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Big drop in MPG

872 Views 7 Replies 6 Participants Last post by  A-Tiller-the hun
The family just went to FLA for a vacation. Here is the car all loaded up.

This is first trip with the new 18" BBS's and roof rack. We went to DC a couple months back and I had the stock 16" Montreals on with no roof rack. On the DC trip I averaged 28.6 MPG. On the FLA trip I avereaged 21.8 MPG. Could the 18"'s and the roof rack make that much difference. Most everything was the same.. [email protected], a couple of rest stops. The wieght might have be 100 lbs more with stroller, crib and golf clubs but thats it. :crazy:
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With the combination of what you stated above, I can see your milage dropping drastically like that. Especially with the stuff on the roof. Imagine how much more your engine had to work to push that stuff through the air at your sustained speed.

That is a beautiful Passat, BTW. :thumbup: The teddy bear sunshade is a nice touch.
Yes, the combination of both could make that much difference.

You probably lost 2 mpg alone going to the 18s (beautiful as they are). They have a wider contact patch and (assuming a high performance radial) a stickier rubber compound. Both factors contribute to a greater resistance to roll which means more engine work to equal the same speed with your 16" Montreals.

And the remaining 5 mph could very easily come from the roof rack with stuff in it. The faster you go, the greater the factor wind resistance plays - without a roof rack. Throw a roof rack and some stuff on it and that wind resistance factor becomes exponentially greater. The amount of energy (engine revs) required to maintain 80 mph is now much greater than before without the roof rack. Roof racks are like kryptonite to aerodynamics, but they do serve a great utility purpose.

Now neither of these is increasing your engine rpms through the roof (you probably never noticed the change), but a slight increase of just a few hundred rpms (sustained for a long period) is going to require more fuel to maintain the required engine speed.

Oh yeah, did I mention how lovely those Chs are? Beautiful set of wheels.

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Rack will do it. I lost 3-4 mpg on a wagon with a bike on top (stock rack). I lost 2-3 mpg going from 195/65/15 to 215/55/16.
I love the wheels and was too lazy to switch out for the trip. But with gas prices I will definately go to the 16's for future road trips. As far as the roof rack goes I had no choice. Although the trunk is a good size, when your hauling the whole family for an 11 day vacation it gets small quick. All in all the car was a pleasure. Not only did everything fit, it was comfortable, fun to drive and I got plenty of compliments on the FAMILY sedan! :lol:
That's a damn sweet family cruiser!! :thumbup: If the lowers were painted that thing would be the sickest family car around!!
With a baby,you have lots more gear. My kids are grown,and we went on a
15 day,6600 mile trip. We had both cold and warm weather,so lots of clothes.

I ripped out the storage shelf for the extra space,I do not have a cd changer.
I also used soft duffel bags instead of luggage,you can fit much more that way.

With my 16's and a 1BE suspension,I averaged 30 mpg. There was over 1000lbs
(passengers and luggage) in the car. On a previous trip with stock tires and H+R
sports,I averaged 32.5 MPG.
i really don't think the wheels affected the MPG as much as the roof rack... that roof rack really increased your COD, and that's what was hammering your fuel mileage...

not sure what the stock 16"wheel and tire combo weighs, but i'm willing to bet the CH's probably weigh a bit less, although there is a little more rolling resistance cause of the larger diameter, but nothing you'r going to notice that drastic on your MPG...
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