Roof racks responsible for 100 million gallons of fuel consumption- Mtbr.com
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    Roof racks responsible for 100 million gallons of fuel consumption

    New study suggests that roof racks account for a pretty sizable portion of U.S. fuel consumption. On my old WRX, my MPGs went from bad (~24mpg) to worse (~21mpg) with the rack and bike up there. Very happy to have a hitch these days, though I'd be curious to know if its any better.

    New Study Finds that Roof Racks Are a Real Drag on U.S. Fuel Consumption - Scientific American Blog Network
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    I believe it. I know that I go from about 32 without anything mounted to 29 with two bikes on the hitch to 25 with two bikes on the roof on my Subaru XV on the highway. In addition to killing fuel efficiency, there is the whining sound when bikes are on the roof. I have my hitch rack mounted the majority of the time, but didn't keep my roof rack on except when hauling something for those two reasons.

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    Putting this in context - the US consumed about 140 Billion gallons of gasoline in the same year (2015), it's so little that it doesn't even show up 2nd decimal. Being precise, it's 0.07% of the US's 2015 gasoline consumption. So it's not even the rounding error on the rounding error.

    Nothing to see here.

    J.

  4. #4
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    I timed taking off my T2 rack AND the receiver it goes into (receiver plugs into a tow-bar behind my bumper), 32 seconds. About 23 for the rack and 9 for the receiver. I just leave it against the side of the garage when not in use. I can't stand to just throw money away for no purpose. Think of all the positive things we could do with the money spent on that gas?
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    I'm debating on switching to a hitch mount carrier...not because of gas mileage but an improvement would be a bonus. I'd miss the roof trays though...they at least look kinda cool and set my car apart...makes it easier to find in the parking lot. Just trying to decide on a carrier and if I want to go to the expense of installing a hitch and buying a whole new system. Leaning towards the Thule T2 Pro due to price and it seems like a solid unit. Maybe not the best, but good enough.
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  6. #6
    007
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    Quote Originally Posted by JohnJ80 View Post
    Putting this in context - the US consumed about 140 Billion gallons of gasoline in the same year (2015), it's so little that it doesn't even show up 2nd decimal. Being precise, it's 0.07% of the US's 2015 gasoline consumption. So it's not even the rounding error on the rounding error.

    Nothing to see here.

    J.
    So to reframe your argument, if I offered you 0.07% of $140B dollars, you're saying that you'd turn it down because "it's so little that it doesn't even show up 2nd decimal?" Converting an absolute value to a fraction of a whole doesn't somehow magically negate or reduce its absolute value. 100 million is still 100 million.
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    Quote Originally Posted by 007 View Post
    So to reframe your argument, if I offered you 0.07% of $140B dollars, you're saying that you'd turn it down because "it's so little that it doesn't even show up 2nd decimal?" Converting an absolute value to a fraction of a whole doesn't somehow magically negate or reduce its absolute value. 100 million is still 100 million.
    To start, that would be eliminating ALL roof carrier usage.

    To illustrate how asinine your statement is, that means you'd personally have to be driving all those miles per year at 383,000 miles per day at 15,000 mph (without a roof rack, mind you at at just below escape velocity to prevent going orbital) in order for it to be yours to give. I'd pay money to watch you try that. And then when you're done, yeah - it would be a kick to watch you pay me to do that (even it if were a single penny).

    Another way of looking at this is if you drove 10,000 miles a year with the roof rack attachments on, it would take you about the life time of the rear rack to pay for it in terms of gas savings. So if you already have the roof racks, it's simply a waste of money to switch.

    This works out to about $0.004/mile savings out of the $0.55/mile cost to drive your car.

    If we were to worry about the percentage of all that roof rack usage that were specifically related to bike carriers, it would probably be another couple of orders of magnitude less of a savings.



    J.

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    Quote Originally Posted by JohnJ80 View Post

    This works out to about $0.004/mile savings out of the $0.55/mile cost to drive your car.
    You are mixing statistics. An individual's savings is on the order of a couple cents a mile. The average American vehicle would hit the break even point to replace their roof rack in 2-3 years if they keep the rack on full time (assuming my above mileage change, which seems about right since my car is pretty near new car fleet fuel economy).

