It's hard for the short crossers! I got an old Jamis Nova 47 that is great but for a while before I tweaked it I was thinking it was too small. I'm keeping it now but my friend was helpful enough to put this together when I was investigating frames. I ride a 48 Ruby on the road. Hope this helps!!




For reference the numbers on your road bike:
Specialized Ruby 48 cm: Top tube length (TT) 50.6 cm, Head tube length (HT) 11.5 cm, seat angle (SA) 75.75, head angle (HA) 71.25, stand over (SO) 71.8 cm.

Specialized Tricross 49cm: TT 51.5, HT 11, SA 75.5, HA 70, SO 75

Kona Jake the Snake 47 cm: TT 52, HT 90, SA 74.7, HA 70.5, SO 74.1

VooDoo Limba 51 cm: TT 51, HT 10, SA 75, HA 71, SO 76
VooDoo Wazoo 51 cm: TT 51.5, HT 80, SA 75, HA 71, SO 75.2

Guerciotti Cross Force 47 cm: TT 50.5, SA 74.3, HA 71.3
48 cm: TT 51, SA 74.3, HA 72

For reference the shorter the top tube and the taller the head tube the more upright you can be. You can modify things a bit via stem length and angle. A longer TT makes you go to shorter stem and the opposite is true. You may be able to trade off a longer top tube with a taller head tube. One other thing that will make a difference with head tube length is what kind of headset it has, integrated head sets don't change the length while conventional ones will add height to it. The Specialized is integrated (although they use a big spacer on top of the head tube (look at your bike, between the stem and the head tube) as is the Guerciotti, while the Voodoo's and Kona use a conventional headset (typically add about 3 cm to the head tube length).

The only other little wrinkles are if it is a sloping frame or conventional frame and the bottom bracket height. Conventional frames will have shorter head tubes than sloping, but it can even things out. Bikes with higher bottom brackets might fit when you are in the seat but you may not be able to stand over the frame. Ridley, older Redlines and Cannondale have higher bottom brackets. A high bottom bracket is ~40 cm, normal is ~25-30.

What ever frame you look at, be sure to look at the geometry. Some manufacturers change there specs even if the model stays the same. If you are curious about a Guerciotti, I have a 48 cm Kangaroo (should be the same as Cross Force) that you can check out.