Inner chainring options

[DevonPete]

Hello all - have introduced myself on other threads, but this is my first post in the Tech. section.

I've recently purchased (2nd hand) a Thorn Audax. It has a Tiagra triple chainset with 50 - 39 -30 rings. I'd prefer to have a 26T inner to help me up the Dartmoor hills after a 200 or 300k audax. Is it possible to replace the inner with a 26T (not familiar with Tiagra chainsets)? If not, then the other option would be to stick a Deore 48-36-26 on there or something like a Stronglight  with similar ring sizes (not keen to do this on cost grounds).

I have a 11 -32 cassette with Deore derailleur and would prefer to keep that.

I'm not very technically minded with these things - have always been a square taper man for BBs! - and would appreciate your advice.

Many thanks,

Pete.

[triaesthete]

Hi Pete
I think the front mech will be the limiting factor here. "Road" mechs are unlikely to reach far enough down to clear the lowered chain top run off a 26 tooth ring. A "mountain" mech handles 26t with ease.
So, if you have an xt or deore front mech no problem there.
I'm not sure on minimum ring size for Tiagra, but bear in mind individual chain rings are quite expensive and it is currently possible to buy a Deore "trekking" chainset with 26/36/48 rings and a bottom bracket for 50 quid. As a bonus the inner ring is steel for longer life.

Best wishes
Ian

[Danneaux]

Hi Pete!

According to Sheldon ( http://sheldonbrown.com/harris/chainrings/74.html ), the Tiagra uses a 130mm middle and large BCD (bolt circle diameter) and a 74mm inner. The 74mm inner will surely fit a 26T and even a 24T if you prefer.

If you go that route, I would suggest adding an inner chain deflector, such as the 3rd Eye Chain Watcher ( http://www.3rd-eye.com/%2801%29.htm ) or N-Gear Jump Stop (my preference): http://n-gear.com/ This will allow you to adjust the front derailleur for more aggressive and positive shifting to the small inner 'ring without fear of dumping the chain onto the BB shell.

it is doable, but you'll have a large gap and poor, sluggish shifting trying to make the jump from the 26T inner to the 39T middle. Best to keep crossover shifts to 10-12T differences between adjacent 'rings. Others have gone before you with a measure of success and caveats. See: http://www.bikeforums.net/showthread.php/397053-Smaller-than-30t-on-Ultegra-triple <-- Same BCD as your Tiagra.

[EDIT: Ian posted some very good advice while I was typing: You may well need to replace your existing front der if you fit the smaller 'ring to your existing setup. Another good reason to seriously consider the Deore setup below]

You'll have much better shifting results with a Deore 48-36-26. It is a good value in cranksets and comes with steel middle and inner rings, which add a bit of weight but also adds longevity for touring/high mileage use. You can substitute alu rings at extra cost, or go up a notch in Shimano's crank line and get all-alu rings as standard.  Do be aware, these cranksets will have external-bearing BBs, which can prove shorter-lived and problematic compared to traditional square-taper BBs (poorer weather sealing and smaller/fewer bearings are the culprits). That said, I decided to go with a Deore HollowTech II on my Nomad as I did on the Sherpa, and have been pleased with it to date. I have a Phil Wood external BB in reserve for when the Shimano unit eventually goes bad. These cranks and external BBs are very stiff and have the added convenience of being serviceable with only a 5mm allen key. On the other hand, a crank arm-mounted extractor will do the same for removing conventional crankarms at a very modest cost. For a full discussion, see: http://www.thorncycles.co.uk/forums/index.php?topic=4344.0

If you're looking to do this cheaply, remember -- new or nearly new cranksets often show up on eBay for very reasonable prices. If you went with a 110/74 BCD crankset, you'll have a good selection of 'rings to choose from and good weather sealing/long life for the BB. It is proven technology, but not the direction the industry seems to be heading.

Hope this helps.

Best,

Dan.

[DevonPete]

Thanks guys.