Son keen to try road biking ... he's 13, 5'6", growing fast, why size to look at ? Guessing 52cm would be good, but would he get away with 54cm and grow into it?
Cheers
You should be looking more specifically at the horizontal top tube length.
A 53cm ETT is probably the max I would ride being of the same height.
Without the frame looking obviously over-sized for somebody of this height you would probably be best off looking at a compact geometry.
Something like a Giant Defy springs to mind.
w/r to the Giant geometry - whereas I would ride a Size S (46.5cm ST 53cm TT). Your son may get away with a Size M (50.0cm ST 54.5cm TT). You could then compensate for the longer TT with a shorter stem and/or inline seatpost.
I would imagine the Size M would go all the way to about 5ft 10in (give or take).
My wife is maybe 5"8 and can ride my 56cm TT bikes happily. My Medium Giant TCR is a compact frame and could have a lot less seat post showing and would be I'm sure fine for someone much smaller.
thanks, really helpful. Compact would be good and appreciate the TT consideration ... more just a start point as we'll be going second-hand so trying not that easy!
I am 5'7" and am a road rider first and foremost. I have two roadbikes, a 50cm and a 52cm, however more importantly the top tube length on both bikes is 525mm and 535mm respectively. I run a 100mm on both bikes. Both are a lovely fit, but possibly the 525mm with a 100mm stem is marginally better for me. If I was inbetween sizes I'd sooner stick a 110-120mm stem on the 525mm than go with an 80mm on the longer bike. Hope this helps