datepalm3@earth

I'm going to begin building a new bike this afternoon (after headset is pressed at LBS), and I'm really uncertain about where to begin with the steerer tube length.

The LBS will install headset and star-fangled nut, but if I'm walking in there with a raw frame and fork I've never ridden, how do you even determine upfront the general length that the steerer tube needs to be?? I'm sure it does need to be cut some, but again, I'm not sure how to ballpark this and it would also seem to affect where the star nut is placed.

Is it normal to start by not cutting anything and just use a ton of spacers?? If I do that, it would then seem like once I do get the bike more assembled (wheels, stem, handlebar) and have a better idea of steerer length, that if I need to cut it, the star-fangled nut would probably need to be driven down further...is that the correct way to do things?? I'd also like to have this pretty set before I start installing cables/housing as cutting an inch or two from the steerer might affect them as well.

If you can offer any advice on the proper protocol or order of doing this I'd really appreciate it.

Thanks

Svr

Leave the steerer un-cut and the star-fangled nut out.

Assemble the bike as normal, install the crown race, and with the fork/headset/stem assembled as tightly as you can get it, decide what stem height and spacers to be used (if any).

Mark the steerer, remove the fork, cut the steerer and install the star nut.

It may see like a bit of extra work, but it's the only way to be sure the fit is right. You can also cut the steerer an inch longer and fill the extra space above the stem with spacers to allow a bit of stem adjustment in the future.

CdCf

Mount the stem and bar and use cheap spacers to fill the stack. Do mount brakes/shifters/brifters, but don't install cables yet.

Move the stem up and down through the stack and sit on the bike (use a trainer or something else to hold it upright with you sitting on it) and find a suitable position. Do an initial cut slightly higher than that position (cut steerer tube first, pound the star nut out of the cut piece, then install in the shorter steerer again). Alternatively, you could just stick the steerer through the headtube, put the stem on loosely and see if you have a ridiculous amount of excess tube, and cut it based on that.

Mount everything, including cables (make sure you have enough cable to be able to move the bar/stem to the highest stack position) and take the bike to a finished state. Ride for a while and see if you feel comfortable in the lowest possible position in the stack. If you do, you can probably cut a little more of the steerer tube, depending on how much you left in the first place. Drive the star nut down just past where you intend to cut, and then cut the tube.

I left about 3/4" above the stem when I cut one recently, and now have two 10 mm spacers above the stem (the stem is as low as it can get).

Sheldon Brown

Yes, if you use a star nut. I strongly advise against cutting the steerer before you have ridden the bike for quite a few miles.

If you use a pinch-clamp, you can omit the spacers and you'll be easily able to adjust the stem up and down on the bare steerer as you try actually riding with various positions.

See: https://sheldonbrown.org/iro/584/pages/09.htm for an illustration of this approach.

When you do finally cut it, leave it a little bit longer than necessary, as your preference may change over time.

Don't worry about that. Cables are cheap, and at worst you would just need to shorten them anyway.

Once you cut the steerer, however, that's it.

Sheldon "You Can't Cut It Longer" Brown

onbike 1939

^^^^^ That is an elegant solution and one that I could have used in the past.

probable556

Favorite Sheldon nickname.

bellweatherman

Be very careful with this very technique. It is very dangerous especially if you are using a carbon steerer. Almost all seat clamps come with a lip on the inside of the top of the clamp. It's design is for the seat clamp to stay put at the top of a seat tube.

1 - That lip, when clamped down hard, is going to put a nasty mark on a carbon steerer tube. I absolutely guarantee it. 100% positive. One of the guys in our club did this. Try it if you don't believe me. You will put a scoring mark on your carbon steerer tube and with enough use and repetitive stress, that carbon steerer tube will break exactly where the mark is.

2 - In the event that the bolt breaks or is stripped during riding, your clamp loses its holding power. Your fork goes sliding out until it bottoms out at the stem and you will most likely crash. If you insist to use this technique at all, best to use two of these clamps instead of one.

