Hey guys, recently I got my hands on an old 105 groupset (the one with the 9 speed cassette) from a friend for pretty cheap. I was wondering if I could use a new 10 speed cassette on bike. Would i have to buy a new shifter and chain along with it? or would the old 105 chain be fine? Thanks!

You cannot use a 10 speed cassette unless you have a 10 speed shifter. Whenever you change a cassette you should change the chain anyway and you need a narrower 10 speed chain to match the narrower 10 speed cassette spacing

So in theory, a 9 speed system and 10 speed system can be made to work. will it be perfect, probably not, rideable definitely.

with that said its important to refine it a little. your derailleurs will work with 8, 9, or 10 speed, you just need to adjust the hardstops.

Shifters and cassettes should match but yes they can be different so long as the shifters are a larger speed than the cassette. your hardstop on the derailleur will stop you from selecting the highest gear and putting your chain into the spokes.

The width of chains gets narrower as the amount of gears go up. A 9 speed chain will work on a 10 speed system but again not perfectly. an 8 speed chain and 10 speed cassette is probably a bad idea.

Heres the kicker, and the most pertinent answer to your question. chains and cassettes are consumable items. It is recommended to change your chain and cassette at the same time to avoid premature wear. chains stretch. once they reach a certain limit their performance degrades. Cassette teeth wear down. If your use a new cassette with a old chain the cassette will degrade quicker and vice versa.

once your cassette or chain reach end of life shifting becomes much less precise/reliable. this results in ghost shifting, noisy/clunky shifts, or the inability to keep your drive train tuned.

is there a reason that you want to buy a 10 speed cassette over the 9 speed?? available gearing ratios?? it is possible to replace a few cogs on the end to get your perfect combination.

I would suggest buying a new 9 speed chain and a new 9 speed cassette. Ive been using 12-26{9** cassette paired to a 39/53 crank. Gluck.

7-8 speed yes. Any other combo no. The spacing differs so the shifting really doesn't match. You can make a 7 speed shifter work with either 7 or 8, but it won't work with 9.10, or 11 speed.

Thank you guys for your help! I just wanted 20 speeds because I commute and do club rides on the same roadbike, so I would want more gearing options, because before I was running on Sora's and now I have an older 105 groupset that's 9 speed. I wanted to have a 10 speed cassette but I wasn't exactly too sure on what to get from the shop.

Eleven speed cassette? Oh joy.

The high end and low end of your gearing can be the same for 9 speed and 10. its just the steps in between are lessened with 10.

A 10-speed cassette puts 10 cogs into about the same amount of space in which a 9-speed cassette only has 9 cogs so the spacing between the cogs is slightly different.

9-speed and 10-speed shifters will not interchange and index properly. A 9-speed chain will be wider and likely have issues with a 10-speed cassette.

Repeat the Mantra "I really dont need 10 speed cassettes and stuff, to ride my bike"

Get a 10spd shifter to go with the cassette. If you want more options,get a wider range cassette,but the cassette and shifter much match.

You don't need a 10 speed for more options. A wide range 9 speed triple will give you plenty of choices.