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I'm thinking of upgrading the 9-speed Tiagra rear mech on one of my (road) bikes to something, still Shimano, but 10-speed.

The obvious replacements I'll need are cassette, right-shifter and chain. But I reckon because of the narrower chain I'm also looking at a new chainset and rear derailleur. However I think the front derailleur and left-shifter should be safe (still keeping the front mech the same). Ditto the bb, regardless of whether I need a new chainset

Has anyone actually done this conversion and is able to confirm (or put me right)? Thanks

Update

Decided in the end that going from 9- to 10- was too much to spend all in one go. But I used a service as an excuse to upgrade the cassette (to a 9-speed ultegra) and the chain (dura ace) at quite minimal cost. Can upgrade other parts as and when, although I'm basically looking at Shim's 6500 range here so all quite dated now.

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You will need a 10-speed cassette, 10-speed rear derailleur, and 10-speed right side shifter and a 10-speed chain to work with the narrower spacing on the rear cassette. There tend to be some compatibility issues with 9-speed derailleurs run on a 10-speed drivetrain (some people seem to have luck using 9-speed shimano mountain derailleurs with 10-speed shifters, but YMMV).

Your 9-speed front chainrings should be fine. Sheldon seems to agree on that point However, I wouldn't expect it to work on 8 or 7 speed chainrings, but it very well may. I've upgraded my own 10-speed outer front chainring with a 9-speed one on a 10-speed Tiagra setup and haven't had any issues with it. There shouldn't be any issue with the left shifter, derailleur, or bottom bracket, those should be fine as well.

One other thing to consider is the brakes. 10-speed STI shifters may have a different lever pull ratio than the 9-speed levers, this may only apply to ultegra and dura ace though (please correct me If I'm wrong on this). So, you'll probably be OK if you're sticking with tiagra. Otherwise, you may want to upgrade STI levers at the same time and possibly get brakes with a matching pull ratio.

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cheers @benzo, I hadn't considered the brakes. I would upgrade from Tiagra if I could, all depends on cost, so what you say could possibly come into play. But as you say I could sidestep this to some degree if I stuck to Tiagra shifters (but maybe fitted an ultegra cassette for example). I haven't really looked at costs yet but I'm starting to think that for the number of parts I'm going to need, it may even work out cheaper to buy them as a bundled groupset rather than individually. In which case this question becomes a non-question... –  PeteH Nov 21 '12 at 16:52
    
When you say that the brake levers "may have" a different pull ratio, are you guessing or did you have a reason to believe that? I didn't think that road pull ratios had changed in the last decade or so but I still run 9 speed so it wouldn't surprise me to find that they had. –  jimirings Nov 21 '12 at 23:20
    
I'm not just guessing about the brakes. The manual for ultegra brifters says "Use the ST-6700/6703, BL-TT79 with the BR-6700. Do not use the BR-6700 in combination with previous STI levers for road riding or with the BL-R770/BL-R550 brake levers for flat handlebars, otherwise the braking performance provided will be much too strong" See bike.shimano.com/media/techdocs/content/cycle/SI/SI_6SC0A/… –  Benzo Nov 22 '12 at 15:50
    
And shimano's website sucks, they don't even mention 10-speed compatibility with the tiagra brifters on their page (I know they come in 10-speed since I have a set). Also, here's a really confusing drivetrain (and brake) compatibility chart shimano.com/publish/content/global_cycle/en/us/index/… –  Benzo Nov 22 '12 at 15:58
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Had a look at cost over the weekend, looks like it would be cheaper to buy the individual parts than the groupset - I thought it may be worthwhile buying everything together but whilst there is a saving its not a lot. Also the costs involved would tend to support a piecemeal approach to upgrading...so this information will all be useful to me. –  PeteH Nov 26 '12 at 12:49
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I'm going to assume two things: 1) Your current setup was is all 9-speed and has never been upgraded from 8-speed, and 2) your shifters are indexed and not friction shifters. If either of those are wrong, it changes things. That said...

You are correct about the cassette, right shifter, and chain. You will also need a new rear derailleur. You'll most likely be ok with your current crankset. You'll also probably be able to get by with your current front derailleur but, because of the narrower chain, shifting may not be optimal. And yes, the left shifter and bottom bracket will be just fine.

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yes and yes to your assumptions. Thanks for the input. I'll have another look on Shimano's site with particular regard to finding out more about chainset/front derailleur sizes, and whether/how they've changed. I think when I bought the bike, the Tiagra range only went up to 9-speed, but this range appears to be 10-speed now. –  PeteH Nov 21 '12 at 13:33
    
Where are you seeing 10 speed Tiagra? Shimano's website only lists 9 speed Tiagra. bike.shimano.com/publish/content/global_cycle/en/us/index/… –  jimirings Nov 21 '12 at 23:22
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we're obviously way, way ahead of you here in europe!! cycle.shimano-eu.com/publish/content/global_cycle/en/nl/index/… –  PeteH Nov 22 '12 at 10:15
    
Lame! But not all that surprising. The rest of the world usually is. –  jimirings Nov 22 '12 at 14:25
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