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I'm riding a Schwinn GTX 2 and using it to learn things on. I am new to fixing newer bikes. I've changed to Altus front and rear derailleurs. Now I'm about to put on a gearset of the same. I've got the new 3 speed crank, I'm just waiting on the new bottom bracket to install.

Question: Should I go with a 7 or an 8 speed cassette on the rear? An 8-speed will take a new shifter, but those are coming anyway. Is it worth it to go for the extra gear, or am I going overboard?

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Depends on your wheel's hub.

  • Cassette? Are you sure?
    Presumably you've checked its not a 7 speed freewheel, which severely limits your options. If you have one, look out for a freehub/cassette based wheel in the future.

  • Width?
    You have a 7 speed cassette now, but are there any spacers underneath? If so, you could potentially fit a 8 or 9 or 10 speed cassette straight on because they're all the same width whereas 7 speed is overall thinner..
    If you have no spacers, then your 7 speed cassette is as wide as you can fit on that hub.

Again, keep your eyes open for a replacement rear hub/wheel that has a 8/9/10 speed cassette already, to give more options. Or a whole donor bike.

ANSWER: If you have to buy any more than a 8/9/10 speed shifter to do this change, then stay with 7 speed for now and just replace the . The parts are cheap, specially using aliexpress grade cassette and chain.

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    Around 6 months ago, my LBS said it would take 4-6 months for chain/cassette to come into stock. I ordered AE parts in under a month. Sometimes having a stash of spares is a good idea.
    – Criggie
    Sep 29, 2022 at 1:23
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    "AE parts" -- what's "AE" here?
    – Paul H
    Mar 8, 2023 at 1:43
  • @PaulH aliexpress.com a Chinese website source for dodgy/aftermarket/counterfeit and third-shift items.
    – Criggie
    Mar 8, 2023 at 3:46
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Go for the 8 speed if you want a wider gear range or closer gear spacing.

An example with gear steps: A 7 speed 11–28 cassette has an uncomfortably large 20% gear step right in the middle, an 18% step and two 17% steps. With a 8 speed 11–28 cassette you have much smaller steps (11–15%) in the middle gears and 17/18% steps for the less used biggest/smallest sprockets. Comparison on ritzelrechner.de. Personally I find anything larger than ~14% gear steps quite annoying in flat terrain since you can never find exactly the right gear combination. So for me this would be a big benefit. It’s less of an improvement if you are changing speed and gears all the time anyway (e.g. busy city traffic, hilly terrain).

Regarding gear range: For 7 speed an 11–28 speed cassette is quite common. With 8 speed you can go up to 11–32 (assuming your derailleur allows it) if you need easier gears while maintaining similar gear steps compared to the 7 speed.

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For some manufacturers, the 8sp cassette is an 11-28 7sp cassette with an extra 32t sprocket added.

If you got a SunRace cassette, where the sprockets are bolted rather than riveted together, you could buy the 8sp and remove the 32 to make a 7sp if that's all that will fit your wheel.

The 8sp shifter should be a no-brainer as it will shift 7 fine, with one position spare. This is how the ST-EF range of shifters function--the 7 is an 8 with one position internally blocked off with a plastic moulding.

Nominally 7 and 8 are supposed to have different spacing but this does not appear to be true in the modern world.

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    Re your last line - 6/7/8 speed chain is all about the same width (simply whacked an extra cog on the cassette each time) then 8/9/10 speed all have the cassette the same thickness but narrow the gap between cogs, and therefore the chain width. That's why a 8/9/10 compatible hub gives the most options.
    – Criggie
    Sep 29, 2022 at 1:26
  • If you look up various charts 8sp is supposed to be 4.8mm spacing, 7sp 5mm spacing. It either makes no functional difference or that information only applied to freewheel systems, not cassettes. @criggie
    – Noise
    Sep 29, 2022 at 6:40
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I would lean towards sticking with 7 speed if that's what your current shifters work with, especially with a 3 speed crankset that should be plenty of gearing options.

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