There are three main bike rack types and some of them will likely cover your taillights. Roof bike racks can’t cause any issues as they are installed on the roof (will cover neither the license plate nor the taillights), whereas hitch racks and trunk racks are definitely troublemakers in this sense.
Answering your question about whether a car bike rack can cover your taillights, the law is very clear. Your taillights must be plainly visible. This is the case in all states in the US. Moreover, in the UK, Canada, Australia, and New Zealand the lawmakers have the same approach to this issue.
However, there is something else to say here. When it comes to the license plate everything is straightforward. Your bike rack can’t even partly obscure the license plate, and that’s it. Taillights, on the other hand, will probably be visible even if partly covered by a rack. So what does it mean to be “plainly visible”? Is it ok for a bike rack to cover 20%, 30%, 50% of taillights?
I have read many forums and talked to some hitch rack owners. I have learned that people are getting tickets for partly obscured taillights extremely rare. Very opposite to obscured license plates as here your chances to get a ticket significantly increase.
In case you would like to be 100% sure that you won’t get pulled over, here is what can be done about bike racks covering the taillights.
Some hitch rack models include additional taillights
This is the best solution, no doubt about that. Not only you will have additional taillights installed on the rack, but an additional license frame as well. So it solves both problems at once.
Moreover, the hitch bike rack is the best rack type overall in my opinion. It will be really sturdy on the hitch receiver. You will be able to open the trunk with the rack installed. And, it is really easy to put a bike on a hitch bike rack (no much heavy-lifting).
The only disadvantage is the price ($400-$800). Anyway, you will be paying a similar amount of money for any other bike rack except for trunk-mount racks, which are significantly cheaper (and lower quality).
Meticulously choose a bike rack
If buying a hitch bike rack with additional rear lights is not an option for you, then you will need to carefully choose a bike rack model that suits best your car’s model. The truth is that there are dozens of bike racks on the market, and different bike rack models will be positioned differently on your car. As a result, the chances are high that some bike racks won’t be covering taillights much being the best choice specifically for your car’s model.
Try to find photos online showing how a particular bike rack model sits on your car (or similar car models).
Install magnetic mount taillights
Even if you have already bought a bike rack and found out later that it significantly covers the taillights, there is still a good solution for you.
You simply buy and install magnetic taillights and consider this problem solved. It won’t break the bank, costs around $20-$50 for a good quality kit.
Make your taillights at least partly visible, and the chances are high that you are going to be fine. Even though it is illegal by the letter of the law, the police enforce it very occasionally. Don’t give the police other reasons to pull you over, and you will likely get away with it.