Interesting from Van Nich...
https://shop.vannicholas.com/en/products/titanium-bike-accessories/Van-Nicholas-Stem-Titanium/8097
Can I use a titanium stem in combination with a front fork with a carbon steerer?
Please do not use a Titanium stem in combination with a carbon steerer tube. A Titanium stem requires a high torque to assemble. This can cause severe damage to the carbon steerer tube by putting too much strain on the part, causing the steerer tube collapse in on itself.
https://www.vannicholas.com/service/maintaining#:~:text=Please do not use a,tube collapse in on itself.
From a materials engineering perspective, there are no issues with pairing CF and Ti components. If anything, Ti is far superior to Al in many respects - e.g. preventing galvanic corrosion.
I suspect the warnings you've read are linked to the way that the clamping mechanism is constructed rather than the material itself. Ti has a higher tensile strength and as such will have different properties and a clamping mechanism that accounts for these (different clamping force offset and higher required torque).
In simple terms - Al stems clamp the tube in a consistent fashion around its circumference with a relatively low torque whereas Ti stems pinch the steerer from one side, at a higher torque, causing it to fail - immediately, or worse, slowly over time.
If you use a puka carbon insert in the carbon steerer I don't see how it can collapse as suggested in the Van Nic advise.
Why doesn't the Ti stem do this? They look ... err "normal" in the pic. Is the contact surface not round? (ok, cylindrical I suppose!)I suspect the warnings you've read are linked to the way that the clamping mechanism is constructed rather than the material itself. Ti has a higher tensile strength and as such will have different properties and a clamping mechanism that accounts for these (different clamping force offset and higher required torque).
In simple terms - Al stems clamp the tube in a consistent fashion around its circumference with a relatively low torque whereas Ti stems pinch the steerer from one side, at a higher torque, causing it to fail - immediately, or worse, slowly over time.
The fracture issue is purely in relation to CF. No need to be concerned about metal clamping metal because the material that's being clamped is not as hard (and brittle) as CF - worst case scenario it will leave some marks but not break anything.Why doesn't the Ti stem do this? They look ... err "normal" in the pic. Is the contact surface not round? (ok, cylindrical I suppose!)
<puzzled>
( And do seat-tube clamps on Ti frames have the same issue? )
The fracture issue is purely in relation to CF. No need to be concerned about metal clamping metal because the material that's being clamped is not as hard (and brittle) as CF - worst case scenario it will leave some marks but not break anything.
As for the clamping properties - it has nothing to do with the inner cross sections of the components (they're all the same) but everything to do with the properties of the material and how the clamping/stem is designed to account for it. Depending on Young's Modulus, tensile strength, etc. different material stems will clamp the same steerer tube with varying consistency throughout the circumference as well as different force overall. Even if you had completely identical components, one from Al and the other from Ti, and applied the same torque on the bolt, the force exerted on the steerer will be different due to elastic properties of the stem material.
Some Ti frames actually have a built in alloy sleeve. If you don't have one of those, I would consider getting a smaller diameter CF seat post and putting in an alloy shim.Sorry - I meant TI frame, carbon seat-post. (i.e. extrapolating from what we're discussing in this thread :P )