Road bike sizing

[Dicky DQ]

On 10/17/2022 at 1:47 PM, Dappere said:

Sure, let's say the OP went with that logic. Aggressive = smaller frame, Endurance/upright = larger frame. 

OP goes for aggressive setup (smaller frame), gets a bike setup and the stack of the bike is too small to get them into the correct position, OR,  OP goes for an endurance/upright setup (larger frame) and has to run a 70mm stem to get into the correct position. 

In order to make decisions on frame size, you need certain guides, guides that a bike fitter could provide, and can save you the hassle of having to sell a bike you just bought. 

Hmm, even if he/she went to a bike fitter and they were between sizes the above still applies. The bikes are a size. So you still need to work within the confines of the frame sizes. 

Old school still works to get to the basics then if you want go to a bike fitter for the detail.

 

[Eldron]

10 hours ago, guidodg said:

BTW a Large Giant TCR has a 58cm top tube...you are referring to 53cm seat tube but all the other postings in this thread are about top tube which is the way road frames are measured nowadays

I am 178cm and rode a Giant M\L which has a 56,5cm top tube...

Since a lot of modern frames are very sloping [thank you Giant] the seat tube measurement means very little...reach and top tube is everything

Top tube is not the way frames are measured these days. Nor is it everything.

Top tube suffers from the same "sloping frame" induced problem that the seat tube does.

The Giant you mentioned above doesn't state whether it is actual or effective top tube length... Canyon Grizl uses actual, Trek Madone uses effective. It's a mine field.

Using a single metric like top tube (whether effective or actual or unknown) to pick frame size is ridiculous.

Plus - without knowing your torso and arm length how do you decide on the right length top tube?

Let's use you as an example - at 178cm Giant recommend the M or the M/L - what data did you use to choose between the two?

[Eldron]

3 minutes ago, Dicky DQ said:

Hmm, even if he/she went to a bike fitter and they were between sizes the above still applies. The bikes are a size. So you still need to work within the confines of the frame sizes. 

Old school still works to get to the basics then if you want go to a bike fitter for the detail.

 

Each manufacturer makes effectively 3 style of road bike: Aero/sprint, endurance and lightweight/in between,

Trek it's: Madone - Domane - Emonda

Canyon: Aeroad - Endurace - Ultimate

Giant: Propel - Defy - TCR

A fitter should measure you up and let you know which geometry suits you best.

Picking a bike then making yourself fit onto it is a terrible way to buy a bike - we do it because we fall in love with a particular brand and model but it isn't the best way to buy a bike.