Road Test
You're buckled comfortably into your seat at one end of a broad concrete runway. You hear throttle-up, and the engine note quickly plateaus at peak rpm as the scenery starts to blur. After about 20 seconds of this, at 100-plus mph, you half expect to feel rotation and to glance down at the receding tree tops, but this is no Cessna Citation taking off—it's Audi's spectacular new A4 3.0 running down the test track. The peculiar soundtrack is courtesy of Audi's new (to our shores) Multitronic continuously variable transmission. The CVT is a have-your-cake-and-eat-it-too idea that promises the comfort and convenience of an automatic with the performance and efficiency of a manual. Stick the lever in "D," and a CVT can maintain the ideal ratio to keep the engine humming along in its power or economy sweet spot. Until now CVTs have only come in petit four and cupcake sizes capable of managing the torque of small four-bangers, but Multitronic is a gastronomic gâteau that can withstand 221 pound-feet of V-6 twist.
The basic idea behind Multitronic is similar to that of the Honda and Subaru CVTs we're familiar with: a metal vee belt running between a pair of pulleys whose diameters vary to change gear ratios. But here, instead of a belt consisting of a number of flat solid-steel plates that are clamped and pushed from one pulley to the other, there is a 28.1-inch-long, 1.5-inch-wide chain, the 75 pins of which are clamped and pulled along by the pulleys. This pull chain can conform to a tighter radius than can a push belt, so a wider range of gear ratios is possible within a given package size. In this car the range spans 2.40:1 to 0.40:1, for a ratio-spread factor of 6.00.
The Honda Civic HX's CVT spans 2.47:1 to 0.45:1, for a ratio spread of 5.49. The spread on Audi's own six-speed manual is just 4.79. Only BMW's new ZF six-speed automatic trumps the Audi at 6.04. Ultra-low gearing negates the need for a power-sapping torque converter. In its place is a light, small, cheap, and efficient planetary gearset that uses wet multiplate clutches to launch the vehicle in first or reverse. These clutches slip when stopped with little or no brake pressure applied to provide the "creep" we're accustomed to, and they engage enough to prevent the car's rolling backward on a hill if the brake is applied at all.
They slip a lot during a brake-torque full-power launch. Audi claims that its pull-chain system requires about half as much hydraulic clamping force as a push-belt CVT needs, which further improves efficiency. (The force to clamp Multitronic's pulleys together is still about 2.5 times that required to engage gears in a conventional five-speed planetary automatic.) Icing on the efficiency cake: A lightweight magnesium case and fewer moving parts add up to a 33-pound weight saving relative to a Tiptronic five-speed box. So how's it drive? Different enough to delight a sensitive engineer's ear, but not so weird as to prompt a warranty stampede, or so Audi hopes.
Evidently, a lot of early CVT customers complained to dealers about transmission slippage. "It sounds like there's a big rubber band between the engine and the wheels," they'd say, to which the canned reply, "They all do that," could be applied sincerely, if not reassuringly. In response, Audi has programmed Multitronic to build revs more gradually. Stand on the gas from rest, and engine speed builds linearly through about 40 mph, after which revs build more slowly, peaking at 6200 rpm at about 50 mph. Likewise, when you kick down from a cruising speed, the revs jump, but not to the power peak; they approach that point gradually, as in a conventional car.
These concessions to customer familiarity rob some efficiency, however. If customers still complain, there's a quick fix. Dealers can simply advise folks to slide the shifter over to the Tiptronic gate, which will cause the engine revs to follow a good ol' six-speed saw-tooth pattern as speed builds. Although more comforting to the Luddite ear, this mode slows the progress. In biz-jet mode, our test car hit 60 mph in 7.0 seconds and flew through the quarter in 15.5 at 91 mph. Sawing through the revs retarded the progress considerably—7.7 seconds to 60 mph, 16.0 at 87 mph in the quarter.
Multitronic is only available on front-drive A4s, and it's the only tranny offered on the A4 3.0 front-wheeler, so direct performance comparisons are out. An A4 3.0 Quattro six-speed we tested in October was 0.2 quicker to 60 mph and 0.1 quicker through the quarter-mile, despite weighing 159 pounds more. Multitronic may not top manual performance, but it trumps the manual Quattro on fuel economy, according to the EPA (city/highway ratings of 19/27 mpg versus 18/25) and our observed mileage (22 versus 20). Driving quickly on twisting roads, we found the automatic ratio selection to be too slow for powering out of a turn, but the fix is to downshift to one of the Tiptronic gear ratios via the steering-wheel thumb switches.
This can be done even with the shifter in "D," in which case it reverts to automatic ratio selection after a brief time with no further manual gear selection (ratios are faithfully held right up to the redline in the manual gate). In manual mode, throttle response feels as immediate as with a manual gearbox, with no torque converter to absorb thrust. Another similarity to manual-transmission driving is noticeable when you lift off the throttle: Even in automatic mode, Multitronic is programmed to provide more engine braking than that of a conventional automatic.
We like the added control. The CVT works exceptionally well with cruise control, as it can smoothly tailor the gearing to suit hills and dales, rather than provide jarring kickdowns, and it can maintain the set speed going down moderate grades as well. No matter what speed the car is traveling when it pulls out to pass that Winnebago, the kickdown is always just right for peak passing power. Multitronic's efficiency and performance advantages pull strongly at the heartstrings of our stick-shifting techies, but if asked to predict whether this is the transmission of the future, we're betting that—except in smaller cars—it's not. We think a high-torque-capacity, wide-ratio six-speed box such as that in the upcoming BMW 745i will have broader appeal here in the truckin' U.S.A., especially when combined with other pending efficiency boosters. That said, we definitely crown Multitronic the automatic transmission of today, and with a year and a half of production experience in European A6s already logged, we feel comfortable recommending it.
