I used to braise Kart frames and although they were made in a Jig- The distortion was so much that we had to use sledge hammers to get the frames out of the jig. Tig and Mig welding were a godsend when it became a viable "Cost" option as the distortion was never as great.

OK, got it.

Here's the next question: How do you measure frame size if the TT is sloped?

My 2011 Specialized Tarmac is a size 56.5. The "effective" top tube length is 565 mm. Specialized says the "TT is measured horizontally from center of HT to center of ST". So I guess the effective top tube length is the new frame size measurement.

“Virtual” top-tube is the same as “Effective” top-tube which is equal to “Horizontal” top-tube.

“Actual” top-tube is the length of the sloping top-tube.

Effective top tube is an important measurement. It can be treated the same way you would the actual top tube length of a horizontal top tube frame. Nominal frame sizing is still generally based on seat tube length. Many frames in the 56-58cm range have top tube and seat tube close to the same measurement. Of course, with the shorter seat tubes of compact frames, both seat tube and top tube may be virtual measurements rather than actual. Confused yet?

I think this question is best answered only if asked by a trusted urologist

When I ordered my Rodriguez fixie in 2009, I ordered it with 2mm of "negative" slope - it's slightly lower in front than in back. The idea was to allow for different fork heights keeping the top tube relatively level.

Besides traditional aesthetics (I grew up with level tt bikes thru the 70's - 00's), the level tube is an advantage when you are stopped and you want something to rest against. With a level-tt bike, you can:

a) stand astride the bike with one foot clipped in, and rest that thigh on the top tube without having to bend your supporting leg too much. You can then rest your elbows on the brake hoods. Quite comfortable as a resting position!

b) you can get off the bike completely and use the bike as a portable rail. You just turn and sit on the top tube while you hold a brake lever with one hand (you can even squeeze it to keep the bike from rolling), and rest your other elbow on the saddle! With a slanting top tube, the sittable portion is either too low or you slide sideways on it.

So yes, there are good reasons for the level top tube besides the aesthetics.

Luis

Good point! The level top tube on my Bridgestone RB-1 came in very handy on that day on BRAG in '92 when we stopped at a rest stop in Braselton, GA. We were greeted by Kim Basinger, who basically owned the town. After my friends and I flirted with her for a while, she said she wanted to ride a bike. I had the quickest reflexes and offered my bike. She immediately realized that with the dress she was wearing, she would not be able to straddle the bike, so she sat on the top tube and I pushed her around the parking lot.
I have carried a camera on every day of BRAG since not having one that day.

Right here, courtesy the wonderful Sheldon Brown.

Wonder how much the bike flexes when hammering out of the saddle?

I have no trouble touching my toes to the floor while standing.

After looking at yours I had to go look at a picture of my Roubaix, could have sworn it was level. I am on vacation and have a different bike with me.

Here is the Roubaix.

Then again, the Sirrus seems to have a slope as well