I’m thinking of getting a bike with a carbon frame for the 1st time, always had steel or alu up to now. Was thinking last night when putting the bikes on the car rack – do you have to be more careful with carbon? For example, on my rack I torque up the straps nice and tight to hold the bikes steady on the motorway. Any issues doing the same on a carbon frame?

I regularly put my carbon frame bike on to the roof of my car just like any other bike, except that I do use one of these:
Frame Protector
Partly to protect it and partly because the downtube is a bit odd and the rack locking thingy tends to push against the brake hoses just where it attaches.
Other than that, I treat it just like any other bike

The bit from 5:00 is very good..

👍🏻thanks. My rack is the cheapest Thule towbar one, which just has toe-straps for securing everything. One of those frame protectors looks just the job. I do the same with an old rag at the mo to stop paint rub, but prob doesn’t protect it much.

It’s definitely easier to crush a carbon frame tube if you don’t take some care. I always try to clamp mine around the top of the seat tube, where the inserted seat-post prevents the tube from compressing.

I also use invisiframe protection film to prevent stone chips, but that’s more cosmetic really. But I would make sure the downtube has a decent rock guard.

It’s definitely easier to crush a carbon frame tube if you don’t take some care.

Really, has anyone actually managed this? The SC boys can’t even dent one smashing it into concrete repeatedly with all their strength!

I have some dings in my carbon frame. Nothing deeper than the top coat and any of the causes would’ve also caused a ding in a alu frame. The decals are an absolute mess cos they didn’t use lacquer coat over the top – so invisi-frame is wise.

That sounds like just the lacquer rather than the frame material itself. I’ve never seen a carbon frame tube ‘crushed’ although seen some pretty big dents in thin walled Al frames.

Thinking about it, I’ve buckled some steel forks, snapped an Al frame but yet to have a carbon frame fail on me (other than ripping the carbon drop out off when the rear mech was swallowed by the back wheel).

I think it needs invisiframe.

I also take extra care. I wont use a clamp on my thule rack and use either a 3d printed clamp or rubber strap.

Really, has anyone actually managed this? The SC boys can’t even dent one smashing it into concrete repeatedly with all their strength!

Or “They couldn’t put a permanent dent into an elastic material that could still have damage you can’t see”

Hard to tell really…

But tbh, I reckon those carbon frames are amazingly strong & resilient!

It’s definitely easier to crush a carbon frame tube if you don’t take some care.

Really, has anyone actually managed this? The SC boys can’t even dent one smashing it into concrete repeatedly with all their strength!

I have seen a road bike down tube crunched by a bike rack.

I have snapped warranty frames by jumping on them out of curiosity. Very strong and hard to break in some ways, very easy/weak in others.

Very strong and hard to break in some ways, very easy/weak in others.

That sums it up well. I worked in F1 racing for many years where everything was carbon. While incredibly strong, it can also be very weak if loaded in the wrong plane. Thin walled carbon tubes are particularly vulnerable to crush damage, which is why you have to be so careful when clamping carbon bars. Same applies to rack clamps on carbon downtubes. Even more so as they are much thinner walled and will have no reinforcement for clamping.

You’d have to be proper ham-fisted to over tighten a clamp on a carbon frame. I just treat mine the same as the Alloy frames. Tighten it enough till you hear a crunch, them back it off half a turn 🙂

No.

My rack is the cheapest Thule towbar one

I have the base rack too (9503), I have no issues pulling it as tight as I can. I did start having issues of the paint wearing where the frame was touching the arm and moving slightly, I now wrap a microfibre cloth around the frame to sit between the vertical arm and the toe strap.

I’ve done lots of journeys with my bike on that rack, well into the thousands with no issues other than the paint rub!

Thanks @oikeith, good to hear. I’ve just bought a bunch of cheap microfibres cloths too, upgrading the old rag I use 😀

Guess most of the issues described above are the ratchet-style clamps, especially the early ones where they give you a mechanical advantage when tightening with no limit.

Just me pulling on a fabric strap is never going to be that tight.

I had my first & last carbon frame recently. I just dont enjoy the sounds of rocks bouncing off the downtube or crash damage on the rear triangle when I binned it on rocks.
Got another alloy bike & none of these things are a worry anymore. Plus the alloy bike isnt a harsh boneshaker.

