Longer steerer or stem raiser?

[mickle]

Not heard about the recent rash of broken steerers on Trek Madones, then? Trek blamed this on NOT fitting a spacer.

Except that it was the stem clamping force wot done it and at the very top of the steerer. Last I heard Trek were still in dispute with FSA about the prob.

I might add that my FSA 120 stem crushed the top of my SID black box carbon steerer.

Made I wince. What's the smiley for 'wince'?

 

[snailracer]

Except that it was the stem clamping force wot done it and at the very top of the steerer. Last I heard Trek were still in dispute with FSA about the prob.

I might add that my FSA 120 stem crushed the top of my SID black box carbon steerer.

Made I wince. What's the smiley for 'wince'?

Trek service bulletin recommends spacers above and below the stem. I think the spacer between stem and headset prevents local distortion of the steerer (due to the stem clamp being not perfectly round, or overtightened) in the region of the headset top bearing, which otherwise results in point overloading of the steerer.

 

[MartinC]

Yes, there've been lots of stem/steerer interface area type failures since we've had threadless headsets and aluminium and carbon steerers, a quick google will find you lots. In the days of steel forks I'd only ever seen rusty old steerers fail. There's been a few product recalls too.

Most manufacturers now seem to say no more than 40mm of spacers. Trek seem to have had some bad experiences and want at least 5mm of spacers either side of the stem and a stem of an approved type too. They clearly don't like the clamping force near the weaker or stressed parts of the steerer.

 

[mickle]

But I think the 'no more than 40mm of spacers below the stem' and 'no less than 5mm of spacers above and below the stem' are two separate issues.

 

[snailracer]

But I think the 'no more than 40mm of spacers below the stem' and 'no less than 5mm of spacers above and below the stem' are two separate issues.

Agreed, but I do enjoy slagging that newfangled threadless stuff .

 

[MartinC]

But I think the 'no more than 40mm of spacers below the stem' and 'no less than 5mm of spacers above and below the stem' are two separate issues.

Definitely. In fact 3 separate issues. I'd guess the spacer at the top is to allow for the top cap to seat without the steerer being cut too close to the topmost stem clamp bolt. The spacer below is to put some distance between the stress concentration points of the top race and the stem clamp. The less than 40mm is to limit the bending force on the unspported part of the steerer.

 

[mattsccm]

Back to the original post??
Ignoring the arguments above which go off on a tangent, surely there can be no logic for cutting then using an extenstion. The leverage on the bearings etc will be the same. maybe the extension will thicken the whole affair where it overlaps but that won't change anything around the bearing compared with a longer steerer and spacers. An extension will however add greater potential for flex etc( yes I know not all do but they can) . A minor weight penalty may apply as well.
Accept the arguments about leverage and make your own conclusions. Go for the lowest bar position viable and use spacers. The ride will be probably better and there is 1 less component in the system.

 

[MartinC]

Matt, that's a reasonable summary of all the discussion (given it's steel we're talking about). The only I'd add is that it's preferable to use a stem with a big angle (and less spacers) than a flatter stem (and more spacers) - less flex.

 

[mickle]

Fewer spacers.

 

[MartinC]

Fewer spacers.

Yup, fair cop.