Anybody know the BCD on the inner chainring on this chainset?

[Globalti]

This Tiagra triple: http://www.chainreactioncycles.com/shimano-tiagra-4603-triple-10sp-chainset/rp-prod67232

I want to fit a smaller granny ring, about 28 tooth or 26. Any suggestions?

 

[byegad]

I bought one from SPA cycles, Harrogate. I told them the year of the Tiagra and they sold me a 26. (Apparently that's the smallest that will fit.) No connection other than I've used them from time to time and always got great service. They are a proper LBS and do online and over the phone orders.

 

[cyberknight]

This Tiagra triple: http://www.chainreactioncycles.com/shimano-tiagra-4603-triple-10sp-chainset/rp-prod67232

I want to fit a smaller granny ring, about 28 tooth or 26. Any suggestions?

Information on the website says 130 bcd

 

[User6179]

BCD is 92 for the granny I think , not sure but think shimano only do a 30 tooth , Ultegra and Tiagra appear to be the same part .

 

[Poacher]

Likely to be 74mm for the inner, I'd guess. Don't know for sure though.

 

[ColinJ]

Likely to be 74mm for the inner, I'd guess. Don't know for sure though.

Yes.

While Campagnolo and Shimano use different BCDs for the outer 2 rings, they both use 74 mm for the granny ring. I have used Shimano inner rings on my Campag-equipped Basso. I ended up replacing the 30 with a 26 so I now have a luxury 26/28 grovelling gear!

Oops ... Maybe they changed it! According to this, it is now 92 mm! Discussed here.

 

[slowmotion]

130 for the two biggest rings, 92 for the granny.

Here's the Shimano tech doc.
http://techdocs.shimano.com/media/t...SI-1MG0A-001-00-Eng_v1_m56577569830746319.pdf

 

[Globalti]

Hmmm.... that's worrying.... the bloke at Spa Cycles in Harrogate (as recommended by byegad) reckons 74mm BCD. Have just called him and we agreed to hold the order until I can check this evening. GtiJ tells me the chainset is a FC-4600/4603/4650.

If it's 92, I'm a bit stuck. Will just have to MTFU on that climb out of Settle.

 

[ColinJ]

Hmmm.... that's worrying.... the bloke at Spa Cycles in Harrogate (as recommended by byegad) reckons 74mm BCD. Have just called him and we agreed to hold the order until I can check this evening. GtiJ tells me the chainset is a FC-4600/4603/4650.

If it's 92, I'm a bit stuck. Will just have to MTFU on that climb out of Settle.

You could always put a bigger cassette on instead?

 

[Globalti]

It's a 12-30, a SRAM 12-32 is about £30 so I think I'm just going to have to "grow some".

 

[ColinJ]

It's a 12-30, a SRAM 12-32 is about £30 so I think I'm just going to have to "grow some".

I reckon you should be ok with 30/30. I got up Park Rash and Fleet Moss on 30/26 (or possibly 30/28?) when I was less fit than you are!

(I just checked the OS map and the worst bit of that climb looks like about 800 m averaging 13.5% which is hard, but doable. No doubt some sections of it are steeper than others though.)

 

[fossyant]

MTFU. Heh heh heh...

 

[ColinJ]

MTFU. Heh heh heh...

I must admit, I was quite surprised how well I did on my Cannondale's double chainset (39/29 bottom gear) on my week away recently. It didn't feel like I was doing my bad leg any favours though, so I am going to change the bike over to a triple chainset and will probably end up with a 30/29 gear for tough climbs.

 

[fossyant]

I must admit, I was quite surprised how well I did on my Cannondale's double chainset (39/29 bottom gear) on my week away recently. It didn't feel like I was doing my bad leg any favours though, so I am going to change the bike over to a triple chainset and will probably end up with a 30/29 gear for tough climbs.

Good stuff there.....

 

[slowmotion]

It's a 12-30, a SRAM 12-32 is about £30 so I think I'm just going to have to "grow some".

I'm curious. Is it possible to use SRAM 10 speed cassettes with Shimano 105 10 speed rear mechs (assuming the tooth capacity calculations are vaguely OK) ?

Thank you.