Cassettes and gearing

[DCBassman]

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]

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

 

[DCBassman]

Time to get the grubby toothbrush out then!

 

[Jason]

or the wife's best tea cloth :-)

 

[DCBassman]

Not been able to find a spec sheet. Too old, I think.

 

[sleuthey]

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!

 

[Cycleops]

Don't forget with a bigger low gear you'll need to revise your chain length.

 

[the snail]

Not been able to find a spec sheet. Too old, I think.

I think there should be a tech doc on the shimano site?

do you know the model no? Usually stamped on the rear of the mech.

 

[DCBassman]

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]

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!

 

[the snail]

this one?
http://www.pigseye.com/bikes/BB/RD-3300.pdf

 

[DCBassman]

Originally I was meaning the spec for the bike - no idea what's fitted as stock, so no clue if mine has been modified at some point.

 

[Illaveago]

Originally I was meaning the spec for the bike - no idea what's fitted as stock, so no clue if mine has been modified at some point.

I've just seen where you are based. It's a bit hilly. Fun going down but not up.

 

[DCBassman]

It's possible to do a 40-miler using NCR 270/27 and only have one steep, short climb (which I've never conquered ) going south.

 

[Illaveago]

It's possible to do a 40-miler using NCR 270/27 and only have one steep, short climb (which I've never conquered ) going south.

I was thinking more of Sidmouth to the East and Porlock to the North. You must be lucky in having a relatively flattish bit.