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Granted I am not a mechanical engineer, but we're talking about extending the steer tube 1 inch! I'd like to hear how my mod, which is a copy of a commercial product, is unsafe. If I get a good answer, I'll take it off.
FYI, the "commercial product" isn't that safe either. Its not intended for mountain biking and it is a band-aid fix to a bigger problem.
 
There are several reasons not to do this, but the biggest one is that there are two different torque requirements here - one to secure the wedge inside the fork, and one to set the bearing preload. You can't get two different torques out of one bolt. If you tighten it enough to keep the wedge secure, your headset will be too tight. If you get your headset just right, the wedge will work loose.
 
This seems a logical useful option when you think about the stresses involved. There isn't much trying to pull your fork down out of the head tube. All the force pushes it into and up.
I've pounded tech sections for lots of miles over time with a stem gabbing with just the lower bolt.
Zero problems even through crashes. The bars would show looseness side to side before they would pop off anyway.
Everything is dangerous if you don't think about it for a minute.
Except when bunny hop those kids or pull a wheelie to get your front tire over a obstacle.
 
There are several reasons not to do this, but the biggest one is that there are two different torque requirements here - one to secure the wedge inside the fork, and one to set the bearing preload. You can't get two different torques out of one bolt. If you tighten it enough to keep the wedge secure, your headset will be too tight. If you get your headset just right, the wedge will work loose.
^
This chap's got it. If you could isolate the steer-tube extension clamping forces from the bearing pre-load forces, you'd be a happier camper. I'd test to expected load conditions or failure and figure out if that's acceptable or not before riding too much. Don't forget about fatigue, corrosion, etc . . .
 
I had to follow the link to option #3 to figure out what you were building. Basically just trying to copy their idea. Problem is, is your version isn't solid, that 1 1/8" "shim" is what you're clamping your stem to? It's split. For $20 you could have bought option #3, which is still a bad idea in my mind, but much safer. You're playing with a chunk of real estate that takes one hell of a beating, even on an xc bike.
 
Discussion starter · #33 ·
Wow... I was looking at some of my old threads and saw this. Thanks for the concerns, btw. It's been a year since I did this mod and so far, so good. I've been riding the bike about 10-15 miles of moderate trails (Lake Chabot, all the trails of Joaquin Miller including Cinderella and Chaparral) and it's performed admirably. Surprisingly, I've got her just a shade under 25 lbs right now. As I said in the beginning, I took a calculated risk but felt it was safe enough based on the stem I had and the amount of steerer tube I had left (I know guys who run equally short steerer tubes without the mods I did and they're also good so far).

Anyway, I DON'T recommend doing this, especially if you're not comfortable with your work or don't understand the physics and mechanics involved. Caveat Utilitor.

And no, I don't baby this bike on the trail. I suck at going uphill but I love the DH. This is my regular ride:


Here she is (sub $500 build, under 25 lbs, 1 X 10 set-up)
 

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