Derailleur compatibility

[phil-b]

For example Shimano deor derailleur’s

What is the difference between an 8 speed and a 10 speed MTB derailleur

Are they interchangeable in either direction

 

[T4tomo]

quite a bit.

I think 8&9 speed are interchangeable as they use the same cable pull ratio from the shifter, but the 10 speed uses a different ratio, so if 10spd RD used with an 8 speed shifter, it wont work.

 

[phil-b]

What if you use a friction shifter

 

[fossyant]

What if you use a friction shifter

That would work

 

[richardfm]

quite a bit.

I think 8&9 speed are interchangeable as they use the same cable pull ratio from the shifter, but the 10 speed uses a different ratio, so if 10spd RD used with an 8 speed shifter, it wont work.

Wouldn't it work with an 8 speed cassette or freewheel as long as it had capacity for the largest and smallest sprocket?

 

[Jameshow]

Irrc
8-9-10 road are the same except new tiagra 10(4700)
10 SPD MTB is different too.

 

[phil-b]

That would work

Does it work because both derailleur’s are the same and the indexing is all in the shifter or am i still missing something

 

[phil-b]

Irrc
8-9-10 road are the same except new tiagra 10(4700)
10 SPD MTB is different too.

I’m just looking at MTB systems for now.

 

[phil-b]

Wouldn't it work with an 8 speed cassette or freewheel as long as it had capacity for the largest and smallest sprocket?

That might be the limiting factor there.

Some derailleurs might not reach the largest cogs. Or the diameter of the cog

 

[Jameshow]

https://bike.bikegremlin.com/1278/bicycle-rear-derailleur-compatibility/

 

[Alex321]

Does it work because both derailleur’s are the same and the indexing is all in the shifter or am i still missing something

Yes.

Each click of the shifter pulls (or releases) a set amount of cable, and the derailleur is designed so that amount of cable movement shifts it one gear.

Whereas of course with a friction shifter, you pull it the right amount yourself, and stop when it shifts.

 

[Alex321]

Wouldn't it work with an 8 speed cassette or freewheel as long as it had capacity for the largest and smallest sprocket?

Because the 10 speed pull ratios are different, no it wouldn't. It would be moving the right distance for one change with one click.

 

[Ming the Merciless]

What if you use a friction shifter

The 10 speed deore derailluer requires more total cable pull that an 8 speed friction shifter can do. You won’t be able to shift through all the gears. You need a newer 11 speed shifter in friction mode like Microshift do. Then you’ll be able to get the full range of gears across whatever speed you are running at the back.

I run the Microshift 11 speed in friction, with 10 speed RD, and 9 speed cassette.

 

[richardfm]

Because the 10 speed pull ratios are different, no it wouldn't. It would be moving the right distance for one change with one click.

But it's the shifter that determines the pull ratio isn't it?

 

[raleighnut]

I use a 105 rear mech, it has 2 positions for the cable clamp which alters the 'pull ratio'