Lbxpdx

How much space can the stem clear above the steerer tube?

my stem is a few mm’s below the top, and I only have one spacer to move which is less than I want. I heard something along the lines of 1/3 the stem can be proud of the steerer tube, but I figured I would ask.

Thanks.

DaveSSS 

The top clamp bolt on most stems is quite close to the top of the stem. Many suggest that the stem sit 2-3mm below the top of the steering tube and
a 5mm spacer placed on top. None would suggest having the stem above the steering tube. Consider changing the stem angle to raise the bars.

I have published a method to lengthen a carbon steerer by 10-12mm, but it's a bit complicated to do.

dsaul

On a metal steerer tube, the stem can be above the top of the steerer, as long as the steerer is not below the top stem bolt. On a carbon steerer, the stem must not be above the top of the steerer and a spacer should be used above the stem.

Lbxpdx

thanks. I was hoping that was the case.

robertorolfo

I haven't heard this before. Do you have some sort of source?

dsaul

Source for what? For metal steerers the source is good engineering principles and common sense. For carbon steerers the source is any number of carbon fork manufacturers. The following was taken from the ENVE fork installation instructions.

• Carefully measure and mark the amount of steerer tube that you will need to remove. ENVE recommends that the steerer tube extend 1mm past the top of the stem and that a 5mm spacer be placed on top to ensure proper compression from the top cap.

Most other carbon fork manufacturers also recommend having the steerer extend 1 to 2mm above the stem and placing a 5mm spacer above the stem.

gsa103

The actual motivation is that the compression plug should be centered with respect to the stem bolts. Compression bolts can be kind of long, so adding a spacer raises the plug. Metal steerers use star washers, and don't need internal support to resist cracking.