Variable M differential lock

[MDORPHN]

Really good thread!

Scott, you may want to talk to Dan Fitzgerald at Diffsonline. He provides built diffs to Turner, Bimmerworld and RRT, among others.

Don't know anyone who knows more about them.

Neil

[Pete_vB]

Originally Posted by scotth944

Pete, have you worked on diff setups as well?

I have, but I consider myself a novice, just enough experience to get a feel for which direction adjusts what. Diff setup is a bit of an art, and the guys that set up for the track often can't set up for autocross and vice-versa.

I'd definitely need to talk with guys that know more than me if I was getting a diff, but my baseline guess would be similar to what Advevo suggested- a plate style diff with moderate lockup on acceleration. I'm used to seeing more lockup on deceleration, 40% acceleration /65% deceleration is what Porsche motorsports uses on cup cars, etc, though that's designed to keep the heavy tail end of a 911 from coming around on you on corner entry, so it promotes some turn-in understeer. Might not be the best idea for a better balanced car.

[Advevo]

On a bmw for track don t go higher then 40% lock on acceleration!

[M3 Adjuster]

Originally Posted by MDORPHN

Really good thread!

Scott, you may want to talk to Dan Fitzgerald at Diffsonline. He provides built diffs to Turner, Bimmerworld and RRT, among others.

Don't know anyone who knows more about them.

Neil

Agree with this as well.

Jim Blanton @ performance gearing is another BMW diff specialist.

[M3 Adjuster]

Originally Posted by Pete_vB

Very interesting... Definitely looks nearly identical to the off the Stig had. So I don't know what's going on here, but I can theorize... It's very difficult to tell what caused it, but it's almost certainly magnified by some kind of interaction with the car that causes instability.

If you look closely at the video you can see both rear tires laying stripes, the rear end fairly loose as you'd get coming hot into a decreasing radius corner, which is expected. The main issue seems to be caused by the way the rear end "bites" when the car straightens out. Watch the skid marks and the path of the rear tires- the correction causes the rear to snap violently back in line.

In shock terms we're seeing load go onto the inside rear (bump), and off the outside rear and outside front (rebound).

In this thread I discussed what BMW appeared to be doing with the shocks and springs vs the M3: they significantly increased the stiffness of the rear shocks, probably in an attempt to promote both corner entry oversteer to help the car rotate, and corner exit understeer to help put power down.

In the case above, however, when you're not on power it looks to me like that same shock tuning probably becomes at least part of the issue. The 1M has maybe 15% higher rear low speed compression than the M3, 2x the low speed rebound, both of which increase rear end grip when the car is unloading (the table here helps explain why), so when the rear shocks start moving that way the rear gains lots of grip and "snaps" back into line and then overshoots. One part of the theory...

What sizes are you running, by the way?

CBC is certainly another possible explanation, for this spin at least, but I now suspect the diff more:

Thanks for jumping in here, very interesting also...

This is the other possible explanation for M3 Adjuster's spin, or at least that initial violent correction when the rear catches. That unlocking might also significantly increase rear end grip. The question is, was the rear end catching also accompanied by lifting out of the throttle?

The video shows the rear out of shape four separate times, and I don't know that every one of the slides could have been accompanied by a throttle lift because I suspect at some point you backed out? Thus I think there is more than just the diff going on, but it could certainly have contributed to the first jump.

This sounds exactly like what Scott originally described. That event sounds different than the Stig or M3 Adjuster's event above. Power on, then violent lockup punts the car sideways.

On balance I'm suspicious that in both of these cases we have two or more events conspiring together, as usual in an accident. It would make sense that in both cases the diff acted violently, either locking or unlocking, and then the stiff rear shock turning contributed to making the resulting slide much harder to catch.

The factory seems to know the diff can be an issue. Not only Dackelone's info from the factory guy, but also the M5's diff and new M3: they add an electric actuator to make the diff function active and under computer control. They would only add this weight, complexity and cost if they felt passive was a problem, letting them regulate the locking and unlocking.

It's just a theory, but it does seem to fit the facts- violent diff lockup and stiff rear shock tuning together could be expected to cause both issues.

