Interesting finding - related to manual tranny only

[grish]

Today, after owning this car for a month, I finally turned off the DTC/DSC completely off. I know... I know... should've done it much sooner.

All of a sudden, driving through the city, I started to have a wonderful feeling of NOT being jerked when shifting to 2nd!!!

Forget the CDV mod, if you want to drive your manual smoothly just turn off all traction controls and give it a try.

[Robert]

really, I will have to try it out. Usually the jerk happens when I slip into 2nd too fast

[scorcherjf]

unless you're shifting really quick and chirping the tires i don't think traction has anything to do with the jerkiness lol

[grish]

Originally Posted by scorcherjf

...i don't think traction has anything to do with the jerkiness...

Traction does not, but it looks like the computer does.

Don't knock it until you try it... it surprised the hell out of me.

[My135]

With the DTC/DTS completely off, our cars drive like a champ with better throttle response and feel more power.

With the DTC/DTS on, the computer would reduce power whenever wheel slip was detected and return to full power after the detection was gone. This unsmooth phenomena is probably what people refered as jerkiness.

[EngPhys09]

I've found driving in the rain is much better with DTC OFF. Yes I know its designed for that weather but I have a friend with an E46 and his computer took a dump when he hit a puddle with it on.
It is much better with it off.
Now where is the always off button?

[scorcherjf]

Originally Posted by grish

Traction does not, but it looks like the computer does.

Don't knock it until you try it... it surprised the hell out of me.

Oh believe me I've tried it. I take traction control fully off at autocrosses and the track, and usually on nice sunny days. I do have the CDV delete as well and I did notice it made a big difference to my 1 to 2 shifts, but I didn't notice the traction control affecting them...

I just don't see how the computer affects the 1 to 2 shift at all. That's pretty much all your left and right foot... with a constriction in the clutch fluid line if you have the CDV still in there.

With better tires you won't be spinning your wheels as much so the DTC won't kick in as often. Then with a real LSD it won't be kicking in much at all. Next mod hopefully (but expensive!)

[grish]

Originally Posted by scorcherjf

...With better tires you won't be spinning your wheels as much so the DTC won't kick in as often...

I don't spin the wheels... I drive normally, but I like to shift to 2nd a little faster than the BMW computer thinks I should... I did feel the difference by the seat of my pants.

[jeremyc74]

Originally Posted by grish

I don't spin the wheels... I drive normally, but I like to shift to 2nd a little faster than the BMW computer thinks I should... I did feel the difference by the seat of my pants.

I don't see any way that's possible. The computer doesn't do anything until it detects slippage, and it's certainly not changing the way the clutch releases.

[Lester]

Let's at least get the terminology correct. It's DSC and DTC

DSC is the default mode- Dynamic Stability Control. In this mode, the computer cuts power to the engine and will apply brakes at one or more wheels to bring the car back into control.

DTC - by pressing the button. Dynamic Traction Control. This is DSC 'Lite', where the computer will allow for some wheel slippage - used for snow, ice, loose gravel etc.

Turn off DSC/DTC by holding the button for 4 seconds. Now all the computer will do is apply a brake at the rear wheel that is spinning, or E-Diff as it is called.

There is no way to connect the functioning of DSC/DTC to shifting gears, as the computer has no control over the manual transmission. But if it makes you think it does, then the more power to you. You are probably noticing not having the computer cut power to the engine, but really - should you be trying to catch rubber on every shift to second?

[cagekicker]

interesting talk

[akak1997]

I've notice the same thing, BUT, I also notice that After I run the car in DTC mode for a while (~15-20miles, my commute to work), the car runs smoother the next time when everything is on (i.e. start the car, didn't touch the Button)... usually it last for a few weeks, then it goes back to what it was, jerky 2nd. Anyone notice this? or Maybe I'm just crazy? heh
The only way I found to shift to 2nd smooth is a more than normal (as in other cars I drove) amount of clutch slip.. or am I just suck at driving a stick on a 300hp car...

[Robert]

Originally Posted by akak1997

The only way I found to shift to 2nd smooth is a more than normal (as in other cars I drove) amount of clutch slip.. or am I just suck at driving a stick on a 300hp car...

+1, how do you guys do a fast shift from 1st to 2nd in hard acceleration. I always get a jerk or two as if the clutch plate hasn't fully engaged drive train after I lift off. Only way to do a smooth transition is as mentioned more slip than usual

[Evice]

I felt the same jerk often, and sometimes I do question myself about what I did so it didn't jerk this time. I have 128i and I change 1st to 2nd around 2000-3000 rpm and my experience is a little random.

In addition; if I change gears between 3k-4k then I have to release the clutch a little faster to compensate the rpm drop in the engine so it doesn't jerk, or give a touch on the throttle while pressing and de-pressing clutch to 'rev match' per se.

[timeg]

I'm going to have to try it because I get that little jerk between first and second to, and it's not just my driving habit I'm sure. I've yet to turn off my DTC, but I've only had my car 4 days now

[MrRoboto]

Originally Posted by Robert

+1, how do you guys do a fast shift from 1st to 2nd in hard acceleration. I always get a jerk or two as if the clutch plate hasn't fully engaged drive train after I lift off. Only way to do a smooth transition is as mentioned more slip than usual

Change your CDV = Problem eliminated.

[JimD]

Lester,

Thanks for the good and simple explanation. I'm waiting on delivery and have read the manual and watched the videos but still did not fully "get it". Now I know what the button does. My SUV has DSC but no way to switch it off without modifying an ABS circuit so you can make the computer think a sensor is bad. Switching between full computer control (DSC), partial control (DTC) and no computer control seems much more friendly to the driver.

Jim

[grish]

Guys, I don't know the logistics but driving to work this morning, same route as usual, with the DTC and DSC off the shifting was much smoother. No jerkiness from 1 to 2 and no over slippage was required to avoid the jerkiness.

The computer must be doing more than BMW makes us believe.

All of the information you provided in regards to the DTC/DSC functionality does not come from the BMW software developers but from a BMW marketing department!

Give it a try and post your findings... don't over rationalize.

[jeremyc74]

Originally Posted by grish

Guys, I don't know the logistics but driving to work this morning, same route as usual, with the DTC and DSC off the shifting was much smoother. No jerkiness from 1 to 2 and no over slippage was required to avoid the jerkiness.

The jerkiness is caused by the engine speed and driveline speed not matching, and the lack of control over the clutch release due to the CDV. It's purely mechanical and the ECU can't control it.

[Monterra]

I've driven my 128 pretty extensively now in all 3 modes. I don't experience the jerkiness or variance in any of them (given no tire slippage) however the feel of the throws seems to improve with increasing revs. The clutch is the best of any car I've driven. The ratios are tight and all gears not needed in light or even moderate acceleration. Short shifting it @ or below 3k requires quickness because of the tight ratios and quick revving motor. This is why I do a lot of 2-4, 4-6 changes when I'm not using liberal doses of throttle. I wonder if the jerkiness being felt isn't due to revs falling faster than shifts executed whereby on re-engagement the revs are brought back up by the transmission like a non-rev matched downshift to a lesser extent.

[grish]

Originally Posted by jeremyc74

...purely mechanical and the ECU can't control it...

Is that a fact? How did you arrive at that conclusion? Did you actually look at the software and what it controls?

[jeremyc74]

Originally Posted by grish

Is that a fact? How did you arrive at that conclusion? Did you actually look at the software and what it controls?

No, but I know how the clutch works, and there's ZERO electronic control of it.