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  1. #1
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    roof rack and mpg loss?

    For you folks that are using roof racks to transport your bikes, what is the mileage loss with the roof rack, and the loss with the bike(s) on top?

    thanks,

    -Sp

  2. #2
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    Not much difference with just the rack because of the fairing. With bikes I lose a few miles per gallon.

  3. #3
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    Quote Originally Posted by fred?
    Not much difference with just the rack because of the fairing. With bikes I lose a few miles per gallon.
    IMO the fairing doesn't really help with gas economy, only reduces the noise. By mounting it on the roof you effectively increase the height/profile of your vehicle, so while it may be reducing the turbulence, it creates additional resistance, so the effects will cancel each other out.
    I drive a Civic with two Thule uprights on the roof rack, and if I drive over 110km/h, I do notice a slight increase in fuel consumption, maybe up to 10%. With bikes and at high speeds, it's obviously even more - I'd say between 13-18%. I actually remember calculating it a few first fill-ups, and it worked out around that.

    Arek

  4. #4
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    those numbers sound substantial. I assume you get about 35mpg on the freeway sans roof rack / bike. 15% loss is a hair over 5mpg. Is that correct?

    thanks,

    -Sp


    Quote Originally Posted by Arek
    IMO the fairing doesn't really help with gas economy, only reduces the noise. By mounting it on the roof you effectively increase the height/profile of your vehicle, so while it may be reducing the turbulence, it creates additional resistance, so the effects will cancel each other out.
    I drive a Civic with two Thule uprights on the roof rack, and if I drive over 110km/h, I do notice a slight increase in fuel consumption, maybe up to 10%. With bikes and at high speeds, it's obviously even more - I'd say between 13-18%. I actually remember calculating it a few first fill-ups, and it worked out around that.

    Arek

  5. #5
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    Quote Originally Posted by SinglePivot
    those numbers sound substantial. I assume you get about 35mpg on the freeway sans roof rack / bike. 15% loss is a hair over 5mpg. Is that correct?

    thanks,

    -Sp
    City and highway combined, I think I was getting on average ~ 34mpg (6.9l/100km). Since I have the rack on the car, it probably dropped to ~ 31mpg (7.6l/100km), and with two bikes - 26mpg (9.0l/100km).
    Mind you, these are not super accurate, just my estimates. Especially the last one - I haven't driven a whole tank's worth of fuel with bikes on top all the time, so the 26mpg figure is an estimate.
    Usually, with 2 rides to the trailhead a week, and normal city nad highwat driving i'm at just over 28mpg (8.4l/100).

    Arek

  6. #6
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    My car with nothing gets about 35 mpg highway (or at least it did when it was new. I have not run it without the rack and fairing since about 6 months after I bought it in '98). With rack, fairing and 2 bikes, it goes down to about 28. With rack, no bikes and no fairing it was about 26. With no bikes and with fairing, about 31. However, on my previous car, I did not notice a change in mpg between rack and no rack. I did not own fairing then. Old car was a subaru justy. New(er) car is a ford escort.

  7. #7
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    Depends on the vehicle. A big SUV with a powerful engine is less affected than a sub-compact like my under-powered Civic.
    My Civic gets about 38mpg on the highway without the roof rack; 32 with the rack and no bikes; 30 with rack and one bike; 26-30 with two bikes. I am very affected by headwinds and how hard I am driving, too.
    With my old Quantum Wagon it was 23 bare; 20 with rack; 18-20 with bikes, any number up to 4.
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  8. #8
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    My VW Passat gets 30 MPG with no rack, 25 MPG with rack (adding bikes lost me another 2 MPG). Thule rack, no fairing. LOTS of wind noise.

  9. #9
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    On my old Trooper it cost about

    3-4 mpg at highway speeds with bikes on top. I use a hitch rack on another SUV these days and see little difference in mpg.
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  10. #10
    Jm.
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    remember, drag is a function of the square of velocity, so your drag at 80mph is 4 times what it is at 40mph. This means your change in MPG due to bike racks may not be huge if you don't go 75-80mph everywhere, but if you do, you could notice a pretty huge difference between your bike-rack and non-bike-rack MPG.
    I know in my heart that Ellsworth bikes are more durable by as much as double. AND they are all lighter...Tony Ellsworth

  11. #11
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  12. #12
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    thanks a bunch! Hitch rack it is!

    -Sp

    Quote Originally Posted by glenzx

  13. #13
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    Quote Originally Posted by SinglePivot
    thanks a bunch! Hitch rack it is!

