Lately it seems like every auto manufacturer brags that their car has more speeds in its transmission than the other guy. 5 speeds, 6, 8! I hear VW is working on 10. Why not 100? I know nothing about cars, obviously, but I do know something about gears and torque having bicycled across the country, pedaling across the continental divide 13 times. There must be a downside to having more and more gears. Weight, incorrect shifting? Why didn’t they have 8 speed transmissions 20 years ago? What is the attraction to more gears? My mini van has just five and seems to run fine. Are more better? Or is this a male phallic issue? You know, my engine is bigger than yours.
More gears equals more complexity and higher cost.
To a point, it’s useful. Engines have something called a power band. They don’t make the same power at all RPM’s (so when someone tells you they have a 500hp engine, you can smile to yourself and think "yeah, but not all the time!). If you draw out the power they make on a graph, there’s a point where the power is at it’s peak - the sweet spot.
Since it only gets to the sweet spot at certain RPM’s, the fewer gears you have, the less time the engine is driving the car while in the sweet spot.
It’s kinda like razor blades. 1 blade works. 2 blades are useful. 3 are really nice. 5 is stupid.
So, a 5 or 6 speed auto tranny is a nice thing to have because it keeps the engine in the sweet spot more often than a 3 speed would. But 8,9, 100 speed transmissions are a dumb marketing ploy.
Great points by shadowfax. I will add that a smaller, weaker engine (with a narrower “sweet spot”) would benefit from a greater number of gears than would a larger, more powerful engine.
In some instances, more gears could translate to better gas mileage, but it seems that car companies are more interested in selling 500hp sedans to the 1% and their wannabe’s.
Actually, the, “100 speed transmission”, already exists.
A CVT has an almost infinite number of ratios, so…
Not only complexity , but SIZE is a huge caveat when adding more gear ratio changes.
When you start adding more mechanical parts , the space needed to fit those in increases, ie; the size of the transmission must increase.
So if your hoping to cram a 10 speed transmission into a Focus…where would you ??
Sure you can make that transmission, just think of the Allison automatic transmissions in otr semi trucks . How large and heavy they are and therefore how on earth would you fit that into your Honda ?
You can go back to the Buick Dynaflow introduced in 1948 or the Chevrolet PowerGlide that became available in 1950. When the selector was placed in “Drive”, the torque multiplication depended completely on a torque converter. There were no gears unless on manually selected the “Low” range. Chevrolet changed this in 1953 and the PowerGlide models, when in “Drive” started in low and shifted to direct drive.
In any event, there was a lot of slippage in these transmissions which doesn’t occur in the CVT.
Unsprung, here is my take on this: More automatic and manual trans forward speeds are a competitive response with doubtful value for the average driver. Someone added a speed to their auto trans to outdo the others and the others then had to catch up probably due to shoppers using more speeds to use in part as a deciding factor when making a new car buy.
The same thing happened to motorcycles; 3 and 4 speeds used to be the norm, now many have 6 speeds. For some bikes, keeping the engine revs in a desirable range in the powerband, as was said, can be good for maximum acceleration. For relaxed car driving you can short shift (skip gears) a manual trans but that is less convenient with a bike.
Actually the CVT does not have an infinite number of ratios. The upper and lower ratios are fixed, by the limits of the drive and driven members, but are variable in between these
There is value to 6, 7, 8 or even 9 speed automatic transmissions. Each increment gives a little better fuel economy but trades off a little more weight and friction. Both of these reduce mileage a little bit. Each gear allows the engine to be in the most economical spot a little bit longer with each extra gear giving a smaller and smaller advantage. 9 is considered point where the tradeoffs cross the gains.
Consider back in the 60’s a 2 speed Powerglide behind a 6 cylinder 5 passenger car that got 19 mpg weighing 3100 lbs and a 0-60 in 12 seconds. The same car today weighs 3800 lbs, gets 30+ mpg and does 0-60 in 7 seconds and is way safer, nicer handling, better features and drastically lower emissions.
“Actually, the CVT does not have an infinite number of ratios.” @pvtPublic
Like there are an infinite number of points between any two points on a line which is continuous and not discrete, there ARE an infinite number of ratios between the upper and lower gear ratio limits. The gear ratios are continuous with the primary and secondary pullies and not discrete as with a transmission with fixed gear ratios. Hence the name, “continuously variable transmission”.
" almost infinite " @VDC, either it is infinite or it isn’t. So, I would argue it is infinite as there are an infinite number of positions that the belt can have between the primary and secondary pulley and each position has it’s own ratio…so there are an infinite number of ratios. So, I have to disagree with these two points. ;=)
I stand corrected in that there is an infinite number of ratios between the upper and lower limits.
Now about this “almost infinite” thing. Is that like the PZEV engines? Is there really something that is partially zero. I always thought that if you had anything at all no matter how small it was something. I would understand almost zero but partial zero eludes me.
Without looking it up, I would guess it’s a definition and like any step function, it “could be defined” as zero if the emmissions fell below a defined limit. For example, fat free milt is NOT free of fat. It is allowed to be labeled as such if it falls below a particlar percentage. Infinity is an indeterminate quantity unlike zero.
“Actually the CVT does not have an infinite number of ratios”
…and that is why I said, “an almost infinite number of ratios”.
It is similar to being…slightly pregnant.
If I read PZEV ( partially zero emmissions vehicles) correctly, it appears to mean they are zero emmissions in some areas like it’s fuel system but not at the tail pipe, which may not be zero there. But again, zero emmissions is never actually zero but may be classified “zero” so when it reaches a certain percent.
The PZEV designation came about because years ago California passed a law stating that a certain percentage of cars would need to be ‘zero emission’ (from the car, not the power plant) by a certain date. As that year approached and it became clear there was no adequate, affordable technology available, the lawmakers instead decided that selling a larger number of cars defined as ‘PZEV’ would be allowed instead. That kept the environmental lobby from yelling too loudly about giving in to automakers but still led to very real improvements in total emissions. Sure does sound stupid, though.
I drive a 6 speed manual. If I am accelerating to 35-45 mph I frequently skip 3rd gear. I rarely use 5th gear.
There is an absurd point,most drivers like an 18 speed road ranger transmission-but with a puny engine all you get done is shift gears and the the seasoned drivers do a lot of skip shifting,I found a 7spd maxitorque Mack transmission to be plenty adequate with a high torque rise engine-Kevin
“I drive a 6 speed manual. If I am accelerating to 35-45 mph I frequently skip 3rd gear. I rarely use 5th gear”.
Different gear ratios are there if you need them, but if you don’t need them, there is no reason to use them. When I was driving age, my parents had a 1954 Buick with a 3 speed manual transmission. When taking off, I often started in 2nd gear if I was on flat ground and did not have to accelerate quickly from a stop sign. If I did start in first gear, I often skipped second gear, because the engine would pull well in high gear above 10 mph. On my 4 speed manual 1950 Chevrolet pickup, I always started in 2nd gear. First gear was used for stretching fence, pulling stumps, etc.
I later bought the 1954 Buick from my parents and when I sold it and bought a 1965 3 speed manual Rambler, it didn’t have the gearing or torque to start in 2nd gear. However, I would often start in first gear and shift directly the high, skipping 2nd gear.