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Help explain cassette and chain combinations

by kalmar
Fri, Sep 27, 2019 16:52
6

Hi, I need to replace my cassette and chain on my Boardman Road Sport bike. As far as I understand, my cassette is an SRAM PG850 12-26t and my chain is a KMC Z72 (that's an 8 speed, I am guessing?). My chainset is an FSA Tempo Compact 50-34.

I don't fully understand what sort of combination to go for. What is the range of teeth and speeds I can combine? I would like to try to install it myself so the simpler the better.

I would like the best value cassette and chain at the lower end of the market. Is it worth replacing the chainset while I'm at it as well? The bike has done around 2000km over 2 years and never had any of the parts replaced. I ride it very casually so don't care that it's not the perfect bike.

 

I was looking at these parts, purely based on what seemed good value online:

Shimano Sora HG50 9 Speed Road Cassette

Shimano Deore HG53 9 Speed Chain 12-25t

Shimano FC-R2000 Claris Compact Chainset 8 Speed (but will that fit the 9 speed cassette and chain?)

Does that make sense?

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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6 comments

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brooksby | 5 years ago
0 likes

Does this help?  https://www.sheldonbrown.com/k7.html

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Simon E | 5 years ago
2 likes

Any 6/7/8 speed chain will be compatible, they are all exactly the same size. I'd recommend KMC X8, Z8 etc. If you get one with a quick-link included it won't require a chain tool to fit or remove (though you will need to make sure the chain has the same number of links as your current chain). If you fit the new chain and it then skips/jumps on any cog of your existing cassette then that's a sure sign that the cassette is worn and needs to be replaced. Chain (and therefore cassette) life is significantly improved with regular cleaning and lubrication.

Your 8 speed cassette is compatible with the Shimano hub standard so you can fit any Shimano, SRAM and Shimano-compatible 8 speed cassette. 9 and 10 speed cassettes will fit on the hub but won't be compatible either with your shifter or with an 8 speed chain. If you intend to fit it yourself you'll need a cassette tool and a chain whip.

The exact ratios you pick for your cassette aren't critical except if there are more teeth on the biggest cog than your derailleur can manage. Anything starting with 11, 12 or 13 teeth and going up to 25, 26 or 28 would be good.

Halfords have the SRAM PG830 on their website at £14, the Shimano HG41 11-28 at £17 and the Shimano HG50 8 speed 12-25T for £18 (be aware that Shimano inexplicably use "HG50" on 7, 8 and 9 speed cassettes). Ebay seller laxzo, who I've dealt with a number of times, has a Tri-diamond branded 11-28T for £9 here. I have used two Tri-diamond 7 speed cassettes from them and they work just the same as the Shimano equivalent but are a lot cheaper.

Avatar
Griff500 | 5 years ago
0 likes

You don't  say why you need to change components. Ordinarily, an 8 speed chain should last several times the mileage you have done, the cassette several times more than that, and chainset several times more than the cassette. (Some people use the rule of changing cassette with every 3rd chain,and chainrings with every 3rd cassette, but its not cast in stone )

If you are changing because you have allowed the components to become rusted, then you will also need to look at derailleur and cables, brakes etc.

Avatar
kalmar | 5 years ago
0 likes

That's helpful, thank you!

And it's fine to switch from 12-26t to 12-25t? What about switching to 13-26t? I only ask because this looks very cheap: https://www.merlincycles.com/shimano-sora-hg50-8-speed-road-cassette-108...

Without having seen what it looks like, would you say it's necessary to also replace the chainring? 

And are there any other essential parts I should look to replace while I'm at it?

Avatar
hawkinspeter replied to kalmar | 5 years ago
0 likes

kalmar wrote:

That's helpful, thank you!

And it's fine to switch from 12-26t to 12-25t? What about switching to 13-26t? I only ask because this looks very cheap: https://www.merlincycles.com/shimano-sora-hg50-8-speed-road-cassette-108...

Without having seen what it looks like, would you say it's necessary to also replace the chainring? 

And are there any other essential parts I should look to replace while I'm at it?

You should be fine with different cassette teeth configuration (unless you go for a big 'granny' gear such as 30t), so that one from Merlin should be fine (I only looked at Wiggle so they may not be cheapest though they're usually quite competitive). I have bought stuff from Merlin before and they've always provided good service.

I's guess that the chainring will probably last a few changes of chains/cassettes, but it depends on how much the chain gets worn before changing it. If you upload a photo of the teeth on the chainring, it should be easy to see if it's badly worn or not.

You could look at changing the rear derailleur jockey wheels - they can last ages, but they do get worn down over time. Also the inner brake/gear cables are worth replacing every so often but it depends a lot on how much usage they get.

If I were you, I'd go for a new chain and cassette and see how the bike is afterwards.

Edit: In case you don't know how to change a cassette: https://road.cc/content/feature/173250-bike-maintenance-how-fit-and-remove-sprocket-cassette

This may help with understanding gear combinations: https://road.cc/content/feature/171317-beginners-guide-understanding-gears

Avatar
hawkinspeter | 5 years ago
3 likes

Okay, if you've got an SRAM PG850 then you're bike supports 8 speeds. Unfortunately, you'd need to change the gear levers to be able to take advantage of a 9 speed system, so unless you want to spend quite a bit, you'd be better off sticking to 8-speed.

8-speed cassette £21.99: https://www.wiggle.co.uk/shimano-sora-hg50-8-speed-road-cassette/

8-speed chain £6.95: https://www.wiggle.co.uk/sram-pc830-78-speed-chain/

8-speed chainring £37.99: https://www.wiggle.co.uk/shimano-fc-r2000-claris-compact-chainset/

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