Frame Size	Top Tube (effective)	Head Angle	Seat Angle	Chainstay	BB Drop	BB Height with 2.5′s
16in	23in	67.5deg	73deg	16.73in	0.8in	12.4in
18in	23.5in	67.5deg	73.5deg	16.73in	0.8in	12.4in
20in	24in	67.5eg	74deg	16.73in	0.8in	12.4in

That’s the numbers as most manufacturers will display them on their site. We’d recommend sizing by HEIGHT though – not top tube length. NOTE :: our numbers displayed above are “SAGGED” geometry, with you sat on the bike, an 140mm fork, set at 40mm sag.

Sizing advice:-

16in – from 5’5″ to 5’10″
18in – from 5’10″ to 6’2″
20in – from 6’1″ to 6’5″

With a 140mm fork topped out gives a standover of the following.

20in – 32.9in standover (120mm head tube)
18in – 31.9in standover (115mm head tube)
16in – 31.0in standover (115mm head tube)

Frame size dimensions are measured from the centre of the BB shell to the TOP of the seat tube (where the post comes out).

Riders coming from some brands may be puzzled about our shorter-than-they-are-used-to top tube dimensions… But if you have a compare with the “new” way to measure dimensions (below), you’ll understand more. As our frames have steep and steeper seat angles (bigger frames get steeper seat angles), this means that larger riders are sat a little more forward than on a lot of frames. We do this to move weight from the back of the bike, forward. To keep your front tyre weighted for steering and grip, to stop you looping out backwards on climbs… Nobody else does  this (yet) that we’ve seen, but it seems pretty obvious. Tall riders with long seatpost extensions don’t want to be way back over the rear wheel (unless you really like doing wheelies).

Also, if you’re into new ways of measuring things – Try this – it’s the new way, apparently. Makes sense!

See more here – http://www.sicklines.com/2008/12/18/reach-and-stack-a-good-idea/

Centre of the BB to the top of the head tube – horizontal and vertical = reach and stack.

You need a plumb bob.

Here’s what numbers come out, unsagged on a Ragley mmmbop, Ti or Blue Pig.

16in – 23in top tube, 73deg seat angle.
reach = 390mm, stack = 576mm (140mm fork)
reach = 378mm, stack = 584mm (160mm fork)

18in – 23.5in top tube, 73.5deg seat angle.
reach = 408mm, stack = 576mm (140mm fork)
reach = 396mm, stack = 584mm (160mm fork)

20in – 24in top tube, 74deg seat angle
reach = 424mm, stack = 581mm (140mm fork)
reach = 413mm, stack = 589mm (160mm fork).

And finally, for those that want it, go on then… here is the geometry UNSAGGED – with a 140mm fork, topped out, and 2.5in tyres. Some companies claim to use this for their frames, but it makes no sense to us here.

Frame Size	Top Tube (effective)	Head Angle	Seat Angle	Chainstay	BB Drop	BB Height with 2.5′s
16in	23.3in	65.6deg	71.1deg	16.73in	0.2in	12.9in
18in	23.7in	65.6deg	71.6deg	16.73in	0.2in	12.9in
20in	24.2in	65.6deg	72.1deg	16.73in	0.2in	12.9in