My experience with lightweight wheels

[RPM]

Hi everyone, I replaced the stock wheels on my Civic with some lightweight ones. The specs are:
- Stock: 15"x6" +45, 7.8 Kg
- Light: 15"x7", +40, 5 Kg

I kept the same exact tires.

The difference in feel is quite large. The car seems to accelerate and brake much more easily. Road feel, steering response and ride quality have improved as well.

Coasting distances seem to have decreased, which is to be expected.

Slightly more surprising to me is that on uphills the car seems to lose speed very easily. This makes me sad.

I am wondering if I should keep them on or not.

Regarding fuel economy, I haven't used a full tank of gas yet and the temperatures are fluctuating so it'll be hard to judge unless I keep them until the Summer.

[user removed]

Each wheel-tire assembly is in essence a flywheel. It takes energy to spin up all 4 wheels including all rotating mass (brake rotors-drums). It will improve you mileage but with colder temps, as you posted, the benefit will be offset by loses due to temperature.

Greater rotating mass requires more power to get to the same speed but coasting will suffer slightly. Overall you should see an increase in mileage. I would keep the lighter wheels due to the better road feel, steering response and ride quality. Ride quality especially with higher inflation pressures.

regards
mech

[Cobb]

I reduced 10 lbs a wheel on my car. Love it as I spend a lot of time in traffic that slows and speeds up.

[wdb]

I had lightweight rims on my Fit and saw improved gas mileage when using them, as well as the advantages in responsiveness and handling you mention. But it was not as pure a test as yours because the tires were not the same. I definitely remember hating to take them off in the winter.

Reducing unsprung mass improves handling and responsiveness. Reducing rotating mass improves acceleration and should improve fuel economy, but how much might depend on what kind of driving you do as much as anything else.

[RPM]

Thank you for the replies. I think I'll try to keep them at least until the Summer so I can properly assess their effect on fuel economy. The car is definitely more fun to drive with them, except climbing on the highway.

Did any of you experience any difficulty maintaining speed while going uphill with the lighter wheels?

[Cobb]

I have a cvt so the car selects the best ratio. Since it has more spunk I drive a bit more aggressive. Before it was a pain to keep up with traffic, now its easy.

[awcook]

That CVT would be great, since you don't have to actually change gear ratios to get better mileage, nor does tire size really relate to RPM at cruising speeds (acceleration is a different story).

I can't speak for my car when it comes to different wheel weights, but driving other cars with obviously heavier wheels, they can take hills easily. With my small wheels, I drop 2-5-sometimes 10 MPH trying to go uphill, but with my Dad's V6 Accord, I can climb up hills with no problem. This is not because it has a bigger engine (I don't think since it should've been on 3 cylinder mode), but because it weighs more. It makes sense that a heavier car should maintain speed uphill because of how inertia works, but at some point on a really long hill, the heavier vehicle will slow down much faster than a lighter car because gravity will catch up to it.

All-In-All I wouldn't worry too much about losing speed uphill. Once you get more used to the wheels, hills won't be as much of a problem. My solution would be to speed up a lot before the hill then coast or DWL up the hill.

[RPM]

Today it rained cats and dogs. The first serious rainy day I've had since installing the lighter wheels. The car coasted so poorly it wasn't even funny. Less momentum plus the need to displace more water make these lightweight and wide wheels no fun in these conditions.

[Vekke]

If you have the same tires it should not have that much difference to rain or snow behaviour. Only difference is the gyro effect which does not allow change of direction so easily with heavy wheels?

But in my experience poor behaviour in rain or snow is due to thread depth or grip problem

[RPM]

I was surprised as well. It's like driving a different car with just the wheel change. Then again I think I'm more sensitive to small changes than most people.

Some of the changes were good (performance, handling, ride comfort), some bad (poor coasting).