acape

I just got a new Salsa threadless stem, and the stack height is 50mm rather than the 40mm I had before. In order to get the bars in the position I want them, I have 8-10mm of stem above the top of the steerer rather than the general 3-5. The top clamp bolt is actually still below the top of the steerer by a few millimeters, and I have about 40mm of stem clamping the steerer. I can't imagine that I'm encountering any safety issues here with such a tall stem stack height and the fact that both bolts are still below the top of the steerer, but does anyone disagree?

waterrockets 

If the centerline of you highest stem/steerer clamp bolt is below the top of the steerer, I don't see it being a big problem. This assumes you have a metal steerer -- I wouldn't mess with it if it's a carbon steerer.

MrCjolsen

I actually ran a road bike with the top clamp bolt above the steerer and it was fine, but I wouldn't recommend it. But if the top clamp bolt is below the steerer, you'll definitely be OK.

acape

Nope, aluminum it is. And the top of the bolt is actually well below the top of the steerer, by 3-5 mm I'd say.

DiabloScott

You've reduced your clamping surface area, and you've introduced a stress riser at the top of the steerer. It's less safe than the way it's supposed to be.

acape

I think I've actually increased the clamping surface area. Before I had a stack height of 40mm with about 3mm above the steerer, for a clamping surface area of 37mm. Now I have a stack height of 50mm, but with 10mm above the steerer. That gives me a clamping surface area of 40mm, more than before.

MrCjolsen

That's right. It's not like you added any spacers.

acape

I actually had to remove one small spacer.

George

I have mine set up that way and it's been fine.

AndrewP

Isnt stack height that of all the top bearing pieces? I think you have increased the stem clamp height.

DiabloScott

Stack height is really a property of the headset, you're talking about the clamp length of the stem.

So you may have more surface area clamping the steerer than you did with your old stem, but you have less than the amount the new stem was designed for. I don't know how much of an issue it is, but it's some amount less safe than if you had steer tube all the way up.

Salsa has a pretty stern warning about having the top of the stem more than 3mm above the top of the steerer.
https://www.salsacycles.com/pdf/Pro.S...m.instruct.pdf

comradehoser

Sorry to dredge this up out of the past, but I have some questions, because I have a similar situation.

Realistically (not company statements made for insurance purposes), what are the possible consequences of running a stem where the steerer tube lines, say, just below the top pinchbolt? Why is this "less safe"? Slippage? Failure? How? Inquiring minds want to know.

And yes, I know, the solution is a stem with more rise.

vpiuva

I would say slippage would be the first thing that could happen, which would lead to failure of some kind; whether it's a suddenly loose headset or an actual breakage.

comradehoser

okay, but I was wondering what kind of slippage/breakage/failure we're talking about.

I had the stem on with the steerer tube just below the first nut, and could not budge it at all with brute force. Granted the nuts on this particular stem (Felt ST) are pretty wide apart.

Has anyone seen or had stems crack or break due to improper clamping?

Moose

Try to imagine the scenarios that would result from the failure of any part of your fork/stem/bar interface. Anyone who ever does any climbing or sprinting, or even a vigorous acceleration from a stoplight should never compromise in this area. It's just not worth the risk.