    Agreed that it doesn't make sense to compare individual savings and economy-wide savings, but don't turn around and conflate them to make your point.

    Regardless of your statement, it is a greater than negligible amount of fuel that represents on the order of 0.1% of the US greenhouse gas emissions.

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    Here's the numbers.

    You have to look this as gallons per mile instead of miles per gallon to see the cost.

    In the example that we were given above with specifics - decrease in gas mileage from 32mpg to 29mpg which is fairly consistent for a lot of modern cars on the road today. That comes out to (1/29)-(1/32) gallons per mile or 0.003 gallons per mile saved. At $2.20/gal (around here) that comes out to $0.007 saved cost per mile. Drive 10,000 miles with the roof rack on and that saves $66 per year. 10,000 miles is based on putting the rack on for half of the year (skip winter etc...) and 20,000 miles per year driving. That's probably really generous from a cost savings perspective since most people don't drive that much.

    Excluding the time value of money, to replace with the hitch rack I have which is 1UpUSA for $498 for two bikes would take 7.5 years to pay back. If I ran over today to REI and bought a Thule T2 on sale for $439, that would be 6.65 years.

    Doesn't make sense on the basis of fuel savings.

    The definition of what is a negligible amount of fuel is largely personal. YMMV - literally.

    J.

  10. #10
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    Quote Originally Posted by JohnJ80 View Post
    Here's the numbers.

    You have to look this as gallons per mile instead of miles per gallon to see the cost.

    In the example that we were given above with specifics - decrease in gas mileage from 32mpg to 29mpg which is fairly consistent for a lot of modern cars on the road today. That comes out to (1/29)-(1/32) gallons per mile or 0.003 gallons per mile saved. At $2.20/gal (around here) that comes out to $0.007 saved cost per mile. Drive 10,000 miles with the roof rack on and that saves $66 per year. 10,000 miles is based on putting the rack on for half of the year (skip winter etc...) and 20,000 miles per year driving. That's probably really generous from a cost savings perspective since most people don't drive that much.

    Excluding the time value of money, to replace with the hitch rack I have which is 1UpUSA for $498 for two bikes would take 7.5 years to pay back. If I ran over today to REI and bought a Thule T2 on sale for $439, that would be 6.65 years.

    Doesn't make sense on the basis of fuel savings.

    The definition of what is a negligible amount of fuel is largely personal. YMMV - literally.

    J.
    I believe you're going to get a bigger hit than just 3mpg, it's usually a bit more significant than that.
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    Quote Originally Posted by Jayem View Post
    I believe you're going to get a bigger hit than just 3mpg, it's usually a bit more significant than that.
    It depends on the car and the gas mileage of the car.

    It's going to take a given amount of gas (energy) to push a given aerodynamic cross section through the air at a given speed. So if you convert to gallons per mile, it should basically take the same gallons per mile (not miles per gallon) for that same cross section as that given speed. If a vehicle gets 15 miles per gallon, then the same gallons per mile will have a lesser impact on the miles per gallon number than it will on a, say, 30 mpg car.

    So if the hit were 3 mpg at 30mpg, on a 15mpg car it would be 1.5 mpg hit. But the gallons per mile hit would be the same.

    On my car that gets 27.5 mpg average over a tank of gas with my typical driving pattern, when I put a Thule Aero rack on the car, with no attachments, there is no hit at all. Same mpg (I just did this over the last week to see). When I put on the RockyMounts Brass Knuckles (2 of them), that have a fairly sizable cross section, I lose 2mpg from my 27.5mpg average. This is a recent test I did in the last two weeks. Before that, i had run the car without racks and totally smooth.

    J.

  12. #12
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    Quote Originally Posted by JohnJ80 View Post
    On my car that gets 27.5 mpg average over a tank of gas with my typical driving pattern, when I put a Thule Aero rack on the car, with no attachments, there is no hit at all. Same mpg (I just did this over the last week to see). When I put on the RockyMounts Brass Knuckles (2 of them), that have a fairly sizable cross section, I lose 2mpg from my 27.5mpg average. This is a recent test I did in the last two weeks. Before that, i had run the car without racks and totally smooth.

