Tiagra triple chainset (50/40/30). Advice needed!

[andy753]

I am recovering from a major knee rebuild (ski crash) and have decided to ride the Bike 4 Cancer London to Brighton bike ride on 6 September 2015 in memory of my dad but also as a rehab ride after my op. If anyone else fancies it, more info at: http://www.bike4cancer.org/london-to-brighton-bike-ride

I am very worried about Ditchling Beacon though. Having ridden the route several times before, I know that my knee will be very sore if I don't have some gentle gears up my sleeve.

I am currently running a Tiagra triple up front (50/40/30) with a 9 speed cassette (12 to 27) via a Tiagra RD-4500 long cage rear mech. This is going to sound really pathetic but this is not enough at the moment while my knee recovers! Does anyone know if I can run a bigger sprocket at the back? The Shimano website is totally useless!

Many thanks in advance for your help!

[beardy]

You probably can go a little bit bigger. You can definitely go to at least thirty with their newer 10 speed dérailleur which will work with what you already have. You should really fit a new chain if you do either of these.

Much simpler and cheaper is to fit a smaller inner ring on the front. You can probably use a 24 on that chainset/derailleur combination if you dont mind over stretching the rear dérailleur's capacity in gears that you would be better not using anyway.

A 28t or 26t inner ring would possibly be more suitable and have more effect than a 30t rear cassette.

You could have a larger (up to 36 tooth) cassette if you buy the right MTB rear derailleur to replace the exisiting Tiagra one.

[OldBloke]

I'm with beardy. If it can fit on your crank, a 24T ring would be the cheapest and easiest to fit (and remove later when your knee improves). Depending on how you set up your chain you may find you can't run from big to big or little to little, possibly both may be outside the range of your derailleur.

[andy753]

Thank you fellas, I didn't think I would be able to get a smaller chain ring! I will have a look on Wiggle now. Thanks for your advice - much appreciated! I wish I had never gone skiing!

[Audax67]

I think you'll get one but you might need a chain catcher (shark's tooth?) as well. Alternatively you could fit a Shimano M443 chainset, which goes 48-36-26. I have one mounted on my Surly: it works a treat with my old 105 3x9 shifters (anno 1999) so should be fine with Tiagra.

http://www.bike-discount.de/en/buy/shim ... 1mm-210549

Doesn't cost the Earth, either.

[markfh]

Noticing tatanab's reply to the same question on YACF "Shimano say that the FC4503 inner PCD is 74mm so you can use chainrings down to 24 teeth. http://bike.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/FC/EV-FC-4503-2594D_v1_m56577569830707832.pdf. That would certainly be cheaper than changing the cassette and chain, especially if it is only for temporary use. Depending on your present chain length you might find the chain runs slack in the little/little combinations but you should not be using them anyway."

Assuming that your's is a FC4503 (your may wish to check the bolt circle diameter (BCD) as later Tiagra chainset had a larger BCD for the inner) then a possible source of chain rings is Spa cycles. Their own brand 74mm BCD inners are a very reasonable £10 http://www.spacycles.co.uk/products.php?plid=m2b0s210p0 IF they will fit your existing chainset.

[fatboy]

Assuming a 74 bcd then a 24t will fit!

[beardy]

I am currently running a Tiagra triple up front (50/40/30)

This is quietly nagging at me. Is it really a 40t middle ring or did you count it and get it slightly wrong?

[andy753]

Thank you everyone for your help. I have measured the BCD and it looks to be a 74 although this estimate is now accurate given the cranks are still on the bike. OK, so I am now on the hunt for a 24, 26 or 28T ring! Thanks everyone.

[beardy]

Here is a start

http://www.spacycles.co.uk/products.php ... b0s149p244

others are available on that same website.