In April of 2010 I purchased a new carbon fiber bicycle, a Rocky Mountain Prestige 70 CR. I had previously owned bike which was made from hybrid materials — part aluminum and part carbon and was looking for something with a better ride. This new frame was 100% HM Monocoque Carbon with other carbon components like a carbon fork (with a carbon steerer tube) and carbon cranks. The handlebars were alloy, which I prefer anyway. Rocky Mountain (based in Canada) is most noted for their mountain bikes, but they also carry a small line of road bikes too.
After two years of hard riding, this frame developed some hairline fractures (report here) and I consequently got a new frame under warranty. Because of this problem I decided to look at getting a titanium frame as they are more durable. During the summer of 2012 I found a used Seven Ti frame (Axiom SL). The geometry was just right for me with a 61cm top tube (1 cm longer than my carbon bike). I was hoping this would be my new long distance bike as Ti frames supposedly never wear out. Later that fall (due to the delays in manufacturing at Zinn), I built it up with new handlebars, new seatpost, saddle, custom 190mm extra long cranks from Zinn and new Shimano drive train & derailleur.
To make a long story short, in June of 2013 I finished my “long ride of the season,” a 1200km (750 miles in three days) brevet, called The Gold Rush, in northern California. My butt suffered big time, like my early days of cycling, before I converted to suspended leather saddles. During 2012 I used my carbon fiber bike (with an alloy seatpost) with the same saddle and wheelset which I used on Gold Rush and had zero saddle issues. Some two weeks after Gold Rush, I had a 600km, in which I switched back to my carbon bike and once again, had no problems.
My conclusion: A carbon fiber frame yields a more comfortable ride than a double-butted Ti frame. Are all carbon frames similar? This one is an average, run-of-the-mill Chinese made model ($3,000 MSRP including a $600 Ksyrium Elite wheelset which I only use for training rides). Could the longer cranks on the Ti frame be causing me butt pain?
Possible solutions? Add a carbon fiber seatpost to the Ti bike? Or a suspension seatpost (urrgh, the extra weight)?
Specs — 2009 Rocky Mountain Prestige 70 CR / 2000 Seven Axiom SL
Frame sizes (seat tube length, cm): 60 / 61.5
Horizontal tube tube (cm): 60 / 61
Head angle (degrees): 73 / 74
Seat angle (degrees): 72.5 / 72.5
Head tube length (each has 30-40mm extra height with spacers, cm): 23 / 20.5
Wheelbase (distance between axles, cm): 101.5 / 102.0
Chainstay length (cm): 41.8 / 41.3
Fork rake (mm): 45 / 41 (frame was designed around a 40mm rake, I am using a Alpha Q carbon fork on the Seven)
Wheelset: DT Swiss 1450 alloy with Continental 4000 S 700 x 25c tires inflated to about 100 PSI
Saddle: Gilles Berthoud Aravis suspended leather with Ti rails
Pedals: Shimano A520 / Shimano A600 road touring pedals
Aerobars: Syntace C2 / Syntace C3 mounted to alloy 44cm wide bars
Cranks (mm): 175 FSA carbon fiber / 190 Zinn