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55cm Road Bike =55cm TT/Tri bike???(2 posts)

55cm Road Bike =55cm TT/Tri bike???Ride-Fly
Nov 14, 2002 1:05 AM
I have 55cm Klein Quantum Race which has an effective toptube of 56cm, and use a 90mm stem w/ zero rise (or 90 deg.) Would I need a shorter, longer, or equal toptube in a TT/Tri bike. The bike I have in mind is a 55cm Cervelo P2K which has an effective toptube of 54cm with the seatangle set at 78 deg or 56.5cm with the seatangle set at 75 deg. Do you (experts) think that it would be a good fit, generally speaking?? I always thought that a tri-bike needed to be a little shorter than your normal road bike because of loss of reach you experience from placing your forearms on the aerobars instead of having the your full reach to the hoods or even the drops. Granted the seattube angle is a lot greater so that puts you more forward to begin with but does it offset the loss of reach?? Thanks!!
re: 55cm Road Bike =55cm TT/Tri bike???Kudzu Kannibal
Nov 16, 2002 5:32 AM

Tri bikes have shorter chainstays (generally) and short top tubes. But their steeper seat angles push those top tubes forward, creating larger front/center dimensions. Generally this is the rule. Remember, the rear wheel is pushed under the rider more, which gives you the forward positioning on the bike.

Also notice that many Tri-bike manufactures have gone to 700C fits for bike sizes longer than 54-55cm. The reasoning for this, is the head tube length on the old taller tri bikes offsets the aerodynamic benefits gained with the smaller wheels. The tradeoff between a larger wheel diameter and head tube length is negligible and actually begins to favor the 700C wheelsets starting about this size or above.

But then again I am an amateur and wouldn't notice the difference regardless. I know I have lowered my times (I am 6') overall going to a road geometry, plus I have gained major benefits of comfort on longer races > Olympic Distances. And SINCE I live in a very hilly part of North Georgia, climbing in the saddle has become a breeze compared to my old tribike.

Good Luck