Fork Spacers Above The Stem

[cachagua]

I was reading the pamphlet that comes with a carbon fork, and it said you must always have a 1cm spacer above the stem. Never heard of this before. My bikes w/ carbon forks have no room above the stem for adding a spacer... does this mean the stem clamp is going to crumple their steerers like a drinking straw under a pickup's tire? Or is it just CYA for the manufacturer?

[Kontact]

Originally Posted by cachagua

I was reading the pamphlet that comes with a carbon fork, and it said you must always have a 1cm spacer above the stem. Never heard of this before. My bikes w/ carbon forks have no room above the stem for adding a spacer... does this mean the stem clamp is going to crumple their steerers like a drinking straw under a pickup's tire? Or is it just CYA for the manufacturer?

Was the pamphlet for the model carbon fork that is on all your bikes?

That's a specific instruction for a specific fork. I would follow the instruction for that fork on that fork.

[cadence90]

Originally Posted by cachagua

I was reading the pamphlet that comes with a carbon fork, and it said you must always have a 1cm spacer above the stem. Never heard of this before. My bikes w/ carbon forks have no room above the stem for adding a spacer... does this mean the stem clamp is going to crumple their steerers like a drinking straw under a pickup's tire? Or is it just CYA for the manufacturer?

A bit of CYA, but definitely not entirely. I think using a top spacer is a prudent practice.

The main reason for the top spacer is that it is not ideal to have the upper stem/steerer bolt extremely close to or flush with the cut end of a carbon steerer, since A) cutting the steerer badly can leave some of the fibers exposed and vulnerable, and B) over-torqueing the stem/steerer bolts can then stress those fibers. A), B), and even A) + B) are not so uncommon, unfortunately.

Basically, the top spacer ensures that the force of the stem bolts is away from the cut end of the steerer and is better distributed against the steerer. Also, chances of the stem rocking (especially a longer stem + heavier rider) are (slightly) decreased.

As far as top spacer height is concerned, 10mm might be slight overkill, but ~5mm above the stem is good. The top spacer height also depends somewhat on where the top stem/steerer bolt is located. On some stems (i.e. Thomson) that bolt is near the top of the stem while on others (i.e. Moots) the bolt is further down, which would allow a slightly shorter top spacer.

On the other hand, too much spacer above the stem (say 25-30mm) is not good because some expanders (the tune bung for example) are really short, and so the stem bolts might clamp against the steerer tube only. For all these reasons I prefer longer (50-100mm) expanders such as the old Specialized (very hard to find now), Deda, Colnago, Columbus, Fouriers.... These essentially guarantee that the stem bolts are being fully resisted by the expander inside the steerer, sort of like nailing through drywall to a stud, rather than only through drywall.

All that said, if a stem is flush with the top of the steerer, but the fork has been cut well and the headset, stem, and expander have been installed correctly, there really is no reason to be overly concerned.

So, top spacer = partially CYA, but is a good idea.

Originally Posted by Kontact

Was the pamphlet for the model carbon fork that is on all your bikes?

That's a specific instruction for a specific fork. I would follow the instruction for that fork on that fork.

10mm sounds like Whisky.
Whisky's rec is steerer end 7-8mm above top of stem and a 10mm top spacer.
ENVE's rec is steerer end 1mm above top of stem and a 5mm top spacer.
Etc.

Those are fairly minor differences to me, and so I wouldn't be worried even if those dimensions were switched.
.
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[oldpotatoe]

Originally Posted by cachagua

I was reading the pamphlet that comes with a carbon fork, and it said you must always have a 1cm spacer above the stem. Never heard of this before. My bikes w/ carbon forks have no room above the stem for adding a spacer... does this mean the stem clamp is going to crumple their steerers like a drinking straw under a pickup's tire? Or is it just CYA for the manufacturer?

CYA mostly with modern, well made carbon steerers..I built with 5mm(not 1cm) above so entire fork steerer thru the stem clamp. Use a torque wrench, you'll be fine.

