Joined: Aug 2003
Posts: 3,520
Likes: 12
From: Colorado Springs, CO
Bikes: 1959 Bottecchia Milano-Sanremo (frame), 1966 Bottecchia Professional (frame), 1971 Bottecchia Professional (frame), 1973 Bottecchia Gran Turismo, 1974 Bottecchia Special, 1977 Bottecchia Special (frame), 1974 Peugeot UO-8
Originally Posted by
LesterOfPuppets
Support a 5ft long 2x4 with two cinder blocks placed under the ends. Stand on it mid span. Measure distance to ground. Do the same with an 8 ft long 2x4.
Assume we'll make two frames out of straight-gauge tubing one with horizontal TT and one sloping. Now consider that you'll have 4 tubes shortened by using a sloping top tube design, assuming all tubes on both frames meet in a fairly typical seatcluster.
Which one would be stiffer?
Sure, the front triangle would be moving away from the "ideal" equilateral triangle, and on smaller frame sizes, the rear triangle would be, but for larger frame sizes, the rear triangles would be moving towards that ideal.
Ok, but the 5ft 2x4 is going to fall on the ground because the cinder blocks can't move. In other words, take a bare seat tube of say 56cm and stick a seat post in it extended out about 10cm and rest the ends on the cinder blocks. Now take shorter seat tube of maybe 48cm or so and a longer seat post so that they both extend to 66cm. AND, make sure they weight the same - that is, use a lighter seat tube for the 48cm one such that the combination of the seat tube and heavier seat post weigh the same and then push on them and see what the deflection is. At any rate I think, as caterham has been pointing out, the interaction of all the various parts is probably more important than any one tube being shorter.
Short of a bicycle engineer coming along to add his 2 cents I think we've beat this topic to death.
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1959 Bottecchia Milano-Sanremo(frame), 1966 Bottecchia Professional (frame), 1971 Bottecchia Professional (frame),
1973 Bottecchia Gran Turismo, 1974 Bottecchia Special, 1977 Bottecchia Special (frame),
1974 Peugeot UO-8, 1988 Panasonic PT-3500, 2002 Bianchi Veloce, 2004 Bianchi Pista