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How much does a bike rack affect MPG?

Many of us use a bike rack on a regular basis, whether it be a roof rack or a hitch rack. The idea that a bike rack can affect the MPG or fuel economy of a car may have already crossed your mind. Turns out, it’s true. According to some studies, a bike rack loaded with 2 bikes can reduce MPG by anywhere around 10%-30%, with roof racks proving more inefficient than hitch racks. In this article, we will discuss this topic in detail. So, keep reading to find out more.

Factors affecting MPG of a vehicle

MPG is short for miles per gallon. It is basically a number stating the distance a vehicle can travel by consuming one gallon of fuel. In other countries, kilometers per litre (KMPL) is used for this. The higher the number the better the efficiency and fuel economy of the vehicle. Bike racks can affect MPG due to two factors – aerodynamics and weight.

Aerodynamics

This refers to how well air flows around the car while it is moving. As a car moves through the air a resistive force known as aerodynamic drag is generated. The more streamlined the shape of the car, the better it can cut through air and reduce drag. A rack with bikes loaded increases the frontal area and hence, increases the drag force. Consequently, the car consumes more fuel to keep itself going. The effect of aerodynamics is very low at low speeds, but increases exponentially with increasing speeds. At moderate to high speeds aerodynamics is the main cause of energy losses.

Aerodynamics of a car with a roof rack
Aerodynamics of a car with a roof rack | Source: https://www.padtinc.com

Weight

Compared to aerodynamics, the weight of a vehicle is not as big a factor when it comes to fuel economy. However, it still plays a part. The greater the weight the harder it is to keep the vehicle running and a higher fuel consumption is required. A bike rack with bikes mounted does increase the overall weight of the car. The effect of an empty rack can be considered to be negligible.

Types of bike racks

There are three types of bike racks that are commonly used on vehicles – roof racks, hitch racks, and trunk racks. The different designs of these racks can affect MPG in slightly different ways. A roof rack places the bike on the roof, and as you can tell, it will significantly increase the amount of drag produced. On the other hand, a hitch rack is installed behind the car. This does not increase drag as much as a roof rack. The same goes for a trunk rack.

The increase in weight will also slightly lower the MPG value. Although, the effect due to weight should be similar for all types of racks since the added weight is more or less the same for the same number of bikes.

Roof rack
Roof rack | Source: https://gearjunkie.com/

Effect of bike racks on MPG

The effects of bike racks, both loaded and empty, on fuel economy have been tested by Consumer Reports. They have used a sedan and an SUV. Each vehicle was tested with an empty hitch rack and then with two bikes loaded. The same was repeated for each car using roof racks. The results are summarized in the table below.

Percentage Reduction in MPG
Hitch RackRoof Rack
EmptyWith 2 BikesEmptyWith 2 Bikes
Sedan3%25%11%28%
SUV2%12%5%19%

Their tests showed that the fuel economy of the sedan took a substantial hit with a loaded bike rack, and even with an empty roof rack the MPG went down more than expected. Only the empty hitch rack proved to have an insignificant impact. The lower height of the sedan meant that the bikes on the hitch rack were exposed to the incoming wind causing quite a bit of drag.

Compared to that, the SUV was less affected by either type of rack. However, the hitch rack was still clearly the better option for MPG. Furthermore, a hitch is easier to take off which could encourage drivers to remove it when not needed and help them save fuel.

Large-scale effect of roof racks on fuel consumption

Roof racks are the most common equipment fitted to cars for transporting large items such as skis, bikes, or snowboards. They are quite common and most people don’t bother to dismount them when not in use. A paper was published in the journal “Energy Policy” which determined the effect of roof racks on fuel consumption. The study showed that 0.8% of the total light-duty vehicle fuel consumption in the United States was caused by roof racks in 2015. This translates to around 100 million gallons of gasoline.

A significant portion of this is due to roof racks carrying no equipment at all. The paper mentions that this value can be brought down substantially if drivers simply remove their roof racks when not required. As proven by other experiments as well, even an empty roof rack reduces MPG of a vehicle. Hence, you should take your roof rack down too when not in use.

F. A. Q.s

Q1. How much money can you save without a bike rack?

Ans.: This can vary a lot depending on a bunch of factors. But just for curiosity’s sake, let’s consider the average commuting distance of 11000 miles per year in the U.S. Let’s also consider the average U.S. fuel economy of 24.9 MPG and the average gas price of $2.87 per gallon. This gives a total of $1268 per year spent on fuel. Finally, let’s consider a low estimate of a 10% reduction in MPG due to a bike rack throughout the year. This will bring your annual expenditure to approximately $1409 which is an increase of $141 from before.

This is a very rough estimate. The extra cost can be a lot more or a lot less depending on how much you travel, how often you use a bike rack, gas prices in your region, etc. Nevertheless, we have proven that you can indeed save some money if you do not use a bike rack. And also keep in mind that we considered a low reduction in MPG.

Q2. Should you stop using bike racks?

Ans.: Of course not! A bike rack is a very useful piece of equipment to bring your bikes along on long trips. Not just bikes, there are also racks for other items such as skis, kayaks, cargo boxes, etc. The only advice we can give you is to take off your bike rack whenever you do not need it. It might not feel like a lot but over time you can save a useful amount of fuel and money.

Conclusion

As you can see from the data, bike racks do indeed affect the MPG or fuel economy of vehicles. However, unless you are travelling everyday with bikes loaded on a rack, there isn’t a very big difference. Besides, the use of a rack is unavoidable for many people. As long as you don’t leave a rack on your car unnecessarily throughout the year, you won’t suffer any significant losses.


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Dion Lewis
My name is Dion Lewis.

I’ve been cycling from my childhood. When I was in high school, I started racing in our local competitions.

At my college life, I took a part time job in a bicycle shop and I learned how to repair and maintain bicycles professionally.

Though I love racing, mountain biking is another thing I do frequently. My friends, neighbors, and colleagues treat me as an avid rider and take my suggestions while they plan for a new bike or a bike gear.

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