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      10-19-2012, 12:18 AM   #1
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Open-diff vs. E-diff- vs LSD (F20 related)

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Warning: This will be a long post. If you don't like reading, or are not into the subject id skip this thread..


Intro:
I have trough many years gotten some experience with RWD cars.
I have found out that there is a huge difference from car to car. Especially the cars with open-differentials. The biggest differences has to do with how easy they end up being 1-wheel drive, and how «drift/slide friendly» they are.

I have rated several cars from 1-10.
10=very drift friendly diff.
1= not drift friendly diff.

Rating of 3 is usually pretty good on snow, but have a tendency to easily spin one tire on wet surface.

Rating - Car
1- BMW E87 318D with M-package (short test drive, so rating might not be deserved)
3 – Mercedes CLK 230 Kompressor (lowered)
3- BMW E36 318TI (97 model, M-tech everything with open diff)
4 -BMW E36 318I Sedan (91 model ,40mm lowering springs and open diff)
4,5 BMW F20 116I (Stock Open E-diff. Rating based on short test drive)
6 -Toyota MR2 Roadster (stock 2001 model, open diff)
7 -BMW 325I (E34 with stock LSD, 25%?)
9,5 -Toyota GT86 (based on short trip, stock torsen LSD)


Open-diffs
There is a huge difference between open diffs. I have rated cars with "same type of diff" from 1-6.
-Am I the only one with that experience?
-Why is it that some cars have a tendency to easy spin one tire compared to others when they all have an open diff?



Open-diffs vs BMW E87 E-Diff
About a year ago I owned a Toyota MR2 Roadster. That car would usually spin both tires easily at the same time and the need for LSD was basically none.
I needed a new car and test drove a used E87 (I was looking for a petrol engine, but ended up test driving 318D with M-package and suspension)
I have never experienced a car wanting to spin one tire as bad as that car. It was one wheel drive no matter what I did. If I remember correctly that car had E-diff in DTC mode. But that mode had way too much electric interference to be fun so I was not able to notice that E-diff was useful on my test drive.
All electronics off, and it was just annoying with the 1-wheel drive.

I bought my Cooper S instead of the old 1-series due to the E87s tendency to only have one wheel drive. I was not planning a long term ownership and therefore it was not an option to buy LSD for the E87.


BMW F20 E-diff vs LSD
So, my Mini was on service, and I got to test drive a F20 116I about 2 months ago. Pavement was luckily very wet, and it was raining. The F20 handled well, felt pretty neutral and was very comfortable. With all electronics off it was much better than the E87 I had tested. Thanks to the E-diff I'm guessing. I could go sideways without one wheel drive, but due to E-diff braking (?) it seemed to lack momentum and power to get the car sliding out of corners. I know it is not that powerful, but it was really slippery that day.
-Do you guys have some of the same experience?
-Does E-diff also make handbrake (u-)turns way harder? Or was the car just strange in that way?
(GT86 and Mini Cooper S are pretty easy to "flick around" with the handbrake when electronics are off)

Right after driving the F20 116I I got to test drive the Toyota GT86 on the same twisty mountain road. (A car I had been waiting for a long time to drive)
Here are sidenotes on the GT86, skip if not interested in that car: Car really lacks torque, and automatic transmission is not approved by me (Im not into Automatic transmissions in general). Overall the engine feels much lazier compared to my Mini. Atleast combined with the automatic transmission I test drove it with. Manual has more sporty gearing. When comparing dynoes with the 86 you can easily see why the 86 did not feel that great when I am used to the Cooper S.Dyno link, scroll down for picture) Cooper S engine is also underrated like many BMW engines. Im guessing a BMW 170hp 118I would feel more powerful than the GT86 with its 200HP NA engine under normal everyday driving. I would probably prefer the 116I engine too. But when the 116I runs out of juice the 86 starts to get fun.
Steering feel is good, for an electric system. But could not compare to the MR2 I owned where you felt the road really good.
The power in the 86 is only good 5000+ rpm. And it is not as powerful as you might expect. Backseats are also very small and basically not suited for grown ups.
Anyway, handling in the GT86 was great. And it is a real sports car in terms of driving position and handling

The torsen LSD was fantastic. Way, way better than the E-diff in the 116I!

Most of you have probably seen the Chris harris review of the M135I and the Audi RS3. Im guessing if the M135I had a proper mechanical diff he would have gone more sideways like he usually does.
This review (press CC for subtitles) shows the car sliding and talks about the E-diff from 3.10-4.05. I have some of the same experience with the lower powered 116I on really wet roads.


LSD in the F20 1-series?
I see birdsauto is one place with a good amount of Quaife LSDs for BMW.
They have have one diff that fits All F20s with « 215LW Final drives».
-Which current F20 cars have a diff with that finaldrive?
-Is there a way to 100% disable the E-diff in the F20? Im thinking that would be a must if investing i a LSD for that car.
It would be brilliant to have an on/off button on the E-diff in combination with a Quaife Torsen Diff...


