Wheels: weight vs width

[RPM]

Hi everyone.

I have two sets of wheels:

Set 1: 15x6J ET +45, 8 Kg a piece.
Set 2: 15x7J ET +40, 5 Kg a piece.

I use set 1 on the street but I wonder if set 2 would provide an FE increase. On one hand they're quite a bit lighter. On the other they're wider, so the tyre contact patch and aerodynamic drag should both increase. Possibly, everything will cancel out and they'll end up being equivalent.

Do think it's worth the expense of swapping tires, rebalancing, etc to find out?

[mcrews]

IMHO I wouldn't bother unless I was able to also increase the existing diameter by at least 5%.

[euromodder]

Depending on the tyre size you need, you might be able to fit the same tyres to a 6 or 7 inch rim.
Or get away with just using one size wider on the 7".

I have 6.5J rims with 185, but a 6.5J would also take 205s easily.


I'd pick the lighter tyre, and not get carried away when choosing the width

[RPM]

Sure, my tires don't need to be replaced yet. They still have circa 5 mm of thread left. And 195/50 R15 tires work on both 6 and 7J wheels. By swapping tires I meant removing them from the current wheels and mounting them on the other wheels which currently have racing tires on them.

All in all I guess this would be something done more for fun than actual savings.

[fjasper]

Short answer: No. Not worth it, money-wise.

Longer answer, all other things being equal (which they almost never are):

Lighter wheel = less energy spent accelerating and decelerating. Lighter is better, efficiency-wise.

Wider tire = less rolling resistance (sounds weird, but it's true) but more aerodynamic drag. Wider is better at "low speeds."

Narrower tire = more rolling resistance (same disclaimer), less aerodynamic drag. Narrower is better at "high speeds."

The aerodynamic effect of a wider wheel seems like it might be exacerbated slightly by the offset. They might expose more tire to the airflow around the car.

Personally, I'd be a little hesitant to run 11 pound, 15x7 wheels on the street. If they're cheap (cast), they're probably pretty tender, and could be damaged by potholes that wouldn't affect heavier wheels. If they're expensive (forged, etc.), they're probably too pretty to risk curb rash, theft, etc. Like I said, that's just me.

Probably you should just send those troublesome wheels to me so I can deal with them.