I want to convert the double Tiagra/Most chainset on my Pinarello to a triple. Obviously need to put 3 rings and new crank arms on but what else do I need to change? Can I use the same front mech and lever? Sorry if its a stupid question.
The front mech should be ok, but you will need a new lever.
depends on the mech. i'd imagine that tiagra mechs are full range. also make sure the rear mech has the capacity for the gear range you will have, again the cheaper mechs tend to be less specific but worth a check
It's cheaper and easier to put a mtb rear mech on and new larger cassette. If you do the maths the ratios are about the same.
I'm with tinribz, why do you need a triple? If you are putting a triple on you may need a new rear mech as well to take up te extra slack on the granny ring. If you already run a long cage on your rear mech why not go for one of the new 30 or 32t 10 speed cassettes?
Front mechs on road triples can be a bit tempremental as well - definitely better to go with a compact up front and a wide range cassette IMHO.
STI prob needs changed too.
Ps, you dont say if you are compact or standard rings, that makes a difference.
These guys have some useful info on bigger cassettes and rear mech compatibilty in their FAQ section:
http://www.interlocracing.com/cassettes_steel.html
Can't think you need a triple unless you live in the lakes or the highlands of Scotland. I regularly do the lakes passes on a compact and a 28t rear cassette.
great info -thanks everyone. I'm running a 50 and a 34 up front and a 12-27 block on the rear. I just don't have the leg strength to keep a descent cadence on hills (and i know I need to train!!). Can i just drop a say 12-34 nine speed block on the back?
You should be able to if it's a long cage mech. You may need a longer chain if yours was shortened to suit.
Can i just drop a say 12-34 nine speed block on the back?
Nope. You can try but think you'll find a tiagra derailler won't stretch to a 34, or 32 for that matter.
^^ im using a di2 with a 11-36t - same cage length, you need to change the b-tension screw for a longer one, and 10t jockey wheel
ive seen a tiagra with a custom 38t rear as well
Can i just drop a say 12-34 nine speed block on the back?
You can so long as you replace the existing road rear mech with a long cage MTB one. Any 9sp mech will do.
TBH though, that's VERY low gearing for a road bike. You say you can't keep a decent cadence on the hills but road bikes aren't designed to sit there and spin at a million rpm like a MTB, you've got to put in a bit of effort!
Nope. You can try but think you'll find a tiagra derailler won't stretch to a 34, or 32 for that matter.
Running a tiagra rear mech quite happily with an 11-32, stuck it on the back of a Cotic >X< for off-road on hilly things, two extra links in the chain and the b screw wound in. A lot easier than changing to a triple and with 50-34 on the front, climbs anything.