Can’t decide between the 16″ and 18″. Im 5’9.5 and wear 30″ inside leg trousers (although I tried measuring and got 32″). The guides suggest I am the absolute smallest an 18″ would fit but at the very top of the 16″.

Im thinking 16″ but only because the 18″ is out of stock. Am I going to make a big mistake with the smaller frame?

16 definitely

They’re so cheap if you decide you’ve bought the wrong size you don’t lose much dosh swapping out.

I would argue that unless you are going for the new swap dropout model they are a better buy lightly used by someone fickle from ebay or the classifieds on this forum.

Going for the carbon so not all that cheap and few appear in the classifieds.

5’9″ here mate and I used to have 18″ but way too big
So bought a 16″ 456 carbon you don’t realise this is the bike for me
Spot on !!!!!

5’11” and ride a 16″ summer season, you’ll be fine with a 16

I’m 5’9″ and had a similar dilemma…. I went for the 18″ with a 60 mm stem… very happy with it… sorry, I realise this contradicts a couple of others so probably doesn’t help you much!!

16

16 all the way. I am 5’10” and went for a 16″ C456. Plenty big enough.
devilman

16

…and he is back in the game 😉

I ride a 16in and am 5 ft 9in -perfect .

I got an 18″ summer season and then an 18″ 456C and I’m 5’10”. It fits fine.

I also tried my mates 456 in a 16″ and that was fine too.

Depends how much standover room you want/need and how short a stem you want to run. You’ll need a lot of seatpost showing on a 16″.

I’m exactly the same size as you and have a 18″ Summer Season which works great with a 70mm stem. Having said that i’ve longer arms than most and don’t like long stems for the sort of riding 456’s are best at.

I think Brant’s succinct reply might be the winner.

Will measure my current hardtail and FS for reference tomorrow but I would rather a small frame than one I am just in the right size category for.