Inside leg

First frame build project imminent and i want to get my geometry and tube lengths right.advice warmly received!

http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

If you do nothing else, download and read the pdf guide and referring to it accurately measure your inseam and use the formula (Greg Lemond method) - inseam x 0.883 = BB centre to seat top. Deduct approx 20cm to get seat tube size centre to centre, but obviously there's more to it than just seat tube length (but saddle height is one of the most important things for good fit). Note this is for traditional geometry frames (horizontal top tube), so called compact geometry frames refer to their sizes differently.

I used that fit n so far so good, was riding 57ctt, now a 62cm and no more neck ache, seems to me a lot of people riding old steel frames with far to much seatpost which is not the way the geometry is designed to fit. Neck ache gone, now need to sort knees. BB centre to seat top seems to be the key, but not by using tons of seat post on a horizontal top tube frame.

^ Sound advice - in among the science there's still a lot of sense in the old approach of 'largest frame you can comfortably stand astride' when it comes to getting a comfortable ride position, especially if you have any tendency toward back or neck problems. Just be aware that generally the bigger the frame to longer the reach as well, and there's a limit to how much you can adjust that with stem length. That said it's not uncommon for larger frames to have shorter top tubes.

@chaliapin
How much seat post pokes out from the top of a horizontal top tube frame makes no difference.

The saddle is going to be at the same height relative to the pedals regardless that you are riding a 57ctt or 62ctt.

If both frames share the same seat tube angle ie 73 degress then the saddle will be at the same spot relative to the BB.

What wont be the same is the head tube height, IE on your 62cm frame it will be taller than your 57, so you probably wont be bending down as far and trying to raise your head to compensate (which would give anyone a sore neck)

@ the OP a critical, but often over looked measurement is top tube length,
and this is dependant on your torso to arm length ratio, and also how flexible you are and what type of riding you'll be doingr.
A shorter top tube length (all other things being equal) will generally give you a more upright stance more suited to everyday and longer rides.

Sadly there is not a lot you can do about this when buying a pre made frame as a shorter top tube will most likely be on a frame with a lower seat clamp.

Shortening a stem is not the same thing as riding a shorter bicycle, although reach will be reduced.

looks like Retro' got in there as I was typing

@ chaliapin, knee probs could be caused by saddle still too low, you could also try increasing set back slightly?

Regardless of frame size, I have allways (initially) set up my saddle height by multiplying my inseam by 1.09 and using that as distance between pedal and saddle, and then tweaking (slightly) as needed.

But surely a lot of seatpost on a horizontal toptube frame means shorter headtube and a greater saddle to bars drop? AH, you said that (re-read), that was all I meant by a lot of seatpost, obviously makes no difference to the legs, but does to the bar height. Will experiment with saddle height and set back, am no expert as many on here but just sharing experience and research.

Steve Hogg would be having a fit at the above posts

He's more into balance and centre of gravity than measurments, but I suspect he's fine tuning those systems; they can be out by 2cm . My saddle height is less than what the lemond method . Worth looking at.

BTW - I have the DVDs if you are interested.

gre4at to read these...ride on

Ta for this guys, great to have this debate. I am thinking that balance, centre of gravity, tube lengths, seat post outage, stem angles and protrutions and rider style all come into play here, but to what extent each factor has may be key to deciding where to chop my tubes!
I do have 6 weeks before the hacksaw blade goes in though so lots of research still on!

Peter, i am interested in the DVDs. I will pm you my mobile.