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BMW Bosch ECU - how it works - what you need to know

145K views 341 replies 79 participants last post by  swes1000rr2016 
#1 ·
I've ignored the ECU tuning comments and information for quite awhile, but there are some seriously confused people on this forum and I think it's time to explain how these things work so everyone can make informed decisions about the "tunes" they use.

I am not in the business, however I have quite a bit of experience tuning these ECU's and working with BMW on them, for racing. I'm going to attach screenshots below to explain how this stuff works.

The Bosch ECU used on the S1000RR is *extremely* advanced, well developed and well thought out. On top of that, the S1000RR uses a fly by wire system attached to a 14,000+ rpm engine making north of 200hp/liter at the crankshaft. This is not the BMW 325ci you got after college. Out of the box, this thing is very well tuned, but for people who need more, there is a kit ECU that opens almost every other option.

First, let's discuss the simple, how do you make more power! There are two simple options, you can advance the ignition timing and/or lean the bike out a little bit. Why would you do this? more power. Why wouldn't you do this? They run it conservative for a reason, these engines grenade, are expensive to repair and BMW is generally a bit hostile towards customers with blown engines. Even when it's their fault, they like to hint it's really all your fault. Very frustrating.

Here's what a BMW S1000RR ignition table looks like via the kit configuration tool:



As you can see, I used a very conservative setup. 2.25 degrees at 100% throttle above 8000 rpm, and that's on race fuel. You should be able to see that any "tune" could advance the ignition as much as they want anywhere in that chart to give you the feeling your bike is "stronger." You can also do this with a dynojet ignition module. "Tuners" can make more or less power on a chart by adding more or less ignition advance.

It's just that simple.

Next post I'll talk about the throttle bodies.
 
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#2 ·
I've seen some alarming commentary about "throttle restrictions" and the like on some other threads. I am alarmed enough that I'm taking the time, with nothing in it for me, to make a dozen screenshots and post them up here with an explanation.

I believe strongly in the notion "In God we trust, all others bring data." So, here's data.

First, let's talk for a moment about intake velocity. If you know your fly-by-wire vehicle will have low RPM's, you build the right size throttle body and you're done. If you think you'll have something that needs golden responsiveness at partial throttle and 3,000 rpm, and you also want it to flow enough air for full throttle at 14,000 rpm, you've got a design problem. What BMW did is to build a really large set of throttle bodies, then map the engine to decide what the maximum amount of air ingestion was.

I.E. you do not want full throttle 100% at the throttle bodies at 4,000 rpm in a straight line with your wrist pinned. Intake velocity will decrease and the engine will make less power. So, they open the throttle bodies in a straight line with your wrist up to a maximum that the maintains the best possible intake velocity. Above a certain RPM, this equals whatever the throttle body is doing on its own and it will match them up.

A "tuner" that helps you out by linking the throttle body and the wrist is hurting you, they are lowering your performance in a straight line. You may observe this as helping you when the intake velocity catches up above 8K rpm and you feel a bigger "kick" than normal. It's a bigger kick because it was a slower ride up there, it was stumbling.

This phenomena can easily be identified with the 2D logger, and I've attached some instructive screen captures.

First, look at this trace from an HP4 on the dyno doing full throttle roll-ons. These are a little hard to read, but you'll get the hang out of it quickly. The scale is to the left, the dashed line represents the mouse position and the little box that says measuring values shows exactly what all of the values were at that exact moment. The red trace is engine RPM.

Here's where it gets interesting, the green trace is grip_pos and it measures grip position, or what your wrist told the bike to do. The blue represents the actual throttle body position that you've got. What it shows is that BMW rolled the throttle bodies open based on their table of the maximum intake velocity, this is normal behavior, this is good behavior, this is the fastest and most powerful behavior possible when you build a throttle body that spans the range of 2,000 rpm 5% throttle and 14,000 rpm 100% throttle.

You can also see from my cursor position that the two became equal at roughly 8,500 rpm, which is the point where you will no longer decrease intake velocity.




Now let me show you what this looked like on an ECU I recently logged that had been "flashed and tuned," note I actually never asked the tuners name (and don't want to know). This tuner "hooked it up" by removing the throttle restriction. You'll see the green and blue traces in sequence, matched up. This is abnormal behavior. This slowed the bike down considerably. However, it felt "punchy" because it was carrying less power up to 7-8K rpm where it then took off.

 
#7 ·
First, let's talk for a moment about intake velocity. If you know your fly-by-wire vehicle will have low RPM's, you build the right size throttle body and you're done. If you think you'll have something that needs golden responsiveness at partial throttle and 3,000 rpm, and you also want it to flow enough air for full throttle at 14,000 rpm, you've got a design problem. What BMW did is to build a really large set of throttle bodies, then map the engine to decide what the maximum amount of air ingestion was.

