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Handlebar relationship to front hub

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Handlebar relationship to front hub

Old 06-06-17, 04:16 PM
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Handlebar relationship to front hub

Random thoughts while riding today:

When fitting someone for a bike, one can usually achieve the same fit, roughly, with two different frame sizes and a different stem.

However, the handlebars will be located different distances aft of the hub/contact patch based on the frame size, if identical reaches are achieved. Similarly, different HT angles and rakes will change this variable.

So, is there a preferred distance for the handlebars behind the front hub for better centering weight on the frame between the two contact patches?

Yes, it was a ride by myself. The mind wanders.
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Old 06-06-17, 04:34 PM
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No.
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Old 06-06-17, 09:10 PM
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Your body contacts the bike at the hands, the feet, and the pelvis. Weight distribution relative to the feet is more important than relative to the wheels.

Last edited by oldbobcat; 06-06-17 at 09:21 PM.
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Old 06-06-17, 09:18 PM
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I used to read an old rule for determining stem length that said when sitting on the saddle with your hands on the brake hoods, the handlebar should "hide" the front hub if your stem length is "proper". I don't know how valid it is but it's something to consider.
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Old 06-06-17, 09:21 PM
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A racy, short-wheelbase bike will have the front hub closer to the center of the bike than other bikes. This is to make it handle in a racy way. To achieve the same fit on a racing bike that you have on other bikes, it is necessary to have a different handlebar-to-hub relationship. As the others said, don't pay attention to this metric.
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Old 06-06-17, 09:26 PM
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Originally Posted by oldbobcat
Your body contacts the bike at the hands, the feet, and the pelvis. None of these parts makes contact with the front hub.
True, but here's what I was thinking about as I was riding.

Imagine two frames with identical angles, but say 1 cm different lengths. (I'm too lazy to draw this.)

Frame A is 540mm ETT, Frame B is 550mm ETT.

You could achieve a 650mm total reach on Frame A with a 110 stem, and on Frame B with a 100 stem.

Only difference is that on Frame A, your center of gravity will be further forward between the wheels, and your handlebars 1cm closer to a perpendicular line running straight up through the tire contact patch/front axle.
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Old 06-06-17, 09:27 PM
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A bike that puts the handlebar too far in front of the front axle will have stability issues, but riders of normal proportions on fairly normally sized bikes will not find this a problem.
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Old 06-06-17, 09:28 PM
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Originally Posted by noglider
A racy, short-wheelbase bike will have the front hub closer to the center of the bike than other bikes. This is to make it handle in a racy way. To achieve the same fit on a racing bike that you have on other bikes, it is necessary to have a different handlebar-to-hub relationship. As the others said, don't pay attention to this metric.
I wouldn't say I'm really "paying attention" to this. Nice 35 mile ride today, alone with my thoughts, and I started musing about this, and bike geometry in general. Not the dumbest thing I've ever pondered on while pedaling.
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Old 06-06-17, 09:30 PM
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Originally Posted by Banzai
Only difference is that on Frame A, your center of gravity will be further forward between the wheels, and your handlebars 1cm closer to a perpendicular line running straight up through the tire contact patch/front axle.
You shouldn't be putting that much pressure on the handlebar anyway. A balanced rider's center of gravity is generally over the bottom bracket.
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Old 06-06-17, 09:30 PM
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Originally Posted by HillRider
I used to read an old rule for determining stem length that said when sitting on the saddle with your hands on the brake hoods, the handlebar should "hide" the front hub if your stem length is "proper". I don't know how valid it is but it's something to consider.
I wouldn't use it as a "rule" but many bikes that fit me well come very close to passing that "test". But I have also observed (for me anyway) that I can place the handlebar tops along a sloped line going from low and close to further forward and higher. For me, that slop is 2 cm horizontally by 1 cm along the steerer tube. (Very, very convenient!) Any bar on that line will have my arms with the same elbow bend and my shoulders and therefore, my overall body position, in the same place. Now, if you think about it, you can see with the right stem, you could position the handlebars on that line where it crosses your eye to hub view on any bike. (It might take a very creative custom stem.)

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Old 06-06-17, 09:37 PM
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Originally Posted by oldbobcat
Your body contacts the bike at the hands, the feet, and the pelvis. Weight distribution relative to the feet is more important than relative to the wheels.
Until you are cornering hard on a poorly paved mountain descent. Trust me, I know this. I've done those descents on both bikes with superb weight balance between the wheels and ones where that was sacrificed for other reasons. The former I raced and took many corners insanely fast and it behaved perfectly. I would have crashed many times trying to do that on bikes with poorer weight balance over the wheels.

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Old 06-06-17, 09:53 PM
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On my road bikes, the hub is always behind the line of sight to the handlebar. Different strokes for different . . . y'know. I use 12 and 13 cm stems, depending on the frame's reach dimension. The center of a bike's fit isn't the front hub, it's the relationship between the bottom bracket (feet), the saddle (pelvis), and the handlebar (hands).

The hips are positioned so the body's center of gravity is over the feet. The handlebar is positioned where the hands can use it most effectively. This is for control of the bike, pulling up and back for power, maintaining torso angle, aerodynamics, and support when tired. Some riders might find "hide the front hub behind the handlebar" works for them, but this is a side effect of their fit, not a cause or factor.
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Old 06-06-17, 10:00 PM
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My general fit algorithm is to first find a torso angle that works, based on the kind of riding you do. Then find a saddle position that lets you maintain this torso angle without using the hands. Then find a handlebar position that puts the bar where your hands want to find it.
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