I was running 285/35/18 BFG R1 on 18 x 10 square at the time.
I had a passenger with me, also a racer and long time track rat... I defnitely know better than to lift throttle but as I got to mid corner and realized I was early (and seeing the corner station and a lot of grass between me and that wouldnt slow me down..) I definitely lifted once, causing the initial rotation and stepping out. From there.. I simply tried to counter the spin and believe that I was holding the throttle stready in doing so. My friend in the video car said that he thought I caught it three times, which was the way it felt to me.... but suddenly the rear just would break free again. My passenger with me also was amazed at what happened and said it was amazing me that I really saved 3 spins only to eventually still get spat off the road.

Humorously... once all the rotations were done and I was back on the road ( i actually consciously rotated the steering wheel as it came back onto the pavement and successfully got it to rotate back the original direction).,
there was an exclamation point in the dash... so clearly the car didnt know WTF happened either!

[Pete_vB]

Originally Posted by M3 Adjuster

I was running 285/35/18 square on 18 x 10 at the time.
I had a passenger with me, also a racer and long time track rat... I definitely lifted once, causing the initial rotation and stepping out. From there.. I simply tried to counter the spin and believe that I was holding the throttle stready in doing so. My friend in the video car said that he thought I caught it three times, which was the way it felt to me.... but suddenly the car just would break free again.

FYI, I suspect it's the tire sizes that are causing your MDM DCT mode to be even more useless than normal. It's expecting 2% slower rear wheel rotation speed to be "zero slip". With a square tire setup it reads the same speed all around as 2% rear wheel slip, and it's probably programmed to allow only around 4-5% slip, so you might be cutting your margin in half on the stock programming, which would really shut the fun down early. I wonder what the actual slip percentage allowed is, US and Euro?
How much did the flash cost, by the way?

It certainly looked like a wild ride, and like the front and rear got very out of phase. Unusual for a stock car, and again exactly what we saw with the Stig.

My friend experienced something a little similar in a 991 turbo the other day, we got it on video. Much lower speed, in his case I'm suspicious the rear wheel steering kicked in as he decelerated into a corner, and that sent the back sideways when he didn't expect it to. It's a recurring theme with good drivers at the limit and highly assisted cars- issues occur when the car steps in and does something you don't expect it to.

Originally Posted by M3 Adjuster

Humorously... once all the rotations were done and I was back on the road ( i actually consciously rotated the steering wheel as it came back onto the pavement and successfully got it to rotate back the original direction.,
there was an exclamation point in the dash...

Ha. Reminds me when I was in a Mercedes SL at the Ring. You can't switch the nannies off, so you need to fight the car, chucking it into corners against its will to try and get it balanced. Eventually the car decided it had lost and threw up the white flag- there was a loud beeping and an exclamation point on the dash, then suddenly the roll bar snapped up just behind my head mid-corner. The car was sure we'd lost it and were going over! Scared the crap out of me...

My technical German sucks- it took 30 minutes reading the manual to figure out how to get the roll bar back down again!

[Dackelone]

Adding more fuel to the fire... in talking to teh guys at Tuning Werk... they tell me on the M235i and 435i... you can not turn all the nannies off. You can... turn them off, but then when you get the car sliding... the CBC and DTC will come back to life. Even TW with their car coding expertise, are trying to come up with a fix for this.

TW has come up with new coding for the DTC... the works far less with their custom lsd's... you hardly see the yellow DTC light blink even with 444 PS on tap.

[M3 Adjuster]

Originally Posted by Pete_vB

FYI, I suspect it's the tire sizes that are causing your MDM DCT mode to be even more useless than normal. It's expecting 2% slower rear wheel rotation speed to be "zero slip". With a square tire setup it reads the same speed all around as 2% rear wheel slip, and it's probably programmed to allow only around 4-5% slip, so you might be cutting your margin in half on the stock programming, which would really shut the fun down early. I wonder what the actual slip percentage allowed is, US and Euro? ...

