look171

Why is it important to have this little spacer on top of the stem for carbon steer tube? Do steer tube have to run all the way through the stem for even camping pressure to prevent cracking of the steer tube?

commo_soulja

Is that what the fork manufacturer is recommending? If so do it, or face the wrath of the bike wrench gods.

Seriously though, I'd do it. Seems like the right thing for carbon steerers. FWIW, I don't have any bikes with carbon steerers. YMMV

look171

I actually do not know what the mfg's suggestions are. I see people have them all the time. I did it only because I was afraid that I would need the extra space under the stem one day when I get really old. I have always want to cut it flush because I think it looks ugly. I have to look at it every time I ride it. If it was in the back, I could not care less.

HillRider

As long as the top bolt of the stem is completely covered by the steerer tube, it isn't essential to have the steerer project above the stem to the point of needing a top spacer even for a carbon steerer. None of the makers I'm familiar with insist on a top spacer.

However, it still a good idea and a worthwhile safeguard and I do it on all of my steerers, both carbon and metal. On the carbon steerers it assures the stem is fully and completely supported and on all of the steerers it gives me the option of raising the bars a bit if I ever decide I need to.

bradtx

look171, While it is aesthetically more plesant to have the stem flush, it does lock the rider into a situation where possibly the only available adjustment is downwards. Not good if you wish to simply raise the handlebars or install handlebars with a deeper drop, for instance.

Brad

fietsbob

Not the spacer per se, but the gap that the top cap has above the steerer tube,
that is required to pull your headset bearings into adjustment.

Once the stem bolts are loosened to do the adjustment , it's just another spacer.

Now by putting the spacer on top of the stem, it sits proud, above the end of the steerer tube,

when the stem is tightened again it grips the steerer tube and maintains the adjustment.

Whole surface of stem and steerer tube meet.

It would function just as well if the top edge of the stem
were 4,5~6mm above the end of the steerer tube.

Looigi

Some manufacturers specify that the steerer extend beyond the stem and others don't. Probably best to go with the recommendation of the fork/bike manufacturer for your specific fork. It certainly doesn't hurt for it extend beyond the stem. Either way, you need enough clearance between the steerer and the cap so that you can tension the headset bearing properly.

KenCarlson

If you want to lower your handlebars, how about avoiding the spacer issue altogether and just get a new stem with a different angle? You can even get a stem with an adjustable angle if you aren't sure what height you want for the handlebars.

https://www.specialized.com/us/en/bc/...jsp?spid=57223

Ken