Why does the M40i not have a DCT box?

[sunnydays]

Hey all,

I am just looking at the specs of the Z4 M40i and have noticed that BMW appears to no longer use the DCT seen in the 35is in the new Z4.
They state "All models come with BMW’s eight-speed Steptronic automatic gearbox"

Is the new "steptronic automatic" box faster than the old getrag DCT, or have they done this to cut costs?

Thanks!

[SO8]

Hey all,

I am just looking at the specs of the Z4 M40i and have noticed that BMW appears to no longer use the DCT seen in the 35is in the new Z4.
They state "All models come with BMW’s eight-speed Steptronic automatic gearbox"

Is the new "steptronic automatic" box faster than the old getrag DCT, or have they done this to cut costs?

Thanks!

Having had the DCT in 2 x Z4 35iS's I can say it does not shift as quick as the DCT up the box but is loads quicker downchanging. Which would I have, which do I prefer ... the 8 speed any day of the week !!! Makes driving easier and it is as quick. Downchanges are far better.

[sunnydays]

Having had the DCT in 2 x Z4 35iS's I can say it does not shift as quick as the DCT up the box but is loads quicker downchanging. Which would I have, which do I prefer ... the 8 speed any day of the week !!! Makes driving easier and it is as quick. Downchanges are far better.

Hey,

Thanks for your input, so from what you have said and reading around it seems that the ZF8 is a better daily driver gearbox where the DCT is a better performance gearbox.

For reference figures I found suggested the following in relation to shift times:
ZF-8: 150ms
DCT: 60ms

Also worth noting that the ZF-8 allegedly has additional drive terrain power loss due to the torque converter.

[GuidoK]

Also worth noting that the ZF-8 allegedly has additional drive terrain power loss due to the torque converter.

Depends on how soon lockup occurs.
But it also contains other engineering features that lower the efficiency of the box. An automatic uses planetairy gearsets that have a lower efficiency than normal gears (because it uses smaller gears), there is a mechanical oil pump thats always running, and the zf 8speed uses stacked gears for some of its gearratios, which means twice the loss for those ratios.
However it has an extra gear.
But how the boxes are geared is maybe more interesting.

[J400uk]

The ZF8 ‘box is exceptionally good, I had it in my M135i and loved it. Super smooth under all conditions, relaxed when cruising and fast shifting. BMW are using it very widely these days, even the new M5 now has it standard. Definitely not cost cutting!

[SO8]

I love the ZF-8 ... I just find DCT/DSG boxes slow compared for multiple down changes.