They aren’t that thin. I can’t imagine how you would be able to apply enough force with a strap, and you’d have to be really working hard to crush it with a screw clamp. Who’d keep tightening that hard?

I’d say they require less TLC because it’s not going to corrode.

Got another alloy bike & none of these things are a worry anymore.

Alu can’t be damaged in a crash? Wow.

Many folk would get a fright if they discovered how thin many aluminium frame tubes are.

They aren’t that thin. I can’t imagine how you would be able to apply enough force with a strap, and you’d have to be really working hard to crush it with a screw clamp. Who’d keep tightening that hard?

They are actually pretty easy to damage with clamps, especially large diameter downtubes which are pretty thin and weak when compressed. Trek felt the need to produce this carbon care page:-

https://www.trekchicago.com/how-to/carbon-bicycle-and-component-care-pg193.htm

which includes this quote: “Car racks that clamp to the frame tubes should not be used because of the enormous loads concentrated in a small area.”

Now you can certainly mitigate this inherent issue by using special clamp adaptors (like the one Thule make) which spread the clamping load over a much larger contact area. Clamping around the top of the seatpost is preferable too because it has the seat-tube to support the clamped tube.

You just have to be a little more careful than you would when clamping a metal tube. As far as clamping a carbon tube goes, it’s pretty much like clamping a plastic tube. Carbon is obviously much stronger than plastic, but only in the direction of the fibres, not perpendicular to them like a clamping force would be.

If it’s a toe strap type clamp, I can’t really see that you’d manage to crush any frame even though I’d accept some road frames really don’t have any allowance for that sort of loading.

Unless you left it really loose so it knocked about I suppose.

More likely is that you could wear through it if you have a bit of mud left on the frame post ride especially (it’s far worse for this than steel and even aluminium). Invisiframe/helicopter tape therefore not a bad idea in case things do move about a bit in transit.

Having tested a lot of composites such as carbon fibre reinforced polymers I’ve no issues riding a carbon frame, most of the negatives happen prior to riding, i.e. cost, manufacturer, etc, and most of the positives are during its life (fatigue life, thermal characteristics, etc).

Having crushed and fragmented a few bits of cfrp, I’m not sure you’d ever use the amount of force to deform or crush a frame

For me though, I do check my frame after crashes for hard impact areas and make sure there’s no damage, the lacquer is just a protective layer, button any of the carbon fibres are showing and have damage that’s the issue, but it’s also protected by the resin matrix it’s held in.

Workstands are another potential concern with carbon frames (also applies to super thin walled alloy tubes to a lesser extent):-

https://info.silca.cc/hirobel-launch

I have witnessed a carbon downtube ‘crunching’ and shattering when clamped by the Thule tray type rack which had a cam type lever (like a cam quickrelease) to close the jaws onto the tube- it took surprisingly little force to do this and wrote the frame off, a RockyMountain carbon hardtail. Obviously a strap is not going to apply similar force if it’s just securing the load so should be fine.

Lightweight thin wall large diameter carbon tubes are surprisingly vulnerable to certain forces and the more high performance high modulus carbons can be even more brittle in this respect. I have seen lightweight road bikes destroyed by such inane things as like falling from stationary onto a sharp edge or tools falling onto them in the back of vans – the centre regions of top tubes or downtubes particularly vulnerable.

Most modern mountain bikes outside of lightweight race bikes are fairly overbuilt with more wall thickness, possibly with features in the layup to mitigate against impacts. So as long as you’re sensible, should be of no concern.

Just watch the clamp forces….

Just watch the clamp forces….

Yeah, that’s what I’ve been trying to say in a lot more words!

Once had a customer in for brake service – we noticed the lightweight carbon hardtail’s top tube was split in two. They had taken two wooden lollipop sized splints and gaffer taped them onto the tube to complete the repair.  They had continued to ride like this assuming the frame was strong enough to compensate for lacking its full requisite of complete tubes. You could grab the bars and twist the bike a good few inches out of axis – they weren’t dead after many happy miles riding like this so ‘may’ have been a genius….what this shows I’m not sure….