Roof Box and reduction of range

[McgR]

We replaced a Countryman SE Hybrid with the electric Volvo XC40, and the Taycan CT4S will replace the XC90. We only use the full luggage capacity twice a year. Winter holiday and summer holiday. I'm not going to size for the exception, so when we need to take a bit more luggage we'll use a roofbox and just add a charging stop or lunch to the trip (or take the plane, drop a kid in friends car, ...)

And if you really need a bigger car for 1 or 2 weeks ... just rent one ;-)
I actually prefer a rental when on holidays, less stress ...

Exactly my situation and my thinking. I think I will rent a 5 series / A6 / V90 for a week for the winter holiday. My bookkeeper advised me that you can put a line in the renting contract that a rental car is allowed for let say 3 weeks a year. Like this the rental car is still on my company and can even be put 100% in cots like an EV. Just have to convince my wife now for the summer holiday.

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[Jrkennedy37]

I was still contemplating to get the (rearmounted) bike-rack and mount some sort of box like the Thule backspace or one of the competing brands that even have a foldable version made of tarp.
But seeing the (very) limited impact on range I'll just go for the roof crossbars and use the roofbox I already have (Thule Motion XT XL 500 liter box).
It actually looks a lot like the Porsche 'optimized' one so don't think I'll lose a lot of range compared to theirs.

Not discounting the prior reported numbers but physics of the roofbox doesn’t change with the Taycan. You’re going to see a significant hit to efficiency. I have the Motion XL box on panamera ST and it’s significant as I reported prior, though less a concern for roadtrips considering the 24 gallon fuel tank.

 

[McgR]

Not discounting the prior reported numbers but physics of the roofbox doesn’t change with the Taycan. You’re going to see a significant hit to efficiency. I have the Motion XL box on panamera ST and it’s significant as I reported prior, though less a concern for roadtrips considering the 24 gallon fuel tank.

That is correct but the shape of different roof boxes can make a difference. The new Porsche roof box is supposed to be good for speed up to 200 km/h. We be nice to know if these better aerodynamics also result in better fuel economy when driving at normal speeds.

 

[Swissbob]

Pretty bad consumption on a recent trip. Box was off but roof bars left on. It was a wet day with quite a lot of water on the road. Maybe that made a difference?

 

[f1eng]

Pretty bad consumption on a recent trip. Box was off but roof bars left on. It was a wet day with quite a lot of water on the road. Maybe that made a difference?

Pumping losses on a wet road are surprisingly high, probably more than many non-scientific types could believe.
It is the reason aquaplaning is real and there the water pumping forces are enough to lift the entire weight of the car at high eneough speed.

 

[Jrkennedy37]

That is correct but the shape of different roof boxes can make a difference. The new Porsche roof box is supposed to be good for speed up to 200 km/h. We be nice to know if these better aerodynamics also result in better fuel economy when driving at normal speeds.

When buying a roofbox I read that all modern Thule boxes are tested to operate at 200kph or what they call “autobahn speeds”. Some of the newer ones cut down on the turbulence between the vehicle roof and bottom of box but they all impact your aero hard.

With the Taycan (and any vehicle) you want to adjust the roofbox as far back as possible, aiming for the front to sit within the wake created by the slope of the windshield. Unfortunately just about every size box mounted to the Taycan/Panamera will overhang the windshield at the furthest to the rear setting so it’s like you have a second small vehicle suspended above your vehicle creating its own drag. If you mount a box on a large Escalade/Suburban and maybe a Cayenne (?) you can position it further back so the box is less obtrusive to the air flow over that vehicle.

 

[Glassdome]

to avoid anyone to have to listen to the whole thing, the conclusion is 13% loss of range. So if we assume in general 15% in average, it is probably a safe assomption. So a roof box in the winter can be something to be cocerned about as we already lose probably 20 to 30% of range already plus another 15%: It is almost half of the whole baterry range being lost.

We did UK to Switzerland in a model 3 this april. With winter tyres, roof box and a separate ski rack. The range drop was pretty significant. The Tesla 3 Long Range should do 318 miles - never does, and so on a good run assume 280 miles with normal tyres. With winter tyres, roof box and ski rack this dropped massively to around 160 miles. We went out with all on. When we came back though we didn't need the roof ski rack and put the skis into the roof box. That improved the range by a fair bit to around 200 miles.

Moral of the story... range drops a lot. Though the ski rack is a killer and the box more efficient then the ski rack on the roof. Which surprised us.

I can't tell you on the taycan as we haven't tried bars and a box yet.

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