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      03-28-2013, 09:54 AM   #23
mowflow
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Yup, denser cold air and all that.

The problem is the engine not being warm. Not sure if it's fact but it certainly feels like the 125d is limited by the ecu or something until it get properly warm. 10 minutes driving in 0ºC wouldn't get it properly warmed up.
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      03-28-2013, 11:00 AM   #24
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A full tank of juice and 40kg in the boot will make a massive difference!
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      03-28-2013, 12:15 PM   #25
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Quote:
Originally Posted by ovekvam View Post
You don't have to involve torque. Looking at the power graph and gear ratios should be enough. When power is higher in next gear, shift up.

According to the specs from BMW, you should shift at the limiter from first to second on the 116i. My dyno graph and real world testing indicates otherwise. The power graph is not flat, but drops off towards the redline. The shift points between the taller gears are even lower.

On all cars I have had before, the shift point was at the limiter between the first gears.
http://robotpig.net/__automotive/pow...ust.php?page=2

When I check the torque graph of the 125d (which stops at 4500rpm), I don't see any reason to shift up earlier. In the brochure you can read yourself that the transmission line multiplies the engine torque with a factor 13,93 in 1st gear (=+5000Nm on the rear axle then ), 7,63 in second gear and 4,75 in 3rd gear. The ratio between 1st and 2nd is 1,8 and between 2nd and 3rd 1,6. This implies that at same engine output torque, the acceleration is a factor 1,6 bigger in 2nd than in 3rd gear. So the torque at the redline should have dropped with 40% before you could gain in an early shift up from 2nd to 3rd.
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      03-28-2013, 12:51 PM   #26
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Quote:
Originally Posted by KoenG View Post
http://robotpig.net/__automotive/pow...ust.php?page=2

When I check the torque graph of the 125d (which stops at 4500rpm), I don't see any reason to shift up earlier. In the brochure you can read yourself that the transmission line multiplies the engine torque with a factor 13,93 in 1st gear (=+5000Nm on the rear axle then ), 7,63 in second gear and 4,75 in 3rd gear. The ratio between 1st and 2nd is 1,8 and between 2nd and 3rd 1,6. This implies that at same engine output torque, the acceleration is a factor 1,6 bigger in 2nd than in 3rd gear. So the torque at the redline should have dropped with 40% before you could gain in an early shift up from 2nd to 3rd.
This is all theoretical, but it's very different in real life. I found two videos of a M550d xdrive (couldn't find a 125d), one shifting at ~4500rpm and the other at redline (~5400rpm). See for yourself which is quicker.

(First video starts at 0:40)





I know finding a video isn't the best argument on the forum, there can be different circumstances, like the outside temperature, wind, loaded weight, the level of the road etc. However I measured the time (roughly) and the one, which was shifting at 4500rpm had a ~0,5sec. faster 0-100kmh time and ~2,5 sec. faster 0-200kmh time, which is a massive difference.
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      03-28-2013, 03:18 PM   #27
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Tried again tonight - I launched from 1800rpm with the car in 'Sport' mode and shifted at just over 4000rpm. Seemed to launch pretty well but when I shifted into 2nd gear the traction control killed ALL engine power (I have had this before on hard shifts). So I aborted. The return of traffic stopped me from doing it again.

It's not easy to get a good 0-60mph time with the manual 125d is it? My automatic 335i easily beat its claimed 0-62mph time by half a second - hell, even my old 4 speed 316i auto beat its claims by a second.

Anyway, I have attached a graph showing the data from my current best time - 0-60mph in 7.38sec, when I shifted at 5000rpm.
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      03-28-2013, 03:19 PM   #28
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Quote:
Originally Posted by Wositsch View Post
This is all theoretical, but it's very different in real life. I found two videos of a M550d xdrive (couldn't find a 125d), one shifting at ~4500rpm and the other at redline (~5400rpm). See for yourself which is quicker.

(First video starts at 0:40)





I know finding a video isn't the best argument on the forum, there can be different circumstances, like the outside temperature, wind, loaded weight, the level of the road etc. However I measured the time (roughly) and the one, which was shifting at 4500rpm had a ~0,5sec. faster 0-100kmh time and ~2,5 sec. faster 0-200kmh time, which is a massive difference.
You're right on this! But the theory certainly holds.

