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At the moment I have a wheel with a Shimano 8speed cassette (HG30-8I) (11-30 or 32T)

and also I have following rear derailleurs:

  • XTR (RD-M952) (9 sp) GS
  • Altus (RD-M310)(7/8 sp) SGS

Questions:

  • Number of speed for shifters(I will buy 2nd hand)

    [I would prefer 9speed shifters if they are compatible]

  • type of Chain to buy

Notes: Bicycle is an old MTB with 3 chain rings Originally it was 7 speed, but rear wheel was stolen. I assume that 7 speed chain as to be replaced

Specs XTR (RD-M952)

  • Rapid Rise no
  • Speeds 9-Speed
  • Max Sprocket 34T
  • Min Sprocket 11T
  • Front Difference 22T max.
  • Total Capacity 33T(GS)

Altus RD-M310

  • Ideal Use: MTB, city, hybrid bikes
  • Compatibility: 7-speed, 8-speed
  • Mount Type: Standard mount
  • Cage: Long cage (SGS)
  • Maximum Sprocket: 34 teeth
  • Total Capacity: 43 teeth
  • Pulleys: 13 teeth G-pulley, 15 teeth T-pulley
  • Clutch: No
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    Also have a look at the below question. One of the answers explains a "hack" in which the 9 speed XTR shifter can be used on 8 speed cassette. In case you get stuck and can only source a 9 speed shifter rather than a 8 speed. bicycles.stackexchange.com/questions/8021/…
    – Superman.Lopez
    Aug 31, 2022 at 17:42

2 Answers 2

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You can't match a 9-speed shifter with an 8-speed cassette. The spacing between gears will be larger than the spacing between shifts.

Your options are:

  1. Buy an 8-speed shifter
  2. Buy a 9-speed shifter and a 9-speed cassette

If you go with option 1, either of your derailleurs will work. (The derailleur is basically just a spring, so the spacing of shifts doesn't matter.)

If you go with option 2, you'll probably want to use your XTR. The Altus might work, but I wouldn't be surprised if the tension wasn't tight enough on the derailleur and the shifting wasn't very precise.

A 9-speed chain should work fine regardless of which setup you go with.

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  • I am not sure about "derailleur is basically just a spring, so the spacing of shifts doesn't matter." As in the past I tried without luck to add the XTR to a combination of 6speed freewheel and 6speed shifter (microshift) but i was having noises at some speeds and it was not able to reach last cog.
    – Daniel Perez
    Aug 31, 2022 at 20:42
  • @DanielPerez That is, admittedly, an oversimplification. Within the context of 8-9 speed everything is close enough that the derailleurs are more or less interchangeable. A six speed setup is a big jump though and pull ratios, cog sizes, and overall travel become factors.
    – jimchristie ♦
    Aug 31, 2022 at 20:58
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Bike gears are very confusing.

5, 6, 7, 8 speed cassettes maintain roughly the same horizontal gap between cogs, so the shifter just has to pull more wire and the RD has to move further horizontally.

8+9+10 speed cassettes share the same total width. To do so, the space between cogs shrinks meaning the chain gets narrower as speeds increase. Upside is an 8 speed bike can be upgraded to 10 speed without changing the hub.

11 and 12 and more is a crapshoot of weirdness where even the MTB and road groupsets diverge from each other.

The XTR is a "better" unit than the altus, but they're both used. Clean and lube both, looking for damage and wear.

In your place, I would either

  1. just buy an 8 speed shifter and make it work while minimising cost. You want an 8 speed chain.
  2. upgrade to 9 speed with a suitable shifter and a 11-34 cassette. You will need a 9 speed chain, shifter, and use the XTR.

Absolutely use new shift cabling inner and outer when re-doing the cabling.

Your 7 speed front mech and chainrings will not care too much about the 8 or 9 speed chain. At worst it will be reluctant to change to the grannie ring on the triple. I successfully upgraded a 3x5 = 15 speed bike to 3x9 and the front derailleur is workable after I reduced the cage width a little with pliers.

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  • option2 seems optimal if i can reuse hub and just add 1(or change few) cog rings to the cassette. Or do i need to change the all the cogs on the cassette?.
    – Daniel Perez
    Aug 31, 2022 at 20:34
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    @DanielPerez you'd need an entirely new 9 speed cassette. The 8 speed spacing is about 0.2mm smaller (can't remember exact) so over 9 gears that's almost 2mm which screws up indexing.
    – Criggie ♦
    Aug 31, 2022 at 22:46
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    @DanielPerez You can still use the current hub since a 9 speed cassette will fit on a freehub that held an 8 speed cassette. You will need a 9 speed cassette (and shifter, and 9s chain) to have the correct inter-cog spacing.
    – Jeff
    Sep 2, 2022 at 11:15

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