2009 E90 DCT - Quick Deceleration When Off the Throttle

[wfdeacon88]

I assumed it was normal, and maybe it is, but just wanted to check and see if its normal on an e90 DCT causes relatively quick deceleration when letting off the throttle on the highway. I would describe is as not close to coasting, and slowing down noticeably in any gear at any speed. I tried searching and couldn't find anything on it.. Any thoughts? Do most people here experience this or is it normal to "coast" when letting off the throttle in Auto?

[Cbozz]

Originally Posted by wfdeacon88

I assumed it was normal, and maybe it is, but just wanted to check and see if its normal on an e90 DCT causes relatively quick deceleration when letting off the throttle on the highway. I would describe is as not close to coasting, and slowing down noticeably in any gear at any speed. I tried searching and couldn't find anything on it.. Any thoughts? Do most people here experience this or is it normal to "coast" when letting off the throttle in Auto?

no coasting in these cars!!!

[wfdeacon88]

Originally Posted by Cbozz

no coasting in these cars!!!

So normal? What spurred my question what reading an old Post on here that essentially said this wasn't normal... but I haven't read anything else so just wanted to make sure.

[Cbozz]

it is normal... unlike my wife's X5 which just glides when I let off the gas my car just starts slowing down with engine braking....
When I'm driving and see the light turn red I just let off the gas and downshift and end up not even touching the brake until the very end when car rolls with 5mph and it's time to stop... it's been like that always and my car is always been running strong. At first it's weird but you'll get used to it.

[Cbozz]

I'm sure everyone else with DCT can attest to this

[wfdeacon88]

Originally Posted by Cbozz

it is normal... unlike my wife's X5 which just glides when I let off the gas my car just starts slowing down with engine braking....
When I'm driving and see the light turn red I just let off the gas and downshift and end up not even touching the brake until the very end when car rolls with 5mph and it's time to stop... it's been like that always and my car is always been running strong. At first it's weird but you'll get used to it.

thanks, very much appreciated. I assumed normal until I read that damn post saying it was a jacked diff. For me, makes for a hell of a ride in traffic as the idiots behind me don't get to see break lights and usually end up slamming on breaks last minute. thanks again.

[thkfast]

My DCT coasts when I let off at highway speed. BUT....if I have cruise control set at say 65mph and gas it to pass, then let off, it'll apply the brakes to slow back down to the set speed. And yes, the brake lights come on when it does that.

[wfdeacon88]

Originally Posted by thkfast

My DCT coasts when I let off at highway speed. BUT....if I have cruise control set at say 65mph and gas it to pass, then let off, it'll apply the brakes to slow back down to the set speed. And yes, the brake lights come on when it does that.

I guess coast is a relative word I used... At 75 mph in 7th, yeah mine coasts also I guess.. This is moreso at 30-50 mph auto mode, where I rarely have to use the break much when coming to a stop/slowdown, even in Auto.

[Sandye90m3]

Yup extremely normal. I've only changed my brakes once after 205,000 kms lol

[wfdeacon88]

Originally Posted by Sandye90m3

Yup extremely normal. I've only changed my brakes once after 205,000 kms lol

thank you!!

[MrGatsby]

The DCT is a manual gearbox with automated clutch.

A traditional automatic uses a torque converter with planetary gears immersed in fluid which makes the transition through the gears very soft, as well as allows it to coast and roll forward at a stop.

In a manual, the gears rotate with the motor. When you let off the gas in gear, you'll slow down with the rotational mass of the motor but once you press in the clutch, you'll coast, since the rotating mass of the motor is no longer connected to the drivetrain.

In a DCT, we do not use a clutch to go into neutral when coming to a stop or letting off the gas, the clutch is automated. So as a result, you'll have engine braking as the gears are rotating with the motor and connected to the drive train.

It is completely normal.

[Van]

Originally Posted by MrGatsby

The DCT is a manual gearbox with automated clutch.

A traditional automatic uses a torque converter with planetary gears immersed in fluid which makes the transition through the gears very soft, as well as allows it to coast and roll forward at a stop.

In a manual, the gears rotate with the motor, when you let off the gas in gear, you'll slow down with the rotational mass of the motor, but once you press in the clutch, you'll coast, since the rotating mass of the motor is no longer connected to the drivetrain.

In a DCT, we do not use a clutch to go into neutral when coming to a stop or letting off the gas, the clutch is automated. So as a result, you'll have engine braking as the gears are rotating with the motor and connected to the drive train.

It is completely normal.

I just recently picked up a 13 e92 M3. First time ever owning a ///M car. I love that motor brake. Makes that DCT feel more like a manual.

[MrGatsby]

Originally Posted by Van

I just recently picked up a 13 e92 M3. First time ever owning a ///M car. I love that motor brake. Makes that DCT feel more like a manual.

Originally Posted by Van

I just recently picked up a 13 e92 M3. First time ever owning a ///M car. I love that motor brake. Makes that DCT feel more like a manual.

Its a fantastic transmission. I've owner north of 15 cars and every one prior to my M3 has been manual save for a Jaguar S Type R. The transmission in the jag was unbearable. Despite its 400 horsepower, it was a slug.

I initially vowed to only get a 6 speed M3, but after driving the DCT, I was beyond impressed as I still feel just as connected to the car as i do with a true manual, yet maintain precise and lightning quick shifts, with the ability to relax during my daily hour commute.

[slowm3]

The deceleration happens on these cars cuz of the tight compression in the engines, it's almost like an engine brake.

[e1000]

Originally Posted by MrGatsby

A traditional automatic uses a torque converter with planetary gears immersed in fluid which makes the transition through the gears very soft, as well as allows it to coast and roll forward at a stop.

Pretty sure you can engine brake in an automatic (planetary gears, torque converter)

[MrGatsby]

Originally Posted by e1000

Pretty sure you can engine brake in an automatic (planetary gears, torque converter)

Sure, theoretically if you use tiptronic you could downshift to a lower gear and hold it. But my point was under normal, every day conditions, you do not experience engine braking with a traditional automatic, but do with both DCT and Manual.

[fatalelement]

Originally Posted by slowm3

The deceleration happens on these cars cuz of the tight compression in the engines, it's almost like an engine brake.

If you have a DCT, it's actual engine braking. My last car had a higher compression ratio than the S65 and had no such characteristic.

[amrazM]

The compression and mapping of the dme makes the rev drop very quickly, under 3k rpm it’s not as immediate as the higher of the rev range.