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The debated steerer tube extension...

kuksul08

Monkey
Jun 4, 2007
240
0
I posted this on MTBR a while ago and pretty much everyone disagreed with the whole idea. Many believed I was putting my life in danger for such a critical area.

Anyway, the story in short was I bought my vp free used. During a complete rebuild I found the steerer tube to be about 3/4" too short, so it barely stuck into my stem.

I could have bought an integrated stem for $20, pressed in a new steerer for $60 or bought a new lower crown for $100 (rough estimate prices). But... I decided to do it my own way :monkeydance:

Short steerer:


First I machined a very simple stepped cylinder at the lathes here at school out of a piece of 6061-t6 aluminum.



Then I pressed it in with a hydraulic press using loctite made for permanent sleeves:


The little thing had a very minor wiggle when it was being pulled on at the end of my bars, so we had to weld it. Our friend did a tig weld all the way around with full penetration (bye-bye heat treatment)...but a few minutes filing off the excess weldment and:


(I also had to round off the inside edge of the top to clear the top cap...)



It's been holding perfectly for several months and I think it's stronger than the original. The added weight from the thickness is negligible. So yea... thought I'd share because I'm bored :busted:
 

freeridefool

Monkey
Jun 17, 2006
647
0
medford, or
Im impressed. As I was reading about the welding part I was thinking bad idea. But it looks really clean and it is probably stronger as stated. I machined a whole steerer tube for my dorado, so I can relate to where you are comming from.
 

kuksul08

Monkey
Jun 4, 2007
240
0
Well....after about 3-4 hours of riding and safely making it the whole time without crashing, I ended the whole day with a nice crash while doing wheelies...right on my back on the asphalt.

The bike flipped up and landed all the impact on the bars and seat.

I thought the stem just slipped on the steerer but...




I guess they heat treat it for a reason! Oh well...

Now to buy some risse crowns or, if anyone has one for sale, a lower crown with steerer :)
 

kuksul08

Monkey
Jun 4, 2007
240
0
lol...how does that make me lucky? It never would have broken under normal use. When I flipped back and all 43 pounds came crashing down on one of the bars it really tweaked it bad. I'm wondering if a normal steerer would have been bent or cracked as well.

Oh well...I can't turn my head because my neck hurts too bad
 

DirtyDog

Gang probed by the Golden Banana
Aug 2, 2005
6,599
0
Well.... that was an interesting experiment. Just glad I wasn't the one testing that :D
 

kuksul08

Monkey
Jun 4, 2007
240
0
Haha yea, double thread action going on here...

It was totally solid the whole time I used it, never had a problem until it landed on there today...ugh

And believe it or not, the carbon fiber bars are unscathed. Azonic ST-1 are BEEFY, they've got aluminum collars near the ends and also where the stem attaches. me like:)
 

CrabJoe StretchPants

Reincarnated Crab Walking Head Spinning Bruce Dick
Nov 30, 2003
11,569
422
Groton, MA
lol...how does that make me lucky? It never would have broken under normal use. When I flipped back and all 43 pounds came crashing down on one of the bars it really tweaked it bad. I'm wondering if a normal steerer would have been bent or cracked as well.
Force due to your weight >>>> force due to weight of bike only.

The bars hitting the ground with the weight of the bike behind it experiences a fraction of the force of you applying a downward force on the bars when landing a drop.
 

kuksul08

Monkey
Jun 4, 2007
240
0
Force due to your weight >>>> force due to weight of bike only.

The bars hitting the ground with the weight of the bike behind it experiences a fraction of the force of you applying a downward force on the bars when landing a drop.
Good point, but all of the bike force was on one side of the end of the bars, and it twisted it too. Usually I have both hands on the bars when landing equivalent-force jumps, and I'm not twisting at the same time.

Either way, I guess I am lucky :busted:
 
Sep 20, 2007
443
0
Champaign, IL
You are extremely lucky. The force of you doing any sort of serious riding on it would have without a doubt been greater than the bike falling on the bars. I think you should take physics before CAD. Haha Props for trying though.
 

kuksul08

Monkey
Jun 4, 2007
240
0
You are extremely lucky. The force of you doing any sort of serious riding on it would have without a doubt been greater than the bike falling on the bars. I think you should take physics before CAD. Haha Props for trying though.
Haha yea, I've pretty much finished physics and statics. One would think the force from me riding would be much greater than the bike falling. Sure, it's a ton more force on the bars and fork, etc, but its all evenly distributed and the steerer doesnt take too much of it above the upper crown (aside from some torsion from steering and maybe a little torque from the length of the stem)

When the bike flipped it had a bit of speed going, and only hit on the left side of the bars. It would be the equivalent of me hitting it with a sledge hammer on the very end of the bars. If it would have landed with the bars straight, I doubt the steerer would have been affected.

That said, I knew going into it I would lose the heat treatment on the metal and it would be a lot weaker on the weld. Since the weld area is clamped by my steerer and the majority of the forces on the steerer normally are sheer and at the headset contacts, I knew it would be safe to ride. I guess I didn't factor in crashing :lighten:


To be honest here, I'm surprised it broke, but even more blown away that my carbon fiber bars are unaffected. I have inspected them closely and can't find any damage at all. +1 for Azonic ST-1 strength I guess.
 

kuksul08

Monkey
Jun 4, 2007
240
0
Someone from MTBR was generous enough to actually give me a new lower crown with steerer. It just arrived today after 2 weeks in the mail...hell it's in better condition than the previous one, 8" steerer too.