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I have an Anti-Gravity fork that features a removable steer tube, but it is a threaded fork. Where can I buy a threadless steer tube to clamp into it to convert it? All I can find are threaded steer tubes or steer tubes pressed into a specific crown.

Here's a picture of the fork: http://www.retrobike.co.uk/forum/files/antigravity_fork_728.jpg . When viewed from the rear, by loosening two bolts I can remove the steer tube (it's already 1 1/8"). Do most forks not do this? Why aren't these more common?

This seems like it would work just fine: http://www.onlinemetals.com/merchant.cfm?pid=6997&step=4&showunits=inches&id=71&top_cat=60 , 1.125" OD, with 0.065" walls for a 0.995" ID would that be close enough to put the threadless cap inside?

Essentially, I'm looking for two things:

1) Where can I get the 1" ID 6061-T6 Aluminum, and

2) Why can't I find this by searching for 'threadless steerer tube'?


Here's a picture of my fork specifically.

Anti-Gravity Fork

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2 Answers 2

2 things:

While many older forks used replaceable steerer tubes, the steerer tube is still specifically shaped for that fork. Tubing will not do it. You need an oem replacement steerer tube. Nobody makes forks like that anymore, hence the lack of google results.

Also, that steerer tube in the photo looks to be steel, and should not be replaced with aluminum.

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1) What shaping would there be? It's 1.125" from bottom to top? –  Ehryk Apr 1 '12 at 6:11
    
2) What would be the problem with replacing it with aluminum? I know they use aluminum steer tubes with 1.125" OD and 1" ID, so the strength of 6061 aluminum should be adequate. –  Ehryk Apr 1 '12 at 6:14
    
3) I already ordered it, 1.125" OD .995" ID, and plan on doing the conversion. I'll post results/pictures when it's done. –  Ehryk Apr 1 '12 at 6:14
    
I don't have your fork in front of me, so I can't be certain, but most alloy steerer tubes are reinforced heavily at the point that they enter the fork, and most steerer tubes have a "collar" of metal machined on the bottom end, where the fork crown rests. Also, most alloy steerer tubes are tempered to resist the forces required of them in a bicycle environment. Material choice is not just about size. You may be fine. But have you ever seen someone whose fork separated from his bike at high speed? I have. He wasn't pretty, anymore. –  zenbike Apr 1 '12 at 9:45
    
The Antigravity forks have that collar as a separate piece surrounding the 1.125" tube, which then clamps into the crown. How else could it be reinforced? T6 is the strongest temper for 6061 aluminum, en.wikipedia.org/wiki/6061_aluminium_alloy#6061-T6 . –  Ehryk Apr 1 '12 at 21:23
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Resolution:

I ordered the 6061-T6 aluminum, and compared it with an aluminum steer tube and I clearly saw the internal difference of the butting. I would have also needed to lathe a groove into the tubing for the shims that surround it for the fork.

Luckily, however, I found someone at a LBS that had some Anti-Gravs in back and sold me a steel threadless steer tube ready to rock for it, so I've abandoned the aluminum retrofit. It does look that in this case, because of the surrounding shims, I could have pressed/hammered some 0.995" OD steel tubing up the bottom of it (like they did on the steel ones) and been fine.

On a side note, I really appreciate this design. I realize that it may be some extra weight to have the two bolts, but given the pain in the ass of having too short a steer tube in a threadless system, making fork swaps painful, I would gladly take the weight hit for the ability to replace the steerer tube only, not half the fork.

The Anti-Gravity forks accommodated both 1 1/8" threaded and threadless, and 1 1/4" systems with this design (and possibly 1" systems as well). Outdated, but I appreciate their thinking!

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