Audi Mileage Marathon: Fuel efficiency strategies
After seven days and 2,832 miles, I'm finally back home. My week-long stint on the Audi Mileage Marathon is over and I believe I've learned a thing or two about hyper-miling. Teams running in the event were scored based on a formula that included fuel efficiency and speed. The fuel efficiency component was weighted twice as much as speed. Audi engineers included speed mainly to ensure that drivers didn't just go unnecessarily slow to maximize fuel economy. Audi officials specifically warned us at the start that this event was not about hyper-miling, but when you put several dozen journalists in cars and ask them to see who can get the best mileage ... well let's just say they are a competitive bunch.
I participated in the first two of four waves of the marathon going from New York to Chicago and then on to Denver. On the first wave, my co-driver Jason Allan and I mainly stuck to just trying to drive gently, avoiding aggressive acceleration or braking. We didn't do any drafting or early shutdown of the engine. Aside from some hilly terrain in Maryland and Pennsylvania, most of the terrain was relatively flat. Compared to what we would see in wave 2 our average speeds were a comparatively low 52.4 mph, due in large part to time driving through traffic in places like Washington, New York and Chicago as well as frequent slowing for toll booths through most of the states on route. Find out how things changed after the jump.
When we started out in New York no one was taking the competition part of this drive too seriously. However, as we started getting the results each morning of the previous day's run, things started to heat up. After most of the drivers changed out in Chicago for wave 2, strategies changed a bit. The daily distances for wave 2 were longer and we had time to experiment. We weren't allowed to make any modifications to the Audi's although one team did attempt to tape up the seams around the hood and headlights with masking tape. Judging by their mileage ranking, it didn't have much impact. The problem is the Q7 is a fairly high riding vehicle with large air openings in the front.
The tires were already inflated to the optimum pressure for maximum vehicle loading. According to Michelin representative Bob Massa who was on hand for the event, inflating the tires further wouldn't have any meaningful impact on efficiency. The construction of the low rolling resistance radials would prevent them from deforming if over inflated. Since mechanical changes were out of the question, we focused on different driving techniques.
For wave 2 I was paired up with Steve Ewing of Winding Road and each day we compared notes with other drivers like Jim McCraw, Kevin Kelly and Royal Ford. With no more toll booths to contend with, speeds climbed to an average of 60.7 mph. We learned that once we get up to speed, putting the automatic transmission into manual mode switches the control strategy so that the torque converter locks up more quickly, improving mileage slightly. Putting the air suspension into dynamic mode firms up the ride and minimizes the ride height. Because the suspension is not trying to adjust the vehicle as much as it does in comfort mode, there is also less energy draw.
I tried shutting off the engine at stops as well as shutting it off early and coasting down. Unfortunately, since the Q7 is only available with an automatic transmission, this technique is more of a nuisance than a benefit. Because the transmission has to be put back into park before restarting, this is only helpful for vehicles with a manual transmission.
One of the most controversial techniques associated with hyper-miling is drafting. Getting in behind a large truck letting it take care of moving the air out of the way, can certainly help reduce the loads on the powertrain, especially for a vehicle as large as the Q7. Unfortunately getting very close behind a truck is also dangerous. First there is the issue of visibility or lack thereof. If anything happens up ahead you can't see it until it's too late. You are also far more susceptible to damage from rocks thrown up or separating re-tread tires.
Following this closely also requires extreme vigilance on the part of the driver. Doing this for any length of time is mentally draining, leading to fatigue and further safety concerns.
With the Q7 we found another method that actually works almost as well and is far safer. The Q7 TDI is equipped with adaptive cruise control. This system uses a radar sensor behind the grille that monitors the distance from the vehicle ahead. When following another vehicle the system automatically maintains a safe following distance, if the leading vehicle slows down, the ACC applies the brakes. When the leader speeds up the ACC keeps pace up to whatever speed the driver has selected. The following distance is adjustable and it turns out that lowering the distance to the minimum still maintains a safe space to the vehicle ahead.
Even at this distance, there is still a noticeable impact on mileage when following a truck. It turns out that at 70 mph using the adaptive cruise control is good for about 1.5-2 mpg improvement in efficiency compared to running in clear air. Moving in tight really only picks about another 0.5 mpg. At the same time if the vehicle you are following slows, your vehicle will also slow to maintain the distance. In the case of the Q7's ACC it will bring the vehicle down to a complete stop, unlike many such systems that deactivate at 15-20 mph.
According to Audi engineer Gunter Schiele, the Q7 ACC has been calibrated specifically to maximize both comfort and fuel efficiency. Often traditional cruise control systems try to maintain the set vehicle speed aggressively which leads to the transmission down shifting and hard acceleration. With the focus on comfort, the Audi's acceleration is kept moderate. The result is smooth behavior that also allows for decent fuel efficiency.
Steve and I didn't bother with any of the more extreme measures like folding up the mirrors or running without the air conditioning. On the run through Amarillo and on to New Mexico and Colorado we climbed from just a few hundred feet about sea level to a peak of over 7,700 ft. In Texas and New Mexico we also encountered heavy cross and head winds. The bottom line is that Steve and I ended up with the second best mileage for a Q7 at 28.3 mpg. That trailed only McCraw and Kelly who averaged 29.6 mpg. Even the worst Q7 managed 25.4 mpg.
It seems that for a long haul, driving smoothly, and staying at a reasonably safe distance behind a truck, is the best approach. If you have adaptive cruise control, especially on an Audi, it's worth using. If you drive in traffic, manually shutting off the engine at stops is really only helpful if you have a manual transmission vehicle. As automatic start stop systems proliferate in the coming years this will become less of an issue though. The most important aspect however is safety. If you don't get where you are going in one piece, it really doesn't matter how little fuel you used.
Our travel and lodging for this media event was provided by the manufacturer.
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