Yes. I concur. Every mod one makes towards improving track worthiness is causing the stock system to reach it's limits sooner ( Wider tires, slightly different gearing from the tires, greater braking from track pads, far more grip from track tires...etc). With street tires on, stock pads and US MDM *ON* I can run quickly enough to keep pace with heavily modded E36 track cars and mildly modded E46 M3s. If I am SMOOTH, I can probably run 85% of the pace I can run with all nannies off.. but there is the included margin for error of having MDM on. I have learned to minimize my slip angles to what the system will allow. The most frequent action is minor braking and minor power cut, unless I slide the car. The system allows for a little bit of 4 wheel drift.. as long as the yaw angle of the entire vehicle is minimal.


My typical routine is to drive with MDM on until I feel that I have a good handle on the track conditions. If my home track.. it may be just a seesion or two to see how the track surface is. On a track I don't know it could be a few more. Whenever the system hampers me tremendously or dangerously (not being able to add throttle in situations where it's *needed* as I approach track out , for example ) then i will turn it off..

With the Euro version of MDM, the slip angles allowed appear to be nearly doubled. For example if 4-5% slip is what is normal with US MDM.. I would estimate the Euro MDM to allow a full 10%. There is a much greater ability to drive the car... and I would estimate that I can do about 90-95% of what I can do with MDM fully off.

In situations where the car is sliding and I want to add power, I can do so... the traction control light does blink a little but generally doesn't result in the car refusing to add power or worse, the dreaded " penalty box " shut down of power.

Euro MDM is great for people that track their cars but it's also probably too much for the street. i don't normally horse around on the street.. ... I am sure that Joe Driver that hates all nannies feels no traction control is best.. Personally, I think the US MDM does do a good job of keepng a driver from getting over their head but should allow a little more slip angle.

Personally... For an M car.. I would think the US version of MDM should be traction control " on", with perhaps a slightly less edgy version of the Euro version of MDM as the next level, and then all off.

Originally Posted by Pete_vB

How much did the flash cost, by the way?
...

MDorpphn found Mike benvo.... and when i asked him about benvo he graciously offfered to let me borrow his cable but when i originally contacted benvo it was $500 or so for the coding. While $500 isn't really a lot to get the worst " feature" of the car removed , that seemed like a TON for relatively simple programming, and I was aware that others can do it as well. Heck there are local guys in my area that offer to do this for $100-200 at Cars and Coffee, but I don't want someone hacking my car if they don't know for sure what they are doing so I didnt really pursue it. After this spin, I decided to make it a priority.

I found and contacted Alex @ Alpine and he charges $115 which includes the $55 cable to connect to the OBD port on the vehicle. he sends the cable to you within a week of you ordering it.

http://www.alpinemss.com/category_s/1.htm

From there it took a few weeks to track him down to get the coding done. It takes about 45 minutes or so including downloading software to allow remote access to a laptop. I needed a laptop (mac or windows) , good WIFI signal in the garage, the cable, the car, and the guy coding. We never spoke on the phone, and handled all via text.

He updated the traction control, and then went down a list of options... Euro Hazards (flash at double US rate), true speedo vs BMW speedo (which reads 3 mph higher than actual) in the display (the speedo guage still reads +3mph) , added instant MPG available in ODO, remove seat belt chime, remove door chime, remove key eject chime. He also added the ability to roll the windows up from the keyfob (which comfort access cars can do). . He can also update NAV maps for a slight added cost, remove Nav screen messages, and some other options for cars that have folding mirrors. Other than tracking him down.. it was very easily done.

Originally Posted by Pete_vB

It certainly looked like a wild ride, and like the front and rear got very out of phase. Unusual for a stock car, and again exactly what we saw with the Stig.

My friend experienced something a little similar in a 991 turbo the other day, we got it on video. Much lower speed, in his case I'm suspicious the rear wheel steering kicked in as he decelerated into a corner, and that sent the back sideways when he didn't expect it to. It's a recurring theme with good drivers at the limit and highly assisted cars- issues occur when the car steps in and does something you don't expect it to.

Exactly.

[M3 Adjuster]

Originally Posted by Dackelone

Adding more fuel to the fire... in talking to teh guys at Tuning Werk... they tell me on the M235i and 435i... you can not turn all the nannies off. You can... turn them off, but then when you get the car sliding... the CBC and DTC will come back to life. Even TW with their car coding expertise, are trying to come up with a fix for this.

