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Can I use a 9 speed shifter with a 7 speed drivetrain, with good shifting and without needing complex adaptations?

I am considering that as an alternative for this need:

Using only the brake lever, separated from an integrated shifter/brake

Suitable Shimano integrated shifter/brake replacement for old STX

Shimano STX rear shifter, broken spring

Assuming that is ok, are there 9 speed shifters integrated with brake levers for cantilever brakes? I have mostly seen 9-speed brifters for disc or V-brakes, but not for cantilever.

PS: There are posts related to 8 speed shifters with a 7 speed drivetrain, but I have not seen anything for 9 speed shifters

8 speed shifter with 7 speed cassette

Can you use a 8 speed Shimano shifter with a 7 speed cassette?

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3 Answers 3

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Can I use a 9 speed shifter with a 7 speed drivetrain, with good shifting and without needing complex adaptations?

Kinda, maybe, sort of... its complicated

You could use a Shimano 7 speed derailleur with a 9 speed shifter, if you also used a wheel with a 9 speed cog. The 7 and 9 speed Shimano derailleurs use the same derailleur ratio of 1.7 (amount of derailleur movement for a given cable pull) despite the two systems having different cable pulls (2.9 and 2.5 respectively) and sprocket pitches (5.00 and 4.35 respectively).

If you used a 7 speed cassette, with a 9 speed shifter and 7 speed derailleur you would not pull enough cable and the shifts will get mangled.

If you are currently on 7 Speeds, this means you have a 7 speed wheel that will most likely NOT take a 9 speed cassette. This would mean you would need to buy a new rear wheel as well as a new 9 speed cassette in order to keep you 7 speed rear derailleur. You would also need a 9 speed chain (which is narrower) to mesh with the 9 speed cassette, which may or may not work okay with your 7 speed chain rings.

For pull ratios see http://blog.artscyclery.com/science-behind-the-magic/science-behind-the-magic-drivetrain-compatibility/

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  • 7 speed derailleur may also have more play in the pivots making 9-speed shifting less precise.
    – Rider_X
    Apr 11, 2016 at 18:42
  • My present case is a complete 7-speed system, with a prospective 9-speed shifter as a replacement. I find it hard to get a 7-speed brifter of good quality (now Shimano only sells ST-EF65 or ST-EF51, or Tourney), even used.
    – sancho.s ReinstateMonicaCellio
    Apr 11, 2016 at 21:57
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    @sancho.s Simply dropping in an indexed 9 speed Shimano shifter (without any other changes) will not work for the reasons outlined above. If you are looking for shifter options, a high quality thumb shifter could be another option. In friction mode it should work regardless of speed of your derailleur and cassette.
    – Rider_X
    Apr 11, 2016 at 22:01
  • I forgot to acknowledge: Excellent answer! Any suggestion for high quality thumb shifter?
    – sancho.s ReinstateMonicaCellio
    Apr 11, 2016 at 22:32
  • @sancho.s - generally product recommendations are frowned upon on SE, but Paul's and Velo-orange make adapters that will let you convert a road down tube or road bar-end shifters (also called barcons) to a thumb shifter.
    – Rider_X
    Apr 12, 2016 at 1:05
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You can try it, but don't expect perfection. The width of a 7-speed chain is greater than the width of a 9-speed chain, therefore the component sizes, and the distance you need to shift, are different, even if only slightly. Whether this is enough to spoil your ride, only you can judge. A shop or a manufacturer might be somewhat more definite in their answer, but there is some grey area here which boils down to your idea of "acceptable".

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    The distance needed to shift is controlled by the shifter (if it is indexed!), and the "ratio" of the derailleur. The 9 and the 7 have the same ratio between how much the cage moves and how much the cable moves ((see Rider_X's answer). This means that from the positioning perspective, they are identical. Maybe the 9 has a narrower clearance for the chain through the cage, and less free play in some of its joints. That's about it.
    – Kaz
    Apr 11, 2016 at 21:37
  • @Kaz - I forgot about the pulley wheel spacing... good point.
    – Rider_X
    Apr 11, 2016 at 22:03
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It won't work.

On a 7-speed cassette, the cogs are 5.0 mm apart (center-to-center). On 9-speed, it's 4.34 mm. This means that if you adjust the derailleur so it's in the correct position on the 1st cog, then by the time it gets to the 7th cog, it'll be 4.62 mm off from where it needs to be.

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    Mike, the defining point here for potential compatibility is the linear pull-per-gear of both shifters (7 and 9 speed). If it is the same, then they are compatible. I do not know the detailed functioning of the whole systems, but in principle it could be the case that, even with the difference you mention, both systems have the same linear pull. The derailleurs might compensate for the difference in cogs size.
    – sancho.s ReinstateMonicaCellio
    Apr 11, 2016 at 22:47
  • @Kaz Mike's answer is just illustrating what will happen, nothing about control.
    – andy256
    Apr 11, 2016 at 23:00
  • @Kaz - Perhaps I formulated my question poorly, out of ignorance. My present case is a complete 7-speed system, with a prospective 9-speed shifter as a replacement. I hope this clarification helps/
    – sancho.s ReinstateMonicaCellio
    Apr 12, 2016 at 1:43

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