04-03-2018, 11:26 PM | #1 |
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BMW E-diff vs Quaife ATB
Could you guess the outcome? Please let me know what you think about the video
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04-04-2018, 01:33 AM | #2 |
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The 0-100 is not the most interesting when purchasing a LSD but the fun is in going sideways on the corners. A test on track looking at time laps would had probably been a better comparison.
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04-04-2018, 10:25 AM | #3 |
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My comments:
- I don't think the e-diff is enabled in traction mode, only in DSC Off mode. At least that is what the BMW documentation and manuals say. If you had selected Sport+, you would have gotten traction mode with the engine response in sport mode. - My experience is that the best 0-100 times are set on cold days. The engine performance drops noticeably with increased heat. - Less wheelspin is not always an advantage in such tests. As an example, I used to have a 1990 BMW E30 318iS. The factory claimed 0-100 km/h in 9.9 seconds. I did a 7.9 second run (GPS logged) with studless winter tyres and limited slip differential on a very cold winter day, with lots of wheelspin. I think the engine was over 5000 RPM the entire run because of tyre slip. |
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04-04-2018, 01:32 PM | #4 |
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Well:
Ultimate acceleration appears a matter of power/grip balance. If you wish to play it simple , make sure you don't have much power: all you have to do is floor it (keep the revs high, more precisely) then - you won't have too much wheelspin anyway. Driving a powerful car is more challenging: you can overwhelm your tires still standing where you are. To measure lots of wheelspin acceleration I'd suggest the speedometer. |
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04-05-2018, 05:13 AM | #5 | |
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We can all agree that the biggest difference should be seen in out-of-corner acceleration and sideways stability, but to measure that with high repeatability and reliable data...I dont know if that would be anything else than subjective. Waiting for some rain so I can do a skid comparison with the E-diff:
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04-05-2018, 05:21 AM | #6 | |
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04-05-2018, 07:30 AM | #8 | |
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BMW says the e-diff is only enabled in DSC Off, but I guess that could be interpreted in different ways. Maybe they mean that everything is off, except for the fake differential brake. |
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04-05-2018, 04:17 PM | #9 | ||
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So it's harkes himself (repainted without notice). I might need to elaborate my impression from the video then.
The topic has been discussed here too many times to mention. ovekvam, in particular, has written quite a book spread over those threads. Here's just one for example: Open-diff vs. E-diff- vs LSD (F20 related). What is "E-diff"? DSC is a complex system (this document, page #18, looks kindly quoted) working with all the wheels (brakes) and the engine (power): . "Quaife Helical" is what it is - an LSD. How can you compare those? Put the simplest, "Quaife Helical" is what helps to drift, DSC(/DTC) taken as "E-diff" is what prevents drifting (still failing to overcome the laws of physics). When you choose DTC to "allow the wheels to spin" it is like you disable LSD to some extent. So taking as "E-Diff" the Active Differential Brake (ADB-Sport) feature (activated "When DSC mode is off" - does that make a bit of sense already?) looks the only correct approach to challenge "Quaife Helical" (which needs not DSC "wrapper" to show itself either, perhaps). Quote:
Quote:
Regarding the 0.1 second - how much does Quaife Helical weigh to add to traction? Last edited by No one; 04-05-2018 at 04:37 PM.. |
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04-07-2018, 09:55 AM | #11 | |||
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Yes, the baby blue wrap is now off the car. Back to factory white
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04-07-2018, 10:53 AM | #12 |
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The Quaife is a TorSen type differential brake, and my impression is that one of their main drawbacks is that they struggle to get the locking going when one wheel has no traction. That could be when one wheel is on ice, or in the air. In your application, you still have the ediff in addition to the Quaife. That means that if the Quaife has issues with too limited traction, the ediff will provide that by braking the spinning wheel. It should be a winning combination, and seems to work very well in your video.
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04-07-2018, 11:40 AM | #13 | ||
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What I meant you had shown neither knowledge of driving modes nor understanding of differential locking practical purpose as we knew them here. Also, you seemed to further insist DTC included "E-diff" because it used the same technology. I thought it was like pointless. Quote:
Michelin Pilot Sport provide amazing grip even worn off! I suffer plenty of wheelspin with my winter runflats and quite some with my summer ones having less than a half of your extended power (watching the first video I felt like the chassis hardly coped ). |
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04-07-2018, 11:55 AM | #14 |
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Judging by the first video from harkes, it does indeed look like there is an ediff feature enabled, as wheelspin is allowed, but both rear wheels seem to spin very evenly. I have tried quite a lot to test it on my own F20, but haven't really managed to find a good way of doing it. BMW documentation indicates that ediff is only enabled with DSC Off, but maybe that is not correct. I am still not convinced if it is enabled or not in Sport+ and DTC mode.
The ediff is very noticeable in corners when it intervenes, but I can't really tell what it is doing when driving straight. Testing corners with DTC or Sport+ causes the stability control to cut in. |
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04-07-2018, 01:00 PM | #15 | ||
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I've just watched a TorSen explanation video (failed to get why only one of the connected wheels can spin the other, not vice versa, I'll think about it ), read the comment and wondered if I really did it right relying on DSC OFF to move a stuck car caring not to have the steering wheel always turned... |
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04-07-2018, 01:24 PM | #16 |
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DTC and Sport+ are supposed to leave some wiggle room for the driver, but it is not possible to do any drifting. The car waits a bit to see if the driver corrects the car, and if not, it cuts in to spoil the fun. You are however allowed to spin the wheels quite a lot in a straight line, which can be practical in snow, to dig the tyres into the surface.
In a corner, it is usually the inside wheel that is unloaded, and starts spinning first. When the ediff intervenes, it will brake the inside wheel. This feels almost like somebody attaches a cable to the front of the car, and pulls it towards the center of the corner, as the uneven brake force rotates the car into the corner and kills the usual understeer you would get with an open differential. As harkes shows, it is not nearly as smooth as a mechanical LSD, but it does get the job done somehow. The trick with the TorSen differential is that the screw gearing is so high that it can only transfer torque one way, not the other. It is the same thing as the screw in many car jacks. The weight of the car does not turn the handle, but turning the handle lifts the car. The one advantage an open differential has, is that it always distributes the torque 50/50, even if that means transferring almost no torque at all. It makes the car very stable in a straight line, so that the rear doesn't step out. It sacrifices traction for stability. It would make sense for BMW to act like that with DSC enabled, but maybe not in DTC and Sport+. |
04-07-2018, 01:43 PM | #17 | |
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04-08-2018, 01:28 AM | #18 | |
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04-08-2018, 01:43 AM | #19 | ||
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One video is trying to compare dry traction, and the two others wet operation - if that was unclear.
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