Why are locknuts on threaded stems capped?
 

I'm installing a new threaded fork on my old Trek 470. Now, as per usual, the stem is longer than it needs to be, and in theory, I simply need to cut it down to account for the particular headset I have. Now, I'm wondering to myself... Why on earth is the locknut capped? i.e. the locknut is designed so that it can't be screwed down below the top of the threaded stem. I'm very tempted to just replace this type of locknut with a normal nut. There is of course an advantage in the design of the locknut, where it has a rubber seal, and will stop dirt etc from going down the tube. But I'd just throw on an O-ring to act as a (reasonable) seal. I can certainly see that having a cut down stem and tidy locknut arrangement is cosmetically pleasing, but that doesn't bother my. Any ideas/comments?

Regards,

Stuart

Maybe to make it easier to screw it down, without risk of over-tightening?
Some headset systems have non-capped locknuts. You could use such.

You are aware you are questioning the cycling gods with this question. And cyclists are turning over in their graves, just imagining bikes with anything besides a proper lockring. You may even be seeing some of their ghosts.

Only problem I see is that you may have some rust on the inside of the steerer. Also perhaps some wobble from the stem the the cap would minimize, being I believe a touch smaller ID than the steerer. (I haven't checked that but it would make sense to have a nice clean smooth chromed surface to contact the jewel of a stem rather than a crude hacksaw cut steerer the may well not have been cleaned up much after cutting.)

All smaller issues than angering the cycling gods which could have serious consequences.

Ben

The headset pieces combined total up to what is called the stack height. When the new fork is installed the steerer tube is cut to a length that allows for the stack height + the length of the head tube through which the steerer passes. Normally, that steerer length is cut to be a millimeter or two shorter to allow for that top nut to clear the top of the steerer. If yours does not you should be able to add a spacer to the stack and use the nut that goes with the headset.

Stack height woes, alas, can keep one awake at night. Be thankful that your steerer tube is too long. I'm not sure why the lock nut has that lip, but it does result in a clean look.

If the locknut won't thread down far enough, put a spacer under it to adjust the engagement. I would not cut the steerer down to exactly match your current headset unless you are absolutely certain you will never replace it with one with a taller stack height.

If you d cut it down and have issues with enough stack height later, you can go with the Tange headsets. They make a cheap OEM HS with very low stack height (but no seals) and several others with varying stacks. The headsets mix and match well. The cheap HS (~$8) is actually a decent HS if you run a fender and pack the bearings with marine grease as well as being a good source of low stack non-bearing parts.

Ben

Actually not all top/lock nuts are capped. Most are but some Asian ones have had a "rubber" seal acting as the cap portion and are easily removable. Also some cheap US made top lock nuts have had no lip or cap.


As to why- I suspect it's a nicer look thing. Andy.

have you considered a Spacer under the top lock nut? if your bike was intended for center-pull brakes
but you did not fit the cable hanger, then there would be more steerer than headset stack uses , then ..

you add a spacer.. in its place..

Yes, the reason for the cap is to be cosmetically pleasing and to protect the threads a bit from corrosion. Allowing the nut to go further down would result in exposed fork threads above it, which are ugly anyway, and worse once they rust.

All you have to do is to cut the fork to the proper length, leaving a mm or so beneath the cap. If you want to allow for a possible larger stack in the future then just add some spacers under the locknut and cut the fork that much longer.

Using a 1" diameter headset spacer is your easiest solution to the problem of a too-long fork. Cheaper, faster, and better looking.

Consider using this space to add a bell?

http://cdn3.volusion.com/ctxtv.wmppt...jpg?1474043677

Good idea! :thumb:

Is that spacer from a grip-shifter mount?

There are a few companies that make headset spacer mounted bells. Mostly marketed for threadless stems, but if you have a too-tall threaded fork they work great. Just be sure to get the 1" version or an appropriate shim.

VO Spacer Bell Mount - Bells - Accessories

Dimension Headset Spacer Bell: Black

Portland Design Works Alexander Graham Bell Steerer Tube Mounted Bell

The bell in the pic is either a Portland Designworks Alexander Graham Bell or a Crane Suzu Mini Lever Strike bell. They are identical in design.

The video is of the Crane bell on my fixed gear bike. The lever strike overwhelmes the microphone on my iPhone but the sustain gives and idea of the musical quality of this bell.



-Tim-

There's a sound structural reason for the locknut to be "capped" (in the OP's words). It may not be as relevant these days, but historically the fork had a keyway milled into it. This weakened the tube and made it vulnerable to splitting if there ther radial loads applied from the inside.

The locknut is capped to reduce the ID to a close running fit on the stem, so as to support it against the side loads as the bar is worked. without that radial collar, the effects of stem flex would be taken up by the fork, and might split it at the keyway. As it is, even with "capped" locknuts, I still run into split forks from time to time.

-----

IMO you aren't going to fine a commercial nut with 1"x24tpi threads that easily. If you have a aluminum lock nut, you can always ream out the hole to 1". But an easier, sounder solution would be to stack spacers on the fork so the locknut fits properly.

Thanks guys. I think it's safe to say that I've managed to tap into a wealth of knowledge in this headset arena! As suggested by most, I'll head down the path of cutting the stem a bit too long, and just use a spacer or 2. Plus of course, it will look a whole lot better than what would otherwise seem a cheap solution with excess thread sticking out the top of a non-capped nut. So, I'm about to embark on the, "measure twice, cut once" method of cutting my stem.

Cheers guys.

Stuart

Just a side note having little to do with anything.

The stem is generally refers to the part holding the handlebar to the fork.

The part you're talking about trimming is the steerer tube, or just the steerer.

It really doesn't matter, but it did create some confusion, and I, for one, had to think a bit before I figured out what your problem was, and almost didn't post on the thread.

I think you hit the nail on the head: The capped nut is meant to protect the fork tube & threads from damage.

Apologies for my rubbish misuse of bicycle terminology (aka stem v steerer(tube)). Yes, it is indeed the steerer I refer in terms of cutting. Plus additional thanks to FBinNY & sreynolds1977 regarding general protection of the steerer and thread. Anyways, will make the cut w spacers.

Regards,

Stuart

The nut is capped to hide the butcher job done when trimming the steerer tube with a hacksaw. ;)

I like That One..

My top lock nut includes an O ring, keeps water from leaking down around the Stem, so It isn't so rusty so quick.




:innocent: