I have a Giant Boulder 520 (1996) and I am upgrading it bit by bit.

I bought a new Shimano 7 speed cassette 11-28T. Now, I want to replace my crank set, however I do not know which size to buy.

Does it have to have the same number of teeth as my current one or does it not matter? I currently have a 42/32/24 crank set, do I have to replace it with a 42/32/24 crank set to avoid having to replace the derailleur or anything else?

I am currently thinking of getting a Shimano crank set FCTY501 42/34/24 compatible with 6/7/8 speed. Will it work with my new cassette and will I need to adjust my derailleur?

  • 3
    Why has this got a close vote? OP asks a specific question about technical compatibility, not requesting a subjective product recommendation. Nov 19 '17 at 15:38
  • Looks like you are renewing rather than upgrading components keeping the original 7 x 3 configuration. Have you considered replacing the entire drive-train with a 9 x 2 or 10 x 2? a 9 x 2 need not be excessively expensive. Nov 19 '17 at 16:42
  • @ArgentiApparatus I'm on a budget and have already bought a 7 speed cassette. I'm not particularly fussed about the Configuration to be honest. Nov 19 '17 at 17:48
  • @ArgentiApparatus any cassette with a triple will have more low gears than the same cassette with any form of double.
    – Criggie
    Nov 19 '17 at 18:53
  • 1
    @ArgentiApparatus From the title and first two paragraphs, it looked like a classic shopping question. I've edited and retracted my close vote. Nov 19 '17 at 20:47

You are not changing the largest and smallest chainring sizes, so if nothing else has changed a 42/32/24 crank would be compatible with the rest of your drivetrain.

However, I looked up the specification of your bike on Bicycle Blue Book. The original cassette was a 7-speed 13-28 tooth. You may have problems with the 11 tooth small sprocket.

If you want to check, you can look up the specs for whatever your rear derailleur is. You can find technical documentation for Shimano products on the Shimano Bicycle Components Site.

Rear derailleurs typically have the following specifications:

  • Minimum rear sprocket size
  • Maximum rear sprocket size
  • Maximum front chainring tooth difference
  • Total capacity

You'll need to ensure that your derailleur can handle an 11 tooth smallest rear sprocket, and a slightly increased total capacity.

The total capacity is the difference between the numbers of teeth on the largest front ring and rear sprocket, and the smallest front ring and rear sprocket. I.e., a measure of the extremes of chain slack the derailleur has to accommodate.

For an 13-28 cassette and 42/32/24 crank: (42+28) - (24+13) = 33, 11-28 cassette : (42+28) - (24+11) = 35.

  • 2
    @Jan Druminski I saw I got a acceptance of my answer while I was substantially changing it, please take another look. Nov 19 '17 at 16:37
  • I can't find the derailleur information on the Shimano site.Right now i'm riding on a 14-28 cassette (which isn't the original) and a 42/32/24 crank (which isn't the original either as original is 48/38/28) And everything works fine except for the fact that it's simply worn out. Do you still think I will have to buy a new derailleur for the 11-28 cassette? Nov 19 '17 at 18:00
  • I think you have a chance the derailleur will work, Do you know what model it is? You can of course just fit the 11-28 cassette and try it out. I'd recommend adjusting the B-screw to accommodate the smaller sprocket. See youtube.com/watch?v=y3x13dD0UiQ Nov 19 '17 at 18:43

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