I'm an inch and a half taller than you and plumped for the 18". You're right – you're right in between sizes, it all depends on what sort of ride you want. Judging by your comments, I really think you need to try one out for size. Not helpful in itself but realistic… Sorry………..

5'7" here and 16" frame. Feels long enough for a long ride but perhaps a tad too long as a mess-about-on bike.

harry too depends how you like your own bikes historically. Do you like the stretched out/XC feel? What have been your previous few bikes?

Harry too, where you at.? Can you meet up with someone who has one.?

As above – it depends on past history. I'm an inch taller than you but with long legs for my height so my "cockpit" needs will be about the same. My previous history is all road bikes and a xc orientated Scott strike pro. I have an 18inch (ti) with a 70mm stem and to start with it felt like a toy bike I was so upright. Got used to it now but I'm slowly building up another bike for more xc/ bridleway bashing duties and that will have a much longer cockpit for a more stretched feel.

Edit – the effective toptube length difference is only 1/2" so in terms of fit that next to nothing and a size up or down in stem will sort it. There is an inch and a bit in standover though, although both are enormous by old skool standards (as a cyclo cross rider, its positively luxury!), so I guess if you have shorter or longer legs for your height that should be the deciding factor.

I'm 5' 11" or 6' (can't make up my mind) and I have an 18" Ti and 18" steel 456, and with a 70 stem they are a good/reasonable fit. I run a straight post and can leave 10mm of rail clear at the back of a Flite Titanium saddle….. if I run a gobi saddle that has a significantly longer distance from end of rail to end of saddle then I have to jam the clamp to the back end of the saddle rail. I quite like running longer stems…90mm or 100mm… especially if I'm using 25.4 bars because it makes things less twitchy (maybe my imagination but with oversize bars I think shorter stems work better and feel more secure..less nervous and twitchy). If I do run a 90 stem on these 18" 456s then the saddle has to be rammed right foreward as far as it will go for me to get a set up where I can still get out over the back wheel for steep descents without lowering the saddle. I'm not a fan of perpetual saddle lowering stops and I'm not going to get an adjustable post until someone produces a decent one!
I've not tried but I reckon I would fit OK on a 16" 456 if I used a 90/100 stem and straight post, and definately ok with a 20mm layback post. I've measured the Thomson post I've got on the 18" and I have got enough length to allow for the extra 2" and still be an inch or so above the Minimum Insert marker.

Ramble, ramble, ramble……..

If I were you I'd go for the 16".

I think the 18" will be too big for you.

5'10" here, 33ish leg. Had 18" 456 which was spot on (had 80/90mm stem). Wife's 16" Inbred feels too small.

I've got a 16" standard Inbred and I'm 5'9"…I run a layback seatpost and 90mm so personally think I should have got the 18" but then there's only 0.5" difference in the reach between a 16" and 18" 456 anyway

You do like to be stretched out especially with a layback!!!

8)

….although 16" 456 is 23", 18" is 23.5". I've got a standard (albeit 853) Inbred which is 23.2" for the 16"

at 5'10 I would say a 18 I am 5'8" and I am top end of being ok for a 16 but the 18 is a bit too big for me

I live in devon if you want to try a 16 you are more than welcome

I'm 5'10" and have the 16" 456 frame. I had an 18" Inbred which felt a bit too long, not as well balanced when the wheels left the ground.

5 ft 10 and a bit with 33 inside leg. Had an 18 inch classic model a few years back and wish I'd gone for the 16 inch. I do prefer a shorter bike though.

I'm 5'4" with 30in leg and ride a 16in 456. Here's me on it :

70mm stem and inline post with saddle forwards. Personally I don't think they're that big. My others are a 16in Giant XTC which fits perfect and a 15in Rock Lobster which I have the saddle right back.

Kev

5'10 with 32' inside leg. Went for an 18 456Ti.

I would agree with the above. Don't stress about it too much. Both will fit. Depends on how much seat post you want to run.

Will someone buy my Velocity track/fixie wheels, 2xmountain king supersonic tyres and a Thule bike carrier please so I can order my 456 frame? 8)

I'm 5ft10 and ride a 16 inch 456, in-line seat post, 90mm stem (should probably shorten this a tad). I have a 31 inch inside leg. I use it as more of a fun bike than a racy bike and wouldn't want to go up to an 18 inch.

In comparison I also ride a 17 inch Kona explosif (1999, 100mm stem more racy setup) and a medium Enduro (2005, 70mm stem, playbike).

On the 456 I do need a lot of seat post for the ups.

happy hora will snap your hand off but buy a pink one and i can have yours and he can have mine 🙂 im five ten mate