Manual vs automatic transmission.

[random]

I was reading a story on msn Canada that claims automatic transmissions are much faster than manual transmissions So I am wondering why do race car drivers prefer manual? In my time at the track (drag strip) it seems all the pro mods had manual transmissions I think Indy cars also do. So is the claim wrong that automatic transmissions are faster? Is it hard to modify automatic transmissions for custom gear ratios or somthing?

[Phi for All]

I think if all you want is speed, like going from 0 to 60 in a straight line drag race, automatic is probably the way to go for regular cars (though iirc, top fuel dragsters don't even have a transmission). But racetracks with other cars on them have a lot more variables that a manual transmission can help a driver deal with better.

[ewmon]

I don't know if you mean that automatics can make a car go faster than manuals or whether they can shift faster, but you're right that automatics are harder to modify (if at all) for specific gear ratios. The last I knew, top fuelers might have had two ratios at most, they let the expansion of the rear wheels effectively change ratios. In any racing, one of the worse things that can happen is to lose traction (which means losing control), which can happen if an automatic transmission suddenly decides to downshift. So it's all about maintaining control, plus automatic transmissions tend to be heavier.

[Moontanman]

Off road I've always preferred automatic transmissions, especially in sand, on road automatics are easier but tend to get less gas milage. I've seen specially set up automatics at the drag strip, they did quite well but I never raced cars I raced motorcycles which at the time had no automatics. the automatics i saw drag raced didn't shift by themselves but had to be shifted like a manual but no clutch was needed. When I drag raced motorcycles I didn't use the clutch anyway, it was a little hard on the shifter forks but I won quite a bit...

[overtone]

I dunno about faster, but on snow and ice I definitely prefer manual - it allows me to feed and let off power to the traction wheels precisely, run in whatever gear works best, etc.

 

All else being equal, a solid mechanical connection will transfer more power than the fluid-mediated connection of an automatic - but that presumes absolutely perfect shifting and so forth by the driver, to match a perfectly set up automatic, which is unlikely. On the freeway for long distances, where shifting skill is not involved, manual's small weight and transfer of power advantages will get you a small gain in gas mileage and/or top end speed.

 

One of the handiest speed advantages of a manual is that it slows down most car thieves.

[Greg H.]

As a self described control freak, I prefer a manual transmission because it gives me a much better feel for what the car is doing. Between the steering wheel, the pedal under my foot, and the shifter, I can tell when we're about to have a problem early enough to stop it from becoming a problem. it provides you finer control of the car, and it also allows you to adjust the amount of torque you're applying at any given time (for example, for driving on ice or snow - living in Iowa in the winter this is an issue).

 

Manual's are simpler, in concept, since they're just a bunch of spinning gears, as opposed to a fluid based vacuum driven system, I find I get better gas mileage from them, and they are lighter if that's a concern.

[lassez]

Automatic transmissions is usualy seen as power shift transmissions, means there is only a short loss of power when shifting, the gears are mostly planetary gears, operated by a clutch for each gear, and using a torqu converter to overcome the different gear ratios. The drawback is the lossis in the gearbox.

The latest in gearbox technology is the dual clutch transmission, a manual gearbox, described in the Wikipedia link it has much lower losses. Probably shifts faster than a traditional automatic transmission.

I have ben designing gearboxes for about 15 years, before retiring i was partly involved in the design of the Volvo Truck I-Torque.

[zapatos]

Automatic transmissions are fast, but the change gears when they want to, not when you want them to. By changing gears manually you have more control over how the car performs.

 

Changing gears in a race car is very fast also, but I've never seen a comparison of gear shifting between manual and automatic.

[akh]

Most "race car" manual boxes are not true manuals. They use paddle shifters.

It used to be that manual boxes were better in all respects; better effeciency and more power to the wheels and more control. The recent trend towards clutch disks over torque converters and transmissions with 7 or more ratios has made todays more sophiscticated automatics better in areas that manuals ruled.

 

Don't forget CVTs.

 

I still like to down shift and engine brake as a form of abs, but again todays cars do a good job of that too. But I drive old manual clunkers .

Edited November 15, 2012 by akh

[At just flattened at!]

Like whatZapatos said, an auto will change up and down when it feels its right to, undernormal road driving conditions that’s fine, on a track the driver/rider willwant to shift down even when revs are high and back the rear wheel/s round thecorner. I reckon an auto would want to shift back up when you're thenaccelerating mid corner and moving in a controlled rear slide even if didn’twant it to. Does an automatic work solely off what revs you are at in aparticular gear? Or does it take into account what’s happening with traction controland the like?

 

[Pantaz]

... Does an automatic work solely off what revs you are at in aparticular gear? Or does it take into account what’s happening with traction controland the like?

Modern automatic transmissions are highly integrated into the vehicle's electronics.

[Cavemonster]

Your question is a little vague, but I will do my best to address it. A "racer" prefers whatever will make him/ her more competitive. As for which is faster? As far as the time it takes to shift gears, no human wil consistently outshift an automatic/DSG. As far as which is faster, or, quicker? It depends on the application. In road racing for instance the manual is lighter, easy to setup, and uses less horsepower in transition to the wheels. It also has fewer moving parts, (lesser chance of breaking). Reliability starts becoming more of an issue when power levels climb towards, and past 1000 hp,( which is rarely seen in roadracing, but has been done). Traditional automatics are used extensively in drag racing due to consistent shift times, and their ability to withstand tremendous horsepower when properly set up,( the GM powerglide has been used at power levels exceeding 2000 hp). I think what you may be referring to are acceleration times between new generation automatics vs. manuals, and in many cases the auto is quicker but the explanation is simple. If both cars, (manual & auto), have the same engine, and the same final drive gear ratio, but the manual has 6 speeds, and the auto has 8 speeds, the auto will probably be quicker for 2 reasons. (1) the auto will shift gears faster than the person driving the manual, and (2) due to the closer spacing of more lower gears the engine will stay in its optimum power range longer, (it wil go thru those gears quicker), hence, the automatic is "faster". The technology exists today to make either transmission as good as the other. It simply comes down to how much you want to spend, or what you prefer.

[ox1111]

If I had to guess I would say that the article was talking about CVT transmissions. These are automatic transmissions that have a single adjustable gear you may have seen similar transmissions like this on band saws. Some milling machines, or drill presses. Basically, you use a V-shaped belt and a sliding pulley to change ratio. The advantage to these is technically you can have the perfect ratio all the time. The disadvantage of these are that they seem to have the worst ratio all the time and they cannot hold up to much power. Although improvements are made all the time and new versions are in use in many new cars.