Cadillac ELR to get new expanded sized Volt battery....

[Neromanceres]

I'm guessing this means that rolling resistance varies according to some chaotic thing in terms of acceleration/deceleration? Or is there some rule of thumb available?

Not so much acceleration and deceleration. Tires are fexible, shape and contact area can vary based on a lot of circumstances (turning, temperature etc..). A car will slow more in a turn than going strait strictly from the increase in rolling resistance. Also all wheels have some continuous slip when torque is applied. The friction force from the tire to the road is never 100%. The more torque or braking force applied to the wheels the more the frictional energy lost at the wheels (which you could see having a loose relationship with acceleration and deceleration).

Overinflating of tires can actually cause a vehicle to use more energy. It decreases the rolling resistance coefficient but can increase the frictional loses of the tire under torque or braking action. For optimal efficiency you need to find the right balance.

Resistance is also felt from frictional loses in the powertrain. Bearings, differential, gearing, clutches all offer a resistance to the car. Some people don't consider this a rolling resistance but in a sense it is a resistance to the rolling motion of the car.

[DonC]

I would too. But the source you cited was an auto blog post. There the possibility of a miss-quote or a miss-speak in this situation. It could very well be right but it doesn't smell right to me and I don't have the tools at my disposal to prove otherwise.

I would discount the possibility of a mis-speak or a mis-communication here. The article is way too detailed, and the numbers were part of a larger story which was being told. Certainly someone can get a number wrong, but not a host of numbers, especially when the numbers are part of an important story which Weber is telling.

Moreover, the article is is consistent with just about every other statement Weber made with respect to the relative importance of aerodynamics. Here is another example: According to Frank Weber, global chief engineer for the Volt's E-Flex propulsion system, good aerodynamics are the most important aspect of a hybrid electric vehicle's design. The car's weight has much less of an impact on total energy use, since any extra battery mass translates to more kinetic energy that can be recovered with the regenerative braking system. How's that for counter-intuitive? http://www.automobilemag.com/new_and..._aerodynamics/ Then there is this from a GM press release: "The electric range of the Chevrolet Volt is most sensitive to improvements in aero, which is in contrast to a traditional vehicle program in which mass typically plays a larger role."

If you think about it this makes perfect sense. For a traditional car, increased mass reduces efficiency in three ways: rolling resistance; accelerations, and hill climbing. Regen can't do anything about rolling resistance, that's just a dead weight loss, but it can recover quite a bit of energy expended in accelerating and hill climbing. This means mass just isn't as important a consideration for an EV as it is for an ICE.

[DonC]

Fair enough, is there an equation to go with that...? The contact patch needn't be affected by weight... thats not an argument if you have sound backing, just an observation.

Yes there is. Rolling resistance is just (mass X gravitational constant X the co-efficient of the rolling resistance). Aero drag is more complicated. It's 1/2 X A (frontal area) X Cd (drag co-efficient) X density of air X the square of the velocity. (At least that's how I remember it). The big deal is the square of the velocity. Aero ends up being exponential.

You can see all this on this nice chart from Tesla. Note that rolling resistance per se isn't a big deal (it's always in fact less than the drive train losses). http://www.teslamotors.com/blog/road...ency-and-range But note that mass also comes into play when climbing hills or accelerating from a lower speed to a higher speed. These two areas are where regen helps a lot. It does nothing for the rolling resistance losses.

[Neromanceres]

Yes there is. Rolling resistance is just (mass X gravitational constant X the co-efficient of the rolling resistance). Aero drag is more complicated. It's 1/2 X A (frontal area) X Cd (drag co-efficient) X density of air X the square of the velocity. (At least that's how I remember it). The big deal is the square of the velocity. Aero ends up being exponential.

You can see all this on this nice chart from Tesla. Note that rolling resistance per se isn't a big deal (it's always in fact less than the drive train losses). http://www.teslamotors.com/blog/road...ency-and-range But note that mass also comes into play when climbing hills or accelerating from a lower speed to a higher speed. These two areas are where regen helps a lot. It does nothing for the rolling resistance losses.

That article is very good from Tesla. I did underestimate the aerodynamic losses in an electric car but you can see in their graphs that aerodynamic losses don't start to exceed rolling resistance untill around 45mph. The Tesla roadster is 1000lbs lighter than the Volt so the rolling resistance will be ~30% higher in the Volt. Also the Drag coefficient for the Tesla Roadster is 0.35 (see source below) vs. the Volts 0.281 so the Volt will have a slightly lower impact from aerodynamic losses than the Roadster.

http://green.autoblog.com/2009/03/26...ile-range-0-6/