    J.
    I don't think that is typical, based on the data that people have posted on this site about how their mileage is affected. In most cases of a ~30mpg car, just having the rack is a 2-3mpg loss. Add the bikes and it's another ~3-4mpg. Obviously it depends on how fast you drive, but most people cruise at least 65mph, so the drag is significant (unlike less than 45mph).
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  13. #13
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    Quote Originally Posted by JohnJ80 View Post
    Putting this in context - the US consumed about 140 Billion gallons of gasoline in the same year (2015), it's so little that it doesn't even show up 2nd decimal. Being precise, it's 0.07% of the US's 2015 gasoline consumption. So it's not even the rounding error on the rounding error.

    Nothing to see here.

    J.
    This.

    Hell, take the wheels off and carry the bike inside the car and it's like all good again. No worries at the drive through or garage door either.
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  14. #14
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    Quote Originally Posted by Jayem View Post
    In most cases of a ~30mpg car, just having the rack is a 2-3mpg loss. Add the bikes and it's another ~3-4mpg.
    There is no golden number for vehicles, you can't pigeon-hole this.

    1) A more efficient engine will use less fuel for added drag than a less efficient engine. Also, combustion chambers are funny things, they don't have linear power/fuel at any given rpm.

    2) Where the rack/bikes sit on the roof affects the drag they exert.

    I lose 4mpg with two bikes in the outer racks, 3mpg with them in the inner racks, 6mpg with four bikes.
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    Quote Originally Posted by Jayem View Post
    I don't think that is typical, based on the data that people have posted on this site about how their mileage is affected. In most cases of a ~30mpg car, just having the rack is a 2-3mpg loss. Add the bikes and it's another ~3-4mpg. Obviously it depends on how fast you drive, but most people cruise at least 65mph, so the drag is significant (unlike less than 45mph).
    This isn't about the bikes on the car. It's about the rack and the point that the racks are responsible for this problem. There is no typical. It varies for each individual car because gas mileage is going to vary by all kinds of things. But, once you have an aggregate average fuel economy, adding the rack to that all things being held constant as before, it should be consistent gallons per mile used car to car.

    Quote Originally Posted by Glide the Clyde View Post
    This.

    Hell, take the wheels off and carry the bike inside the car and it's like all good again. No worries at the drive through or garage door either.
    I'm not willing to worry about a couple of miles per gallon and compromise my safety. There is no way I want a bike in a car with me in a collision.

    Quote Originally Posted by Flamingtaco View Post
    There is no golden number for vehicles, you can't pigeon-hole this.

    1) A more efficient engine will use less fuel for added drag than a less efficient engine. Also, combustion chambers are funny things, they don't have linear power/fuel at any given rpm.

    2) Where the rack/bikes sit on the roof affects the drag they exert.

    I lose 4mpg with two bikes in the outer racks, 3mpg with them in the inner racks, 6mpg with four bikes.
    Doesn't matter. You should still consume a given amount of gas to push those bikes in the same configurations through the air at the speeds you typically drive. Work it backwards as gallons per mile not miles per gallon. Should be the pretty much the same gallons per mile at the same average speeds.

    Relative miles per gallon doesn't tell you about the energy consumed. Gallons per mile does.

    J.

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    Quote Originally Posted by 007 View Post
    New study suggests that roof racks account for a pretty sizable portion of U.S. fuel consumption. ]
    I'm going to just get a Suburban and carry my bikes inside. Thanks!
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    Quote Originally Posted by J_Westy View Post
    I'm going to just get a Suburban and carry my bikes inside. Thanks!
    Might want to rethink that.

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  18. #18
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    I don't speak Spanish, but I think the gist of that video was to show that as long as I put a seatbelt on my bike, I should be good...

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  19. #19
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    Lol. I get 17mpg in my ram. Suck it up


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    Quote Originally Posted by JohnJ80 View Post
    Might want to rethink that.

