https://www.rideapart.com/news/727055/solar-e-clipse-race-edition/
Solar Scooters’ new E-Clipse Race Edition is a full-carbon EV motorcycle that looks like tons of fun to ride around town.
Wondering why this material isn’t used more in cars — too fragile? Not enough impact safety? Too expensive to make? Too expensive to replace?
Too expensive.
The more complex the structure and load profile, the more expensive it gets to design and produce.
Carbon composites are stupidly strong, but they have to be "designed". It's a composite material, so depending on how you lay out the fibres inside the material you get different properties. You can do extreme rigidity, or you can do flexibility, you can do strength in one direction only, while wasting no weight on strength in a direction where there won't be a load.
And once you make a design, you have to make it. Laying down the carbon, layer by layer, so each fibre inside the material goes where it needs to, to provide strength in all the places where it's needed.
A bike frame, even a motorized EV motorbike, is much simpler than a car.
The emissions of producing carbon composites are also absolutely massive.
It's also basically unrepairable. It can't be welded, it has to be bolted together or glued, and once broken, will never be as strong as it was as a solid piece.
In general, agree with your explanation here, but would disagree on the repairability point. Lots of carbon repair shops will repair carbon parts. Often just needs paint sanded off and additional carbon bonded on. Generally doesn’t bend and deform like metal parts, so the cracked bit can just be cut out and reinforced.
On the other hand the aluminum alloys a lot of car parts and bikes are being made of end up quite difficult to weld and re-heat-treat in practice, so no easier than carbon.
Aluminium is extremely easy and cheap to recycle, in comparison.
I know that carbon composite structures can be mended in a variety of ways, but like you say, it's typically done my layering on more carbon.
Depending on the part, this may or may not result in something that can serve its purpose again.
It's expensive and can be finicky: Failing in unexpected ways after too much stress. Something like a motorcycle or bicycle is easier because it's much less complex than a car and much smaller so it's both less expensive and has far fewer things that can go wrong.