Using a roof rack is often a great way to save space and conveniently transport bikes from place to place. However, mounting a roof rack and adding bikes can significantly change how your vehicle handles. Roof racks and bikes can also affect mileage. Learning more about how a roof rack and mounted bikes affect your vehicle can help you adapt your driving, which often makes for a safer, less stressful journey.
How Fast Can I Drive with a Roof Rack and Bikes?
There’s no hard rule about how fast you can drive with a roof rack and bikes on your car, but in general, it’s recommended that you stay at or below 75 miles per hour.
Anything mounted to the roof of a car or SUV creates air resistance. The faster you go, the more air resistance is created. Air resistance can make vehicles more unstable, leading to difficulty when maneuvering or making turns.
Maintaining a safe speed is particularly crucial during inclement weather. Slippery road conditions, due to rain, snow, or ice, or windy conditions already make driving more hazardous, and these conditions paired with the air resistance and instability created by a roof rack and bikes can make turns, lane changes, or other maneuvers even more challenging.
Attempting not to drive during bad weather is the safest option, but if it can’t be avoided, try to stick to slower roads and maintain an even, low speed as much as possible.
Are There Speed Limits When Driving with Bikes on the Roof?
Although there are no additional legal speed limits for driving with bikes mounted on a roof rack in the United States, it’s always a good idea to maintain a safe speed. The best option is to drive at or slightly below the legal speed limit for the road.
If you intend to do some highway driving, ensure that you’ll be maintaining a safe speed of 75 miles per hour or less. If the speed limit feels too high, choose slower surface roads in order to protect yourself, your bikes, and the vehicles around you.
Drag Caused by Bikes
Today, most vehicles are designed to be as fuel-efficient as possible. This means that even larger vehicles such as trucks or SUVs are crafted to be aerodynamic, creating less air resistance or drag. This not only helps with fuel economy but can also make driving and maneuvering safer and more stable.
Adding anything to the outside of the vehicle can change the aerodynamic aspects of the car. Even a roof rack alone will cause drag, and adding bikes increases wind resistance significantly.
In addition to changing the fuel economy of the vehicle, drag also exerts a good amount of force on the roof rack and bikes. At high speeds, particularly those over 75 miles per hour, bikes can actually be pulled off the roof. Not only can this cause severe damage to the bikes, rack, or roof of the vehicle, but it can also endanger other drivers.
No matter how fast you plan to drive, always ensure that your roof rack and bikes are properly installed and mounted and that they’re securely strapped down.
Fuel Economy
Although bikes aren’t very heavy, mounting them to your car can drastically decrease your fuel economy. How much your fuel economy changes, however, depends on what type of vehicle you’re driving and how the bikes are mounted.
SUVs or other large vehicles don’t tend to be very fuel-efficient, to begin with, so their fuel efficiency doesn’t change quite as much when bikes and a rack are added. If an empty roof rack is added to an SUV, the fuel economy drops by about five percent. When bikes are added, the fuel economy drops by about 19 percent.
For a vehicle that gets an average of 24 miles per gallon, a 19 percent drop in efficiency equals a decrease of about 5.5 miles per gallon. On a 25 mile drive, you will burn around 0.31 gallons of extra fuel over the course of the drive. On longer trips, the extra fuel burn can be significant. A bike rack and bikes mounted at the back of the vehicle, on the other hand, only causes a decrease in mileage of about 12 percent.
Smaller vehicles such as sedans or compact cars see an even greater decrease in fuel economy. An empty roof rack causes a decrease in fuel efficiency of about 11 percent on a sedan, and a decrease of between 28 and 31 percent is common when bikes are mounted. This is a loss of about eight or nine miles per gallon.
A rack hitched to the back of a sedan, however, causes only a three percent mileage decrease. When bikes are mounted to this type of rack, sedans generally see a fuel efficiency decrease of about 25 percent. For these reasons, if a longer drive at higher speeds is necessary, it’s often best to stow bikes inside the vehicle, in an aerodynamic box at the top of the vehicle, or mount them on the back of the vehicle.