Bicycle Mechanics - Carbon Steerers and Spacers

I have a carbon steerer/fork with a compression plug setup. Right now my stem is sitting on top of all the spacers.

LBS told me that if I want to lower my stem/handlebars I can't rearrange a spacer or two on top of the stem, I need to have the steerer cut and the compression plug reset. If I don't get the steerer cut the stem would be putting pressure in an unintended area. Any truth to this, or can I simply move the spacers around as I see fit?

If I don't get the steerer cut the stem would be putting pressure in an unintended area.

Sounds goofy to me.

Actually, I've heard of a carbon fork manufacturer which specified a stack spacer be installed ABOVE the stem. The idea was to prevent the stem tightening bolt from exerting pressure too near the cut end of the steerer tube. That's the exact opposite of what your bike mechanic told you.

Unless the LBS guy mis-spoke, he is wrong. You can move the spacers around however you wish. Just as one example, I remember seeing a close up of Lance Armstrong's bike in the tour with a carbon spacer on top of the stem. The only thing you need to be careful of is making sure the spacers+stem are just a hair higher than the steerer tube, so that the cap presses on the spacers and not the steerer tube.

I see absolutely no reason not to put any number of spacers above the stem if the steerer is left long enough to be 2-3 mm below the top spacer and the compression plug installed.

You can't stack spacers too far above the top of the steerer or the compression plug's bolt or cap won't reach. Maybe that's what the LBS is thinking.

I imagine the LBS guy was thinking that the compression plug needs to be located where the stem bolts are compressing the steerer, so the carbon steerer will be supported from within and the steerer will not be crushed. Whether this is the case or not, I have no idea.

The opinions are mixed on whether the compression plug only serves to anchor the top cap bolt or whether it performs a vital function, supporting the steering tube against possible crushing by the stem. If you want to support against stem clamping forces, some models that use an M6 clamp bolt can be inserted deeper with a longer bolt. The FSA style with the threaded top cap can't.

FWIW, I once did a test on a scrap piece of carbon steering tube. I installed a stem and tighten the two M6 bolts as hard as I could with a long handled hex wrench and it didn't hurt a thing. Occasionally, someone will crack the top of a steerer when the steering tube is 2-3mm below the top of the stem and the top bolt is way overtightened. If a steerer cracks under any other situation, it was poorly constructed.

The opinions are mixed on whether the compression plug only serves to anchor the top cap bolt or whether it performs a vital function, supporting the steering tube against possible crushing by the stem. If you want to support against stem clamping forces, some models that use an M6 clamp bolt can be inserted deeper with a longer bolt. The FSA style with the threaded top cap can't.

FWIW, I once did a test on a scrap piece of carbon steering tube. I installed a stem and tighten the two M6 bolts as hard as I could with a long handled hex wrench and it didn't hurt a thing. Occasionally, someone will crack the top of a steerer when the steering tube is 2-3mm below the top of the stem and the top bolt is way overtightened. If a steerer cracks under any other situation, it was poorly constructed.

Ya, the mechanic in question really seemed to think the compression plug acted as support for the steerer tube when you clamp the stem down.

I've heard the story before about people unable to crush a steerer tube even when they were trying to, might've even been a post of yours, that's why his statement seemed pretty fishy to me.

Thanks everyone, I'm not sure how long I'll have this frame (less than 5 years probably) and was trying to avoid cutting the steerer and making it harder to sell.