Frame size advice

Flexisurfer

I'm going to have a go at cyclocross this winter and would like to build a bike, I have all the bits apart from, frame, brakes and tyres plus a few minor sundries. I've been looking at the Graham Weigh cyclocross frame and can't decide if I would fit and race better on the 54 or the 56. My current race bike has a measurement of 54 cm from the centre of the seat tube to the centre of the head tube and a 57cm seat tube centre to top. I also have a 56cm Allez as my commuter but this isn't as aggressive as the race bike. I've added the frame dimensions below. Is it best to go for a smaller frame to make it more aggressive for this type of racing or is comfort more of an advantage?

I would appreciate any advice as I want to enjoy the racing rather than hate it because my bike is too big or too small.

Size: 54cm

Seat Tube (C/T) cm: 54

Top Tube (C-C) horizontal cm: 54.5

Seat Tube angle: 74.0

Head Tube angle: 73.0

Head Tube Length mm: 110


Size: 56cm

Seat Tube (C/T) cm: 56

Top Tube (C-C) horizontal cm: 55

Head Tube Length mm: 160

uptheswa

having gone through the same process recently and taken advice from experienced cross riders i would say this

look for a frame either same size as your road bike or up to 1.5cm shorter top tube

make sure the stand over height is ok

check the head tube height, this will affect how high or how low you can go

in my opinion, i would go with slightly shorter top tube and slightly longer head tube than the road bike you feel comfortable on, this gives you a shorter reach and bit more sit up position

you might have to search through A LOT OF FRAMES to find one that suits

kentphil

I found it difficult to compare my road frame to a cyclocross frame as the geometry is very different. For what its worth I ride a M size giant TCR and decided on 51cm Caadx. The 54 caadx felt too big for me. Cyclocross bikes do tend to have a taller head tube and shorter top tube than road bikes. I'm 5' 10" tall.

Mike67

Remember the bottom bracket height on a cross frame tends to be higher for better ground clearance.
Just looking at frame size/seat tube length would be a bit misleading as for a like for like frame size you'd be higher off the ground with the same saddle/BB height.

Reach/top tube and standover are more important.
As others have said..a slightly shorter top tube is a good idea...you don't want to be at full stretch on the flat and THEN have to drop down a steep slope and not be able to move back in the saddle a bit/lot.
Equally it has been known for me to come off the saddle at inoportune moments (more like bad skill levels) so you want to have a least a bit of standover (or maybe a lot...I don't know you )

Flexisurfer

Thanks for the advice, it's given me a better idea of what I need to look for.