Re: Where do M drivers meet their Expert Mech's?
Hi Drk,
That lag you refer to from 1st to 2nd gear is normal. I have tried updating the SMG II software to the lastest patch and SMG clutch relearn. Both of which did not provide any noticeable difference in Shifts, in fact none at all.
I did however tried experimenting with how the SMG behaves when upshifting and my conclusion is that the rate at which SMG changes is Throttle positioning dependent rather than RPM based.
Scenario A
When stopped at the lights, 1st gear, S3-S5 mode, apply 20-30% throttle (constant).
Accelerate at a pace as what a normal 1.3L car would and drag the RPM all the way to 4000 RPM and Upshift to 2nd.
Result: The upshift is almost just as slow. This is probably what you are currently experiencing.
Scenario B
Same settings as above.
This time give it gradually 70%-100% throttle. Definition of gradual means it takes about 1.5-2 seconds for you to apply the throttle from 0-70%, not slamming it. This time, Upshift when you hit 3000rpm or even 2500rpm.
Result: You will notice the gear changes from 1st to 2nd at a markedly improved rate. In S5 you'll hear a "thud", this is normal.
Give the above a try and let me know what you think.
So the question is, why is does SMG shift from 1st to 2nd slowly when dragged to higher RPMs in light throttle application but yet when under higher throttle application, SMG shifts from 1st to 2nd quicker and at even lower RPM ?
I'm no gearbox engineer or mechanic and I can't explain why the SMG II behaves this way.
I did however notice that in higher gears, 3-4-5-6 the gear changes are quicker than 1-2 in 40-50% throttle (normal accel). However I did notice that the shifts from 3-4-5-6 were markedly quicker had I given it 100% throttle. I can't provide any numerical figures to the meaning of "quick". This is something you have to interpret yourself by trying.
That is why I arrive at the conclusion that the more throttle you give it, the quicker SMG shifts instead of RPM.
The DCT functions on roughly the same concept as SMG but better. Similarities between DCT and SMG is that you have a hydraulic pump that operates the clutch work for you.
SMG: This works pretty much like a manual gearbox without the H pattern gear lever and clutch pedal.
Eg: To upshift from 1st to 2nd, Hydraulic pump clutches in, changes from 1st to 2nd, clutch out. The above motions take time (interruption of power) at low speed and the people who hated it did not understand the mechanics of it and expected seamless Auto gearbox like smoothness. In spirited driving, this is where the SMG shines because it is able to change gears quicker than any human beings could. For its time, the SMG was really high tech stuff.
DCT: Is pretty much the same but instead of 1 clutch, it now has 2 clutch packs.
Clutch Pack A handles all Odd gears (1,3,5).
Clutch pack B handles even gears (2,4,6).
Example:
At the traffic lights, Clutch Pack A is engaged in 1st gear, Clutch Pack B is ready in 2nd gear.
As you accelerate and Upshift, Clutch Pack B's 2nd gear is ready for you. As you Upshift from 1st to 2nd, there is no power interruption.
Meanwhile you are in 2nd gear, Clutch Pack A uses this time to change from 1st to 3rd gear and now 3rd gear is ready for you.
As you Upshift from 2nd to 3rd, again no interruption in Power and the whole cycle goes on.
Conclusion:
SMG: From 1st to 2nd, SMG clutch in, slots from gear 1 to 2, clutch out ---- Takes time, power interrupted
DCT: Clutch Pack A in 1st gear, upshift, Clutch Pack B's 2nd gear is ready ---- No time delay, power not interrupted.
Because of power interruption, this is probably why drivers thought SMG is rough.
Having said that, I did however try skipping a gear in both Upshifts and Downshifts. Eg. 2nd to 4th or 4th to 2nd. Because both are even gears, this means I am using the same Clutch Pack. I did notice a slight delay as it goes from 4th to 2nd or 2nd to 4th. You really have to pay attention to it otherwise you would not have notice. This has more to do with the mechanical side of things where technology has been improved over the years.
In regards to your 5th Gear jerk at 2000rpm. I think its normal. I experienced the same thing. I suspect the Jerk has more to do with the clutch disengaging to prevent the engine from stalling.
As you get back on the throttle, it almost feels like the clutch engaged again. There is also a very tiny slight hint of delay in power as you get back on the throttle.
Again, I'm not SMG expert and I'm not sure if the SMG software is written to behave this way. The reason why I suspect the clutch disengages is when at 6th gear coming to a complete stop, the SMG drops from 6th to 2nd and 2nd to 1st.
If you notice, as you are braking at say 20% to slow down while in 2nd, at a certain RPM there is almost a hint where the car lurches forward and you have to apply say 25% or maybe 30% to slow down at the same rate as before.
This is synonymous when driving a manual car, downshift to 2nd, you can feel the engine brake but as you near the stop line, clutch in, you feel the car rate of deceleration is not as much as when the engine was slowing the car down and you need to apply more brakes to slow the car down.
The above doesn't always happen as it depends on the rate of deceleration. If you brake too hard, the G force masks it. If you come to a complete stop too gradually, the speed is too slow for you to feel it. There seems to be a sweet spot when the SMG does this.
In saying that, if indeed the clutch disengages if you are in 5th at 2000rpm, why is the RPM still at 2000RPM and not at idle ? Honestly I can't explain this one.
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I never had any problems with upshift. There really isn't much you can do about the 1st to 2nd gear delay. Its just how the SMG works.
You can however drive smoothly if you plan your downshifts well ahead. My first 2 weeks of driving was especially jerky when I downshift to 2nd to turn at a junction. I overcome this by planning my downshifts well ahead.
I noticed that as you are slowing down for a turn, if SMG goes from 3rd to 2nd at 2000rpm or lower, it helps eliminate this sudden deceleration jerk-like feeling.
The trick is to anticipate well before hand when you are going to downshift and when the gearbox actually downshift and at what RPM.
Example:
Slowing down and braking for a left turn at the junction, at about 2200-2300rpm, press the downshift paddle, by the time the SMG is in 2nd gear (it takes time for SMG to do that), your RPM matches 2000rpm nicely and you commence the turn.
If you were driving at a slightly higher speed and braking slightly more, you need to take that into account and press the downshift paddle at 2500RPM (eg.) so that by the time SMG is in 2nd gear, your RPM is at 2000RPM or about.
This takes some practice. Took me about 2 weeks. Once you're used to it, it becomes natural and you don't need to think that much.
Give this a try for the next 1-2 weeks and let us know what you think. I'm happy to meet up and demonstrate this if you're still having difficulties with it.
DrK;695824 said:
Dear AC, I have a couple of related questions.
1.) When driving an SMG M3, it is normal to feel a slight 'lag' in the shifting especially from 1st-2nd gear? The lag seems to get less noticeable from 3rd-4th gear, 4th-5th gear and so on. This is assuming that I'm at S2 and M button is off. I read that this is a fairly common feel in SMG from other M3 forums. Having driven other newer models of 135i and 335i, some with DCT, the SMG feels rougher and not comfortable for daily driving. Would that be correct to say so?
2.) When driving the car on 5th gear and rpm is around 2k, I can feel very faint (not that noticeable but my butt can feel it) jerks from the car. Once I pressed on the accelerator abit more, this slight jerkiness is gone. Keep accelerating and no irregular jerking can be felt. Is this some kind of parts issue or that I wasn't driving with optimal gear selection to match that kind of rpm?
I think driving an SMG can be quite tricky. Appreciate that you can share some tips if you have any. Thanks.
