eugeneloke

just upgraded the stock 16" rims to 17" on my e60

noticed that the consumption (journey) goes up to 20L/100km on idrive - looks very unusual to me
will take car on highway tomorrow & see if it improves

my usual used to be 12+ L / 100km

Ricracing

You seem to drive quite a lot in the city, 20 l / 100 km is outrageous!!!???

My 525i goes with +8 l / 100 km driving nicely (about 90 km/h) on the highways but my normal driving with 70 % city and 30 % highway takes about 11 l and 12 l in the winter.

It's true that wider tires needs more gas to get around.
Have you tryed to increase the tyre pressure?

Are your 17" with 245's or 225's?

See my signature for tire dimsensions!

znod

Did your tire diameter remain constant when you changed? If it got smaller, then that might account for some of the consumption increase. And, as mentioned above, wider tires would increase the rolling resistance.

rodneyremington

Just to pile it on, increasing the mass of any rotating element of your drivetrain or chassis (ie. heavier wheels, driveshaft, etc) effectively reduces horsepower at the rear wheel. So not only do ridiculously large wheels look silly (not your 17s obviously, I'm talking 20+ IMO) they also make your car slower.

znod

And, one's brakes are not likely to function as well as with wheels that are too large/heavy, other things equal. Basically, if one gets wheels that are too large/heavy, other things equal, then some BMW's careful engineering goes out the window. I am not sure how far 20's would take one down that path, but I am confident that they would cover some of the distance toward not good unless the wheels are relatively light, given their size, or lighter tires are used to provide some compensation.

znod

Here is some info from tirerack.com.

"A vehicle's fuel economy is the direct result of its total resistance to movement. This includes overcoming inertia (Newton's Law), driveline friction, road grades, tire rolling resistance and air drag. In order to offer the same level of performance, heavy vehicles require more power (and more fuel) than light vehicles. All-wheel and four-wheel drive vehicles require more power than two-wheel drive vehicles; and boxy vehicles require more power than low drag aerodynamic vehicles.

But how much influence does each of these elements have and when are their influences felt? The relative percent of influence that these factors represent during stop-and-go city driving are very different then during steady, state highway driving.

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

Now, lets explore a scenario where a High Performance replacement radial tire has a whopping 20% increase in rolling resistance over a low rolling resistance Original Equipment standard passenger radial. To calculate the potential change in mpg resulting from using the High Performance tires in place of the Original Equipment tires, we would multiply the tire's percentage of influence in the vehicle's overall resistance (15% in the city and 25% on the highway) times the High Performance tires' 20% increase in rolling resistance.

If the vehicle equipped with standard Original Equipment low rolling resistance passenger tires normally provided 25 mpg in the city and 30 mpg on the highway, installing tires with 20% greater rolling resistance would only drop fuel mileage by a calculated 3% (to 24.25 mpg) in the city, and a calculated 5% (to 28.5 mpg) on the highway. While this is a measurable difference, it probably isn't much more of an influence on real world fuel economy than being stuck in rush hour traffic a couple of times a week or being stopped at every red light instead of continuing through a string of green lights.

Additionally, the easiest way to reduce rolling resistance to enhance fuel economy is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle's tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become underinflated to just 28 psi. Therefore, maintaining the vehicle manufacturer's pressure recommended for light load and heavy load conditions may almost be as important as the tires being used."

mr_djurgarden

Ricracing

Great vnod,

I just love facts, but...

The iDrive calculates gas consumtion / driven miles or kilometers .
It doesn't understand that the car could be jammed in traffic etc, and I also belive that it is calibrated optimistical.

Using the speedometer trip compared to gallons / litres filled at the gas station, I always get the gas consumtion much higher than what the iDrive indicates.

If wider tires gets the gas milage i.e. 20 % worse, it still doesn't explain any 20 l / 100 km for a 525i.

eugeneloke

How about posting pics of the red car?

vnod, i will post pic of the red car as soon as i take delivery - before end of nov 2005.

eugeneloke

after running 30+ KM at 100 kmh on the highway today, the fuel consumption is still 15.8L/100km - this is a 520i on "D" on the tranny

something is probably wrong - will bring it into the dealer tomorrow