17's to 18's fuel mileage drop.

[Jekyll991]

Last Summer I finally replaced my factory 17's with a set of 18's. Running Nich Targa m129 and BFgoodrich g-force all seasons. The wheels are supposed to be the same weight as stock (25lbs) but I'm not sure on the tires. Lifting the two side by side there was no real noticeable difference.

However, my MPG dropped from getting 36-40 without really trying hard (running 65-80) to not being able to best 32 MPG running 60-70 on the same roads and trying everything to get good mileage.

Is this normal? I know 1-2 mpg is from a discrepancy with the speed reading according to GPS, but I still would not expect that significant of a difference.

At the exact same time my coil packs starting giving out so I had hoped that would fix my mileage but it didn't seem to change it all.

Just wondering someone else's experience going from 17s to 18s. Thanks.

 

[snobrdrdan]

Lifting the two side by side there was no real noticeable difference.

Well that's very accurate
Use a scale

Heavier wheels/tires hurt MPG's.
As do stickier tires, and also wider wheels. Bigger contact patch/more grip = more resistance.
And overall diameter plays a roll too.

 

[ChrisB1]

I went the opposite direction but I have yet to compare my MPG on the stock Lugana wheels verses my lighter Enkei wheels. Regardless, the lightweight 17s held up better on my horrible, pot hole laden, roads.

 

[DASVDUB]

You put on heavier bigger wheels and you get worse gas milage? *GASP* science and common sense says yes this will happen. :thumbup:

 

[Philimon]

Well that's very accurate
Use a scale

Heavier wheels/tires hurt MPG's.
As do stickier tires, and also wider wheels. Bigger contact patch/more grip = more resistance.
And overall diameter plays a roll too.

X2

Most of that is pretty easy to accept without more explanation except the wider diameter part. That one if you google has something to do with moving more weight towards the outside of the wheel which makes it become more difficult to rotate or something like that...

Sorry about your regretful purchase.

 

[mophisto]

X2

Most of that is pretty easy to accept without more explanation except the wider diameter part. That one if you google has something to do with moving more weight towards the outside of the wheel which makes it become more difficult to rotate or something like that...

Sorry about your regretful purchase.

I think you mean: I = ∑ ri2mi = ∫ r2 dm

 

[Jekyll991]

Don't have a scale, I wasn't that worried about it.

I'm a mechanical engineer, so I know that the diameter actually has a greater effect than weight. I went with stock width/size tire, can't remember if the width was the same between 17s vs 18s.

Just wondering anyone else has done the same and got such a dramatic, or at least what people running the stock 18s are getting.

Should have expected everyone wanting to prove they know something would come out instead of answering or at least ignoring the question.

 

[DASVDUB]

I get 34ish on my stock detroits goin 75-80mph


Sent from my iPhone using Tapatalk

 

[Philimon]

My mileage has increased from avg 28mpg to 29mpg. That is going from stock detroits with all seasons to 16" steelies with winters. I was surprised at the improved fuel economy even with winterized fuel. It used to be the other way with my last car. 15" lightweight wheels with summers to 15" heavy stockers with winters. The winter mpg was always 2-3mpg lower on avg. (unleaded n/a engine).

Sorry I couldn't help.

 

[snobrdrdan]

Should have expected everyone wanting to prove they know something would come out instead of answering or at least ignoring the question.

Your question was answered: YES your MPG's will be worse
Like DASVDUB said "it's common sense"

It'll all depend on driving conditions, habits, wheels/tires, tire pressure, gas blend, location, etc....which will all vary. There's no factual number to tell you


BTW there's no way you were getting or averaging "36-40mpg without trying hard" in the GTI like you claimed earlier, NO WAY.
Unless you drive all down hill or 45mph in 6th gear for 50 miles with no stops or something...even then, that's a stretch.
And if you're going by the MFD alone, it's very generous (i.e. inaccurate versus hand calculations)....but even so I've never seen a GTI average that high.
That's TDI territory

 

[zrickety]

It could also be a maintenance issue. Are you due for transmission fluid or spark plugs? Do you check tire pressures? It could be just the tire compound.