Smooth, fast launch with DSC on/DTC off?

[MrPT]

Now, it is quite possible that I can't drive the thing, but before I jump to that conclusion, has anybody had any success pulling away cleanly and rapidly without turning on DTC [EDIT - to be clear, one short press of the button]? I can't seem to be able to build up a decent amount of revs and be quite aggressive, clutch-wise, without throttle intervention, even when there seems to be plenty of traction. I just end up buckarooing down the road like a fool.

I know the CDV is also playing a part here, but that mainly feels like it is affecting the 1st -> 2nd change and not the initial launch. The most success I've had so far is by slipping it off the line gradually and then short shifting into 2nd. Maybe more practice is in order... I normally drive like a bit of a wimp, but it would be comforting to know that I can get a pregnant lady to the hospital in good time, if needs be.

 

[ben g]

sounds like you need better rear tyres. i don't have a problem getting off the line in mine.

 

[bcworkz]

For max. acceleration from standing start, you want to see a bit of wheel slip to tell you you are at the limits of traction. Any time this happens with DSC on, it will intervene with braking and throttle cutting, so it is just not possible with DSC on. Short shifting is not a good strategy, you loose the advantage of the huge torque at the wheels of 1st gear. It doesn't last long, use it while you can.

For optimal launch, you simply must have at least DTC engaged, or turn off the entire system. For optimal 1-2 shift, you must get rid of the CDV.

 

[Cibbers]

One press of the DSC button, Sport mode engaged, revs around 2500 - 3000, Green Lights GO! Practise makes perfect with regards to balancing throttle with clutch but ideally you want a tiny bit of slip but only enough to feel the limits of the grip at the back end. Be careful out there!

 

[corsaire77]

One press of the DSC button, Sport mode engaged, revs around 2500 - 3000, Green Lights GO! Practise makes perfect with regards to balancing throttle with clutch but ideally you want a tiny bit of slip but only enough to feel the limits of the grip at the back end. Be careful out there!

+1

It requires practice, but it's perfectly attainable - even without the CDV mod. Wider/better rear tyres (255) might help, if you're running a non-staggered setup.

 

[MrPT]

I am running a staggered setup. With DTC on (one press of the button) it's a lot better - but I haven't had the confidence to drive with it on very often, as I've only owned the car since November, i.e. road conditions have been rubbish, and I'm also new to RWD. Sounds like the way forward though. :driving:

ben g - you are probably right. OEM Bridgestone RFTs all round can't help much!

 

[Grant Adey]

You think you have it hard, I've the SMG box and with mine being a 2003 3.0 as far as I know there's no launch sequence so it's foot on brake and then floor it, DTC on and it's great but all off and it just spins the wheels so much.

 

[srhutch]

The CDV will not release the clutch as quick as you, I would get it removed as it will transform the car even in day to day driving.

 

[MrPT]

The CDV will not release the clutch as quick as you, I would get it removed as it will transform the car even in day to day driving.

Will probably do it once the dealer warranty runs out - not going to mess too much before then.

Smooth, fast launch with DSC on/DTC off?

So, to sum up, the answer to this is basically "no".

 

[Bing]

I am running a staggered setup. With DTC on (one press of the button) it's a lot better - but I haven't had the confidence to drive with it on very often, as I've only owned the car since November, i.e. road conditions have been rubbish, and I'm also new to RWD. Sounds like the way forward though. :driving:

ben g - you are probably right. OEM Bridgestone RFTs all round can't help much!

According to BMW DTC is for precisely the conditions we have had recently - lower traction, so snow, water etc. It allows just that bit more slip - as you have discovered - so that the electronics don't cut in unexpectedly and actually cause complete loss of traction by reducing power or applying braking force to one or more wheels. It's a very complicated and clever system that I cannot claim to know all about from a technical perspective. When on a hoon, Sport on, DTC on - and for me in an auto, manual changes engaged. Loads of fun :driving: 8)

 

[domsz4]

You think you have it hard, I've the SMG box and with mine being a 2003 3.0 as far as I know there's no launch sequence so it's foot on brake and then floor it, DTC on and it's great but all off and it just spins the wheels so much.

This isn't a launch sequence it's just what they do. Basically just get used to feeling for the grip. This car is pretty communicative I find. When you know where the limit is your off like billio.


Short shifting isn't such a bad thing. I have no idea on the torque curves for our car but I would say the best place to be would be where the torque curve is steepest for each gear. This would usually be liked to a rev/gear. Assuming good traction there is no point in staying in gear if your torque is dropping off. Moving quickly into a better gear would give better acceleration.

Basically if you want to launch off a line every time figure out for you car what revs you accelerate the best (you feel is the fastest) for each gear and change there.

I would say weather/road conditions play a big role as does the red mist of the trafic light derby.

 

[hype]

Smooth, fast launch with DSC on/DTC off?

So, to sum up, the answer to this is basically "no".

Not sure about it not being smooth - but DTC will certainly make it harder to get away quickly because as soon as those wheels slip the DTC will cut power.

For what it's worth I've never really had a problem, so long as DSC is on - and I haven't had the CDV mod.

