On the rivet's 56cm bike has 15cm head tube and 2.5cm spacers ....total 17.5cm
56 Domane has 17.5cm head tube......no different, if we ignore differences in headset/fork crown height....probably safe to ignore.
Paulatic's 10 year old bike......be useful to know head tube length. Also you say "75mm of steerer tube" . surely thats not 75mm of spacers under the stem? That would have been deeply unfashionable even 10 years ago on a road bike.
I don't think top tube length is the most important metric for a first road bike.rogerzilla wrote: ↑22 Jul 2021, 9:58pmTop tube length is the most important.
The ability to get the bars level with the saddle (or almost level) until the rider gets used to drop bars is likely to be more important.
Also frame reach is only 3mm longer on the 58 than the 56, but stack (head tube) is 20mm greater. THIS could be useful