Hi I posted this question before but got no answer. I was trying to find info on what determines if a rear derailleur is a 7,8, or 9 speed? My LBS told me that there's no real difference because a derailleur doesn't know how many cogs you have, it's determined by the shifter. If this is the case then a 9 speed shifter should work on a 7 speed cassette right? So labeling shifters is only a marketing thing?
Differences between rear derailleurs?
slonoma98
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Hi I posted this question before but got no answer. I was trying to find info on what determines if a rear derailleur is a 7,8, or 9 speed? My LBS told me that there's no real difference because a derailleur doesn't know how many cogs you have, it's determined by the shifter. If this is the case then a 9 speed shifter should work on a 7 speed cassette right? So labeling shifters is only a marketing thing?
You're mixing up shifters and derailleurs now. Your LBS is right in saying that the derailleur doesn't know how many cogs there are, it just follows directions from the shifters. You can use 7/8 speed shifters on 7/8 speed cogs but not on 9 speed because the spacing between the cogs is different. I have used both 7 and 9 speed derailleurs on an 8 speed set-up with no problems whatsoever.
Your LBS is correct. The indexing is determined by the shifter, not the derailleur. The derailleur only needs to be able to reach the two ends of the cassette but its the shifter that will tell it when to stop in between. So a 9 or even 10 speed derailleur will work on 7 or 8. The only exception is with some 10 speed models because the cage can't fit the wider chains for lower speeds groups.
The shifter is a differnt deal though. A 9 speed shifter will NOT work on a 7 or 8 speed system. The 9 speed will have closer indexing within the same total end to end span for the cassette. A cassette does not have more gears by merely adding cogs. The cassette has a total fixed length that has to fit onto a standardized freehub shell size. That means that more gears mean the cogs have to be brought closer together. The shifter needs to move less cable with each click to compensate.
The shifter is a differnt deal though. A 9 speed shifter will NOT work on a 7 or 8 speed system. The 9 speed will have closer indexing within the same total end to end span for the cassette. A cassette does not have more gears by merely adding cogs. The cassette has a total fixed length that has to fit onto a standardized freehub shell size. That means that more gears mean the cogs have to be brought closer together. The shifter needs to move less cable with each click to compensate.
Yeah, sorry. I meant a 9 speed derailleur should work with a 7 speed cassette. Thanks for the replies, I appreciate you all helping a noob out.
Also, what is different between the entry level and higher level derailleurs. Is it just material or is there some mechanical differences as well, say comparing an Acera with a LX or XT?
Also, what is different between the entry level and higher level derailleurs. Is it just material or is there some mechanical differences as well, say comparing an Acera with a LX or XT?
With some Shimano components, Deore and up are going to function very similar whether it is Deore, LX, XT, or XTR. The differences become smaller at this point. The extra expense is for weight savings or waiting for the trickle down effect of new technology from XTR to Deore. A rear derailleur is one place where a Deore will work similar to an XTR.slonoma98 said:
Anything below Deore such as Alivio or Acera is usually quite compromised in design, durability, and function.
Between my wife & I we have MTB's with Alivio, Deore, LX, and XT derailleurs. Alivio is much rougher shifting than the others and requires more frequent adjustments. Avoid anything below Deore. Deore is quite decent, but definately not as smooth (or long wearing) as LX or XT. Difference between LX and XT is very slight, although pulleys are nicer on XT. XT is a bit lighter than the others (if that matters to you).
This may all change with the newer Shimano stuff coming out.
This may all change with the newer Shimano stuff coming out.
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