Roof Racks, What to Expect?- Mtbr.com
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  1. #1
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    Roof Racks, What to Expect?

    Hey guys, I am going to be putting a Thule rack on my VW GTI and I was curious as to what it would do to the fuel mileage without a bike and with a bike. I am doing it either way just curious in what to expect.
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    still processing the data on the wind tunnel tests, but you can expect a small bump in fuel mileage with and without a bike on top...more obviously with the bike. people tell us between 5% - 10%,

    i would recommend a fairing for your roof rack on the vw. it will help with aerodynamics and also decrease wind noise.

  3. #3
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    I've done calculations based on averages of users reports, fuel costs, and average amounts of driving. What I've found is that in a year to two years (due to how variable the amount of miles driven is), a hitch-rack setup (~400 total cost) will pay for itself and a roof-rack will cost about that much in additional gas. A good roof-setup usually costs about this much in terms of it's initial cost, so honestly the way it comes out is that the roof-rack costs about twice the total purchase price in that time period, whereas the hitch rack doesn't really take any hit (and can usually be removed fairly easily/quickly).

    If you want I can dig it up the calcs I did, and there are a lot of variables, but once you get to around 50mph that is where the parasite drag starts building up quickly. If you are at least reaching those speeds you are reaching the dividing line where having that drag on top makes a difference.

    One theme with the reported milege is that if your milege already sucks, it doesn't go down that much. If you get 15mpg, you might see 14 with the rack and 13 with bikes on top. If you get 35mpg, you might see 30 with the rack and 27 with the bikes, you might say that "27 is pretty good", but if your original was 35 that's a pretty significant loss and in terms of $$$ it makes a pretty big difference. Again, these are highly variable (depends on how you drive, etc).

    Don't forget the noise associated with a roof-rack, that is also often continuous (regarless of whether the bike is mounted or not).
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    I have a 02 VW Golf (2.0 gas engine) with a Thule rack. I commute 550 miles a week, almost entirely highway miles. The results of my unscientific testing: (tried as much as possible to keep same average speeds, about 75mph highway)

    No rack: ~400 miles per tank
    50# load bars and single tray, no bike: ~375 miles per tank (bike on makes it worse)
    All of the above, plus fairing, no bike: ~320 miles per tank (bike on makes it worse)

    My experience has been that although the fairing looks sweet, it actually kills my MPG.

  5. #5
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    What to expect?

    Wind noise, reduced mileage, lots of parts, frustrating to put together and installed properly, loss of good sunroof usage, looks great on some cars, stupid on others, but with bikes on ALWAYS looks good, maximum convenience, always ready to load and go in seconds.

    Just my 2 cents....on my third rack now on my TSX. I went with the new "Whispbar" that is claiming to solve half of the issues I spelled out above.

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    i think you've done a good job articulating this - good information that i would reference in the future.

    Quote Originally Posted by Jayem
    I've done calculations based on averages of users reports, fuel costs, and average amounts of driving. What I've found is that in a year to two years (due to how variable the amount of miles driven is), a hitch-rack setup (~400 total cost) will pay for itself and a roof-rack will cost about that much in additional gas. A good roof-setup usually costs about this much in terms of it's initial cost, so honestly the way it comes out is that the roof-rack costs about twice the total purchase price in that time period, whereas the hitch rack doesn't really take any hit (and can usually be removed fairly easily/quickly).

    If you want I can dig it up the calcs I did, and there are a lot of variables, but once you get to around 50mph that is where the parasite drag starts building up quickly. If you are at least reaching those speeds you are reaching the dividing line where having that drag on top makes a difference.

    One theme with the reported milege is that if your milege already sucks, it doesn't go down that much. If you get 15mpg, you might see 14 with the rack and 13 with bikes on top. If you get 35mpg, you might see 30 with the rack and 27 with the bikes, you might say that "27 is pretty good", but if your original was 35 that's a pretty significant loss and in terms of $$$ it makes a pretty big difference. Again, these are highly variable (depends on how you drive, etc).

    Don't forget the noise associated with a roof-rack, that is also often continuous (regarless of whether the bike is mounted or not).

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    Quote Originally Posted by Jayem
    I've done calculations based on averages of users reports, fuel costs, and average amounts of driving. What I've found is that in a year to two years (due to how variable the amount of miles driven is), a hitch-rack setup (~400 total cost) will pay for itself and a roof-rack will cost about that much in additional gas. A good roof-setup usually costs about this much in terms of it's initial cost, so honestly the way it comes out is that the roof-rack costs about twice the total purchase price in that time period, whereas the hitch rack doesn't really take any hit (and can usually be removed fairly easily/quickly).

    If you want I can dig it up the calcs I did, and there are a lot of variables, but once you get to around 50mph that is where the parasite drag starts building up quickly. If you are at least reaching those speeds you are reaching the dividing line where having that drag on top makes a difference.

    One theme with the reported milege is that if your milege already sucks, it doesn't go down that much. If you get 15mpg, you might see 14 with the rack and 13 with bikes on top. If you get 35mpg, you might see 30 with the rack and 27 with the bikes, you might say that "27 is pretty good", but if your original was 35 that's a pretty significant loss and in terms of $$$ it makes a pretty big difference. Again, these are highly variable (depends on how you drive, etc).

