Why do the frame sizes of the Dual have such a huge jump from 51 to 54?
What’s in the name? We can call the 51 a 52cm? The sizes are just names, what matters is the difference in toptube length between the 51cm and the 54cm is 2cm, which is what we feel a reasonable step. Any difference smaller than that would be less significant than the differences between various riders, your position on the saddle while sliding fore and aft, the weight shifts going from aerobars to basebars, etc. There is obviously no reason to have a toptube length steps smaller than these kinds of influences, hence we use around 1.5-2cm for the steps between sizes.
Gerard.
Indeed, my mistake, I misread the geometry overview. The more thanx for your extensive answer.