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On my road bike, I have an old 8 speed Shimano 600 Cassette like this:
enter image description here

I'm not 100% sure about tooth count on each cog, but I think it's something like:
23, 21, 19,17,15, 14, 13,12 (probably?)

I'm having issues with the size of the cogs. Climbing even basic hills is very hard even on the biggest cog. (It's wearing out my knees).

Can I change the cassette to one with bigger cogs without replacing my rear derailleur? Or would I have to get a new derailleur also?

While at it, can I get smaller front chain rings without replacing the front derailleur? I have 53T/42T chain rings.

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    You should probably update this with what chainrings and cassette you're running. And also, play with your position on the bike -- having your saddle too low can also cause kneepain, even with good enoguh gearing. – Batman Apr 15 '16 at 15:34
  • Thanks, I updated the question. (I found that 53/42 was written on the side of the big chain rings) – Leo Ufimtsev Apr 15 '16 at 16:05
  • +1 for @Batman comment about seat position. Also, if you're wearing cleats, be sure to your cleats are adjusted properly as well. I did a lot of flat land riding one summer and knew one foot wasn't positioned quite right on the pedal, but it didn't bother me, it was just a bit annoying. I drove to the hills and did 2 days of hilly riding and could barely walk from the pain in my knee from that slightly mis-adjusted cleat. – FreeMan Apr 15 '16 at 17:43
  • I use cleats. What would properly adjusted cleats mean? Would one move them further to the front or the back of the shoe? – Leo Ufimtsev Apr 15 '16 at 18:32
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The derailleurs are usually matched to the size of the cassette/chainrings.

the cage length of the rear derailleur is matched to the largest cog. that is why you see mountain bikes with a 34 tooth in back with long cage derailleurs and road racing bikes with the little derailleurs matched to the corn cob size cassettes.

The curvature of the front derailleur is often matched to the size of the chain-rings. This feature improves shifting.

if the differences in tooth count are not too drastic, you might be able to get away with only swapping out cassette and/or chain rings. Also the number of links in your chain may have to be adjusted.

  • Thanks, good to know. I guess I'll ping my local second hand bike shop for parts. – Leo Ufimtsev Apr 15 '16 at 16:53
  • 53/42 is a very heavy combination for the front rings. You might want to upgrade to a compact 50/34 but that would most certainly require a change of the crankset and possibly of the bottom-bracket. The FD should just require a height adjustment (i.e. be lowered). – Carel Apr 15 '16 at 20:08

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