Cycling downhill fast

[overmind]

I have 2 bikes:
- A Triban 3 with aluminium frame and front carbon fork (mostly summer use)
- A Trek 720 trekking with steel frame and forks (winter use + touring)

When am cycling downhill the faster I go the more uncomfortable I feel on the bike with the carbon forks (Triban) - so much so that I tend to brake alot going downhill which seems a bit of a waste of energy.

The Triban feels much more unstable that the bike with the steel frame; particularly when I hit any kind of bump or road damage.

Is this irrational? Are the carbon forks more or less likely to break or does it make no difference?

 

[Alex321]

I dion't think the likelihood of breakage is significantly different.

And the material of the frame and forks is unlikely to be what is causing the bike to feel less stable. That will be more down to differences in geometry between the two bikes. And a small amount down to weight.

 

[cyberknight]

geometry, fork rake, tyres
so many variables

All my bikes now have carbon forks, the eldest is only 12 years old but i its done many thousands of miles with no issues .
Obviously worth checking the fork out just in case but as a material it shouldn't be a problem

 

[Peter Salt]

The material is nearly irrelevant. Manufacturing quality is far more important. When it comes to handling - geometry is key. What are the angles on each bike, width of bars, length of stem, etc.

 

[roubaixtuesday]

Frame geometry and tyre spec are probably what makes it feel different.

 

[numbnuts]

My trike feels quite stable at 48mph, I wish my anus could be the same 💩

 

[presta]

Aluminium & carbon bikes are stiffer than steel.
https://www.cyclingabout.com/why-frame-stiffness-is-critical-in-understanding-ride-feel/

 

[Slick]

I'm not sure I would be worrying too much about the materials if I felt uncomfortable on the bike. If you aren't confident above certain speeds, slow down.

 

[HLaB]

I have 2 bikes:
- A Triban 3 with aluminium frame and front carbon fork (mostly summer use)
- A Trek 720 trekking with steel frame and forks (winter use + touring)

When am cycling downhill the faster I go the more uncomfortable I feel on the bike with the carbon forks (Triban) - so much so that I tend to brake alot going downhill which seems a bit of a waste of energy.

The Triban feels much more unstable that the bike with the steel frame; particularly when I hit any kind of bump or road damage.

Is this irrational? Are the carbon forks more or less likely to break or does it make no difference?

All my bikes have carbon forks and I ve done something like 160,000miles. That includes circa 7,000miles on a Triban 500 and 42,000 miles on bike which was hit side on when it was new, folding the front wheel in half. Carbon is stronger than you think. Aeroplanes and Formula 1 cars etc have parts made out of the stuff too.

 

[Sallar55]

As the above post points out.
https://simpleflying.com/boeing-787-wings-flex/
If you think that carbon is not safe don't bother about flying anywhere.

 

[lazybloke]

As the above post points out.
https://simpleflying.com/boeing-787-wings-flex/

As impressive as the video is at showing the stength and flexibility of the wings, I wonder what testing has been done to simulate the cumulative stresses and fatigue that would result from years of active flight?

If you think that carbon is not safe don't bother about flying anywhere.

I saw a video of Stockton Rush making a similar claim.


Not saying that carbon forks are unsafe. Just that their sudden failure mode makes me a tad nervous.

 

[ianrauk]

Not saying that carbon forks are unsafe. Just that their sudden failure mode makes me a tad nervous.

I've done 100,000 miles+ with carbon forks. Failure doesn't even enter my head.
Maybe it should after reading this as my bike is a PX Tempest with PX Carbon forks. But I'm not going to let it.

 

[roubaixtuesday]

On the failure of different components and materials, it would be interesting to know what actual data there is.

I'd guess that forks, stem/bars, front mudguard, frame are the most critical, but I'm probably wrong.

I've had a few failures of components in mine and the wider family's bikes: frames (1xsteel, 2x Ti), Axles (steel, I think, several), a crank (Al) come to mind. I've never had a CF component fail but of course that could be just chance.

Ti is the one material I'd avoid. It seems to be critically dependent on manufacturing control, and lots of examples of unexpected failures can be found. Both Mrs Tuesday's and eldest Tuesday's Ti frames cracked.

 

[Bristolian]

As impressive as the video is at showing the stength and flexibility of the wings, I wonder what testing has been done to simulate the cumulative stresses and fatigue that would result from years of active flight?

I can answer that for you. Complete wings are suspended from an overhead beam in a climatic chamber and several electro-mechanical vibrators are fitted underneath so that they are pressing up against the bottom of the wing but not taking any weight. Each of the vibrators is then connected to a computerised controller that send it a series of pre-programmed sine-wave frequencies of varying amplitudes and durations. During the tests they can also simulate the climatic conditions that the aircraft would see in use. They are able to simulate each phase of the aircrafts life and the overall result is to mimic the forces and stresses experienced by the wing both in normal use and in extreme conditions. In this way, they can simulate the lifecycle of the wing in a few days (or weeks).

This type of testing has been used in the aerospace industry for decades and they are very good at it - how many times do you hear of a wing shearing or falling off?

 

[Bristolian]

On the failure of different components and materials, it would be interesting to know what actual data there is.

I'd guess that forks, stem/bars, front mudguard, frame are the most critical, but I'm probably wrong.

I've had a few failures of components in mine and the wider family's bikes: frames (1xsteel, 2x Ti), Axles (steel, I think, several), a crank (Al) come to mind. I've never had a CF component fail but of course that could be just chance.

Ti is the one material I'd avoid. It seems to be critically dependent on manufacturing control, and lots of examples of unexpected failures can be found. Both Mrs Tuesday's and eldest Tuesday's Ti frames cracked.

The manufacture of carbon fibre components is much more dependent on manufacturing processes and quality controls than metallic parts. The Ti frames that you cite above at least gave warning of failure - they cracked and probably creaked as a consequence - whereas CF components simply fail without warning, or with insufficient warning to be able to do anything about it.

The pursuit of ever lighter bikes means that components have to be made with less and less material. If the designer does his job correctly the frame is theoretically strong and durable enough but ultimately other factors (e.g. variations in raw materials, who does the assembly, who carries out the quality inspection, etc.) determines which frames are good and which are bad from any production run.