How much do roof racks hurt Prius gas mileage?

<div class='quotetop'>QUOTE(teddy b @ Apr 20 2006, 01:43 PM) [snapback]242725[/snapback]</div>

I am not sure about roof racks, but I took my kayak on the roof for a 700 mile trip and my milage dropped from 47 mpg to 36 mpg.
Hope that helps.

 

Road and Track had a very extensive article on how to get better mileage this month, along with their hybrid comparison.

They pointed out that Roof Racks are a double hit. They increase both CD and Frontal Area, so the effects on mileage can be, in their words 'profound'.

 

It's not just the mileage you need to worry about. The Prius is already fairly sensitive to crosswinds, and a loaded roofrack could make that considerably worse. Any significant weight on the roof will also affect the centre of gravity in a bad way.

 

<div class='quotetop'>QUOTE(teddy b @ Apr 20 2006, 02:43 PM) [snapback]242725[/snapback]</div>

Roof racks do not hurt fuel economy near as much as you may think. I have permenant Yakima racks, I can take them off, but too much of a hassle since I ride bikes 3 to 4 times a week. Anyway I still average about 48MPG with the racks. This would include when my bikes are on top. I drive conservatively rarely hitting interstates. I would get about 50 to 51 if I did not have the racks on there 100% of the time. I recommend the fairing and taking time to make sure you get the racks installed correctly. Hope this helps. I assure you it does not hurt your mileage near as much as you may think. All of the people bad mouthing the racks and its adverse effects on fuel economy don't have racks, so they are merely drawing unproven conclusions. Don't let 3MPG change your lifestyle. And by all means don't throw the bike in the hatch, and risk getting chain lube on your seats which will cost way more (in resale) in the long run than the loss in fuel economy.

50000 miles divided by 48 mpg average = 1042 gallons times $2.80 avg cost/gallon = $2917 fuel cost
50000 miles divided by 51 mpg average = 980 gallons times $2.80 avg cost/gallon = $2744 fuel cost

$2917 - $2744 = $173 bucks for 2 years of driving w/racks always on and kayaks, bikes, and skis sometimes on. Not a bad price to pay for the luxury and convinience and distinguishing looks of 58 inch load bars on a Prius. Just another way to stick it to the Hummers and Tahoes with weak factory racks and the occasional Huffy, inflatable kayak atop.

 

B)--><div class='quotetop'>QUOTE(teddy b @ Apr 20 2006, 01:43 PM) [snapback]242725[/snapback]</div><div class='quotemain'><!--quotec-->
Hi y'all

Just wondering how much permanent roof racks hurt your mileage?
Thanks!
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I had roof racks on my Matrix and it did drop the MPG by 2-3. I'm kind of crazy about this so I installed a hitch and bought a Yakima (or Thule if you want) hitch bike rack and it seemed to have no effect on my average MPG. The other nice thing about a hitch rack is that you don't have to worry about pulling into your garage and killing your bikes and second, it's much easier to get the bikes on and off.

 

I was worried about that too - that's why we made sure we could fit 2 people + 2 bikes (+camping gear) into the Prius before we bought it. I know that's not big enough for everyone, but for a couple who likes to go biking and camping, the Prius fits just right.
Put an old sheet down in the back, and you can roll a medium size road or mountain bike in the back without even taking a wheel off (front wheel first, leaned up against back of seats which are protected by the sheet). Take the front wheel off the second bike, and lift it in (rear wheel first, cranks up). Even then, you can still see out the back no problem.

 

<div class='quotetop'>QUOTE(ajrowell @ Apr 21 2006, 06:51 AM) [snapback]243091[/snapback]</div>

Would like to stress this important point. A roof load will hurt fuel economy especially at high speeds, and hardly at all when going slow. One of my best mpg stretches in 2001 Prius was getting a legal file cabinet home from a yard sale - 62 mpg; all below 40 mph. On the other hand, if you load up and fly down the highway, it's gonna hurt.

Aero drag dominates the energy components at high speeds, while tire rolling resistance has a higher relative importance at low speeds. Those switching to wide draggy tires will probably see the larger impact at lower speeds, under the same logic.

 

If you want official numbers, i can tell you right now that adding my Saris roof rack did nothing to hurt my MPG (did the same trip from cleveland to columbus and back both with and without, no effect). During a short extent with the rack fully loaded (two kayaks) on the highway, the MPG droped by about 10. I can give you exact numbers in about a month when i move to Minessota with 1 kayak on the roof and get several tanks worth of data.

 

Eagle, do you have a fairing on your rack?

 

no, i didn't get the fairing (mainly cause i've been pushing my budget a little since i got the car...).

On the plus side, just drove back home (cleveland) from visiting my mom (columbus), a 2 hours drive, mostly highway and averaged 53 MPG, so i think it's safe to say that it's not hurting my mileage. (the roof rack was unloaded, though)

 

<div class='quotetop'>QUOTE(eagle33199 @ May 6 2006, 11:37 PM) [snapback]250954[/snapback]</div>

We have Yakima racks with the Kayak Stacker add on. We loaded up 2 kayaks and filled the car to the brim with 2 adults, 2 kids and camping gear for the weekend. We drove from Largo to Rainbow River in Florida and averaged 40 mpg. Normally I get around 51 without the racks and 48 with the racks (and nothing else). I typically take the racks off when we are not using them. Even with the fairing, I lost 3-4 mpg. Here are a couple pictures - we just got back. BTW, this was one of the most crystal clear rivers I've ever seen!
[attachmentid=3458][attachmentid=3459]

 

I just had Yakima racks installed on my Prius and I have lost 10 MPG. I am a bit bummed it dropped so much. I also get a ton of noise off the racks. How much does the fairing help with the noise and will it help the mileage. I have had friends tell me in the past the fairing actually made the mileage worse.

 

the fairing is designed to be an extension of the windshield and move air up and over the roof rack. if may improve aerodynamics.

the fairing will def reduce the noise though. it may not eliminate it, but it will be quieter for sure.

 

I too thought the fairing might help improve mileage, found the opposite is true..
Mileage is worse with the fairing, but much quieter.

 

I tried the same 130km commute in a Prius NHW10 (1998) repeatedly with roof racks and without, and with 8ft surfboard in the car or on the racks. There was no discernible difference in fuel consumption or noise levels whichever way I transported the stuff.
The commute involved about 50% driving at 100km/h-110km/h and the rest 50-80km/h.
I used the Thule rapid system with "Wingbar".