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Road bicycle handlebars fitting

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BikeGremlin

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I got this question in the "(Road) bicycle frame sizing and stem length" YouTube video comment section (quoted hyperlinks to the video and the article are mine - for context):

Love the channel, each video is great and I'm very grateful for your efforts, as I'm learning a lot. Just to clarify - in the video you're viewing the axis from the hoods grip, eyeballing the correct stem length, but in the article, you're mentioning the grip from the drops to do this. Which is correct? In any case, it seems to me like this method only works when the fork is straight and not having a curve like with the old models...
 
Solution
There are two things to discuss here:

The optimal method​

As far as the optimal method is concerned: eyeballing from the hoods will result in a shorter stem, compared to eyeballing from the drops.

With modern "compact" handlebars (and huge hoods of modern STIs) that difference is very small, but it is still worth mentioning and can be noticeable.

For riding on the road (especially if the rider is fit and flexible), the drops method will be better. For riding off road/gravel (or for the less flexible riders) the hoods method will be better (for most riders). It boils down to whether you want the stem to be on the shorter side (better for...
There are two things to discuss here:

The optimal method​

As far as the optimal method is concerned: eyeballing from the hoods will result in a shorter stem, compared to eyeballing from the drops.

With modern "compact" handlebars (and huge hoods of modern STIs) that difference is very small, but it is still worth mentioning and can be noticeable.

For riding on the road (especially if the rider is fit and flexible), the drops method will be better. For riding off road/gravel (or for the less flexible riders) the hoods method will be better (for most riders). It boils down to whether you want the stem to be on the shorter side (better for off road riding in my opinion and experience).

Another caveat is the handlebar height. A vast majority of road bikes and cyclists have the handlebars set too low (for the rider's flexibility and riding style), so riders almost never ride in the drops. Such riders may also prefer the hoods eyeball method (it will make the bars more comfortable for them).

Fork shape​

Old forks were made of steel and had the lower section curved towards the front and thinner. Why?

The lower section was thinner to minimize weight. With rim brakes, you could afford to use weaker lower fork section because the loads and the torques were not huge in the lower fork leg section (see disc brake forks section of the frame design article for more details).

The reason for curvature was to achieve the optimal steering (it affects trail to put it briefly). With stiff disc brake rigid forks, and with suspension forks, this is achieved by making the entire fork legs start at an angle, right from the crown. Old rim brake steel forks started in line with the steering column and then curved at the bottom section.

So, those are two ways to achieve the same wheel position. That is why the fork leg shape does not affect the optimal stem length.

Final notes​

This "eyeball" method is a rough guide to get the ballpark stem lenght. It often happens that a +-1 cm (or even a bit more) stem length ends up with the wheel's axle blocked from view (i.e. being optimal according to this method).

So, the method is not a be all end all, but more of a way to get a decent starting point, and do fine adjustments from that point.

Relja
 
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