Top Tube Length or Reach for New Frame

what brakes

Hi

What is the more important measurement for a new frame?

Cervelo claim that reach is the more important measurement than top tube length! However one companies frame for say a 55" the reach is 380mm while another 54" top tube the reach is 393mm!!! looking at other companies there seems to be anything upto 15mm difference in reach/top tube length to another comapnies!

So if you currently ride a 555mm top tube with say a 110mm stem. If you were to get a new frame would you go by the reach (which could in essence make the top tube 15mm longer or shorter depending on company) or the Length of the top tube?????

:?: :?: :?: :?:

Monty Dog

Reach is a combination of TT length, saddle setback and stem length. Bike fit is always done in the following order:
1. Saddle height
2. Seat setback - typically defined by rider's femur length (combination of seat-tube angle, seatpost setback and saddle)
3. Handlebar reach - rider size and flexibility

Therefore it is feasible to play tunes with these and achieve the same rider position, on frames with slightly different geometries - although they are likely to handle differently as a consequence. You can also take into account riding style and strength - a heavy rider with powerful quads will probably suit a more laid-back seat position that a lightweight gear-twiddler - the bike fitter needs to make a judgement.

In answer to your question - it also depends on seat-tube angle and saddle set-back

cookiemonster

Hi Monty Dog

Not quite right; "reach" is measured from the vertical above the bottom bracket to the top of the headtube, so does not depend upon saddle height or setback

See here: http://www.cervelo.com/en_us/engineerin ... entations/

To the OP; reach is more important, but only useful if you're using comparable headtube lengths (as the reach measurement assumes no spacers!)

jon

Berk Bonebonce

In respect of frame size, there was a time when people only really spoke in terms of seat tube length. But then came along sloping top tubes, and talking about frame size just in terms of seat tube length lost its meaning somewhat. The recent trend has been one of giving an indication of frame size by quoting 'effective horizontal top tube length', even if the frame in question has a sloping top tube. So, Cervelo are not necessarily saying that 'reach is more important', they are saying that 'effective horizontal top tube length' is a better index of frame size.

I've just bought a new carbon frame and didn't pay a huge amount of attention to seat tube length. Instaed, I paid more attention to the lenght of the top tube.

Added to the above comments is also the fact that seat posts can go up really high these days and this is down to the crossover with mountain bike commonents. Not that long ago seat tube length was critical because seatposts only ever came in one standard length - buy a frame too small in error and you had to get rid of it.

Monty Dog

They might be Cervelo's definition of reach and stack, but they do nothing to assist in getting the right fit - yer put the ar$s in the right place and work from there!

what brakes

the science of bike fit?!?!?!?!

My idea is similar to Monty.

Once you feel comfy on the saddle i.e knees not too far infront of pedals or too far back then go for reach to handle bars, not the reach from centre of bottom bracket etc... That way your legs/feet are where you feel comfiest.

To buy a frame blind then as above the top tube effective length is the most important?????

Berk Bonebonce

what brakes wrote:

To buy a frame blind then as above the top tube effective length is the most important?????

You miss the point. No one is saying that 'reach' is the most important factor when buying a new bike, least of all, I would think, Cervelo. However, if you are talking in terms of frame size, length of effective horizontal top tube is a key dimension because these days top tubes aren't horizontal anymore, they can join the seat tube at different angles, and because of this 'seat tube length' has become somewhat of a vague indicator of frame size.

cookiemonster

More importantly the distance bewteen saddle and bars is quite different between bikes with the same horizontal/effective top tube length that have different seat and head tube angles. So a cervelo with 73 degree seat tube, 73 degree head tube and a 56cm effective top tube will give a different saddle to bars distance than a trek, say, with a 74 degree seat tube and 72.5 head tube, still with 56cm effective top tube

The use of "reach" in the cervelo sense of horizontal distance from the bottom bracket vertical makes it simpler to compare across different frame angles

IMO you've got to take all three into account - reach, effective top tube and effective headtube (i.e. what head tube you'll run after you stick your spacers in, if any)

jon

on-yer-bike

A frame with a 74 degree seat angle and 555 cm top tube is effectively the same length as one with a 73 degree seat angle and a 565 cm top tube. This is why Cervelo talk about reach because it takes the seat tube angle out of the equation.

hopper1

Stack height and reach is the way to go for frame sizing.
I'll dig out a link to a data base, which lists loads of frames as "Stack height and Reach', to make life easier. It also allows for spacers!

I agree with cookiemonster about the measurements...

EDIT: Taken from slowtwitch.com