    -Sp
    I HATE hitch racks!
    • Blocks my rear vision.
    • The bikes get dirtier (I had my disc brakes contaminated on the back of the truck).
    • Blocks access to the rear of the car.
    • More exposed to damage in traffic.
    • Can be fussier to load. I can load 4-5 bikes on the top of my Civic. Could only get 3 on a 4 bike hitch rack and only after moving seatposts and stems.

    Roof top racks all the way for me!
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  14. #14
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    Which is pretty close to saying the same thing I said.

  15. #15
    Jm.
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    Quote Originally Posted by shiggy
    I HATE hitch racks!
    • Blocks my rear vision.
    • The bikes get dirtier (I had my disc brakes contaminated on the back of the truck).
    • Blocks access to the rear of the car.
    • More exposed to damage in traffic.
    • Can be fussier to load. I can load 4-5 bikes on the top of my Civic. Could only get 3 on a 4 bike hitch rack and only after moving seatposts and stems.

    Roof top racks all the way for me!
    I could see how bikes could block your view in a civic, but if you really need access to the rear of the car, just reach your arm back from the drivers seat.

    More exposure to damage? Talk about subjective, you can rip your bikes off a roof rack easy, not to mention it increases your CG...

    5 bikes on top of a civic...wow.
    I know in my heart that Ellsworth bikes are more durable by as much as double. AND they are all lighter...Tony Ellsworth

  16. #16
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    Not much difference for me.

    I am somewhat neurotic about keeping track of my mileage on any car I have owned. I currently own a 2003 CR-V. I put a Thule rack on top of my car along with a fairing (I needed it for the noise) and I noticed my mileage drop from around 25 to about 22. When I added a Thule box to it the mileage did not seem to change. Finally it occured to me to try taking off the fairing with the box still on, and my mileage was back up to 25. No noise either. It seems that in my case the fairing is about the only thing that had any real effect on my mileage. When I moved across the country last summer I had a bike on a roof tray, two on a Spare Me rack on the back and a big Thule box, and I could not tell a difference in my mileage. I was in a caravan with several others moving with me along with a 25' Penski, so we were averaging about 70.

    I know this result is unusual. Perhaps it has something to do with the shape of the vehicle. Someone above mentioned that SUV's with big engines are less effected. While this certainly does not have a big engine (4-banger) it is the size of some smaller suv's (explorer, cherokee).

    Kapusta

    Quote Originally Posted by SinglePivot
    For you folks that are using roof racks to transport your bikes, what is the mileage loss with the roof rack, and the loss with the bike(s) on top?

    thanks,

    -Sp

  17. #17
    Jm.
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    Quote Originally Posted by kapusta

    I know this result is unusual. Perhaps it has something to do with the shape of the vehicle. Someone above mentioned that SUV's with big engines are less effected. While this certainly does not have a big engine (4-banger) it is the size of some smaller suv's (explorer, cherokee).


    Kapusta
    It could be that the fairing causes the airflow to seperate from the vehicle. This is what happens when a wing stalls, but the drag as a result of seperation is extremely high, higher than parasitic drag at lower speeds. This is why the golf ball is dimpled.

    But, parasitic drag still increase as a function of the square of velocity, so your results may vary depending on the speed at which you drive, again at 60mph with no fairing you might get the "same" gas milege, but at 80mph the parasitic drag (drag as a result of cross-section) may take over and be the largest factor.

    Your results are possible though, if the fairing causes the airflow to seperate, it would be the reason why.
    I know in my heart that Ellsworth bikes are more durable by as much as double. AND they are all lighter...Tony Ellsworth

  18. #18
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    Quote Originally Posted by Jm.
    I could see how bikes could block your view in a civic, but if you really need access to the rear of the car, just reach your arm back from the drivers seat.

    More exposure to damage? Talk about subjective, you can rip your bikes off a roof rack easy, not to mention it increases your CG...

    5 bikes on top of a civic...wow.
    The hitch rack blocks my view on my Ram pickup with a canopy and restricts access to the bed. I like to be able to load and unload through the back without having to move or remove the bikes. NOT the same as "just reach(ing) your arm back from the drivers seat."

    I have backed (and been backed into) a rear rack full of bikes into something several times (partly the vision issue). NEVER damaged a bike (knock wood) on top in 20 years. Never had another driver run into the TOP of my car either. I have also seen rear mounted bikes being drug on the road and tires melted by the exhaust.

