If you are carrying bikes on a car roof-rack, remove the bikes before you drive into your garage. Sounds like stating the obvious, but over the years I lost count of the number frames I repaired after being damaged in such a way.
Often the owner would be embarrassed and tell me he was in an accident, but the front fork bent forward was always a giveaway. Even if a person was talented enough to ride backwards at a high rate of speed, I doubt they could hit something hard enough to bend a fork forward.
Usually if the fork was bent this way it could be easily straightened cold with no damage to the paint. On the other hand, if the bike was facing rearwards on the roof-rack, it usually meant the top and down tubes would buckle just behind the head lugs as they would in a front end crash. These tubes would have to be replaced, and the frame repainted; a costly proposition.
A steel front fork blade has a fairly stout wall thickness, and will usually bend without rippling, whereas the thinner main tubes of the frame will ripple quite easily.
The steel blade starts out as a round tube of uniform diameter. It is rolled between rollers to make it tapered; this operation is done cold. The top end is made oval, also done cold, and finally the framebuilder bends the fork blade to the desired rake, again cold.
So if a steel fork blade should get bent in an accident and is re-straightened again cold, it is well within the safe limits of what the material will stand.
I emphasize, such straightening only applies to a steel frame; it is one of the advantages of steel.
As long as the tube is not kinked or rippled. (Picture left.) If it is it must be replaced as it will eventually break at that point.
If you have just bought yourself a roof-rack and are carrying your bikes in this manner, the first thing you need to do is remove the garage door opener from the sun shield, and place it in the glove box or some other place out of reach.
Because at some point you will arrive home, probably tired, hit the automatic door opener, and pull into the garage as you always do. There will a tremendous crash, followed by a sickening “Oh No” moment. If the remote opener is not there, you can’t do that.
It is not just your own garage that is a potential bike buster, but anywhere there is limited overhead clearance; like indoor public parking, drive through restaurants, etc, etc.
One tip I would suggest, get a tie on label and write the words, “Bikes on Roof,” on it; then tie it to the top center of your steering wheel. Failing that, tie a ribbon, or a bandana to your steering wheel.
The bikes on the roof are out of sight, and out of mind, so some other visual reminder in front of your face really is a good idea.