How much fuel consumption difference: 1 person vs. 2 people
 

Has any of you ever done rough comparison in terms of fuel usage when driving the car only by yourself versus driving with 1 passenger in the car?

I got 2mpg better after Taco Bell shits the other day

By myself, I typically get 6-8 mpg worse, but I don't think it's related to weight. I drive a lot more aggressively when the wife isn't with me...

Must agree there

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lol - but seriously, say carrying an extra load of 1 person, which is say on average what, 120-160 pounds, that's not light at all - surely it must affect fuel consumption a bit?

As stated above, driving style may have a bigger effect on gas mileage than having more weight from a passenger. I also drive more conservatively when my wife is riding with me.

I'm not sure about MPGs because I'm averaging less than 20 but when I drive my co-worker home (250lbs) I notice a HUGE difference in performance. As a result I push the car harder so I'm sure the fuel economy suffers.

I don't really notice any difference in economy unless I am seriously pushing it. 100-200lbs might be noticable on performance/track driving, but if you are just driving around town I would not imagine it would have too much of a negative impact.

With 150lb person on board you are talking about ~5% increase in vehicle weight. Therefore if it actually directly translated into a 5% fuel economy change, it would be about 0.05 * 28mpg = ~1.4mpg. However weight is not the only factor, rolling resistance of tires, aerodynamics, and grade of the road are all important factors as well. So we will say 2% (which I think is probably still a very generous amount) is more likely, 0.02 * 28mpg = ~0.55mpg. Either number is pretty easily lost in the noise of driving habits, and likely to not be noticeable for most drivers.

*disclaimer* I pulled these numbers out of my ass to make a point, please do not hold them to any standard...

I also drive more conservatively when driving with friends or family.

I don't know how it impacts fuel consumption but a body in the trunk helps with traction in the snow.

If your passenger is a woman, you would be well advised not to mention this in her presence unless you're just itching to have the "Do you think I'm fat?" conversation.

I have the opposite problem. Every time I have a body in the trunk and corner hard, that dead weight shifts and my rear end breaks traction...

mom in car - 35 mpg

just me - 20 mpg

Don't know, all of my friends are far too wide to fit in the seats...