Interesting article regarding roof racks and mileage

[bobswire]

http://reviews.mtbr.com/that-roof-ra...r-fuel-economy

[KidWok]

Noticed this years ago when I had a Honda civic...it was anemic to begin with, but darn near scary to get up to speed on a freeway on-ramp on long road trips where I had two bikes on top and the car loaded down with stuff. And the fuel economy of course took a huge hit. Will no longer do roof racks...only rear hitch mounted for me.

Tai

[denapista]

Jesus!

15mpg difference between no rack and loaded with (2) bikes? WOW! I think everyone knew having bikes on your roof would create a wind drag, but not this much. I have an old A4 wagon and I lay the seats down and lay my bike down. Glad that I do!

[batman1425]

I used to take mine off and on when needed - but I had hidden bolt style mounts in my roof - so on and off took all of 5 minutes - just drop the whole thing on and tighten 4 bolts into the roof. If I had a car that used traditional door jam style mounts - no way I'd be taking it off an on for regular use. IME the door jam systems inevitably leak, even if you don't mess with them and the ones I had were super fiddly to instal.

[Geeheeb]

I noticed the hit, and started using a saris bones rear rack a few years back, but it seemed more like 5 mpg to me.

[benb]

The article doesn't mention it a lot but the Facebook comments did, they are reporting #s from some of the cars effected the most by fuel economy, other cars are not nearly as badly affected.

It's maybe 1 mpg on my Outback with the empty rack. I have the stock aero shaped crossbars, 2 Yakima fork mount racks that have a little aero shape at the front, and 2 Thule wheel carriers that make no attempt at being aero. Carrying bikes might be a little worse than that but who knows. I carry a bike around on the roof quite often but I don't go on the highway with my bike more than 2-3x a year for vacations. Most of the time when I'm driving traffic is almost a 10mpg effect so I'm not going to worry about the bike rack.

I get the impression the rack penalizes you more when you have the following variables:
- Car that is very clean aerodynamically (e.x. Prius) to get excellent fuel economy
- Car that has a relatively low power engine that relies on careful tuning and you driving in a particular load/rpm range that the engine is really efficient in.

I bet if you look at less aero vehicles with torquier engines the effect of the rack is lessened. Some of the fuel penalties in that article get mentioned as worse than pickup truck drivers get towing big trailers.

[bikinchris]

I have had as many as 5 bikes on the roof of our old Explorer. 4 singles and a tandem WITH bra, and it obviously made less mileage, but only about 5mpg less at highway speeds.
Since historically, most of my bikes were worth more than most of my cars, making it the rear bumper is NOT an option. Buying a minivan to carry bikes is way expensive. But I already have a shop van WITH a roof rack.

[carpediemracing]

Our standard summer set up is to put the rack on the TDI wagon. With no rack we'll see as much as 50-53 mpg, but that's a rare thing; normal is more like 46-48 mpg. With the rack and two bikes we normally see 42-43 mpg, like going to/from races.

With a tandem, 3 single bikes, 4 adults, and a lot of stuff (two of us raced and then we spent a week at a vacation house so racing gear, spare wheels, and regular vacation gear) it was down into the 35 mpg range.

In the winter subtract a solid 5-10 mpg. We rarely see over 42-43 mpg on the highway, we will see sometimes 30 mpg locally.

Cruising speeds 70-75 mph for the most part.

I know that if you put on one of those bug shield things on the bike (like a bike bra sort of thing) it'll knock a few mpg off by itself.

[Tickdoc]

Yeah but not if the bikes are aero bikes

[Ralph]

Love my 1UP for 3 bikes.

[eBAUMANN]

just did a real-world test of this...it is apparently very legit.

i usually have a roof rack with 4 trays and faring on the roof of my 98 volvo T5 V70, which is far from what you might call a "fuel efficient" vehicle.
i generally average around 23.5-24mpg with that combo, mixed use--sometimes with bikes sometimes without, probably 60/40.

i had to have my windshield replaced recently and needed to remove the rack in order to do so. tonight, rack still off, i drove 100mi and averaged 31.8mpg doing so.

id say thats a fairly meaningful improvement...

[Ralph]

I would think where you put racks on the roof matter also....especially when empty. The further back toward rear of vehicle the better. I've seen wind tunnel flow charts of how air goes up windshield and over top of car. Move those racks rear ward.

[shovelhd]

My wife drives a 2016 RAV4 Hybrid that gets 35mpg. We had my Felt, the front wheel, and my Thule Road Trip bike case set up as a cartop carrier on it for a vacation trip. She got 31mpg, and the car was packed with stuff and three passengers. It all depends on the vehicle.

[benb]

Actually it looks like CR only tested one car, the Honda Accord 4-cylinder.

The big spread they saw could have been some oddity where the Honda is tuned just right at 65mph to be in top gear right in the most efficient part of the power band and the bikes on top caused it to downshift or something.

It really doesn't seem to be enough of a study to make the claims they are making. I would expect is very possible there is some other model of car that does really bad with a rear rack.

[eBAUMANN]

Originally Posted by Ralph

I would think where you put racks on the roof matter also....especially when empty. The further back toward rear of vehicle the better. I've seen wind tunnel flow charts of how air goes up windshield and over top of car. Move those racks rear ward.

problem is, the majority of the time you are limited to where the mounting points on your car are (for clip systems like yakima), so not much choice as to wear the rack ends up unless you are drilling holes in your roof for it.