Part of the Tesla Model S's world-leading electric range comes from aerodynamics — so what happens when you stick a bike rack and a bicycle on the roof? That's what Tesla enthusiast Bjørn Nyland set out to test:
If you don't want to watch the video, here's what you need to know: with a bike rack and a single standard road bike on the roof, he saw a 12% increase in energy consumption at 40mph (controlling for various factors). The increase in consumption doesn't come so much from weight — the roof rack and bike combined will weight less than 40 pounds — but from atmospheric drag. Even with a nice slim profile, they're simply not as aerodynamic as the deliberately sculpted lines of the car alone.
What does that 12% increase in power usage translate to in range? Roughly a 10-11% decrease in range, which would cut the range of the 294-mile Model S 90D to 263 miles. It's not a huge decrease, but it's notable. Of course, a gas-powered car would see a similar hit to its mileage, so Tesla's not alone here. And if you put a larger bike or more bikes on the roof you'll generate more drag, and increasing the speed will intensify the drag for further hits to your mileage.
Bottom line: when planning a trip with a bike rack on your Tesla's roof, expect to loose at least 10% of your car's range.