    Don't forget the noise associated with a roof-rack, that is also often continuous (regarless of whether the bike is mounted or not).
    I would definitely like to see what you put together.
    2011 S-Works Epic 29er

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    We have been running the factory VW bars with Thule fork carriers on a MKV Rabbit for the last three years. Wind noise is of course higher. Gas mileage w/o a bike is pretty much the same as it was without it (MAYBE a 2-3% decrease for highway driving). Mixed city/highway driving the car gets the same MPG as it did without the rack.

    Fairing was a waste of money. We tried a fairing for about six months and it didn't really reduce the wind noise (in fact it introduced some different more annoying wind noise in certain cross winds). Save your money and skip the fairing IMO.
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  9. #9
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    '96 GTi, 2.sl0

    Quote Originally Posted by Mdrnizd
    Hey guys, I am going to be putting a Thule rack on my VW GTI and I was curious as to what it would do to the fuel mileage without a bike and with a bike. I am doing it either way just curious in what to expect.
    .... when I had it. I would get a pretty consistent 32 mpg in mixed driving.

    With factory roof racks, no fairing, Thule wheel-on trays, but no bikes: 27 mpg (like, when I was too lazy to take it off)

    With bikes: 22 mpg

    Calculated by miles driven as per the trip computer divided by gas used to fill up the tank back to full.

    Hitch rack: no hit at all.

    That said, on my 2002 Audi A4 1.8t manual quattro sedan (with GIAC chip), I get a consistent 28 mpg in mixed driving (mostly commute freeway, some stop and go) and I get more hit with a bike on the hitch rack. Being a sedan, the bike sticks up in the breeze. With a bike on the back, it drops to around 26 mpg.

    The GTi had a 115 hp NA motor, so I could drive like a hoodlum, and not take much hit in mileage. The Audi is 205 hp chipped. Driving heavy footed eats way more gas when that turbo spools up... Lots of dead dinosaurs fly out of the tailpipe. I got it down to 16 mpg once.

    ... and the roof rack doesn't jack up the paint!
    Last edited by pimpbot; 08-31-2010 at 04:30 PM.

  10. #10
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    Quote Originally Posted by Mdrnizd
    Hey guys, I am going to be putting a Thule rack on my VW GTI and I was curious as to what it would do to the fuel mileage without a bike and with a bike. I am doing it either way just curious in what to expect.

    without a bike on my passat wagon... I take about 1 mpg hit.

    with the bike about 2-3. Depends on how aggressive you drive.

  11. #11
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    Quote Originally Posted by Mdrnizd
    I would definitely like to see what you put together.
    A rough example can be used with Pimpbot's numbers. You can maybe count on what, 8000-10000 miles a year? If you got 32mpg, it would be 250-312 gallons. If you cut that to 27mpg, you use an additional 46-58g $126-160 if fuel costs $2.75/g. That doesn't take into account the hit you get when you put bikes up there though. For me, I do a bigger trip once or two times a month where I drive to Phoenix or Flagstaff to ride. These trips probably constitute a good 4000 miles a year according to my calcs (obviously that's a good deal of the total miles I drive in one year). So then, assuming that we're starting with 27mpg, that's an additional 34 gallons, or $93 bucks. So we are looking easily in the neighborhood of $160-250 in additional gas the first year. If you don't drive as conservatively, or have more highway miles, or just more driving overall, these numbers will be quite a bit more obviously. 8000 miles/yr is probably WAY conservative (for me as well), but even at that relatively low amount I think you can see how significant the cost is. Most people probably don't realize it due to how much it's "spread" out over the year, but $250 is a huge amount of money to waste on drag IMO.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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    "What to expect?"

    Destroying your bikes at least once.

  13. #13
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    I had a Thule rack w/ two full trays and a fairing on my '07 Rabbit for about a year. Decrease in mpg was negligible imho. I will say that w/ the fairing it seemed "draggy" - like I could feel the wind pushing on the roof. Probably just my imagination. I would say that you're probably not going to notice any decrease in numbers unless you're doing a lot of 60+ mph highway driving; in town will likely have no effect on your mpg. Previous posters were right about the fairing; it's a waste of money and probably acts more like a wall than anything. Roof racks look cool if you're into impressing other drivers. I could care less. I wound up selling the rack, getting my money back, and now I just use an Allen trunk rack if I'm carrying more than one bike. Otherwise I drop the back seats and put the bike inside where its safe and secure and there's no effect on mpg whatsoever.

    Just my $.02 though. Do what you want.

  14. #14
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    I got the Thule put on and we will see what it does. I would love to just throw the bike inside but I have two car seats so taking those in and out multiple times a week sucks. haha
    2011 S-Works Epic 29er

  15. #15
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    CARSEATS?! Sheeyat. I make the kids sit on each other's lap in the front seat.

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    I saw a drop from an average of ~25mpg to ~24mpg in mixed driving when I put a set of Thule bars and a pair of Yakima King Cobras (fairly large frontal profile) on my Nissan Maxima. I don't have a lot of mileage with bikes mounted, so I can't say how much of a hit I get then. I've had the rack on for over a year, and am happy with the results, despite the slight hit in mileage. I save a lot of time compared to putting my bike in the trunk with wheels off, and had a bad experience with scratches in my car's paint when using a trunk rack. When I first mounted the rack, I noticed an increase in wind noise, but am now used to it. I don't use a fairing.

    If I had a garage I'd consider a hitch rack next time around, but I think a roof rack remains a very good option for those whose vehicles aren't too tall.

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