Cannondale System Six sizing/Who's 6ft and rides a 58?

I’ve got a Giant Propel in a size ML and I’ve got an option to buy a System Six in a 58 frame. The other night, I rode one of the club members SS which was in a 56 and I felt a bit cramped. I obviously just hoped on his bike and didn’t change anything. For context I’m 6ft and my inside leg is 35"

I’m 6 ft and feel that I’m often between a 56 and 58. I just look at the geometry table and go by stack and reach. Stack tells me, generally how many spacers I’ll need under the stem and reach tells me what sized stem I’ll need.

So comparing the two, it’s really 8mm on the top tube and 20mm on the stack. So if I slammed the stem, it’s nearly the same. Hmmmm

Slammed stem and maybe 1cm less in stem length will get you really close. Remember that spacers also reduce total stack because they are pushing the bars backwards. I think it’s 3mm per 1 cm of spacers so if you had 30mm of spacers on the smaller bike, you’d have to shorten the stem by another 9mm. (something like that. you might want to look up the exact details)

FWIW, I just went through this and bought a 58 instead of a 56. (Tarmac SL7)

I’m also 6’0 and have ridden 58cm frames for 20+ years.

If I were a better road racer, I’d ride a 56cm for the shorter headtube and get a longer stem, but alas, I am not.