TOUR Which is the most vulnerable carbon component on a road bike?
Zedler That’s still the fork steerer tube. I see broken fork steerer tubes regularly, although not as often as before.
Why do fork steerer tubes brake?
Unfortunately, the issue is complicated. There are five influencing factors: the quality of the steerer tube, the clamping position and the number of spacers, the expander, the quality of the stem and the assembly. If both manufacturers and mechanics do everything right, it’s a safe thing.
Practically, this seems to be difficult, because almost every manufacturer has already experienced a fork recall. Wouldn’t it be better to design the connection in a completely different way?
With integrated solutions where everything comes from a single source, we have seen a significant leap in quality. I think with this the manufacturers are on the right track.
Why do the test standards exclude the issue?
Unfortunately, the standards are developing very slowly, and the manufacturers have been testing better for a long time anyway. In connection with fork recalls, we tested fork stems with the standard forces of the handlebar test and were unable to reproduce the fractures in the field. We therefore perform harder tests and can thus reproduce the damage pattern from practice. Carbon is damaged especially by heavy loads.
How do I make sure that the fork steerer tube of my bicycle is ok?
To check the steerer tube regularly, is a good idea. It’s extremely rare that carbon breaks suddenly. Furthermore, I do recommend using a good expander.
How do you recognize a good expander?
It should be long enough, extend beyond the lower edge of the stem, fit snugly and should be able to be tightened with little force. What helps in addition is a rough surface, grease inside the clamping mechanism and carbon assembly paste on the surface. Carbon assembly paste always helps; without this paste we were not at all able to test many carbon parts.
Is the fork steerer tube necessarily affected by damage, when the handlebar is twisted in a fall?
When we prepare expert’s reports, we replace forks after such accidents. But falls are nothing unusual in road racing and a replacement after every fall is not realistic. We do not see a connection between scuffed handlebars and broken fork steerer tubes.
Is my bike unsafe if I cannot use a solid expander, for example, because of the fork steerer that has no cylindrical shape?
It’s up to the manufacturer to make the connection safe in design and to test it appropriately. Apart from the fork steerer the stem has also an important influence on safety.
The interview was held by: Robert Kühnen