Gas milage dip 10-15% less?????? Tires?

[themacs]

I put new Continental tires on my '09 M 35. These are the ones that most on this board seem to like. I'm very happy with them. Better handling, cornering and less cabin noise over the OEM's. I now have over 2,000 miles on them.

HOWEVER, my average milage (combined freeway and street) was 25 (OEM tires) and now it is 22. This is done by hand calculation and not using the car's computer.

Have any others had this issue when switching?

Any other thoughts?

Thanks!

[EniGmA1987]

Has it been a lot colder in your area lately? This also will greatly change your MPG. Also make sure the tires are inflated to 37psi cold

[antzrus]

Now that it handles better, feels safer & more in control, you are probably pushing (read using more pedal) the thing like your vette. Enjoy the sucker-a helluva' lot more comfortable than that 400 hp extension of your pen-is..!!!

[themacs]

If I could only get it down to 400 HP my milage in the C6 would be better LOL!

On the PSI, is 37 pounds the # for these tires at 60-80 outside temp in So. Cal??

[DaSerb]

I have had decrease in mpg since I had last oil change. I am not sure why or how, but just before I changed the oil, I was getting about 18mpg. Since the change, I am averaging 16.4-17 mpg.

Maybe I am going crazy....would mpg depend on what oil I use?!!!?

[EniGmA1987]

A dealer and often places like Americas Tire put in 33PSI, when that is not what should be in these tires. On a 51psi tire you should normally run 35-37psi cold. It is a proven fact that increasing the PSI in your tires will also help your MPG, with diminishing returns as you go higher. 37 is a good balance of performance, comfort, and mpg on a 51 max psi tire.

[M35 Eagles fan]

It could be winter gas causing the drop in mileage. Here in Arizona, starting Nov 1st the gas changes and I notice a drop in mileage of 1-2 MPG even though my driving is the same.

[merlinq2]

Agreed, here in Canada the same thing happens and no matter what you drive the winter gas has a negative effect on milage? Anybody know why?

[merlinq2]

Maybe this will help shed some light on the subject - note point # 7:

9 reasons your winter fuel economy bites

1. More idling

This should be a no-brainer, yet parked idling cars are a common sight in cold weather. Resist the temptation to idle your car to warm it up. An idling engine gets 0 mpg. Consider also that idling the engine does nothing to warm up the tires and drivetrain.

Even in the coldest weather, you can begin driving after 30 seconds from a cold start - keep speeds low/moderate and use gentle acceleration until the temperature gauge starts to climb (source).

2. Low tire pressure

Of course you're smart enough to keep up your tire pressure as the temperature drops, right? A 10-degree (F) change in ambient temperature equates to a 1 psi change in tire pressure (source). Fuel economy declines 0.4 percent for every 1 psi drop (source).

3. Increased rolling resistance

Even if you're completely attentive to proper tire pressure, cold ambient temperatures will still cause your tires to return worse mileage. That's because a tire's shape isn't completely round - the sidewall bulges out at the bottom, and where the tread meets the road the small contact patch is actually flat. As the tire rotates, it constantly deforms to this shape, and this deformation requires more energy when the rubber is cold and hard. Rolling resistance at 0 degrees F is 20% greater than at 80 degrees (source 1, source 2).

4. Crappy road conditions

It's increased rolling resistance of another kind: driving through slush and snow. And then there's its wasteful polar (no pun intended) opposite: no friction at all! (A.K.A. wheelspin on ice.)

5. Lower average engine temperature

In the winter, an engine takes longer to reach operating temperature and cools off faster when shut off. Since the engine management system orders up a richer mixture when cold (proportionately more fuel in the air/fuel combination), more fuel is being burned overall.

A block heater can offset this problem (improving fuel economy by 10% in sub-zero conditions - source), as can garage parking, and combining trips (to minimize the number of cold/hot cycles).

Also related...

6. Higher average lubricant viscosity

Engine oil thickens as it cools. So does transmission and differential fluids and even bearing grease. Significantly more energy is needed to overcome the added drag these cold lubricants cause.

Using synthetic fluids can address this problem, since their viscosity changes less at extreme temperatures than traditional mineral fluids.

7. Weaker gasoline

Gasoline doesn't vaporize readily at very cold temperatures. So oil companies formulate fuel differently for cold-weather markets in the winter. Unfortunately, the changes that provide better cold vaporization characteristics also result in less available energy for combustion. You won't get as far on a liter of winter gas as you will on a liter of summer gas. (Source.)

8. Higher electrical loads

In colder temps, you use electrical accessories more often:

- lights (in higher lattitudes it's darker in the winter)
- rear window defroster (because it's easier than using the ice scraper, right?)
- heater blower motor (I don't have a/c, so this isn't balanced out during warm conditions); heated seats/mirrors
- windshield washer pump (because it's easier than using the ice scraper, right? And for frequently cleaning off dirty road spray.)

9. More aerodynamic drag

No, I'm not referring to the layer of snow you're too lazy to brush off the top of the car (though that would hurt mpg too).

A vehicle’s aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10 degree F drop in temperature, aerodynamic drag increases by 2% (source).