I put this in "Mechanics" but I bet there are some brains in the 41 who know...maybe.

I am working on putting together a winter project road bike.

I have a full carbon fork and it's unclear what the maximium height above the headset is "allowed" or recommended.

I have heard 3 inches and/or 8 cm.

Is there any clear-cut guidance on this?

If it matters, the fork is a no-name all carbon fork. Frame is nashbar aluminum. Headset is Cane Creek S-3.

According to Cannondale, max stack height is 40mm.

https://cdn.cannondale.com/Manuals/20...echnote_en.pdf

8cm/80mm sounds way, way high for a carbon steerer tube. This no-name fork didn't come with any manual or documentation?

To be safe it should be no more than what other CF fork makers recommend for max stack height on a full CF steerer.

Not if you're counting both the spacers AND the stem... That'd be ~35mm of spacers and 45mm of stem.

SP
Bend, OR

Dat's a good point.

For my Easton 90 I think they recommend a max of 50mm.

I am thinking 8cm total, which allows for 4cm of stem and 4cm of spacers, does that sound about right?

The 50mm of stem for your Easton, is that including stem or in addition to stem?!?

The no-name fork came with no manual or instructions.

This can vary by fork manufacturer.

However, the general rule of thumb is that you should have no more than 40 mm of spacers.

Pretty much what I planned on doing.

Is it also a rule of thumb to have at least 5mm spacer ABOVE and BELOW stem? That's what I have heard.

My EC90SL fork's instructions say no more than 40mm of spacers.

Make sure you use an expansion plug and not a star nut.

Bob

Yeah thanks I know. Luckily the fork did come with an expansion plug. So I can chuck the star nutz that came with the headset.

ps some folks use the term star-fangled nut rather than star nut. What's up with that??

Not necessarily. I was recently surprised to find out that Cannondale specifically says NOT to use any spacers above their stem. If you click the PDF link I posted above, you will see that they actually recommend cutting the steerer 2-3mm below the top of the stem. However, I think this is because Cannondale requires the use of a special compression cap with an aluminum sleeve that extends into the steerer to reinforce the area where the stem clamps down. If spacers are used above the stem the aluminum sleeve won't be able to reach down far enough to fully support the stem clamp area. IMO it would have been safer and even stronger if they required a 5mm spacer above the stem and simply extended the aluminum sleeve by 5mm. Not sure why they intentionally wanted the steerer below the top of the stem. That goes against what most people consider common practice today.

Also, FWIW, you can use a star nut in some carbon steerers. Cannondale forks have (or had) nylon sleeves that line the inside of the fork steerer, so a star nut is safe to use. Other fork manufacturers have star nuts inside aluminum carrier sleeves and the aluminum sleeve is epoxied into the steerer. It just depends on what the manufacturer recommends, but more and more are using compression/expansion plugs these days.

As for the term "star-fangled nut," I can't stand it either. A mechanic at my LBS said it yesterday and I was like..star-spangled banner what?

Specialized stems are installed flush because most of their original equipment stems and half of their 'aftermarket' stuff has an elliptical top mount so you can use different shims and get 4 degrees of adjustment in one stem.

I agree with you in principle, though. If you're worried about breaking or crushing the steerer, it seems counterintuitive to install the stem above the top of it.