Cassettes and gearing

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Fairly soon, I will need to replace chain and cassette on my Scott, it's a Sora 8-speed system.
From reading various threads, it seems likely I can lower the gearing a bit by selecting a larger sprocket set, so long as it's still within the range of the Sora mech. Fine. But how do I determine what's on there? I can't see any markings, so is it just down to counting teeth?
 

mjr

Comfy armchair to one person & a plank to the next
Count the teeth. There will be markings on Shimano cassettes, like "27T" just inside the line of teeth to denote a 27-tooth cog, but they're probably hidden by the oil crud so counting the teeth will be quicker/easier. If you look carefully, current Shimano cogs have some teeth with a groove on the front edge to aid shifting, which can help you pick a point to start counting and avoid double-counting or missing some. The smallest cog may not if it's an 11T.

Another dodge is to look up your bike's spec on the manufacturer's website and hope the shop didn't change it for local conditions or you ;)
 

sleuthey

Legendary Member
I have just changed from 11-32T to 11-34T. I knew I may or may not have to change the rear mech. I seem to have got away without changing it as it works well. To find out what range I had on there to begin with it was simply a case of putting a mark on one of the teeth and slowly turning the rear wheel whilst counting the teeth. Be careful not to count the one with the mark twice at the start and end of the revolution!
 
There's a spec for the 9-speed Sora, and another spec for the 8-speed cassette. Three options: 12-21, 12-23, 12-25.
 

mjr

Comfy armchair to one person & a plank to the next
There's a spec for the 9-speed Sora, and another spec for the 8-speed cassette. Three options: 12-21, 12-23, 12-25.
There's also 11-28, 11-30, 11-32, 13-23 and 13-26 at least, but I can't find the Shimano tech docs either.

But the benefit of the spec sheet was to tell you what was fitted to the bike as new. Not sure what we're doing now! :laugh:
 
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