TW has come up with new coding for the DTC... the works far less with their custom lsd's... you hardly see the yellow DTC light blink even with 444 PS on tap.

Ugh. That would NOT be a good trend for them to continue.

I think we all definitely understand protecting the driver from themselves but if you are going to give the driver a mode for nannies to be off, it would be nice if they were actually ALL OFF.


. Ferraris have like 5 traction control modes. BMW could give us truly all off in another level at the most. Of course the problem is that most drivers think they are better than the car out of the box.

[Pete_vB]

Originally Posted by M3 Adjuster

I found and contacted Alex @ Alpine and he charges $115 which includes the $55 cable to connect to the OBD port on the vehicle. he sends the cable to you within a week of you ordering it.

Thanks, I just emailed him. I'd be nice to be able to leave TC on at least occasionally.

[Pete_vB]

Originally Posted by M3 Adjuster

With the Euro version of MDM, the slip angles allowed appear to be nearly doubled. For example if 4-5% slip is what is normal with US MDM.. I would estimate the Euro MDM to allow a full 10%. There is a much greater ability to drive the car... and I would estimate that I can do about 90-95% of what I can do with MDM fully off.

The extra slip in euro MDM is available with or without the M button pressed, isn't it? I'm not a big fan of the throttle mapping in M mode. I've ordered, we'll see how it goes...

[eeghie]

Originally Posted by Pete_vB

The extra slip in euro MDM is available with or without the M button pressed, isn't it? I'm not a big fan of the throttle mapping in M mode. I've ordered, we'll see how it goes...

To have a better feel for your DSC module coding options, be sure to read this: Euro MDM Coefficient of Friction

[M3 Adjuster]

Originally Posted by Pete_vB

The extra slip in euro MDM is available with or without the M button pressed, isn't it? I'm not a big fan of the throttle mapping in M mode. I've ordered, we'll see how it goes...

Originally Posted by Ian///M

Only without. Agree that car just doesn't need the current M button, esp with a tune

wow. really? Interesting! I just learned something! I didn't know because I don't use the M button either. it makes the throttle mapping overly sensitive to me.

Originally Posted by eeghie

To have a better feel for your DSC module coding options, be sure to read this: Euro MDM Coefficient of Friction

that's dropping the science!

[Robin_NL]

Getting rid of the PS2s and changing them for proper wintertyres helps a lot to keep 1M on track and sideways in a rather easy way like this video below shows us with a Ferrari Speciale.

But that would not be good for 1M laptimes I'm afraid.


So IF I'm ever going to trade in my 1M , it's probably for a Speciale(daydreaming), currently the world's 'best' sportscar? Look at the ease of throwing it around rather sideways.

Cheers
Robin

[MDORPHN]

As I recall, someone asked about diffsonline. This recent FB post says alot!

Neil
______________________

Diffsonline LLC

Monday Math Fun:

If you have 5 BMWs in the top 10 of the ST class at Road America’s IMSA/CTSCC race, that makes 50% of the top-10 finishers.

If ALL 5 of those top-10 BMWs are running Diffsonline setups, then that means Diffsonline was in 100% of the top-10 BMWs.

We’re not rocket surgeons, but those seem like pretty strong numbers to us.
HUGE congratulations to Borcheller & LaMarra in the #23 Burton Racing, LLC 128i for taking the win! Great work to Liefooghe & Cooke in the #81 BimmerWorld 328i for 5th, Giovanis & Murry in the #64 Team TGM 328i for 6th, Clay & Briedis in the #84 BimmerWorld 328i for 7th, and Rogers & Thomas in the #82 BimmerWorld 328i for 8th place.

Note: Those are unofficial results, and it sounds like those placing might all bump up a bit...

[Pete_vB]

Originally Posted by MDORPHN

As I recall, someone asked about diffsonline. This recent FB post says alot!

Are you running one of their diffs Neil, or are you still stock? I don't recall a diff on your mods list...

[MDORPHN]

Originally Posted by Pete_vB

Are you running one of their diffs Neil, or are you still stock? I don't recall a diff on your mods list...

Still stock. Ran one of their diffs on my supercharged '99 M Coupe.

Neil