One question I get asked a lot is the impact of the RazerLift on the fuel economy of the vehicle. A recent study claims that roof racks can add an astonishing 25% to your fuel consumption, even if they don’t have any cargo on them at all.
Naturally, many people are curious about how well the RazerLift does. Well, I did a little research into that.
First a quick note on the results; something smells suspicious. Can we realistically expect a roof rack – without anything on it – to add 25% to the fuel consumption? This paper, published through SAE International, measured the impact of a cargo box (which is a whole lot larger than just the roof rack) as adding 25-27% to the fuel consumption of a sedan. I think I’ll have to read the fine print on this new study; but let’s consider how the RazerLift performed.
I started with some basic hand-calculations in a spreadsheet, and I had somebody do some CFD modeling. Both of these analyses suggested a reasonable impact on fuel consumption; less than the A/C in your vehicle. But nothing beats a real-life road test. Before the RazerLift was installed I did some road tests at different speeds, over a 9km stretch of road that is relatively flat and recorded the fuel consumption. I then repeated that same test after the RazerLift was installed, but without any cargo mounted to it. The difference in fuel economy is shown in the chart below, with the solid blue line.
There are obviously many factors at play in such an experiment (like not hitting other vehicles on the road) so the dotted blue line was added to the chart to show a more “averaged” impact on the fuel economy at different speeds. Most Albertans seem to drive a little on a quick side, so an impact of about 1 – 1.25 L / 100 km is likely for most drivers.
We also need to remember that all this testing is being done on a prototype; we aren’t finished designing it yet! We have some drag reduction plans we are going to investigate, so these numbers are likely to drop a little by the time we get it to market.
The aerodynamic impact is really only going to be noticed at highway speeds. Aerodynamic drag at city speeds is a very small contributor to the fuel consumption of any vehicle. And most people really want to know how this is going to impact their wallet, so let’s consider that next. How much extra you will pay in fuel will depend on how many highway km you drive each year, and the cost of fuel. The following chart summarizes the typical range most people might find themselves in if the RazerLift adds 1.25 L / 100 km (again, this is probably a high estimate).
Our family probably drives about 10,000 – 15,000 highway km each year, on average. The price of fuel these days is about 90 cents per litre; shown by the green line on the chart. So we can expect to pay somewhere around $150 more in fuel each year if we leave the RazerLift mounted on the vehicle at all times, whether we have cargo on it or not.
Considering I pay roughly that much in fuel each month, that’s less than 10% impact on the fuel economy for us. But we drive a Honda Pilot, so for smaller vehicles the impact might be 10-15%.
Of course, all kinds of disclaimers and warnings are in order – “actual mileage may vary” is quite literally the case here – but this should help give you a rough idea of the financial impact of having a RazerLift mounted on your vehicle. I hope that helps!