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I need some advise on compatibility between the components my bicycle already has and the ones I want to upgrade to.

My current cassette and chain are worn out so I will have to replace them. I need a new shifter anyway since my current is broken. Upgrading could be fun!

Current setup - Scott Sportster 50

  • Cassette: Shimano CS-HG31-8 11-32T
  • Rear Derailleur: Shimano Altus RD-M370 24 Speed
  • Crankset: Shimano FC-M171 48x38x28
  • Rear hub: Formula DC-25 RQR disc

Upgrade option 1 - upgrade to 9sp Cassette: Shimano CS-HG400/CS-HG201/CS-HG50 9 speed 11-32T

Upgrade option 2-upgrade to 10sp Cassette: Shimano CS-HG500/CS-HG50/CS-HG51 10 speed 11-32T

It is assumed I will be getting a compatible 9sp/10sp chain and shifter. I want to continue with the 11-32T. The price is irrelevant.

Q1: Which above upgrade options will my derailleur work with?

Q1a: Will I need to adjust the L/H screws and B screw on the derailleur for any of the upgrade options?

Q2: Will the existing backwheel/hub take the 9sp and 10sp cassettes?

Q2b: Will I need a cassette spacer for either of them? Size?

Q3: Will the existing crankset take to the 9sp and 10sp cassette change?

Q4: If I were to go for a 11-34T cassette, would the L/H and B screws on the derailleur need to be adjusted?

Thank you! :)

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  • When I'm in this situation of doing multiple replacements, I look for what I already own in the spares pile, and see whether that's enough to make one solution more attractive. What other parts do you have already, if any ?
    – Criggie ♦
    Jul 8, 2021 at 0:28
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    @Criggie None in the spares pile :D Just the ones already on the bicycle
    – ldmvcd
    Jul 9, 2021 at 18:24

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10-speed "MTB" shifters use a different cable pull ratio. 9-speed uses the same ratio as 8 speeds. So if you downgrade to 9 speeds (downgrade since with 8 speed you have a large jump between gears so a shift results in meaningful change in gear ratio whereas with 9 speeds you need to click...click...click a lot to get a meaningful change), you don't need a new rear derailleur.

L/H/B screws shouldn't require any change because the cassette width is the same and gearing is the same too, but I would still check they are correctly set.

Spacer is only needed if you have a "road" 11-speed hub which you probably don't have.

The existing crankset will work with a narrower chain, with the caveat that if you are in big ring, little sprocket gear and then downshift in the front before downshifting in the rear, the chain can possibly "skate" over the small ring teeth shortly before engaging the small ring. It isn't reasonable to shift that way: usually you downshift in the rear few gears before downshifting in the front. The risk is small with 9 speed chain and 8 speed chainrings, and a bit larger with 10 speed chain and 8 speed chainrings.

The 11-34T cassette would require you to adjust the B screw, but so little the existing B screw position might work reasonably well.

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  • Thank you! I suppose it would be better to upgrade to 9sp instead of 10sp then
    – ldmvcd
    Jul 7, 2021 at 19:28
  • As you are not looking to meaningfully change your gear ratios, you may wish to consider sticking with 8 speed components - they are likely cheaper than 9 speed, and more robust, as the cassette gears are slightly thinner and the chains slightly weaker in 9sp vs. 8sp.
    – Armand
    Jul 7, 2021 at 20:48
  • @Armand Considering I am sticking with 11-32T won't I have smaller jumps and more ratios in the mid-range in a 3x9 as compared to a 3x8?
    – ldmvcd
    Jul 9, 2021 at 18:09
  • You're the one who gets to decide how meaningful the differences are :)
    – Armand
    Jul 9, 2021 at 18:26
  • :D No but please correct me if wrong @Armand
    – ldmvcd
    Jul 9, 2021 at 21:36

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