Bike Sizing?

biggoffy

Following a rather strange failed secondhand bike buying experience yesterday can someone(s ;-) ) give me a sanity check on how the size of a road bike is determined?

I have always used the seat tube length (latterly the effective length) as the headline measurement.

However the Ebay seller, a local cycle retailer, insists that the correct method is by top tube effective length and that this has always been so!

Result was that I went to collect a lovely 58cm Secteur, only to find a 61cm one awaiting me :-( MUCH too big.

Thanks, Goffy.

N0bodyOfTheGoat

Stack (horizontal plane distance between bottom bracket and top of head tube) and reach (vertical plane distance between bottom bracket and head tube centre) is the modern way of sizing.

My Cube is a 58cm, which would be too big for me in other brands but Cube have rather odd frame sizing specs (not one tube is 58cm on the bike), given I'm 178cm tall with a small cycling inseam of ~83cm.

imposter2.0

biggoffy wrote:

Following a rather strange failed secondhand bike buying experience yesterday can someone(s ;-) ) give me a sanity check on how the size of a road bike is determined?

I have always used the seat tube length (latterly the effective length) as the headline measurement.

However the Ebay seller, a local cycle retailer, insists that the correct method is by top tube effective length and that this has always been so!

Result was that I went to collect a lovely 58cm Secteur, only to find a 61cm one awaiting me :-( MUCH too big.

Thanks, Goffy.

Simplistically (without getting into the complexities of stack & reach), the measurements you need are seat tube, top tube and head tube (most of those should be available online anyway). Seat tube measurement on its own may not give you an accurate picture of the frame size, so the guy you were talking to is broadly correct...

kingrollo

I always use a combination. To select the closes size for me I aim for top tube of 535-545 - next I look for a head tube of around 145 +

Then look at stack and reach (not that these are any less important)

Its best to have some idea what these measurements are on your current bike.

mariamartinez

use your main contact points centered on the BB: bars / pedals / saddle. If those dont work (and cannot be adjusted) then bike is wrong size

mfin

Horizontally, If you're not looking at reach and are going by ETT instead, then you have to take into account seat tube angles.

Vertically, if you're not looking at stack and are going by head tube length, then you have to take into account bottom bracket drop.