My advice? Foot to the floor, and don't change before 7k rpm.

 

[bcworkz]

Short shifting isn't such a bad thing. I have no idea on the torque curves for our car but I would say the best place to be would be where the torque curve is steepest for each gear. This would usually be liked to a rev/gear. Assuming good traction there is no point in staying in gear if your torque is dropping off. Moving quickly into a better gear would give better acceleration..

I suppose it depends on how short and if you're trying to shave a few hundredths of a second or just showing off. What you propose about torque curves makes sense, and depending on the car's gearing, could be correct. However, most street cars, including 6 speed Zeds even, have relatively wide gearing, such that the torque at the wheels in the next higher gear is significantly lower than what you are getting in the current gear, regardless of where you are in the torque curve.

This means you should stay in the current gear up to as close to redline as you dare. That is the physics of it, but it just feels wrong, you can really feel the torque dropping during that last 1000 rpm. Coupled with a satisfying lurch when engaging the next gear, it just feels wrong to hold on to redline. You have to trust the physics of it all. Even if you don't and slightly short shift, it really won't make that much difference, except with electronic timing, so do what feels good.

 

[krusty]

For max. acceleration from standing start, you want to see a bit of wheel slip to tell you you are at the limits of traction. Any time this happens with DSC on, it will intervene with braking and throttle cutting, so it is just not possible with DSC on.
For optimal launch, you simply must have at least DTC engaged, or turn off the entire system.

Spot on.

 

[domsz4]

I suppose it depends on how short and if you're trying to shave a few hundredths of a second or just showing off. What you propose about torque curves makes sense, and depending on the car's gearing, could be correct. However, most street cars, including 6 speed Zeds even, have relatively wide gearing, such that the torque at the wheels in the next higher gear is significantly lower than what you are getting in the current gear, regardless of where you are in the torque curve.

This means you should stay in the current gear up to as close to redline as you dare. That is the physics of it, but it just feels wrong, you can really feel the torque dropping during that last 1000 rpm. Coupled with a satisfying lurch when engaging the next gear, it just feels wrong to hold on to redline. You have to trust the physics of it all. Even if you don't and slightly short shift, it really won't make that much difference, except with electronic timing, so do what feels good.

yeah like I said I don't know what they are and I suspect in lower gears its probably not that noticeable. if they are dropping off before red line then there is no point in going that far znd a change would be needed

my westy has a hard red line at 7500 rpm but really above 7000 is not worth it in 3 or 4.

 

[Mr Whippy]

On the 3.0i the peak power is 225bhp at 5900rpm, but due to the gears and the drop of power it's still faster overall to rev to about 6400rpm before changing gear... though only very marginally.
I usually shift at 6250 tops, if you end up near 6500rpm and hit the soft rev limiter (easy to do in 1st) then you lose any benefit of having tried getting near it to start with.

This is the best (and only iirc) 0-60mph run I did which I was pretty chuffed with.

This was on FK452 tyres and with all the traction stuff turned off.

And this is my calculated output curve from a G-tech accelerometer run. Please note the correction is out but something didn't stack up so I adjusted it to get the peak power/torques in the right range. The actual curve shape is what is important here, it's pretty clear that although power is dropping off after 5900rpm, it's still higher up there than in the next gear up right out to 6500rpm!

I find the DTC mode (first press of the button) is perfect for faster driving... though from what I read in the tech documents after about 50mph it functions exactly like the DSC mode... basically it allows some wheel slip at lower speeds which is useful when you want maximum acceleration.
DSC is very excessive and if you get any slight slip it trims the throttle for too long. It's ok most of the time though.


DTC off is pretty pointless on the road really unless you want to do some silly stuff. Generally I find that the inside rear just spins away and is actually slower and more likely to see you fish tailing around vs DTC on which does what it says on the tin and gives you more traction and more performance.


So, DTC on for the best all-round driving imo.


I've not done CDV yet but in my experience you can get a fast time with it fitted. It just stops transmission shocks from what I can tell and in practice I never really notice it and get frustrated at all.

Cheers

Dave

 

[mad4slalom]

in the M i find a quick launch harder with sport botton on, i sometimes find that i have trouble getting off the the clutch so it rides for too long , dont get it with sport off , i think it is to do with the speed at which the revs come in when sport is on.

 

[Mr Whippy]

It's just a sharper throttle mapping from what I can see, and in 1st gear that is gonna make matching revs and clutch release harder.

This is why TVR's for example have really long throttles, so you can gauge out the power better. It doesn't feel as sharp, but then again they have 300bhp+, 1 tonne weight, and no driver aids at all

Dave

 

[MrPT]

Yeah, Sport mode does sometimes catch you out if you are lazy with the clutch, even in a non-M.

 

[domsz4]

whats the yellow curve at the bottom and what gear was that power run in.

i dont use the sport button much either but thats cos i drive alot in the city and find its not as smooth to drive with it on. plus when your crawling in trafic between lights whats the point?

i found a website with some curves on yesterday and i would have said about 6K would be the place to change. by the time you see the dial and do the change i guess you'd have jumped up a few more rpm anyway.