The Wheels of Chance

With my new Neo Primato frame due next week I thought that I’d discuss how I chose the size 54cm and talk a little about bike fit. I’m in the enviable position of having a few bikes and so I should know what size fits me, and I do up to a point. You see all my bikes have the relaxed geometries of tourers or sport touring bikes. They have 72ish degree seat and head tubes, long chainstays, 43 or 44 cm and slightly upward sloping top tubes. The result is a stable ride with the handlebars about level with the saddle. The fit is what would be described as French. This is an old school relaxed position favored by touring cyclists and randonneurs. There are two other generally accepted fits, “The Eddy”, named after Eddy Merckx, is more aggressive with the bars a few cm below the saddle and the most aggressive fit is the “Racer “or “Competative” fit which might have ten or more cms between bar and saddle height. I am not a fan of the Competative fit for recreational riders as it often causes back and neck pain and there’s no point to it’s questionable speed advantage if you aren’t racing. So with my Neo Primato I decided to go for an Eddy fit. Why not the French fit like my other bikes? Well the Neo Primato’s geometry just isn’t set up for a really relaxed riding style as it has fairly steep head tube and seat tube angles, short chain stays and

Neo Primato Geometry (from De Rosa)

the horizontal top tube means that it is difficult to get the bars up to saddle height without having ridiculous amounts of stem showing or getting a bike that is simply too big. To decide what size of frame I needed I started with my Pubic Bone measuerment which is the length from the pubic bone between your legs to the floor. For me that’s 81cm. This is short for someone of my height of 5′ 10″ (178 cm). I then subtract ten cm to find my seat height which is the distance form the center for the bottom bracket and the top of the saddle measured parallel to the seat tube. A further subtraction of 15 cm gives the bike size that I like measured to the top of the seat lug. For a more race fit it’s better to subtract 16 or 17 cm. Given that I like a saddle height of 71cm and I’m comfortable on a 56 cm Rambouillet (measured from center of the bottom bracket to the top of the seat tube lug) I decided to get a 54 cm Neo Primato. De Rosa measures its bikes from center of the bottom bracket to the the center of the top tube and seat tube intersection, so a 54 cm De Rosa is equivalent to a 56cm Rambouillet as it’s 1.4cm to the top of the top tube from its center and say another 0.5cm to the top of the seat lug. However, the 74 deg seat tube angle puts the seat tube and top tube intersection about one cm higher than my Rambouillet. With all these angles and triangles, Euclid comes into his own. Some calculation shows that the 54cm Neo Primato and the 56cm Rambouillet stand over heights at the middle of the top are both 80 cm with the top of the Neo Primato top tube at the head tube beingone cm lower than that of the Rambouillet. The Rambouillet also has a couple of cm head tube extension to get the bars up further giving the French fit. So the top of the Neo Primato head tube will be about three cm below that of the Rambouillet and the top tube is also one cm shorter so that I will have to use a slightly longer stem to get the fit just right. It looks like I’ll be able to get the handlebars to within three cm of the saddle without showing unsightly amounts of stem, however, there’s a final quirk as Rivendell tends to have long steerer tubes and puts 12 or 18 mm of spacers in the headset. But I have that covered as De Rosa tells me that the steerer is long enough to add a few spacers as well. So all should be good for my Eddy fit. Of course after all this calculation and measuring I went down to the local De Rosa dealer and got fitted. He set up the 54cm Neo Primato geometry on an adjustable geometry bike and I rode for a while. It felt good.