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I have a 2001 Honda Civic with a Thule T2 on the back. I get about 38 mpg with the rack off, about 30 with the rack on and in the folded up position, and less than thirty with bikes on. I switched from a roof rack to a hitch rack in hopes that I wouldn't lose mpg anymore. Has anyone else noticed a reduction in gas mileage with a hitch rack?
 

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Elitest thrill junkie
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I notice a reduction, but not a significant one. When I put two bikes on the rack (also more weight in the car from an additional body and gear) I notice more of a loss, but that's when I'm being pretty anal about MPG. With just the rack on+bike I notice very little loss of mpg, and if I were to quantify it I'd say just a few mpg at the most. The small loss in mpg is why I got a T2, and the fact that I can take it off easily is a big bonus.

On the other hand, given a real small vehicle (civic?), I could see the T2 with a bike adding significantly more drag to the vehicle. It's something you'd only experience at highway speeds, but given that a fairly large bike would extend into the slipstream pretty far, I wouldn't say it's impossible to see a more significant loss. Most of us get the T2 because we realize our vehicles will create an area of seperated-airflow behind the vehicle where it doesn't really matter what you add, because the drag is already there and an object in that area doesn't contribute to more drag.

Maybe think hard about your driving habits? I tend to need to get to a trailhead when I have the rack on, and for big group rides if I'm a little behind I tend to drive faster, which eats LOTS of fuel with a turbo-car, so it's not really indicitive of the drag caused by the bike or rack.
 

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I am not an engineer...

nor do I have a degree in aerodynamics but I am not going to let that stop me from giving you my two cents. I have an Accord and use a Thule DoubleTrack rack. I don't really pay attention to my MPG with it on or off, but I can see how it can cause drag. My bikes sit up high on the rack and actually the seat is near level with the roof of the car, based on my memory. As the the slipstream comes over the top of the car, I can see how that would act like a sail or parachute and cause more drag. Now if a real expert on the subject would like to pick this apart, have at it. But it makes sense in my brains.

Kinda sucks when you buy a small car to do your part and increase your MPG only to have your bike rack/bikes suck you back down. I guess the lesson here is just ride your bike everywhere. Easier said than done in my case I am afraid.

Dirt
 

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Is the rack new (new like you got it since the temps have fallen this winter)? You might be noticing a the normal winter mpg drop and blaming it on your rack.

How religiously did you calculate your mileage before the rack? Is that 38mpg a lifetime number, or just an estimate? Was your 30mpg a calculated tank, or are you basing it off an in-car computer? Was the drive a "normal" drive for you? There are SO many factors that will cause your mpg to swing around that I doubt it is from your rack. I'd say to check your tire pressure and don't worry about the rack.

K (mpg geek)
 

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10% to 12% reduction

Regardless of the type of rack or car, with bikes on top, I loose about 10% - 12% MPG. It has been consistently like that for years.

I think the loose in MGP for the racks alone is very small, in the 2% range if I remember correctly.
 

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I don't have a T2 but definitely get worse mileage with the top-tube holder type hitch rack on with bikes on my car. I get about 31mpg with mixed, modest driving without the bikes on the back. I did an all highway tank with two road bikes on the back and got about 27mpg, should have been around 35ish without the bikes.
 

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Just about anything you add to the outside of your car will affect your aerodynamics and your gas mileage. Driving with an open window will also cause a slight reduction. For a small car it will have a more noticeable effect, especially if the normal gas mileage is higher than the average car. I only put my hitch rack on when I'm carrying bikes, and take it off when I don't need it. For me, it only takes a few minutes to put on/take off. My advice is to not worry about it when you're carrying bikes. If it is an issue for other times, you might want to take your rack off.
 

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I have a Saris Cycle On hitch rack on my Toyota Matrix and notice almost no effect on MPG.

I think it has a lot to do with being a hatchback, so there is not a big dead space between the roof and bikes, on my car the bike seats sit almost even with the roof line.
 
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