No.

Unless they are red. Red carbon is more aero.

I actually kind of like alloy ones better, as nearly all carbon ones I have ever had are at least kind of flexy, especially if you need long extensions. But I still run carbon ones.

I have bent alloy extensions...I have not broken carbon ones.

I agree that for longer extensions alloys are nice because they seem to flex less, but then you also have a very long lever to bend them.

PS-i'm a clydesdale (hence the username) so YMMV

Not that I care but I always just figured carbon was lighter but not true. I recently upgraded to PD's double bend 4525. Having a hard time coughing up $166 for the carbon ones, I opted for the Aluminum ones at 1/3 the price and 42g lighter. The bonus is that I won't have a fit when they get scratched from the brackets or Aerodrink bracket. YMMV.

Awesome! Thanks for all the feedback. I figured this was the case, but just wanted to be sure.

has anyone cut their carbon extensions? i'm looking for a flush end to route the shift cable down the stack spacers into the base bar.

This would not be a statement I would not generalize. Carbon Extensions are going to be much stiffer in general...Of course the wall thickness and layup will largely dictate the performance, but given the same geometry I would not say an alloy extension is stiffer


Cutting extensions is quite easy and quite common (just as you would a steerer) but definitely be sure your manufacturer is OK with this, and that you leave a little bit of extra length beyond the clamp to ensure proper clamping

The carbon ones look nicer 😎


More seriously, I've got the Profile Design 'T1+' carbon extensions (a J bend shape).
On the Alu version its a round bar all the wau to the end. So your gear cable outer pops out of a hole in the bottom surface of the bar, an inch or so short of the end, so to go to the shifter.
On the carbon version the last few inches of bar is a teardrop profile. So the gear cable is totally inside the bar right to the shifter unit.

The Alu one is as a result little easier to do cable changes on. But isnt quite as sleek looking. (The aero difderence must be the sqare root of fechkall).

Obvs if you're on Di2, the above mau be irrelevant.

As you can see in this list, most carbon extensions are not all that light compared to alloy (note that there are some mixups between single weight and pair weight) so there is no performance advantage.
Profile Design has some properly light carbon ones on the way (half the weight of current) but if you don't like the cost of existing carbon...

Also, be careful comparing weights. Aluminum extensions are often offered in multiple lengths because the length isnt affected by tooling. You can easily have a 300, 350, and 400mm for the same extension, and manufacturers will often only post the lightest weight (shortest)

In comparison, a carbon extension is molded to length, so you often only get 1 length (usually longer than the shortest alloy because it can be cut down)

I have always preferred alloy simply because there’s zero performance advantage to carbon and I’m more comfortable cutting alloy. Also I change out extension shapes fairly frequently and alloy is much cheaper