Epilogue
Thanks for reading! Hope to get some input from you guys!
I am really considering the F20 1-series or the GT86 as my next car. (not sure when that time will come) But how the car behaves on and beyond the grip limit is crucial for how fun a car is for me. Especially if im going to us a lot of money on a new RWD car.
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      10-19-2012, 04:29 AM   #2
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The need for a limited slip differential depends a lot on load distribution. As long as both driven wheels are equally loaded, there will not be any problems with one wheel spinning. The problem is that the inside wheel is usually unloaded in corners, and can not get much power down. The stiffer the suspension is, the more unloaded the wheel gets.

To get more power down, you can soften the suspension (swaybar) on the driven axle, and stiffen the other end of the car. That will reduce inside wheelspin significantly, but will usually also upset the balance of the car. In a RWD with soft rear suspension, you will get plenty of understeer that has to be compensated in other ways.

I have always been a big fan of limited slip differentials, and that is usually the first modification I do to my cars. They need a stiffer rear swaybar and an LSD. With the F20, I have found that it probably isn't necessary, since the e-diff system is working surprisingly well, and the car is well balanced.

I am a big fan of driving sideways in slippery conditions, and the F20 is well suited for the purpose, even the 116i. You can drift it nicely around an ice track. I have however found that drifting in summer conditions is very difficult. There is not enough power compared to grip, and the e-diff can not cope with the high loads involved. The turbo lag is also making it difficult to steer with the throttle.

Driving on the limit with the car in balance works well. The car can be set up sideways under braking, and you can go very early on the throttle out of corners. When trying to drive good lap times, I do not miss the LSD. I also find that the F20 is cornering more on rails than older BMWs. While you used to balance them with the throttle, you now control the car a lot more with the steering wheel. The balance does not change much when you alternate between braking and full power in corners. It stays well balanced and just changes the velocity. Almost like a computer game. And this is with DSC completely off.

There is no way to disable the e-diff in the F20 without doing modifications to it.
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      10-19-2012, 05:50 AM   #3
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I have been thinking about the issue with installing an aftermarket LSD on cars with e-diff. It might work just fine. The LSD will keep the velocity difference between the driven wheels at a minimum, which would prevent the e-diff from doing anything. And if it interferes, it would only do so when necessary (like when you lift a wheel with TorSen LSD).
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      10-19-2012, 09:50 AM   #4
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Thanks for you reply Ove.
Have been reading many of you posts on the old BMWCCN forum, some on the new forum and some here. Thanks for all the good and informative posts!

Softer rear swaybar is out of the question. And I would not bother with other adjustments to compensate for the understeer that would cause.
They easy and right fix for my problem is naturally a LSD.

I know your new car is fast around a big track (Considering its HP/weight/comfort), but im more interested in handling and "drift ability" on wet pavement while on the power. How would you compare the F20 116I playfulness and fun factor with your previously E36 323ti with LSD?


Side question: Did you test drive 118I and compare it to the 116I?
Would be nice to see a side by side real world dyno comparison on those engines.

Im not sure, but with my limited experience on wet pavement it felt like the E-diff did its job on removing 1-wheel drive. But at the same time I think it "removed" power when braking the spinning wheel. Do you think that is the case too?
Quote:
Originally Posted by ovekvam View Post
I have however found that drifting in summer conditions is very difficult. There is not enough power compared to grip, and the e-diff can not cope with the high loads involved.
Explain further please... I am not expecting that the new 116I can powerslide on dry pavement in the summer. That would not be my goal either.
I would believe 118I + LSD + stiffer rear swaybar could be a a very entertaining car. At least in theory if the engine is as underrated as the 116I.


Quote:
Originally Posted by ovekvam View Post
I have been thinking about the issue with installing an aftermarket LSD on cars with e-diff. It might work just fine. The LSD will keep the velocity difference between the driven wheels at a minimum, which would prevent the e-diff from doing anything. And if it interferes, it would only do so when necessary (like when you lift a wheel with TorSen LSD).
Im basically having the same thoughts when combining E-diff + LSD. It could be a real benefit when staring on ice or when one wheel is in the air.
But in a low powered vehicle it is important to not have any braking what so ever when doing a little sideways fun. If the E-diff is very sensitive it might interfere a little. Probably not enough to be of difference, but I would feel better if it was not there.
And if spending 15000,-++ NOK it would be nice to be sure the system would not interfere. That is why it would be nice to have a button for activation/deactivation. That way you could also try out the combination and see if the E-diff actually made things better or worse, to a minimal degree..
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      10-19-2012, 10:21 AM   #5
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In my old E36 323ti I could drift from corner to corner on rainy days, but it quickly ran out of power on dry tarmac. Because of the rear axle geometry from the E30, the E36 Compact was very steerable with the throttle. The F20 116i is not. When you get it sliding, you need to stab the throttle to get the wheelspin started. Then the turbo lag kicks in, and nothing happens. By the time you have power available, the rear tires are gripping again, and the car accelerates instead of rotating.