    J.
    That was a joke actually. Don't think I really want a 15 mpg daily driver to avoid a roof rack
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    Quote Originally Posted by cmonkEP View Post
    I don't speak Spanish, but I think the gist of that video was to show that as long as I put a seatbelt on my bike, I should be good...

    Viele Gre-

    M
    Your Spanish sounds more like German to me. Then again, my German sounds a lot like Spanish.

    I don't think you want it in your vehicle either with or without a seat belt. You're also presuming that there is no deformation of the passenger compartment. If there is no room for that bike, it's going to have to go somewhere.

    Having been a first responder a long time and having seen many car accidents (and associated injuries and deaths), there is no way you want something like this in your vehicle. There is so much energy in a car accident that you're playing a very dangerous game if you think that this stuff is going to stay in place even if you secure it. Bear in mind that no one (to my knowledge) has tested the efficacy of a bike staying in place with a seatbelt in a car.

    There are two collisions in a vehicle accident - the collision when the cars hit and then (to the occupants) the rebound collision and/or the collision of the stuff flying around in the passenger compartment.

    J.

  22. #22
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    Bikes inside the vehicle? Where would I put the tent, cot, sleeping bag, air pad, chair, grill, propane tank, lantern, toolbox for the bikes, toolbag for the car, beverage cooler, food cooler, fire pit, and firewood?
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    Quote Originally Posted by JohnJ80 View Post
    This isn't about the bikes on the car. It's about the rack and the point that the racks are responsible for this problem. There is no typical. It varies for each individual car because gas mileage is going to vary by all kinds of things. But, once you have an aggregate average fuel economy, adding the rack to that all things being held constant as before, it should be consistent gallons per mile used car to car.
    This misses an additional point. The energy required to push the bikes through the air may be the same but if you screw up the airflow on an otherwise slippery car you'll pay an additional penalty for that.

    Also, it's not a given that a rear rack detracts less from fuel economy than a roof rack as was previously argued. On a sedan I was very familiar with it was a wash fuel-economy wise between the roof/hitch rack.

    Lastly, lets say my roof rack is on 50% and a pair of bikes are on 20% of my miles. It's still much better to have this penalty on a smaller car than to drive a bigger rig for 100% of traveled miles just so I can fit the bikes every once in a while. I think roof racks probably save much more fuel than is spent on them for just this reason.

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    Quote Originally Posted by bugshield View Post
    This misses an additional point. The energy required to push the bikes through the air may be the same but if you screw up the airflow on an otherwise slippery car you'll pay an additional penalty for that.

    Also, it's not a given that a rear rack detracts less from fuel economy than a roof rack as was previously argued. On a sedan I was very familiar with it was a wash fuel-economy wise between the roof/hitch rack.

    Lastly, lets say my roof rack is on 50% and a pair of bikes are on 20% of my miles. It's still much better to have this penalty on a smaller car than to drive a bigger rig for 100% of traveled miles just so I can fit the bikes every once in a while. I think roof racks probably save much more fuel than is spent on them for just this reason.
    FWIW, I have a slippery aero car. I put on some aero Thule bars on the top and there was zero change in gas mileage. This has been the same for the three cars (one other "slippery" and the other a pretty aero SUV) on which I've done that. So, while possible, I doubt it makes any real practical difference at all in the broader market and is sure has heck hasn't been even been measurable on any of my cars (one gets 25mpg, one gets 27.5mpg and the SUV gets 21mpg).

    But I think this misses what the real issue is - what is the alternative? Not everyone can drive a tiny small car for a lot of reasons - work, family, comfort, terrain, weather etc... And it still makes no economic sense to change cars based on rack preference, or even to select a car based solely on rack preference. Heck, it makes little sense to select a car on gas mileage alone when you factor in the real expense of owning a car - depreciation.

    So I think this whole issue is a canard.

    J.

  25. #25
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    I get about 40 MPG with the bike on the receiver rack on the back of the Ford Fiesta.

    I never have, and doubt I ever will have interest in a roof mounted rack.

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