How bad is this, Aerodynamically? (rear-mounted bike rack on SUV) - Fuel Economy, Hypermiling, EcoModding News and Forum

campisi · 10-30-2012, 01:10 AM

Hard to pinpoint exactly but when my bike is on the back of my Forester I seem to take a 1-2MPG hit on the highway. Doesn't seem like it should affect the MPG (one of the reasons I got a hitch rack rather than a roof rack). Would the factory rear 'spoiler' (2nd pic) do any good?

Cd · 10-30-2012, 05:25 AM

Can you easily remove the handlebars ? I would think you could, but you would have the brake lines holding it on.
You could simply zip-tie it to the bike frame and re-attach it once at your destination.

The handle bars are right inside where your wake spills over the rear of the vehicle ( unfortunately, so are the edges of the tires, but I would see if the handle bar removal helps any. )

renault_megane_dci · 10-30-2012, 05:45 AM

Much better than the roof rack obviously but I have been told by a fellow van engineer that the aero concept over those is that they want the wake to somehow "push" the vehicle.

If the concept is true, then a bike would affect it.
And let's be honest, your car is more van sized than car sized ...

MetroMPG · 10-30-2012, 08:51 AM

It's far, far better than a roof rack.

If the bike's tires extend past the sides of the vehicle, then it's worse than not having anything at all back there. In fact, even if the tires only approach the sides of the vehicle, it'll be worse than nothing.

That rear spoiler will help if extends the downward "taper" of the roof line at the rear (should be easy to eyeball). If there's no obvious downward taper, it may still help, but only careful testing would confirm. Regardless, it would not undo the effect of having the bike's tires extend wider than the rear of the vehicle though.

MetroMPG · 10-30-2012, 08:52 AM

PS: delete your roof racks.

campisi · 10-30-2012, 11:17 PM

The tires do, in fact, extend a few inches past the car on both sides. This is probably where most of the MPG hit is occurring. Not much I can do about that, but on long trips I may go ahead and remove the bars and velcro to the frame. Sometimes I use an extender for a 2nd bike and I'll bet the bars (and seat for that matter) would have even more effect.

Roof rail delete is on the list of things to do!

redneck · 10-31-2012, 04:35 AM

Just a suggestion...

Remove the front wheel, turn the handlebars parallel to the frame, center bike on rack. Use motorcycle tie down straps to secure the bike to the rack.

>

euromodder · 11-01-2012, 09:01 AM

Have you tried transporting it inside ?
With the front wheel out and the seats partially folded down, it looks like it'll fit inside.

campisi · 11-01-2012, 10:08 PM

It easily fits inside .... if I fold down the rear seats. I don't particularly like to do that because mo matter how careful I am I end up scuffing up the inside of the vehicle (the headliner, sides) and chain lube and dirt gets everywhere. If I remove the front wheel it becomes easier. I like to just throw it on the rack which takes less than 30 seconds no exaggeration and be on my way. I guess it's a choice I'm making. Yeah, I know I'm whining.

For long trips I have lots of other stuff inside not to mention the wife and her bike. For those long trips I may do as you suggest and use a tiedown to hold the fronts to the rack. This would allow me to get the rear wheels out of the side airstream of the vehicle.

euromodder · 11-02-2012, 08:59 AM

Quote:

Originally Posted by campisi

It easily fits inside .... if I fold down the rear seats. I don't particularly like to do that because mo matter how careful I am I end up scuffing up the inside of the vehicle (the headliner, sides) and chain lube and dirt gets everywhere.

There's a neat solution to that : Bicycle bag !
They come in all sorts and sizes.

Sure, it's a bit more work than putting the bikes on the rack.

Quote:

For long trips I have lots of other stuff inside not to mention the wife and her bike.

Use more bags