If you have gone fast enough into a corner to make the car start sliding, and you get a powerslide going, it works smoothly. I can usually not hold the slides very far, as I run out of power. My Michelin tires are quite grippy in the wet, and the car accelerates rather well also when sliding. Then engine feels weaker when it runs into high RPM, and there is no way the slide can survive shifting up a gear.

On ice or snow you have enough power to keep the slides going, and it feels almost like the car has an LSD, but not quite. It is a lot better than an open differential.

One thing I have noticed, is that the e-diff seems to help rotate the car. If I am driving around a corner on the limit, and add some throttle, I would expect the car to squat a little, spin the inside tire, and understeer. What really happens, is that it squats, accelerates, and remains neutral. My guess is that the e-diff is braking the inside rear wheel. This causes some torque vectoring that helps rotate the car into the corner, killing the understeer that should have been there. I can start accelerating earlier in corners with this car than any cars I have had before, and still not understeer over the outside kerbs.

I have not had a chance to drive the 118i.
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      10-19-2012, 10:31 AM   #6
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Thanks for your informative post Ove.
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      10-20-2012, 04:28 AM   #7
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We had a slightly wet day recently (greasy surface), so I had some fun in my 125i M Sport on some back roads.
In the Sport+ and manual shift selected (Sport auto) you can drift to a fair degree if you keep it in first or second gears and the revs in the 4k+ range.

The answer is if you are serious

Buy a M135i and play with it in Sport+
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      10-20-2012, 04:39 AM   #8
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Quote:
Originally Posted by AusF20 View Post
Buy a M135i and play with it in Sport+
The base price of an M135i with no optional equipment in Norway is more than 100 000 Euros.

And if you want to play, it is better to switch DSC completely off.
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      10-20-2012, 05:28 AM   #9
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Car taxes in Norway makes me cry...



Just the taxes alone on the M135I is much more in Norway than the total price of 118I out of the dealership.
The base 118I costs more here than base M135I in UK..

"Norwegian PRICE" x "0.13564 = EURO

Everything above 178hp, and 165g CO2 gets expensive very fast! And even a lower powered car gets a lot of taxes..

EDIT:
Actually 116I is more expensive here than M135I in the UK!

Last edited by BMW-RaceR; 10-20-2012 at 05:41 AM.
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      10-20-2012, 07:33 AM   #10
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Taxes in Norway are really high.

A UK advisory body is looking at increasing taxes on new cars and doing away with our yearly road tax. Just an excuse for more tax in my opinion.

Also noticed that 0-62mph/0-100kph times on the auto's differ from country to country.

Cheers
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      10-20-2012, 08:21 AM   #11
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Quote:
Originally Posted by logiclee View Post
Taxes in Norway are really high.

A UK advisory body is looking at increasing taxes on new cars and doing away with our yearly road tax. Just an excuse for more tax in my opinion.

Also noticed that 0-62mph/0-100kph times on the auto's differ from country to country.

Cheers
Lee
Ok, this will be some more off topic. But I made this list earlier this year. Prices in EU. Aygo is basically the cheapest car we can buy, and GT86 is the cheapest proper sports car we can buy.

Price difference between Toyota Aygo and Toyota GT86.
Sweden (SEK): 101.900 vs 304.900= 3
United K. (GBP): 7999 vs 24999 = 3,1
France (euro): 9.400 vs 29.900 = 3,2
Germany (euro): 8.990 vs 29.990 = 3,3
Norway (nok): 131.400 vs 459.000= 3,5
Iceland (isk) 2.195.000 vs 8.090.000 = 3,7
Finland (euro): 10.844 vs 46.624 = 4,3
Netherlands (euro): 7.990 vs 39.990= 5
Denmark (dkk): 79.990 vs 539.997 = 6,7


Prices translated into USD - (Highest GT86 price last)
Germany :10903 vs 36371
France : 11400 vs 36371
United k.: 12384 vs 38705
Sweden: 14631 vs 43778
Netherlands: 9690 vs 48499
Finland : 13151 vs 56545
Iceland : 17057 vs 62867
Norway: 21648 vs 75620
Denmark:13074 vs 88263

Price difference between Aygo and GT86 in USD
France: 24971
Germany: 25468
United k.: 26321
Sweden: 29147
Netherlands: 38809
Finland: 43394
Iceland 45810
Norway: 53972
Denmark: 75189

Luckily, our paycheck is much higher than in the UK. But a brand new M135I will only be a dream car for most of us. And the "affordable" GT86 is pretty expensive here due to taxes..

So, basically if we Norwegians want to buy a fun car, most of us will not afford new cars with bigger engines. That is why we need to drive like Petter Solberg when roads are slippery so that we can have some fun in the corners (a little exaggeration there)
Straight line speed/fun is very limited with the average car in Norway since HP is pretty low. And you will also endanger people, risk extreme tickets and easily loose your licence by speeding...
That is why I aim to optimize fun in corners. And a limited slip diff will help with that!
If they produced low grip performance tires I would buy that too!
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