Just got into work and there's a Orbea road bike chained up and it has no cap on top of the stem or even a SFN in the steerer.

Is running a stem without a headset cap ok or rather unsafe?

No, not unsafe at all. The cap is only for tensioning the headset. Once the stem is clamped the top cap serves no purpose other than making it look neat (and maybe preventing you core sampling yourself if you fall on it!)

it's ok in theory as long as the cap was there when the steerer/forks etc were put in; to tighten up the whole assembly.

Theoretically, once the stem is on and tight following this compression, you should be able to remove the cap without a problem.

I wouldn't though.

HTH

edit: clubber beat me.

Headsets do tend to come loose more often if you don't run a SFN, I've often thought about it, particularly with carbon steerers, where the expander plugs can weigh a fair bit. Harder to do though as when you clamp the steerer it gets a lot harder to remove the expander. As this is a road bike, I'm guessing that's what he's done.

With an MTB with a hole in the bottom of the steerer you can tension the headset with a long bolt and some big washers, you don't need the SFN at all.

Edit: clubber AND pook beat me, giving too much detail!

Weight weenie thing…

Ultralight alternative to a bung for carbon fork on a road bike – lightweight spoke, cut the head off, twist/loop it round the front brake bolt (inside the steerer) and use a spoke nipple to tighten it at the top (using a normal top cap)

Nope – as long as the stem is done up tight 🙂

I ran a bike for ages with no top cap. It never came loose at all. if it comes loose then something is very wrong with the clamping of the steerer.

some headsets use a different tensioning method.

or you can add a ring go star to any headset.

A favourite of the sorts that like to change their frames paint to save weight 8O.

>Headsets do tend to come loose more often if you don't run a SFN

If that's the case you're not tightening up the stem bolts enough.

>A favourite of the sorts that like to change their frames paint to save weight 8O.

Or possibly :
a) you don't have a spare one to hand when assembling a bike
b) someone's nicked it.

Just pray you don't crash it during a ride…