Originally Posted by
bruce19
I started riding back around 1980. I knew nothing about cycling. So, I bought Greg LeMond's book. In it, and other books, I read two things that still ring true. The first is that there are a range of frame sizes that can work. The French, Competitive and Eddie fits. The second is that the way to get into that range is to measure your inseam...socks w/no shoes...convert to cm and multiply by .667. That will give you your base frame size when measured Center to Center. Funny how it still works for me.
With respect and no quibble it works for you, it may not apply to others. But yes, old stand by of .667 x inseam will fit a large population of riders. But the landscape is quite a bit different today with un-square frame proportions aka endurance geometry frames many seek for a bit more upright position. Skewing of this proportionality may work well for a given rider or may work against them...depending on torso to leg length ratio. So selecting frame size today in particular with all the different geometries available is a slippery slope. But never been a better time to buy a bike today with all the frame geometry options. Issue is...sorting through the complexity what may work best for a given rider.
As an example, I am longer of inseam and shorter of torso. A Roubaix will fit me identically to a Tarmac for another rider the same height with opposite proportions aka long torso and short inseam.