.
Thanks that is helpful, might use use a 10sp one and it is a useful spare for the other bikes as well.
PH
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Re: Daft Derailleur Question!

Post by PH »

VinceLedge wrote: 19 Jan 2022, 4:31pm
PH wrote: 19 Jan 2022, 4:23pm Shimano 8 & 9 speed and road 10 speed rear derailleurs all have the same ratio (1.7) so are all interchangeable, possibly 6&7 as well, though I haven't used those. MTB 10 speed gets complicated.
Thanks that is helpful, might use use a 10sp one and it is a useful spare for the other bikes as well.
Everything you ever wanted to know is here
https://www.cyclinguk.org/cyclists-libr ... s/shimergo

The only exception to what I said above is pre 1997 Dura Ace.
tenbikes
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Re: Daft Derailleur Question!

Post by tenbikes »

Indoor bike? Fit a friction shifter and use any speed you like?
peetee
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Re: Daft Derailleur Question!

Post by peetee »

VinceLedge wrote: 19 Jan 2022, 4:31pm
PH wrote: 19 Jan 2022, 4:23pm Shimano 8 & 9 speed and road 10 speed rear derailleurs all have the same ratio (1.7) so are all interchangeable, possibly 6&7 as well, though I haven't used those. MTB 10 speed gets complicated.
Thanks that is helpful, might use use a 10sp one and it is a useful spare for the other bikes as well.
But not Tiagra 4800.
As I say, check a compatibility chart.
The older I get the more I’m inclined to act my shoe size, not my age.
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Mick F
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Re: Daft Derailleur Question!

Post by Mick F »

tenbikes wrote: 19 Jan 2022, 5:39pm Indoor bike? Fit a friction shifter and use any speed you like?
Absolutely spot on. :D

When my Campag Ergos wear out, I'll be fitting my friction DT levers.
Given my (cycling) life again, I wouldn't have one down the indexed road. Expensive and pointless.
Mick F. Cornwall
PH
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Re: Daft Derailleur Question!

Post by PH »

peetee wrote: 19 Jan 2022, 5:44pm But not Tiagra 4800.
As I say, check a compatibility chart.
OK, are we at least agreed 6 - 9 is interchangeable?
gxaustin
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Re: Daft Derailleur Question!

Post by gxaustin »

I wouldn't have one down the indexed road. Expensive and pointless.
:roll:

That's a bit harsh. I always hated down tube changers and love indexed shifters.

I'm sure Sheldon Brown has articles on derailler compatibility.
TheBomber
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Re: Daft Derailleur Question!

Post by TheBomber »

VinceLedge wrote: 19 Jan 2022, 4:31pm Thanks that is helpful, might use use a 10sp one and it is a useful spare for the other bikes as well.
You might get issues with chain rub on the cage with an 8 speed chain in a 10 speed derailleur. If so it should be fixable by swapping to 8 or 9 speed pulleys, or get resourceful and add some shims and longer bolts to widen the spacing. Moving only 1 speed away from the design spec is usually trouble free.
VinceLedge
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Re: Daft Derailleur Question!

Post by VinceLedge »

Thanks for various advice. As it is the dérailleur that isn't very good as worn, there isn't much point in changing the shifters.
I am usually on Zwift on the turbo and that needs quite frequent gear changes, there is no way I would change to a downtube friction shifter, never liked them when I had them before!
peetee
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Re: Daft Derailleur Question!

Post by peetee »

PH wrote: 19 Jan 2022, 7:51pm
peetee wrote: 19 Jan 2022, 5:44pm But not Tiagra 4800.
As I say, check a compatibility chart.
OK, are we at least agreed 6 - 9 is interchangeable?
In terms of rear mech compatibility, yes. You may, however struggle to get an 8 speed chain between the cage plates when in the extreme gears on some mechs designed for 11 speed.
The older I get the more I’m inclined to act my shoe size, not my age.
gxaustin
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Re: Daft Derailleur Question!

Post by gxaustin »

In terms of rear mech compatibility, yes. You may, however struggle to get an 8 speed chain between the cage plates when in the extreme gears on some mechs designed for 11 speed.
An 11 speed mech will have the wrong pull ratio.
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