Why would an auto be higher emissions than a manual?

[paddyhasneeds]

As subject really. Same car, same engine, looking at specs for manual vs. auto and the manual is listed as 165 g/km and the auto as 185 g/km.

[groomi]

They usually have a gear less than the equivalent manual, are heavier, have greater transmission losses and have to 'react to' when to change gear, rather than a driver 'anticipating' when to change gear.

All in all, just less efficient - but not by much and they have other things in their favour.

[GTIR]

Manual gearboxes are physically connected to the engine but auto's are not - instead using fluid to create a connection - so more "slip" and less drive than a manual.

Cheaper branded cars are less efficient than premium brands IMO. Drive a base model Ford auto and then a Merc auto and you'll notice the engine on the Ford revving a lot more but not actually going anywhere.

[dowahdiddyman]

Also effects the ved alot as well.

[Mave]

Short answer - emissions directly related to fuel consumption. Autos normally drink more fuel than manuals.

[anonymous-user]

These days (when most auto's have torque convertor "lock up" clutches) the main fuel economy defficit over the drive cycle comes from 2 sources:

1) Driving the gearboxes oil pump all the time (even at idle,)
2) Often the transmission will "kickdown" to get up some of the drive cycle "hills" when a manual will just stay in the same gear, hence engine friction is greater and fuel economy worse.



(manual cars must follow the mandated "shift points" unless they have other "driver indictor" to show when to change gear (hence the widespread adoption of the silly flashing "change up" arrows on the dash so OEM's can set their own shift points)

[eldar]

GTIR said:

Manual gearboxes are physically connected to the engine but auto's are not - instead using fluid to create a connection - so more "slip" and less drive than a manual.

Cheaper branded cars are less efficient than premium brands IMO. Drive a base model Ford auto and then a Merc auto and you'll notice the engine on the Ford revving a lot more but not actually going anywhere.

This is true. My merc auto is quicker and slightly more economical than the manual, probably as it has an extra gear.

[Patrick Bateman]

It's easy to forget that the emissions that are given are a rate.

When you think of it like that it's easy to understand that an auto, being less economical, will produce a higher number.

Edited by Patrick Bateman on Saturday 8th January 16:16

[texasjohn]

There are exceptions to the rule, 3.0 Legacy auto - better co2 and MPG than the 6 speed, manual.

[paddyhasneeds]

Mave said:

Short answer - emissions directly related to fuel consumption. Autos normally drink more fuel than manuals.

Perfect answer and now I feel a plank - essentially stick 5 tons of car on a 1L engine and it wouldn't be very efficient based on g/km travelled.

Thanks,

[Doofus]

dowahdiddyman said:

Also effects the ved alot as well.

Well of course it does! You do know that VED is linked to CO2 emissions, don't you?