could my mileage decrease by 3 mpg just - Honda CRZ Forum: Honda CR-Z Hybrid Car Forums

midnight8 · 03-18-2011, 08:32 PM

by mounting my bike on the back end of the car? I bought a trunk mt bike rack today and mounted my bike up since I have some riding to do this weekend and during hwy driving I was around 34 mpg today. I just made my 2nd fill up but I have not yet got this low on any single trip. Car was going from green to blue with cruise on 65 mph. Could there be that much added drag? The rack does sit high up on the car

Mike · 03-18-2011, 08:40 PM

I think so. I lost 2 mpg on my 370Z when I added the AP Racing wing on it, and 7mph on the top end at Road Atlanta.

Ludercrz · 03-19-2011, 02:16 AM

creating more drag would decrease your aerodynamicness (new word i just invented) and therefore you'd have to use more gas on acceleration and your mileage would go lower.

TCroly · 03-19-2011, 05:58 AM

I would expect a 5 to 10% decrease in fuel economy as a result of the increased drag of a roof rack or bike rack. On a 15 mpg truck this would be 0.75 to 1.5 mpg, but on a 35 mpg CRZ, it would be 1.75 to 3.5 mpg decrease.

TCroly · 03-19-2011, 05:59 AM

Quote:

Originally Posted by Ludercrz

creating more drag would decrease your aerodynamicness (new word i just invented) and therefore you'd have to use more gas on acceleration and your mileage would go lower.

But can anyone get any lower MPG than you?

tsh · 03-19-2011, 09:45 AM

It won't have a % impact on mpg, but it will add l/km (i.e on a 15mpg truck, the effect is not noticable, but with a 40mph car, the effect will be significant). With my Rx7, top speed dropped from 150 mph to about 130 with either a (folding) bike on a boot carrier, or the roof down. Wasn't looking at mpg's or the price of filling up

dr61 · 03-19-2011, 12:52 PM

Since the bike adds aero drag, the fuel economy penalty will go up with the square of speed. So you can reduce this effect by driving more slowly at highway speeds especially.

midnight8 · 03-19-2011, 07:49 PM

After 2 days of driving around with the bike on the car I am at less than 34mpg on this tank. Since I am done with my charity ride for the weekend It is now off the car and We will see how much it goes up. I guess the other variable that goes into this is that I filled up at the same time I put the bike on the car. Still on the same tank of gas so We will see if it immediately goes back up.

midnight8 · 03-20-2011, 12:21 AM

Well, Bike rack off the car and just made a 70 mile round trip. 40.2 mpg on that trip so I guess the bike on the car was about the only explanation. I knew it was gonna hurt the mileage a little but did not think it was going to be that much.

Ludercrz · 03-20-2011, 04:39 AM

Quote:

Originally Posted by TCroly

But can anyone get any lower MPG than you?

<--- i'll be over there

03-18-2011, 08:32 PM	#1 (permalink)
midnight8 Member Join Date: Mar 2011 Location: Orange, Texas Posts: 75	could my mileage decrease by 3 mpg just by mounting my bike on the back end of the car? I bought a trunk mt bike rack today and mounted my bike up since I have some riding to do this weekend and during hwy driving I was around 34 mpg today. I just made my 2nd fill up but I have not yet got this low on any single trip. Car was going from green to blue with cruise on 65 mph. Could there be that much added drag? The rack does sit high up on the car __________________ 2011 CR-Z Pearl white EX w/ Nav

03-18-2011, 08:40 PM	#2 (permalink)
Mike Senior Member Join Date: Feb 2011 Posts: 244	I think so. I lost 2 mpg on my 370Z when I added the AP Racing wing on it, and 7mph on the top end at Road Atlanta. __________________ Momentum, Momentum Performance

03-19-2011, 07:49 PM	#8 (permalink)
midnight8 Member Join Date: Mar 2011 Location: Orange, Texas Posts: 75	After 2 days of driving around with the bike on the car I am at less than 34mpg on this tank. Since I am done with my charity ride for the weekend It is now off the car and We will see how much it goes up. I guess the other variable that goes into this is that I filled up at the same time I put the bike on the car. Still on the same tank of gas so We will see if it immediately goes back up. __________________ 2011 CR-Z Pearl white EX w/ Nav

03-20-2011, 12:21 AM	#9 (permalink)
midnight8 Member Join Date: Mar 2011 Location: Orange, Texas Posts: 75	Well, Bike rack off the car and just made a 70 mile round trip. 40.2 mpg on that trip so I guess the bike on the car was about the only explanation. I knew it was gonna hurt the mileage a little but did not think it was going to be that much. __________________ 2011 CR-Z Pearl white EX w/ Nav

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03-19-2011, 12:52 PM	#7 (permalink)
dr61 Member Join Date: Dec 2010 Posts: 34	Since the bike adds aero drag, the fuel economy penalty will go up with the square of speed. So you can reduce this effect by driving more slowly at highway speeds especially.