Results are in - Rooftop box range reduction quantified

[Pigwich]

The results are in - After my earlier awesome beautiful hack job roof crossbars, I drove 1200+ miles with a fully loaded Bolt and a fully loaded Yakima box on top, and I'm confident that we can accurately quantify range reduction with the addition of a Yakima Skybox.

Our usual range of about 3.9 miles per kWh went down to 3.2 to 3.3 miles per kWh. Not great, but the speed limit IS 70 MPH going up and down the 99 here in California, and we drove at the speed limit. And for the record, it was hot. Thinner air, but more AC power.

Reducing speed helped a LOT. Way more than if we had a bare roof.

AC only ended up being about 4% of our usage, and battery conditioning sometimes hit 1% in the crazy heat and with all the fast charging, but overall, it wasn't horrible. But don't plan on doing 200 mile legs by any means. It's not going to happen on the highways.


Welcome to your new 160 mile car.

View attachment yakimabox.jpg
This was the beast - The box was crammed with baby equipment and camp furniture, and two adults and two kids in two car seats down below. Epic 4th of July EV camping weekend.

Taking the 99 is WAY more humane than taking the 5. Never done it before, but even if we're in the gas car, we'll still avoid the 5 in the future. The food options on the 99 are way better.

Also, still furious about EVGo's awful 30 minute policy and the constant babysitting.

 

[EldRick]

Welcome to your new 160 mile car.

Agreed - and that's not even in winter.

 

[NeilBlanchard]

Aerodynamic drag is already the vast majority of the load on the drivetrain at 70MPH, so the angle of the underside of the rooftop carrier increases the Cd (a LOT?), and the increased frontal area are going to take a big hit.

Drag goes up with the square of the speed, and the required power to push it goes up with the CUBE of the speed. You'd be much better off with a hitch box mounted down behind the car. Or, if the rooftop carrier could be leveled, that might help reduce the drag.

 

[dandrewk]

Even driving with your windows down will affect range. So naturally, adding a sail to the top of you car will have a huge impact.

 

[LeftieBiker]

Yeah, that Bolt looks like it could briefly take flight at 70MPH. The box needs to be repositioned, and I'd also try shaping some stiff plastic sheet to make a dam around the front underside.

 

[Pigwich]

Yeah, that Bolt looks like it could briefly take flight at 70MPH. The box needs to be repositioned, and I'd also try shaping some stiff plastic sheet to make a dam around the front underside.

An air dam would probably help the drag situation quite a bit. As for taking flight, I suppose it's possible, but I will say that the vehicle "felt" exactly as it did without the box, even at high speeds and outrageous winds, cross and otherwise. I would prefer to have it much further back than it was, but unfortunately the rear hatch would hit the box when we opened it. Thankfully, that box sits in the garage but for a few days a year, and honestly, after the range penalty (among other things), the whole family is getting behind packing lighter in the future.

I wonder when GM is going to come to our rescue with approved, engineered accessories?

 

[boltage]

Since you fabricated your own "towers" for the roof crossbars, would it make sense to remake them so that the front ones are shorter than the rear ones, so that the two crossbars are at the same height, allowing you to carry roof boxes and other longer loads level instead of tipping up? (The rear mounting points in the rails are lower than the front mounting points.)

 

[Pigwich]

Right - I could shorten the ones in the front pretty easily by just sawing and re-drillng them to some extent. Unfortunately, the crossbars are not exactly commodity aluminum tube, they're from some ebay seller for a Honda Odyssey. It's actually the cheapest way for the average joe to get streamline tubing, but insanely expensive as tube aluminum goes.

http://www.ebay.com/itm/OE-Style-Ro...rier-For-2011-2017-Honda-Odyssey/252891101581

The risk is that every time I iterate the design I have to (probably) order more Honda roof rack to the tune of $50, strip the horrible paint off, re-cut and re-weld...

 

[boltage]

Alternatively, for your roof box, you may want to see if it is possible to shim the rear crossbar where the roof box clamps to it, so that the roof box rides level even though the rear crossbar is lower. However, the amount of shimming that can be done may be limited by whether the roof box clamps can close around the crossbar with shims.

 

[bro19991]

What's the cargo rating of the Skybox?

My Thule hitch mounted box (13 cubic feet) setup. Minimal range impact.

 

[Pigwich]

Alternatively, for your roof box, you may want to see if it is possible to shim the rear crossbar where the roof box clamps to it, so that the roof box rides level even though the rear crossbar is lower. However, the amount of shimming that can be done may be limited by whether the roof box clamps can close around the crossbar with shims.

I checked the amount of offset that the front and rear bars have - The front is a half inch higher, so not ideal, but not crazy amounts of offset. I can easily shim it, but I think I can saw and re-drill the risers.

As for my Skybox, I'm pretty sure it's a 16. That's 16 cubic feet. It's good because I can put LONG things in it. I have it because we had it for all our other cars over the years, from a Scion xA to a Nissan Rogue to my Spark EV and now the Bolt. It's probably not an ideal solution. I do like the trailer hitch one because I don't have to be the exclusive loader and unloader, but I like the roof one because it's a little more secure, as in,slightly harder for some idiot to break in to, and it wouldn't block the cameras.

What's the cargo rating of the Skybox?

<span>My <a href="http://www.amazon.com/s/?field-keywords=thule&tag=myelecarfor-20" class="interlinkr" target="_blank">Thule</a> hitch mounted box (13 cubic feet) setup. Minimal range impact.</span>

http://www.renegadejuggling.com/walking-globes-24-inch-diameter