Why dual-clutch transmissions are still the best

A sectioned model of Volkswagen’s DSG twin clutch

A question often asked by many is: What is the best transmission? The answer really is: It depends.

First off, there’s the traditional H-gate pattern manual transmission. Passenger cars, light trucks, utility vehicles, pick-ups, sports cars and supercars use this type of transmission. Most modern manual transmissions have five forward gears, although six-speed manuals are becoming the norm. Well, Porsche even has a seven-speed manual.

Manual transmissions are all made by companies such as ZF, Getrag, Aisin and Borg Warner. Almost all car companies use these brands in their cars. The traditional manual is the most involving transmission—handy when you want to enjoy a drive through your favorite winding road; blip the throttle, heel-toe downshift, rev-match and double declutch just for fun. The hard part? Try driving with a manual in traffic. Manual transmissions are also the cheapest and easiest to maintain because parts (clutch-friction disk, pressure plate, clutch-flywheel bolts, throw-out/pilot/centering bearing) are simple and easily replaced.

Then we have the conventional automatic transmission with a torque converter. The torque converter is the big, finned, squashed-pumpkin-looking device inside the automatic transmission. It is a fluid coupling device which functions as a clutch, allowing the engine to smoothly drive the transmission and then the wheels. An added bonus of torque converters is that by playing around with fluid pressure, they multiply torque to the wheels, acting like gear reduction drive devices. Most modern luxury cars utilize this type of transmission, particularly Lexus, BMW, Mercedes-Benz and the Volkswagen-Audi Group cars.

It’s still tough to beat the smoothness afforded by the conventional automatic transmission. Currently, the norm is the ZF eight-speed automatic transmission used particularly by Lexus and BMW. Mercedes-Benz, however, has both seven-speed and  (even newer) nine-speed automatic transmissions.

Typically, in normal driving, you move off from dead-stop in third or fourth gear in this high-number transmissions. But if the car’s various sensors detect a steep incline, or you are towing something, or boot the throttle all the way down to the carpet, the transmission will start in first gear followed by a succession of lightning fast shifts.

Physically heavy

The downside of traditional automatics is that they are heavy due to the number of moving parts. If you do a lot of stop-start traffic driving, it takes a tremendous amount of energy to move all the associated rotating parts of an automatic transmission even before the power gets to the wheels. It is also physically heavy: Aside from all the hydraulic moving parts, most automatic transmission-equipped cars use anywhere form 12-30 liters of automatic transmission fluid, heat exchangers and hydraulic lines. A typical manual transmission uses only 3-4 liters of gar oil. And since you can’t engine brake as easily in an automatic, your disc brakes and pads tend to get a beating versus manual transmission equipped cars.

The automatic transmission does claw back for attention because it requires very little maintenance, and service intervals are far and few in between. Car manufacturers also prefer traditional automatics from a warranty point of view because it is easier to detect the cause of parts damage/failure and remove factors such as driving styles (i.e., in traditional manual transmissions, a clutch driver will wear out the friction disk, pressure plate and flywheel faster, but you don’t have these problems with an automatic).

From a purely fuel-efficiency/economy point of view, a CVT or continuously variable transmission is often used. Smaller passenger cars in the B- and C-segments use a CVT; it is also widely used by the Volkswagen-Audi group in their entry-level models, and Nissan has used them in their line of premium SUVs. In a CVT, there are no actual gear sets inside, replaced instead by two conical devices connected by a metal chain. These two conical devices simulate the gears, acting as pulleys on which the metal chain moves up and down to simulate gears. This allows power delivery to be seamless and step-less (i.e, you don’t feel or hear the engine revs drop as the CVT transmission constantly adjusting the metal chain between the two conical devices, simulating the best possible gear depending on your desired speed and throttle input or load).

Also, a great thing about CVTs these days is that they can simulate the ideal gear to give the lightest load on the engine, thereby improving fuel efficiency. CVTs are ideal if you do a lot of open-highway, steady-state cruising at legal speeds. Sounds great, but CVT transmission technology is only in its third generation for cars, meaning it still isn’t as reliable as a modern automatic transmission or the dual-clutch transmissions which seems to be all the rage now. There are very clear limitations on torque rating and weight capability for these oft-misunderstood CVTs, and older CVT technology had questionable reliability beyond five years of use. Typical CVTs tend to also be dim-witted, not very responsive and delivers a substantial lag in throttle response. If you’re an aggressive driver, CVTs might irritate you.

