>> Older steel forks are probably less of an issue, because we weren't
>> designing things for ultra light weight, and things tended to be
>> overbuilt. But modern forks generally don't have material where they
>> don't need it, and the strength and weakness of carbon is that you have
>> complete control over placement of the material... so an area presumed
>> to have relatively low stress may be built accordingly.
>
> Mike, I share your concern. I've often wondered about the sideways
> jostling in roof racks, and fatigue in the dropouts. But if it were a
> problem we'd have seen failures by now.
But we do. We see a number of disbond failures where the dropout has
separated from the fork blades (on bonded aluminum or carbon forks). This
happens very rarely with bikes not used on roof racks. I've not kept track
of it, and perhaps should have, but my guess/estimate is that probably
greater than half of the failed disbonded dropouts we've seen have been from
bikes used on roof racks, which is a hugely-greater percent than the number
of bikes transported that way.
> I can't imagine large bike companies not considering this in their
> engineering.
It's not just the engineers dealing with this, it's also the lawyers. Funny
thing, those legal issues. Trek, for example, won't list a "maximum" rider
weight for a product for two reasons. First, your mileage may vary, and they
try to build products strong enough for any reasonable use. But there's also
this weird thing going on that says don't list a max rider weight because
that opens you up liabilities if something happens with a lighter rider
(regardless of how the product might have been abused).
How does this tie in to roof racks? Simple. A roof rack isn't considered
normal use of a bicycle. If you design something to specifically hold up to
such use (and somebody finds out about it), and there's a failure... bad
news for the manufacturer.
> The only problem I've seen is bent dropouts from bikes being tipped
> sideways as they're going in and out of the rack. This is probably what
> you've seen too. I think this has gotten worse as cars have become trucks
> and gotten taller, making it harder for people to reach the roof rack
> safely when mounting/dismounting their bikes.
>
> Once the bike is in the rack and secured though, it's probably OK.
Looking up at bikes strongly vibrating in the wind (on a roof rack), it just
doesn't seem like "it's probably OK." It's always made me nervous, and the
times I paid attention to it, the times when I used to use a roof rack that
fastened at the fork tips, those times were with a heavy steel bike, many
years ago. These days I actively tell customers that's not a way I'd attach
a bike to a roof rack.
And yes, we stopped selling roof racks in general maybe 5 years ago. As our
roof-rack vendor, a well-known & respected company, once told me- "There are
two types of roof rack users. Those who have driven their bikes into
something, and those who will." The decision had nothing to do with fork
damage, since there were already many alternative ways to attach bikes to
roof racks available.
>
> Matt O.
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
