Ribble Gran Fondo derailleur clamp size?

jameses

Just picked up a new ribble gran fondo frame, but I'm a bit unsure about what size derailleur clamp I need. It takes a 31.8mm seatpost, so I'm assuming that makes the seat tube 34.9mm, but the part of the tube where the clamp would be attached has a flattened section. Is this just to better accomodate a 34.9 clamp, or would I need a different size?

Thanks for any help.

nochekmate

Built one up the other month (since sold so cannot double-check in garage) - 34.9mm as far as I recall

smidsy

34.9 according to the Ribble site.

jameses

Thanks very much!