Worst place to save weight, this is genuine!

Discuss light weight issues concerning road bikes & parts.
youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

CallumRD1 wrote:Just the opposite. Because there are bearings on both sides of the holes acting as fulcrums, that portion of the steerer tube will be flexed whenever load is applied to the fork.


That's not quite right. Most modern headsets use angular-contact cartridge bearings that don't permit the bearing to transmit bending moment very well. Because of this resistance to moments, modern headsets (and most headsets period) can't act as fulcrums because they resist bending forces. By definition, a fulcrum prevents translation while permitting rotation. Annular-contact bearings as used on modern headsets constrain the steerer in both translation (sliding up and shown in the head tube) and, to a significant degree, in rotation (except for rotation about the steering axis).

If the headset bearings only had point contact with the steerer tube, then they wouldn't constrain rotation and things would work more or less as you describe. But 1.5" lower bearings with 6-8 mm of steerer contact length resist any significant angular displacement of the steerer tube.

They don't permit the "flex" you're postulating, at least not in the way you describe. Putting a normal riding load on the fork and bars will only cause relatively small bending stresses in the drilled part of the steerer. Big bumps and crashes are another story.

The problem is, the person who developed the fork probably knew this and didn't put much excess material in the drilled part of the steerer. In other words, those are load-bearing holes. Fulcrums or no, drilling your steerer like this is really dumb.

CallumRD1
Posts: 118
Joined: Mon Apr 03, 2017 2:54 pm

by CallumRD1

You're completely correct. I wasn't think about how much contact the lower bearing has with the bottom of the fork. I was thinking more along the lines of the upper bearing which has little contact with the steerer tube and thus does little to prevent it bending. As you point out, the lower bearing provides the necessary rigidity.

by Weenie


Alexandrumarian
Posts: 167
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Sure human stupidity is greater than the universe but this might be a hoax. Probably dropout area was damaged in a crash and guy drilled the holes to make a viral pic. Which is as stupid as thinking 2 grams is worth it. Could shed more by sanding the finish...

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bikerjulio
Posts: 1901
Joined: Fri Dec 11, 2009 10:38 pm
Location: Welland, Ontario

by bikerjulio

CallumRD1 wrote:Just the opposite. Because there are bearings on both sides of the holes acting as fulcrums, that portion of the steerer tube will be flexed whenever load is applied to the fork.


Agree. The only steerer tube failure I experienced was on a generic carbon fork exactly in the middle of the head tube. Right where those holes are.
There's sometimes a buggy.
How many drivers does a buggy have?

One.

So let's just say I'm drivin' this buggy...
and if you fix your attitude you can ride along with me.

http://www.youtube.com/watch?v=GekiIMh4ZkM

tarmackev
Posts: 235
Joined: Sat Jan 15, 2011 9:59 pm

by tarmackev

Alexandrumarian wrote:Sure human stupidity is greater than the universe but this might be a hoax. Probably dropout area was damaged in a crash and guy drilled the holes to make a viral pic. Which is as stupid as thinking 2 grams is worth it. Could shed more by sanding the finish...

Not a hoax, a guy in his late 50's, 90kg. New-ish to cycling, apparently a nice guy who likes to do hill climbs but always finishes way down the rankings.



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Alexandrumarian
Posts: 167
Joined: Mon Mar 28, 2016 6:34 pm
Location: Romania

by Alexandrumarian

Just yesterday i shortened a canyon steerer. The piece had more surface than those holes and was 3 grams. The interesting part is that i crushed it in a vise and it had to go very oval before fibers started to snap and delaminate. Then it sprung back to round. I then did it from the opposite direction and the same. It still feels pretty solid, these thing are really impressive. Still drilling it is beyond...more so at 90k. I'm over 90 and i simply live with the fact i'll never be fast on long hills even if the aliens sponsor me with a 500g bike.

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