The gear spacing on the 8-AT is around 1,5 for the first 3 gears, meaning that when you undercut 500Nm, there is not much to gain to rev further in that lower gear. On the torque graph you see that this already happens at 4800rpm. In higher gears, this point even drops to 4400rpm. When you shift at 4800 rpm from 1st to second, you end up at 3200rpm in second which is already over the torque top of 740Nm. So the longer you delay the gear change, the more you also loose in the next gear. So in flat out acceleration, you'll never encounter the max torque. Makes me wonder why they are so proud the M550d revs high... there is apparently no gain in it! Tx, you opened my eyes on this one!

What is the limiter of the 125d since the torque graph ends at 4500rpm?
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      03-28-2013, 03:21 PM   #29
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5400rpm, just like the M550d
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      03-28-2013, 03:54 PM   #30
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Quote:
Originally Posted by jhbodle View Post
5400rpm, just like the M550d
OK, my mistake then. I checked the end point of the torque curve that only reached uptil 4500rpm. I guess that like with the M50d, there is certainly no point in exploiting the rev range beyond 4700rpm in 1st, nor beyond 4500 in 2nd. So also for the 125d, the last 700revs don't have a reason to exist actually.

You state the traction control kicks in, this means you didn't disengage the DSTC I guess. It will be absolute required to mimic a "launch control" start.

What I would do (this is the way I do it actually):
1. disengage the DSTC by pushing the button long enough until he indicates "no assistance", push clutch in, put it in 1st gear, then floor the accelerator, the rpm will settle at 2500.
2. Then you release the clutch rather violently and what you aim for is controlled spin, no frantic rubber burning though. So you probably need to dose by releasing the accelerator a bit, try to sustain the controlled slip as long as possible.
3. Shift up as fast as you can at 4700rpm, the slip you have now you can't sustain, just don't try to control it since you need to keep the accelerator totally burried. Repeat this at 4500rpm now to shift to 3rd.

You see, it's not soft on the mechanics of your car. Even trained pilots can easily loose half a second in this exercise.

Check out Steve Sutcliffe here in the Golf R:
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      03-28-2013, 06:42 PM   #31
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Quote:
Originally Posted by KoenG View Post
http://robotpig.net/__automotive/pow...ust.php?page=2

When I check the torque graph of the 125d (which stops at 4500rpm), I don't see any reason to shift up earlier. In the brochure you can read yourself that the transmission line multiplies the engine torque with a factor 13,93 in 1st gear (=+5000Nm on the rear axle then ), 7,63 in second gear and 4,75 in 3rd gear. The ratio between 1st and 2nd is 1,8 and between 2nd and 3rd 1,6. This implies that at same engine output torque, the acceleration is a factor 1,6 bigger in 2nd than in 3rd gear. So the torque at the redline should have dropped with 40% before you could gain in an early shift up from 2nd to 3rd.
You theory is right, but somewhat simplified. In reality, first gear is more limited by inertia than second gear. The faster the revs are climbing, the more power loss you have to inertia. This means you should shift up slightly sooner than your graph indicates.
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      03-28-2013, 06:51 PM   #32
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Totally agree, revving to redline in a diesel is a total waste of time. 4800 max 4500/4600 optimum

Also what's this app? How did you time it in the past before apps?
I wouldn't trust an app

Surely Sport+ should allow enough spin for this test?
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      03-28-2013, 08:09 PM   #33
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The app is the same one I used for my 335i when I had it. That was supposed to have a 0-62mph time of 5.7secs but the app showed that it could actually do it in 5.23secs. That was an auto though, which I am now starting to realise makes a big difference.
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      03-28-2013, 08:11 PM   #34
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Quote:
Originally Posted by ovekvam View Post
You theory is right, but somewhat simplified. In reality, first gear is more limited by inertia than second gear. The faster the revs are climbing, the more power loss you have to inertia. This means you should shift up slightly sooner than your graph indicates.
Yes...also correct!
You're right but there is some "neutralization" in play, in 1st gear the rotational intertia is high, but seen the higher drive axle torque, the acceleration of the car and longitudenal acceleration is also high. In 6th gear both are much lower and stay relatively balanced. Consequently relative loss is rather constant.

But when you find here an argument to shift up a bit earlier, I can only confess you're 100% right! So when you read the torque curves and factor in the transmission reductions, you need to correct with rotational mass inertion (of the engine and all following rotational parts until 1st ax in the transmission, since the remainder, as from 2nd ax, rotates at the speed of the wheels and is not listening to engine RPM).
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      03-29-2013, 03:11 AM   #35
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Quote:
Originally Posted by KoenG View Post
Yes...also correct!
You're right but there is some "neutralization" in play, in 1st gear the rotational intertia is high, but seen the higher drive axle torque, the acceleration of the car and longitudenal acceleration is also high. In 6th gear both are much lower and stay relatively balanced. Consequently relative loss is rather constant.

