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Threaded Steerer question(4 posts)

Threaded Steerer questionEd
Mar 6, 2001 7:56 AM
From previous board,
If I have a threaded fork that after cutting does not have much threading left, what options do I have? What is the minimum amount of threading required for a standard headset? Any big cons to adding a spacer, or what about having additional threads cut - what kind of $ are we talking about and do most lbs's have the die tool?
re: Threaded Steerer questionSpoke Wrench
Mar 6, 2001 9:32 AM
You said "standard" again. "Standard" doesn't go with bike parts. Very, very often, new bike parts will be just enough different that they won't work well, or at all, with the rest of your bike. Surprise! Your new upgrade turns out to be a downgrade. You can almost never change only one part on a bike. It almost always affects something else.

Now to answer your questions.

The threads have to go far enough down the steer tube so that the upper headset cone will screw down enough to provide adequate pre-load against the bearings. When you have done this, you need to have enough threaded steer tube sticking up for a washer and so that your lock nut will almost, but not quite bottom against the steer tube.

Most people do this by trial fitting the components. A more elegant way is to accurately measure the height of your bike frame's head tube. The paperwork that comes with new threaded headsets will have a "stack height" measurement. Add your headset's stack height to your headtube height. That sum is your minimum steer tube length. Headset stack heights can vary from 30mm to 42mm or about 1/2". That's too much difference to just cut your steer tube and assume that every headset is going to work.

Most new forks come with about 1 1/2" of threads cut. If your upper headset cone will screw almost all of the way down, you can add a spacer which will allow you to tighten your lock nut snugly against the rest of the headset components. Otherwise, the lock nut will bottom against the steer tube before it locks the headset cup into place. That's the only difference a spacer makes.

I would think that older bike shops would be more likely to have fork thread dies than newer ones that specialize in mountain bikes. I'd expect to pay in the $30.00 to $50.00 range to have an additional half inch or so of threads cut into a steel steer tube. It takes a fairly expensive tool that doesn't see much use, and it's pretty physically hard work.

If you have average mechanical ability, this is going to be one of those jobs that is more complicated to talk about than it is to do. Once you trial fit everything together, you will immediately see what you have to do to make everything fit. It's not that hard.
As always, your advice is appreciated, thanks Spoke Wrench (nm)Ed
Mar 6, 2001 12:01 PM
nm
re: Threaded Steerer questiongrz mnky
Mar 6, 2001 1:38 PM
Just to emphasise what Spoke Wrench said:

Keep an eye on being able to get the upper race cup threaded down enough and also having the lock nut not bottom out. Both of these conditions will lead to a loose fork which may not be noticable until you start riding.

I bought a used bike where this was over looked and it took a little bit of investigating to figure it out. Adding a few extra threads beyond the minumum required will not hurt you.