Replacing 12-28 tiagra cassette - keep or change ratios

starbuck

I have a 2013 defy 1 which has 50x34 on chainrings and currently a tiagra cassette which is 12-28.

I need to replace the chain (probably stick with KMC), so I'm going to replace the cassette at the same time.

Looking at 105 and ultegra cassette options, they don't have the same ratios (they're anything from 11-28 or 12-30), so I guess (unless I get another tiagra cassette) I'll need to change the ratio on the cassette.

If I do change the ratio and go for a 6700 or 6800 ultegra cassette (or maybe 105 if I can't stretch to an ultegra), which ratio would give me good climbing ability and also good range on flat/downhill?

jameses

First of all, do you actually need to replace the cassette? I would normally expect to get through 3 or 4 chains before having to replace a cassette.

Second, different cassette ratios won't magically make you faster uphill or on the flat. If you're struggling with 34/28 uphill (as in you actually come to a standstill), then go for 12-30 or even 12-32. It will make climbing easier, but not faster.
I personally don't think you would ever need anything higher than 50/12 for general riding - what speed do you spin out at? I find it's good for 45mph on a downhill, and there are few roads where that kind of speed is safe!

northpole

I think that 11-28 should be fine for you if you are happy with the 28 cog on the Tiagra.

The 11 will give you slightly higher gearing for descents if you feel the need to go quicker!

I'm not sure where the extra tooth is lost across the ratios on the cassette but basically there will be a gear change on the 11-28 which is wider than you have on the Tiagra.

You could always stick with a Tiagra cassette if you've found nothing wrong with your existing cassette (and as previous poster asked, if you really do need to change your cassette right now).

Peter

dowtcha

Ultra 6700 is 10 speed and compatible but 6800 is 11 speed and not. I had the same cassette as you and went for 105 12-27. I seldom use the 12 cog so 11 would be pointless and the jumps between gears a bit on the large side. I took the 27 as a bailout/tired/hugehill/headwind gear. 105 is only a few bucks more than tiagra so why not.
As others have said if this is your first chain replacement and you have less than 2500 miles on the cassette it should be fine.

dj58

Are you not happy with the gear ratio's as they are, do you want a closer ratio set or need a lower cog for climbing?
What do you want to achieve by changing the Cassette?