But when you find here an argument to shift up a bit earlier, I can only confess you're 100% right! So when you read the torque curves and factor in the transmission reductions, you need to correct with rotational mass inertion (of the engine and all following rotational parts until 1st ax in the transmission, since the remainder, as from 2nd ax, rotates at the speed of the wheels and is not listening to engine RPM).
Yes. About 20 years ago, I made some computer programs to simulate acceleration based on car specifications. Before I added rotational intertia to my data model, the computer car was always faster than the real car, particularly in the first gears. By comparing the computer graph to real life acceleration logs, I found some suitable factors for how much intertia actually slows the car down.

It is in the ballpark of 400-500 kg added weight to the car in first gear, and around 100 kg in the top gear.
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      03-29-2013, 05:01 AM   #36
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Just my 2c. A couple of years ago, I ran a number of apps, including Dynolicious, at the drags against the official clock. Not great correlation, in my experience. Of course, they may have improved over time.
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      03-29-2013, 05:55 AM   #37
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Can't say i trust the app either. It only uses the phones internal hardware. Good for comparing your own car before and after a performance mod perhaps but not much else.
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      03-29-2013, 06:42 AM   #38
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A friend of mine and I made a stand alone GPS logger some years back. With a 1 Hz GPS antenna, we managed to make it quite accurate compared to drag racing timing. It rarely missed with more than 1 tenth of a second. We did have the advantage to tune it specifically to one specific antenna. That helps quite a lot. We also discarded the readings if the antenna reported low accuracy.

With any random built in mobile phone antenna, the results will probably not be very reliable. It works okay for lap timing at trackdays, though.
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      04-03-2013, 01:24 AM   #39
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Quote:
Originally Posted by tawia View Post
. There is no twin turbo on 125d.
...
how many is there?
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      04-03-2013, 03:38 AM   #40
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Got my OBD2 adaptor in yesterday and spent some time setting it up last night.

Had 2 rather poor attempts at 0-60 while commuting into work in rush hour traffic.

Run 1:
Time - 8s
Conditions - slight damp, smooth road, ambient temp 0.5C. Car was up to running temp after 30 minutes regular driving
Details - Put the car in sport+, launched with 1st gear at around 2k rpm and floored it, quite a bit of wheel spin, missed the shift and bounced off the limiter. 2nd gear bounced off the limiter again then missed 3rd gear and went straight into 5th. Bit of a disaster to say the least

Run 2:
Time 7.2s
Conditions - same as above only rougher road surface.
Details - Launched from traffic lights using 2nd gear in Sport+ again. Still a fair bit of wheel spin but felt a bit more controlled. Shifted to 3rd around 4,5k and got a good shift this time. Backed off towards the end as was fast approaching another set of lights and was worried I was going to die.

I think that with a fully committed run i could get the claimed time and possibly better it marginally. A trip to the nearest industrial estate errrr, I mean private track this weekend for some proper tests.
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      04-03-2013, 04:08 AM   #41
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How accurate is this app if it runs of the OBD?

Wouldn't make any difference to the acceleration times would it?

http://www.babybmw.net/viewtopic.php...46802&start=30

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      04-03-2013, 05:14 AM   #42
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Same app. Not sure what your question is Matt.

The app requires data from the OBD port, the phones accelerometer and the GPS to display data. You have to set up the car profile inputting weight including driver and fuel weight. I set the fuel weight at half a tank and my runs were done with 3 quarters which would be completely negligible at this level i would imagine.

I honestly have no idea over it's accuracy but it's great fun.
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      04-03-2013, 05:22 AM   #43
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Sorry, my mistake.
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      04-03-2013, 08:40 AM   #44
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Quote:
Originally Posted by tawia View Post
Totally agree, revving to redline in a diesel is a total waste of time. 4800 max 4500/4600 optimum
Same goes for some petrols too.

The 116i will rev past 6500rpm but maximum torque is between 1350-4300rpm and maximum power is at 4400rpm.

As this unit is detuned electronically boost is tailed off at higher rpm. In Sport mode the Auto changes up at 5900rpm but I find even this to be too high. I find 5500rpm to be a sweet spot for the 8AT box and 116i.

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