# why do conventional automatic transmissions shift so sluggishly?

**URL:** <https://boards.straightdope.com/t/why-do-conventional-automatic-transmissions-shift-so-sluggishly/709160>\
**Category:** Factual Questions\
**Created:** [January 6, 2015, 8:40pm UTC](https://boards.straightdope.com/t/why-do-conventional-automatic-transmissions-shift-so-sluggishly/709160 "2015-01-06T20:40:56Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\
**Post date:** [January 6, 2015, 8:40pm UTC](https://boards.straightdope.com/t/why-do-conventional-automatic-transmissions-shift-so-sluggishly/709160/1 "2015-01-06T20:40:56Z")

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Dual-clutch transmissions have become popular options for mainstream cars (e.g. Ford Focus) because they are more efficient, but they were initially seen on more performance-oriented cars because they could shift gears very rapidly: flick the paddle shifter, and the transmission declutches one power path and simultaneously clutches in the other power path, changing gears in a fraction of a second.

This is a big contrast to what I’ve seen for conventional automatic transmissions that employ an array of planetary gearsets: flick the shifter, and it takes maybe 1.5 seconds to complete a shift. Isn’t this type of transmission dealing with a shift process that’s fundamentally the same as that of a DCT? That is, engage and/or disengage clutches as necessary to establish a new power path through the planetary sets? Why does this necessarily take so much more time?

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**Author:** ![Morgenstern](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@Morgenstern](https://boards.straightdope.com/u/Morgenstern)\
**Post date:** [January 6, 2015, 8:58pm UTC](https://boards.straightdope.com/t/why-do-conventional-automatic-transmissions-shift-so-sluggishly/709160/2 "2015-01-06T20:58:59Z")

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Dual clutch transmissions typically use one clutch for the odd numbered gears, and another for the even number gears. That’s why they shits are quick and crisp. However, must people could care less about crisp, quick shifts as they float down the highway in their cars, preferring instead, less expensive transmissions.

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**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\
**Post date:** [January 6, 2015, 8:59pm UTC](https://boards.straightdope.com/t/why-do-conventional-automatic-transmissions-shift-so-sluggishly/709160/3 "2015-01-06T20:59:56Z")

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> [@Machine\_Elf](#):
>
> Dual-clutch transmissions have become popular options for mainstream cars (e.g. Ford Focus) because they are more efficient, but they were initially seen on more performance-oriented cars because they could shift gears very rapidly: flick the paddle shifter, and the transmission declutches one power path and simultaneously clutches in the other power path, changing gears in a fraction of a second.
> 
> This is a big contrast to what I’ve seen for conventional automatic transmissions that employ an array of planetary gearsets: flick the shifter, and it takes maybe 1.5 seconds to complete a shift. Isn’t this type of transmission dealing with a shift process that’s fundamentally the same as that of a DCT? That is, engage and/or disengage clutches as necessary to establish a new power path through the planetary sets? Why does this necessarily take so much more time?

couple reasons:

1. the two gearpaths in the DCT (which you already mentioned)

2. while a conventional planetary transmission has one “gear path,” there is a _lot_ that has to happen during a shift event. Rather than type out a long reply, I’ll just give a few links that explain what’s going on:

> **[Saturation Dive: The ZF 8HP 8-Speed Automatic Transmission](https://www.thetruthaboutcars.com/2014/03/saturation-dive-zf-8-speed-automatic/)**
>
> Analysis of the power flow of the ZF 8HP design

> **[Saturation Dive: The GM 8L90 8-Speed Automatic Transmission](https://www.thetruthaboutcars.com/2014/04/saturation-dive-the-gm-8l90-transmission/)**
>
> Analysis of the power flow of the GM 8L90 design

and it is possible to speed up the shift events if you’re willing to tolerate harsher gear changes. The ZF trans behind the 707-hp Hellcat in the Challenger and Charger shifts a lot more quickly than in other cars to minimize clutch slippage under hard acceleration.