There is soooo much that I have learned from Sheldon's web pages, but I just cannot agree with this technique that I see as quite dangerous.

Sheldon Brown

I always strongly advise against buying a fork with a plastic steerer.

Right, a seatpost clamp won't work for this application unless you file off the lip. It won't fit over the steerer.

Oh, give me a break!

What if the pinch bolt on your handlebar stem "breaks or is stripped during riding" and your handlebars start flopping aroung? This just doesn't happen.

In the inconceivably unlikely event that the collar (which is under MUCH less stress than the handlebar stem) should fail, the fork couldn't slide out as long as the front wheel was on the ground! The only effect of this would be that the headset would get loose, hardly a crisis. This is an imaginary "problem."

Sheldon "Why Borrow Trouble?" Brown

Al1943

When working with a carbon fiber steer tube you need a good 1/4" drive torque wrench. You only need 5 nm of torque on the stem pinch bolt. Do not go by the torque spec shown on the stem. Trust me on this.

Al

bellweatherman

I think that a person should file the lip of the seat clamp in this technique, but you never mentioned this before until I pointed out the potential safety issue especially with carbon steerers being nicked with a scoring mark which could lead to eventual steerer breakage. It would be easy to dismiss this as a problem with carbon, whereas I see it as a problem with this dangerous technique. The average Joe wouldn't even know to file the clamp lip unless told to. In fact, if I am not mistaken, you have the lip still on the seat clamp on your own bike. Without filing the seat clamp's lip, it is still very easy to pry open a clamp a smidgen and slide it down the steerer.

With all due respect to your fantastic website and helpful crib sheets, I just can't go along with what I see as a safety issue, especially not without advising people to do this without extra precautions.

Sheldon Brown

You are mistaken. That's not a seatpost clamp, it's a clamp made for use on a steerer, though a modified seatpost clamp could be used for this.

I never advised using a seatpost clamp for this purpose, though it is certainly possible to do so.

If someone tried to use a seatpost clamp with a lip, it would immediately become obvious to anybody with half a brain that the lip would need to be filed off. I don't believe that it would be "very easy to pry open a clamp a smidgen."

I have updated that page with a warning not to use that technique with a plastic steerer.

Sheldon "Metal Is Good" Brown
https://sheldonbrown.org/iro/584/pages/09.htm

bellweatherman

It would be very easy to slip a 28.6 seatpost clamp over a 28.6 steerer, even with the lip of the clamp. In the old days, people had to slightly pry open the stem clamp to fit the stem around the bends of a handlebar to put it in position. Was it hard to do? No. Simple penny trick between the bolt and clamp and tighten the bolt to widen the clamp. How hard was that to do? So, how hard would it be to do the same or similar to open up a 28.6 seatpost clamp over a 28.6 steerer? Easy.

I'll concede that you know more about mechanics than myself or most, but don't insult me. That "half a brain" comment is not appreciated.

Sheldon Brown

I wrote:

If someone tried to use a seatpost clamp with a lip, it would immediately become obvious to anybody with half a brain that the lip would need to be filed off. I don't believe that it would be "very easy to pry open a clamp a smidgen."

Actually, most folks don't know that rather obscure trick. That trick only works on stems (or seatpost clamps) that have the female threads cut directly into the part, as opposed to using a separate nut. (Actually, a nickel is better than a penny for this, pennies are pretty soft...;-) )

Stems don't have a lip like seatpost clamps do. The lip is for the specific puropose of keeping the clamp from slipping down over the tube.

The seat clamps I've dealt with have been pretty beefy and pretty stiff.

I think you're being a bit touchy here. The "half a brain" comment clearly wasn't intended to apply to you, as it is obvious to you, as it is to me, that the lip would need to be filed off to use a seatpost clamp for this purpose.

I think it would be equally obvious to anybody with enough on the ball to install a headset.

Sheldon "Adjustable Stem Height" Brown

doggo

Oh, if only I could get my money back from the LBS that cut my steerer tube after I told them not to. When I get my new fork, I'm going to insist that they install a new headset & crown race at no charge, then never go back.