[reply]of course, the top rider in the world got his a$$ handed to him yesterday by a dude on a sloping tt cervelo, so there ya go. :)
seriously tho - i don't know of anybody who is actually trying to say the sloping thing is a performance advantage in a serious/nonmarketing sense.[/reply]
The differences are actually very easy to measure and understand, unfortunately few people in the industry are interested in the actual differences or in testing and rather just make up stuff for their brochure.
The differences between sloping and horizontal are small, but if you use the same tubeset for both frames, the following differences will occur:
1) slightly higher bottom bracker stiffness for the sloping frame
2) slightly higher torsional stiffness for the horizontal toptube frame
3) slightly lighter frame with the sloping toptube
4) slightly lighter seatpost wit the horizontal toptube frame
5) slightly more seatpost compliance with the sloping frame.
issues 3 and 4 are a wash, and for us at Cervelo the choice between sloping and horizontal depends on whatcombination we are looking for out of 1, 2 and 5. For our Alu bikes, which have plenty of bb and torsional stiffness anyway, we go with a sloping toptube (or a dropped toptube on the tri bikes which has the same effect) to get a bit more seatpost compliance.
For the steel frames, this is not necessary and so we can increase the torsional stiffness by keeping the toptube horizontal, especially nice for the twisting and turning on rough roads.
For the new carbon frame, the seatpost compliance wasn't an issue but we did want to get the highest possible bb stiffness, so we opted for a sloping frame.
Gerard Vroomen
3T.bike OPEN cycle