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The Key to High Mileage: Understanding the Smart transmission

The biggest key to high mileage in the Smart is probably understanding the transmission. A lot of people - and a lot of journalists who should know better (and even some dealer reps!) - seem to think the Smart has an automatic transmission and it has a problem of being too slow between gears. But that's not the case at all. The Smart has a manual transmission with an automatic cluch that shifts according to an optimized high mileage program. It is marvelous and it works perfectly. It even allows you to defeat the high mileage overlay with manual shifting similar to a Tiptronic that you find in high end sports cars and sports sedans.

This is the first transmission I have ever seen that is designed to do this. It even took me a while to figure out what it was. I was also under the illusion that the transmission was faulty in some way. I was even told at the dealer that I should lift my foot between shifts for proper operation. That is not the case.

One can make the Smart behave like a performance car and impress people who think its really cool to go fast and waste energy. I've been there, done that, and if that's where you want to be, there are a lot of cars that will make you very happy and do a much better job than the Smart. This is because the Smart was designed to go a long way on a tank of gas. That was the primary design goal, urban or highway. That's why I bought it. I'm a hypermiler.

Most of all, the Smart reminds me of big, big trucks. Not in size, of course, but the way it shifts. some of you have probably driven big trucks. Big two axle, three axle, maybe some eighteen wheelers with 5 axles. Possibly a few of you pulled the heaviest 5-axle jobs, bulk liquids with a gross vehicle weight of 80,000 pounds. But I'm talking about the trucks I drove in the western states. Supertrains. Tank trucks with two trailers. 9 axles. 34 wheels. 120 thousand pounds. 105 feet long. Big, big trucks. Over mountains. Big, big mountains.

Those trucks are so heavy you don't use a clutch. You'd burn it up in one trip. Instead, you dog clutch through all 15 or 20 gears. That's right. You put it in low gear and drop the clutch at idle to get going. The flywheel gives you the momentum to start moving. Not the engine. Not the clutch slipping. From there on, you never touch the clutch again. You match the gears. You match the gears perfectly for every shift, for thousands of shifts. You pull through the torque curve, let off the accelerator, slip the shift lever into neutral, drop the revs to the insertion point for the next lower ratio gear, slip into perfect engagement, give it throttle, then repeat the process. You don't rely on the synchros to make your shifts work. Pros like me use the tach to slip the transmission teeth in neatly. We know every shift point for every gear, upshift or down shift. Our lives depend on it. So do yours if you are on the highway with us.

Anyway, I don't do that anymore. But the Smart shifts like that. Try it. Put the transmission in D and give the Smart a tiny bit of gas and lock your foot against the carpet to the right of the pedal to hold it in place. Don't move it. Moving the pedal wastes gasoline. The Smart knows what to do to give you the best economy possible. It moves you up through first gear, stops delivering fuel to the engine (even though your pedal's down), gives the engine just a little fuel to match the revs for the next gear, smoothly engages the teeth, then brings the power up to your pedal setting and repeats the process through all five gears.

To this old truck driver, that is not a fault. That is magnificent technology, perfectly applied for optimum economy and power delivery. It is hard to improve on that but you can really screw it up by not understanding it.

Tags: mileage, shifting, transmission

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Comment by Ian Pellant on November 15, 2008 at 1:42am: Stop and go traffic and the clutch is a good question.

The non-USA Owners Manual has a section "Economic driving style" (p121) that recommends:
"* You should always switch off the engine when stopped at traffic lights, level crossings and in traffic jams because you begin to save fuel after just ten seconds at a standstill." This puts the car into N a lot.

The non-USA transmission shifter is different - no D or P positions, just N and R. R will immobilse the car when the key is removed. It must be in N in order to start the engine. If I know I'm going to be stopped for more that ten seconds; I put the transmission in N... as fas as I know the clutch is the traditional manual thrust plate and bearing design; holding the clutch in (open) puts load on the thrust bearings and they usually fail first in most cars. In N the actuator releases the load on the clutch, so wear should be reduced (?). I don't switch the engine off.

When in log jamed traffic that moves a metre, then stops, then moves a few more metres and stops and then moves further with the promise of escape; but stops again.... my pulse turbo does not like being in Auto mode. It tends to stick in first and becomes snarly and jerky. What works best in my smart is to leave it in manual mode and shift into second as soon as it has moved a few metres; if the speed drops, the transmission will shift back into first. Use the engine to slow the car. Avoid using the brakes until almost stopped. The paradigm of a manual shift that automatically drops down gears as the car slows to a stop took me a while to adapt old driving habits to!

There are differences between the USA transmission programing and what the rest of the world has. With mine, I need to slack off the accelerator when in Auto to get a smooth shift. Using Ricks' technique produces a lag and jerk. I know the tranny is ready to shift at a bit over 3200 rpm under light loads, so easing off the accelerator seems to signal the transmission to shift up immediately. I can get smoother and quicker shifts in manual. Auto mode will not shift into fifth gear below 80 kph (50 mph); neither will it hold in fifth below those speeds. In manual mode; it will signal to upshift to fifth at speeds a bit below 60 kph and once shifted will hold fifth. When new, that sounded like it was lugging; that has eased off as the engine was run in.

I'm guessing that USA Auto program upshifts at engine speeds in the 2000 to 2500 rpm range under light loads (?) Mine is programmed to upshift at over 3000 rpm. As a consequence I am obtaining better fuel economy using manual mode that Auto.

Since the smart has a computer between the accelerator pedal and the engine fuel injection systems; putting your foot down too hard or too quickly is interpreted by the computer as to what action to take... in Auto program that seems to spinup the turbo boost on my car and I almost expect to see flames come out the rear. (LOL) There is a reference in the Owners manual to a kick down function that kicks in when the accelerator pedal is depressed beyond the "pressure point"... I'm still trying to get that to work predictably. My daily drive involves cruising at 60 kph in fifth then a slight downhill before a right angle turn onto a minor road up a steep grade. My smart needs to be in third to lug the grade or second to nip it (at 40 kph). If I apply the brakes approaching the turn, the car will downshift into some unknown gear... so I need to manually shift down two gears to avoid smart confusion. Then sometimes if it is in third and I depress the accelerator past the pressure point, it will downshift to second; other times it will not. This is but another case of the smart computer interpreting accelerator pedal action and engine load conditions as well as brake pedal actions. The driver is not hard wired to the throttle valve or the clutch.

Poorest fuel economy is achieved when the driver confuses the smart program by accelerating too hard then hitting the brake pedal too often... dumkoff driving.

Comment by Not so smart on November 14, 2008 at 11:46am: To know it is to love it. Thats the smart car.

Comment by Vjklander on November 14, 2008 at 3:59am: Great post. I pretty much figured that out on my own. What I still have trouble with is working the clutch in stop-and-go traffic. Any ideas??

Comment by Stuart Berman on April 3, 2008 at 1:14am: Great post! I remember reading this post and getting much more enjoyment from driving the car.