Which size?

[Monsieur Remings]

I'm going to have to see this bike in the flesh and try it out but can anyone tell me which size frame Cannondale Supersix I should consider, given that the measurements for the Ribble are a medium? I thought initially a 54 as I ride a medium in the geometry for the Ribble New Sportive given, but perhaps a 56 might be more appropriate? What do you think?

As I said, the bike I have which is a good fit is the medium measurement above. Below is the bike I'm intending to buy...

I know I'll have to go a bit further than this but first impressions would be most welcome.

(Please note that the size for the Ribble versus the equivalent B in the Cannondale appears to be a different measurement... the Ribble is to the top of the seat tube and the Cannondale measurement is to the top of the top tube along seat tube axis).

Thanks

 

[Rob3rt]

Look at horizontal top tube lengths. This is the most important measurement. If the medium Ribble definatelly fits, then either the 54 or 56 Cannondale will most likely fit (there is a less than 1cm difference either side, the 54 is about 9mm shorter than the medium Ribble, the 56 is about 6.5mm longer).

It will come down to which you like the feel of and what you would prefer customise. More seatpost showing, longer and more upright stem or less seatpost showing and slightly shorter stem.

You will struggle to compare sizes based on seat tube length, c-c or c-t because IIRC the Ribble frame is more compact, Cannondale bikes do have a sloping top tube, but it is not as dramatic as most other brands. Although that said if you guestimate that the centre of BB to top of the seat tube is 1.5-2cm more than the centre of bottom bracket to the top of the top tube size measurement given for the Cannondale (which is a fair guestimate based on the CAAD9 I have), i.e. converting the Cannondale sizing method to match that of Ribble, the M (which measured 53cm) is closest to the 54cm Cannondale (which will measure approx 53.5-54cm based on the quoted c-t measurement of 52cm + the 1.5 to 2cm fiddle factor), so within 1cm.

 

[Monsieur Remings]

Fantastic Rob3rt, many thanks. I'm glad you're able to confirm the difference between the C-C measurement of the Ribble and the C-T of the Cannondale.

 

[Monsieur Remings]

Okay, having tried a 56 which was too big, I'm fairly adamant that the 54 is the right size even though they didn't have it in stock....

But, the one remaining thing that bothers me is the head tube - a 14 on the 54 Cannondale but 17.3 (cm) on the Ribble which seems a significant jump to a far lower position. Is there any other dimension/angle that I am forgetting which mitigates or extends this significant drop?

Many thanks...

 

[outlash]

IIRC, the taller the head tube, generally the more upright you are. 14 on the supersix bears this out as it's a pretty racy bike. The CAAD8 has a similar head tube length to the Ribble which is a bit more upright than the CAAD10/supersix.

Robert's right on the top tube length being the important measurement, having used a 60cm frame on my old bike which if anything felt slightly small. So I checked my measurements of my anatomy and my CAAD8 is a 58 which fits me much better.

Tony.