Derailleur Differences

[CharleyFarley]

I know there are different brands of derailleurs, and that there are derailleurs for mountain bikes and road bikes. I saw a question about a Shimano derailleur on Amazon where a guy was asking if a certain derailleur would work on his road bike. The answer was that it won't work on bikes with drop bars, only on flat bars. That puzzled me. I don't see what the bars have to do with the derailleur. Also, what is the difference between a road bike derailleur and a mountain bike derailleur? Don't they do the same job?

 

[vickster]

I presume it’s not to do with the actual handlebars but the shifters which have different pull ratios between MTB triggers and road STIs (which also vary between models and speeds)

 

[presta]

I know there are different brands of derailleurs, and that there are derailleurs for mountain bikes and road bikes. I saw a question about a Shimano derailleur on Amazon where a guy was asking if a certain derailleur would work on his road bike. The answer was that it won't work on bikes with drop bars, only on flat bars. That puzzled me. I don't see what the bars have to do with the derailleur. Also, what is the difference between a road bike derailleur and a mountain bike derailleur? Don't they do the same job?

When you move the lever from one position to the next it pulls a length of cable, and that cable then moves the derailleur by an amount equal to the sprocket spacing. The problem is that sprocket spacing varies dependent on how many speeds you have, and cable pull varies depending on the type of lever. In addition, the amount of chain that the derailleur has to be able to wrap depends on the difference between the largest and smallest sprocket & chainring, so there's another consideration for derailleur choice. Finally, the size of the largest sprocket affects the distance the mechanism needs to reach from the mounting on the dropout. They're not all the same, and the manufacturers like to keep changing stuff so that you have to replace the whole lot, and not just the broken bit.

 

[figbat]

On older stuff up to 10-speed they are generally interchangeable. New Tiagra and higher gear numbers get incompatible. I use a 9-speed XT derailleur on a drop-bar bike with Tiagra 4600 10-speed levers.

 

[rivers]

There are workarounds to getting mtb dérailleurs to work with road shifters and vice versa. You need either a jtek shiftmate or a wolf tooth tanpan- they're little pulleys that change the pull ratio of the cable. Bit faffy to install, ut does the job.

 

[CharleyFarley]

I presume it’s not to do with the actual handlebars but the shifters which have different pull ratios between MTB triggers and road STIs (which also vary between models and speeds)

It was the vendor who said the derailleur won't work with drop bars, only flat. That's what I couldn't figure. How would the derailleur know the bike has drops?

 

[CharleyFarley]

There are workarounds to getting mtb dérailleurs to work with road shifters and vice versa. You need either a jtek shiftmate or a wolf tooth tanpan- they're little pulleys that change the pull ratio of the cable. Bit faffy to install, ut does the job.

Oddly, while I was looking around, I saw those tanpan devices. I was aware they existed. Tanpan has a whole page devoted to the installation of it.

 

[Ming the Merciless]

It was the vendor who said the derailleur won't work with drop bars, only flat. That's what I couldn't figure. How would the derailleur know the bike has drops?

If you fit trigger shifters on drop bars it’ll work.

 

[CharleyFarley]

When you move the lever from one position to the next it pulls a length of cable, and that cable then moves the derailleur by an amount equal to the sprocket spacing...

I've been trying to figure out cable pull ratio. I understand the Shimano and Campagnolo shifters have different ratios, and that's why a Campy shifter won't work with a Shimano derailleur. There's some kind of equation for figuring out the ratio, like the width of the centers of two cogs (one cog thickness plus the space) divided by the cable pull of the shifter. This stuff loses me. I have a 7-speed and a 20-speed which I will probably never have to replace the derailleurs simply because I'm too old. The 20-speed is on a Specialized Fatboy, but I did have to replace the freehub. And being I like to do the jobs, myself, I had to special order a 12mm hex wrench (not sold in hardware stores) to remove it. And it may never be used again. It's all fun and games until you realize you don't know what you're doing.

 

[CharleyFarley]

If you fit trigger shifters on drop bars it’ll work.

That's what I figured. Perhaps the vendor meant the derailleur won't work with brifters.

 

[All uphill]

It's all fun and games until you realize you don't know what you're doing.

I have been there so many times!

 

[Alex321]

It was the vendor who said the derailleur won't work with drop bars, only flat. That's what I couldn't figure. How would the derailleur know the bike has drops?

That would have been on the assumption that you would be using integrated brake/shifters on drop bars, while you would have the thumb shifters on flat bars.

That derailleur won't work with the brifters without an adapter.

 

[Dogtrousers]

Friction shifters FTW

 

[Ming the Merciless]

Friction shifters FTW

Peak Shifter, been in decline ever since

 

[T4tomo]

Peak Shifter, been in decline ever since

I would say Suntour ratchet / friction bar-con were the peak of peak friction