    Raising the CG? Get real! We are not driving race cars.
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  19. #19
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    Quote Originally Posted by kapusta
    ...When I moved across the country last summer I had a bike on a roof tray, two on a Spare Me rack on the back and a big Thule box, and I could not tell a difference in my mileage. I was in a caravan with several others moving with me along with a 25' Penske, so we were averaging about 70...
    Kapusta
    Drafting, especially behind a box van/truck can HUGELY increase your gas mileage. I had headwinds all the way to Sea Otter last spring. On my own, flat-out was 60 mph and I got 25 mpg. Drafting a truck I could do 65 mph and jumped to 34 mpg.
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  20. #20
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    Quote Originally Posted by shiggy
    ...and restricts access to the bed. I like to be able to load and unload through the back without having to move or remove the bikes.
    The Yakima "Full Swing" (I think thats the name) just swings off to the side, allowing full access with all the bikes still on her. Yes, you have to detach the big t-bolt and rotate the whole get-up away (takes maybe 10 seconds?), but the few times access is needed via the liftgate (Jeep Cherokee) it's never seemed like a big deal. If we had a lower car, way lower - like a civic, I'd have stuck with a roof set-up. The main issues were mileage and access for my wife - who had a legitimate complaint about hefting bikes up onto the roof, as she could barely reach the trays with a bike over head! Love the civic, just can't haul firewood via trailer from deep in the fuelwood areas with one!

    In the thread I posted the link to, I explained the huge improvement in mpg, which continue to this day. Average highway cruising gets us 25-26 mpg! This is between 5-10 mpg different than with a roof rack set-up on an already aerodynamically challenged Jeep. On a trip last spring to Lakewood, CO., I got an abysmal 16 mpg with 2 bikes on the roof on I-25, with moderate winds. Last week I drove about 500 miles and needed 18.6 gallons! WooHoo! I'll stick with the 'inconvenience' of the swing-away rack.

    Incidentally, I've wrecked 3 bikes on a roof rack, in the old days, on a Toyota Celica. Of course it ripped the rain gutters apart too, and damaged thew garage. Neve backed into, or been run into, with the hitch set-up.

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  21. #21
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    With our Jetta (TDI, not gas) we got 38mpg WITH two bikes on the roof visiting Shiggy and friends in Oregon. Without bikes and just racks, mph is around 44mpg. Without racks or bikes...about 48mpg. Yes, that's right, 48mpg. That's on the freeway mind you. Around town, all stop and go, mpg drops all the way down to about 34mpg.

    That said, we're thinking of selling the car because roof racks have been a nightmare for us. We've been spoiled by the hitchmounted Sportworks and it's ease of use, dependability, etc. Looking to get another economical vehicle that can accept a hitch, aka suburu/element/etc
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  22. #22
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    Not really, 3 FREDS...

    Quote Originally Posted by fredł
    Which is pretty close to saying the same thing I said.
    He provided more detail and actual numbers as opposed to using trivial words such as 'few'.
    He also put it more eloquently.

  23. #23
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    hmm

    on my 94 honda accord, with roof rack/no bikes, about 27-28, with no rack/bikes 29-30, and with bikes/rack, about 25 or so. I havent seen the huge difference everyone else is talking about.
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  24. #24
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    Similar loss here

    Quote Originally Posted by Arek
    City and highway combined, I think I was getting on average ~ 34mpg (6.9l/100km). Since I have the rack on the car, it probably dropped to ~ 31mpg (7.6l/100km), and with two bikes - 26mpg (9.0l/100km).
    Mind you, these are not super accurate, just my estimates. Especially the last one - I haven't driven a whole tank's worth of fuel with bikes on top all the time, so the 26mpg figure is an estimate.
    Usually, with 2 rides to the trailhead a week, and normal city nad highwat driving i'm at just over 28mpg (8.4l/100).

    Arek
    I drive a '96 GTi with a 2.0l 4 banger, 5 speed day in and out, prolly about 2k miles a month. I have the factory VW Thule racks, the ones that clamp the down tubes and let you keep the front wheels on. I tend to drive at 70-80 most of the time.

    No roof racks: 32 MPG with my semi-heavy-footed driving, mostly freeway miles.
    Roof racks, no bikes: 30 MPG
    Roof Racks and two bikes: 26 MPG

    In addition, the roof racks are so noisy with or without bikes, I can't open the sunroof without going deaf. That means more running the AC (and the car is black, so I have to run it whenver it gets to 70 F outside), so that drags on the engine as well... although not much.
    Last edited by pimpbot; 12-01-2004 at 06:35 PM.

  25. #25
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    Quote Originally Posted by shiggy
    Drafting, especially behind a box van/truck can HUGELY increase your gas mileage. I had headwinds all the way to Sea Otter last spring. On my own, flat-out was 60 mph and I got 25 mpg. Drafting a truck I could do 65 mph and jumped to 34 mpg.
    I'm not sure if you are refering to my situation in particular, but I was rarely drafting the truck. We all had walky-talkies so I just tried to stay within sight. I even spent a day on my own because I wanted to get to Breckenridge a day ahead of everybody else.

    I may loose the box at some point just to double check the mileage without it.

    Kapusta

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