Alloy stems and carbon steerers

[Peter Salt]

I have some bad experiences with using alloy stems on carbon steerers. Specifically, stems that provide relatively low internal surface area - due to various cut-outs - leaving nasty marks on the steerer, despite applying the right bolt torque.

I'm doing a new bike build and once again came across an alloy stem that I really like, that seemingly hasn't been designed with carbon steerers in mind (cut-outs wherever possible). Said stem is available in 1-1/8 as well as 1-1/4 inch versions (steerer OD). The steerer on the bike is 1-1/8 OD.

Would it make more sense to get a 1-1/4 version stem, alloy 1-1/4 to 1-1/8 shim, and put that on the carbon steerer? Instead of fitting the 1-1/8?

Never used a shim like that before, any bad experiences out there?

 

[Smokin Joe]

Assuming you are using a bung in the steerer (Preferably a long one) the marks are no problem as the tube is supported by the said bung and cannot be crushed or split. The marks are probably just cosmetic anyway, but if you want to avoid them just soften the edges of the stem with emery or a file.

 

[fossyant]

Defintely use a bung, and use a small spacer on top of the stem, so the stem is clamping the whole supported part of the steerer (same goes for any material IMHO).

 

[Ian H]

I've had no problems with shims on stems or bars.

 

[fossyant]

I wouldn't use a shim on anything critical like steering. Just introducing something else for no reason.

OP's issue is they want a stem with the cut out - yes it will mark the steerer more, that's the issue with the cut out, but hey ho !

 

[wafter]

Personally I'd share your caution re. the stem cutouts - at best you get an uneven stress distribution over the steerer tube and concentrations at the edges causing the damage you describe, at worst this damage will be intensified massively if there happen to be high spots or burrs on the edges of the cutout.

Luscher Tecnik (sp...), a compsites engineer on Youtube cites such issues as a potential cause of steerer tube failure. Any damage like this on CFRP is bad news as it can cause de-lamination than can spread and cause catastrophic failure of the steerer tube - something that seems especially prevalent in terms failure locations on placcy bikes.. the steerer tube / fork assy being one of the most stressed parts on the bike and of course one of the nastiest if it fails.

Tbh in your situation I'd be inclined to go for a stem with no cutout; although the idea of a a shim is intriguing as in theory it should give the best chance of minimising damage to the tube.

 

[Drago]

I've had no problems with shims on stems or bars.

I've never had a problem with all sorts if things, that doesn't mean others don't.

 

[Ian H]

I've never had a problem with all sorts if things, that doesn't mean others don't.

Obv.

 

[Peter Salt]

Thanks for the input. Some really good points here.

Assuming you are using a bung in the steerer (Preferably a long one) the marks are no problem as the tube is supported by the said bung and cannot be crushed or split. The marks are probably just cosmetic anyway, but if you want to avoid them just soften the edges of the stem with emery or a file.

Somehow, I never thought about slightly filing off the edges - good thought - probably something I should do no matter what the material is. Bung - some more details about that below.

Defintely use a bung, and use a small spacer on top of the stem, so the stem is clamping the whole supported part of the steerer (same goes for any material IMHO).

It's a bit trickier with this frameset. The way that it's designed means that the fork is kept in place by the crown piece (it doesn't fall out without the stem installed). There is a top cap with an alloy tube attached to it (about 50mm long so goes all the length of the stem) but it just slots into place - doesn't have any kind of expansion mechanism - stays in place once you bolt up the stem.

I wouldn't use a shim on anything critical like steering. Just introducing something else for no reason.

OP's issue is they want a stem with the cut out - yes it will mark the steerer more, that's the issue with the cut out, but hey ho !

I get your point - why make something more complicated than it should be. But I guess that's the main point of my question - can I complicate it slightly and make it better

Personally I'd share your caution re. the stem cutouts - at best you get an uneven stress distribution over the steerer tube and concentrations at the edges causing the damage you describe, at worst this damage will be intensified massively if there happen to be high spots or burrs on the edges of the cutout.

Luscher Tecnik (sp...), a compsites engineer on Youtube cites such issues as a potential cause of steerer tube failure. Any damage like this on CFRP is bad news as it can cause de-lamination than can spread and cause catastrophic failure of the steerer tube - something that seems especially prevalent in terms failure locations on placcy bikes.. the steerer tube / fork assy being one of the most stressed parts on the bike and of course one of the nastiest if it fails.

Tbh in your situation I'd be inclined to go for a stem with no cutout; although the idea of a a shim is intriguing as in theory it should give the best chance of minimising damage to the tube.

Just watched the video you mention. That is EXACTLY what I meant. And because it's a critical part of the bike, despite the steerer being reinforced with Kevlar - I'm now inclined to get the shim, or at the very least try it.

 

[fossyant]

Personally, I get the propper parts to fit, and don't do cut outs or shims. Works for me. No failures. Steerers get marked, so a cut out will show that !

 

[biggs682]

I've never had a problem with all sorts if things, that doesn't mean others don't.

What about getting those y fronts clean