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Is TT length critical for CX frame sizing??(4 posts)

Is TT length critical for CX frame sizing??Cima Coppi
Aug 14, 2001 6:46 AM
Hi all,

I searched on sizing a cx bike, but could find little information on sizing based on tt length.

Here are my questions. On my road bike, the TT is 58cm c-c, and the ST is 59cm c-c. My road stem is 120mm. My inseam is 87cm. I fully understand the reasoning for downsizing on a CX frame. I looked at a couple of CX frames that are 56cm c-c on the ST and 56cm c-c on the TT. The standover height is perfect, but I felt very crammed in on the reach. It seams that all of the frame specs I can find on the Net are close to the same. I don't want to go up to a 58cm because of clearance.

Suggestions?? Should this really be an issue? Will a longer stem be the only option short of a custom frame?

As always, your responses are greatly appreciated. Thanks in advance.

re: Is TT length critical for CX frame sizing??climbo
Aug 14, 2001 8:48 AM
this is the CX frame dilemma lots of people have. I'm having a similar problem too but I prefer to have the correct standover because getting on and off that thing if it's too high will really suck after 20 or 30 dismounts and re-mounts (ouch!!). For cross racing I don't mind being a little shorter on the "cockpit" as it's nicer to be a little more head up during tricky descents etc. If the "cockpit" is too long, when you get in the drops and can be a little tricky to handle the bike. Also, in the mud you can get plenty of weight towards the back of the bike if you need traction on your tires and then you can still keep the front down as the wheelbase is not too long.

I would say that dropping 2cm on the TT is not a big issue, that's what I am dropping too. I will probably run a similar size stem as my road bike (13cm).
re: Is TT length critical for CX frame sizing??Jan Gerrit Klok = "TUFO-man"
Aug 14, 2001 9:32 AM
I assume that you measure TT C-C horizontally to the ground, not along the TT, for TT's are no longer all alike.
My TCR roadbike is TT 58,5cm and my stem 12,5cm. That's a total of 71. I had my custom frame built with a 56 ST and a 60cm TT. Stem is 10cm, I want the bike to feel easy cornering. It seems like 1 cm shorter in total is not much, but the higher placed STI and Aerolever make up for maybe 3cm or more. I hate kicking the stem with my knees, with the long toptube that problem was solved.
Why 56cm high you might ask, well I 'm new at cross and I kinda like the technique of demounting by swinging my right leg over the TT, it seems much safer and faster to me. I had the diff c-c to c-t of the ST made at 7,5cm, so the TT is really sloping, the frame looks just like a Mountainbike. For shouldering I've always used the underside of the saddle, it's just a much simpler movement for me (6'4") with the bike closer to the ground, and putting it down is like half a movement. Also, the low top-tube makes picking it up much easier.

I built this, my first CX bike, up this summer and it fitted like a glove.

MTB racers to choose CX toptube : decide your CX stem length and make CX TT = total of MTB - stem CX - 4,5cm. The diff is in the bars, bended bars make a bike longer. The 4,5cm compensates for a more upright position. At least, it works swell for me.

Good luck at deciding!
re: Is TT length critical for CX frame sizing??badabill
Aug 14, 2001 2:31 PM
My cross and road bikes use the same TT, 54cm. On my cross ST is 52cm on my roadbike 54cm. Stem on cross is 10cm rise, road is 12cm drop. What this does is to raise my riding position slightly on my cross and gives me a little more standover clearence. I am still a true "fred" on mounts and dismounts but it makes it a little easier:-)