[lhuerta]

....also, b sure to remove any burrs/rough edges from ur stem. Use fine emory/sand paper and smooth all inside edges of steertube clamp area , otherwise, rough edges might damage ur carbon steertube (do same for handlebar clamp end if ur using carbon bars). And finally, and most importantly, remember that the max torque stamped on side of ur stem is NOT recommended torque...it is instead max torque rating of the bolts.

[FlashUNC]

ENVE specs a spacer above the stem. Ain't no big thing.

[PacNW2Ford]

[QUOTE=lhuerta;2280128]....also, b sure to remove any burrs/rough edges from ur stem. Use fine emory/sand paper and smooth all inside edges of steertube clamp area , otherwise, rough edges might damage ur carbon steertube (do same for handlebar clamp end if ur using carbon bars). And finally, and most importantly, remember that the max torque stamped on side of ur stem is NOT recommended torque...it is instead max torque rating of the bolts.[/QUOTE]

Good point that all of 5 N-m or printed spec isn't necessary to secure the stem, but the last part isn't correct.

[pdmtong]

another way to think about it is that by having a 5mm spacer above the stem you ensure the 100% of stem has a clamping interface to the steerer. this should be best practice.

10mm above IMHO is overkill

FWIW I have had the top cap flush to the stem with no issues. But, note, I am 170#s rec rider not twisting the bars a lot while riding and not winding up for my mega-watt sprint.

while it is ideal to keep some expander inside the steerer where the stem clamps, often times it may not be desireable. take for example the case where the stem has 5-10mm below and you may want to leave some spacers above the stem (yes, aesthetic fail) to age with the frame or maximize the potential resale population (I would probably have bought more of ryun's cast offs if only he had left some steerer. at his saddle, i can handle 8.0 drop but NOT 10.0+...)

[yashcha]

Looks like the pro vibe and zipp sl stems do not require the spacer to be on top. I wonder what is different about these stems. The looks is so much cleaner without the soacer above the stem.

[zank]

The Vibe is designed to allow you to use a battery in the steerer tube. It has a little port to allow the wire to enter the stem before putting the special top cap on. You need to cut the steerer 3 mm below the top of the stem to make it work. They make a profiled spacer that allows you to put spacers above the stem, but you can no longer mount the battery in the steerer.

[arik]

I do it and I appreciate the ability to raise the bars a few mm if I need to tweak things.

[R3awak3n]

I have always had a spacer above stem. Not only it does not bother me, I don't mind the look (then again I also always have some spacers under the stem).

I have either a 3mm or a 5mm over the stem. On carbon, never was a problem.

[lhuerta]

[QUOTE=PacNW2Ford;2280293]

Originally Posted by lhuerta

....also, b sure to remove any burrs/rough edges from ur stem. Use fine emory/sand paper and smooth all inside edges of steertube clamp area , otherwise, rough edges might damage ur carbon steertube (do same for handlebar clamp end if ur using carbon bars). And finally, and most importantly, remember that the max torque stamped on side of ur stem is NOT recommended torque...it is instead max torque rating of the bolts.[/QUOTE]

Good point that all of 5 N-m or printed spec isn't necessary to secure the stem, but the last part isn't correct.

NOPE, your mis-read/misinterpretation of spec printed on side of most stems is PRECISELY why so many hamfisted DIY-ers end up with crushed steer tubes. The spec stamped on the side of most stems is indeed max torque rating of the bolts, and should never be interpreted as recommended torque. The correct torque needed to install a stem is simply the torque necessary to mate stem with steertube and hold it firmly, without exceeding the max torque rating of bolts stamped on side of your stem (and without exceeding max clamping torque on steertube, in those cases where a manufacturer has specified).

When u purchase a stem from manufacturer X, they do not know the specific spec of the steertube on which you will install the stem, and cannot account for production variances of the steertube diameter, thus the reason they only stamp max torque value of bolts. In other words, when mating two parts, if you reach the max torque rating of bolts and parts is still not held firmly, then that is a NO GO install.

[Bob Ross]

btw, just to throw a wrench into this common practice: Cannondale (possibly still now, definitely back in the mid 2000s) explicitly recommended not having a spacer above the stem on their carbon forks. Clearly their star nut widget is the odd man out.