CVTs getting better

But they are getting better. Toyota uses a CVT for the Altis, and Honda uses a refined and stronger CVT on the all-new Jazz and City. Subaru in particular has introduced a CVT on their WRX and Forester models which supposedly have a torque limit of 500 Newton-meters, as tested by engineers from Fuji Heavy Industries and Subaru Technica International, Subaru’s Motorsports Division. If major manufacturers are introducing CVTs in mainstream models, that means they have confidence in this technology.

Interestingly enough, CVTs perform incredibly well, in relation to moderate off-road use. Up to a point, CVTs can mimic low-ratio transfer case gearing found on traditional off-road vehicles. Hence CVT-equipped vehicles such as the Nissan’s X-Trail and the latest Subaru Forester perform incredibly well up to moderate off-road trail conditions. It is also lighter than a transmission, which utilizes a low-ratio transfer case.

Finally, we come to the dual-clutch transmissions. The dual-clutch transmission is essentially two transmissions running in parallel: The odd-numbered gears are on one main shaft, and the even numbered gears are on a parallel shaft. Dual-clutch transmissions preselect the next higher gear, giving you almost seamless power delivery akin to a CVT transmission, but with far better torque and weight capacity. There is also a fully-automatic mode for many of today’s dual-clutch transmissions, so it gives the convenience of a typical automatic transmission but with better performance and responsiveness, although there is a noticeable loss in smoothness.

Small weight penalty

But the best part is the small weight penalty: Typical automatics tend to weigh 50-100 kilograms heavier than manual transmission-equipped cars of the same make and model. Dual-clutch transmissions have a much smaller weight penalty, as opposed to automatics  which are heavier than manuals by 20 to 40 kg. It seems to have the best of everything: the control and efficiency of a manual transmission car; the seamless power delivery and efficiency comparable to a CVT, with far higher torque and weight capacity; and the convenience of an automatic transmission. But the downside is the added cost and complexity of these dual-clutch transmissions.

If you like modifying cars, changing to a higher-capacity clutch is your ticket to making and holding big power. For drag racers, an automatic transmission with a high stall speed, plus a massive fluid cooler and a torque converter equipped to handle oodles of torque for consistent shifts, were the key. But for dual-clutch transmissions, it’s a little of both: You upgrade the clutch packs, add in a fluid cooler for the gear oil and upgrade the valve body (just like an automatic) to handle the added pressure generated by the upgraded parts to hold the power and transfer it to the ground efficiently.

Many high-horsepower cars come equipped with these transmissions: Almost all models of Porsche sports cars and even the 918 Spyder hypercar come with a dual-clutch transmission, as well as all modern BMW M cars (M3, M4, M5, M6), Ferrari’s complete model-lineup (California, FF, F458, F458 Speciale, F12 and the LaFerrari Hypercar), the new Lamborghini Huracan, the Mitsubishi Evo X MR with SST transmission, and  the Mercedes-Benz SLS and Black Series of AMG cars come with a dual-clutch transmission. Of course, we should not forget Nissan’s budget supercar, the R35 GTR, which made dual-clutch transmissions come into universal consciousness.

Massive cost to upgrade

But blow up any of these complex dual-clutch transmissions and the cost is massive: In the Philippines alone, there are a number of heavily modified Nissan R35 GTRs pushing well into 800 HP and even 1000 HP++ capacity. A few of them have destroyed their transmissions and have changed to newer, modified ones. The cost of a brand-new, unmodified transmission is P1 million with the modifications adding another P200,000 or so. The fluid is also expensive: The GTR’s transmission retailed by Emperor Motorsports, either Will-All or HKS, is about P40,000 for 20 liters; it also  needs changing every 10,000 kilometers.

Cutaway view of Volkswagen’s DSG gearbox

There is a stop-gap technology prior to the dawn of dual-clutch transmissions, which is the electro-hydraulically clutch actuated transmissions. Ferrari utilized this system in their F1 gearboxes on the F355, F360, F430, 599 and Enzo. It was brutally effective on the track, but prone to overheating the clutch system in stop and go traffic, and in hanging situations like moving off from an incline. Audi also utilized this system called R-Tronic, and BMW with their SMG line of transmissions. Today, Peugeot still uses this technology in their 3008 Cross-Over. For all-out performance, this system was in many ways good: fast, brutally effective and light, weighing in not much more than a conventional manual with the convenience  of an automatic. But it was far from smooth.

So what’s the best? Technically, the dual-clutch transmission is the absolute best. But for me, it still lacks the emotional connection afforded by a true H gate-pattern manual transmission. And the manual is slowly fading away.