I.E. you do not want full throttle 100% at the throttle bodies at 4,000 rpm in a straight line with your wrist pinned. Intake velocity will decrease and the engine will make less power. So, they open the throttle bodies in a straight line with your wrist up to a maximum that the maintains the best possible intake velocity. Above a certain RPM, this equals whatever the throttle body is doing on its own and it will match them up.
Let's assume that we are talking straight line only for a second. As you stated that BMW made the mapping conservatively, can we not then assume that there is additional airflow available? Or are you saying that, even given straight up and down riding, that adding any additional air flow at RPMs below 8500 will have a negative impact on the performance?

A "tuner" that helps you out by linking the throttle body and the wrist is hurting you, they are lowering your performance in a straight line. You may observe this as helping you when the intake velocity catches up above 8K rpm and you feel a bigger "kick" than normal. It's a bigger kick because it was a slower ride up there, it was stumbling.
I don't remember anyone stating that they are getting bigger kicks now at 8k than they were. Most all reviews I have read have stated that the kick is less and there is a more smooth transition in that range.

First, look at this trace from an HP4 on the dyno doing full throttle roll-ons. These are a little hard to read, but you'll get the hang out of it quickly. The scale is to the left, the dashed line represents the mouse position and the little box that says measuring values shows exactly what all of the values were at that exact moment. The red trace is engine RPM.

Here's where it gets interesting, the green trace is grip_pos and it measures grip position, or what your wrist told the bike to do. The blue represents the actual throttle body position that you've got. What it shows is that BMW rolled the throttle bodies open based on their table of the maximum intake velocity, this is normal behavior, this is good behavior, this is the fastest and most powerful behavior possible when you build a throttle body that spans the range of 2,000 rpm 5% throttle and 14,000 rpm 100% throttle.
Can you define normal and/or good behavior further?

Now let me show you what this looked like on an ECU I recently logged that had been "flashed and tuned," note I actually never asked the tuners name (and don't want to know). This tuner "hooked it up" by removing the throttle restriction. You'll see the green and blue traces in sequence, matched up. This is abnormal behavior. This slowed the bike down considerably. However, it felt "punchy" because it was carrying less power up to 7-8K rpm where it then took off.

I know you say no names, which is fine, but is this one of our two? The reason I ask is because this has not been my experience and I'd be very surprised by this. Did the customer specifically request this behavior? I truly don't believe either of our tuners are sending this behavior out as a standard and I don't recall either describing anything similar to this behavior.
 
#3 ·
So I believe both our tuners here have admitted to advancing ignition timing.

It sounds like me like you're questioning whether or not the amount they advanced is safe?

Or another way, how did they determine how far to advance?

Clearly they arent going to answer question 2, but I'll play devil's advocate. First let me say in no way do I mean disrespect, literally just playing devil's advocate.

You say the engine is conservative for a reason, who's to say they aren't more qualified to make a determination on how far to advance than you are?

If George is really as tied into Alpha Germany and has access to the WSBK mapping, I'd argue he has enough information to make these determinations.
 
#6 · (Edited)
You caught me mid-stream. I'm not criticizing anything with regards to ignition timing or leaning out the fuel map, just trying to add clarity for everyone to make their own interpretations.

The argument as to Bren vs. Alpha (which I'm not going to get involved in and don't care really) shouldn't be boiled down to which one makes more HP on a dyno, they'll each make whatever they want to make. No doubt you could call them up and ask them to dial in more ignition and make more power.

The only thing I will say in the Bren vs. Alpha debate - and I know Alpha has encountered some negative publicity on this forum somehow - is that practical experience and access to information with practical experience in setting up the Bosch ECU is more important than anything.

So, someone who knows how to use a kit ECU, knows how BMW and Alpha AG have been tuning these things, that's more important than knowing how to hook a cable up to the ECU and change things in a table.


EDIT: I guess I need to clarify that what George-Alpha is doing - with limited info - is that he is bringing lessons learned from the race ECU's and moving the settings into the street ECU's. If this is correct, then that is a much better strategy then one that is purely dyno driven. But again, he is rather secretive about the details of what he does and I've never seen a 2D trace on one of his ECU's vs. stock, so I'm assuming he's using his considerable resources and access to good settings to guide his hand in these ECU flashes, and if so then it's good and an excellent value.
 
#4 ·
Great, that's straight line, power etc...

The BMW S1000RR Bosch ECU uses torque control, with those throttle bodies for a ton of other VERY IMPORTANT uses. In the other Bren Tuning thread, it was mentioned with an accompanying photo that the throttle maps were being altered, and by mode. Everything I mentioned above is mode irrelevant. It may not even be in the maps, it may be a separate map. I don't know because I've known anyone that wanted to screw with the intake velocity before.

So, what does BMW and Bosch uses these "throttle restrictions" for? Well, get this, an absolutely amazing concept called "Reduction Pre-Control." Bosch/BMW sat down and thought about implementing the perfect lean-angle and mode-integrated solution for making you the most awesome bike they could. What it does is build a map that delivers the maximum amount of torque that they believe the tire can take AND THEN the traction control takes over for torque above that amount - which will result in wheel slip.

An example might help, say you're on the track with a brand new Pirelli slick, you're at 8,000 rpm and you crack the throttle open. The BMW ECU will deliver exactly the amount of power that it believes that tire can take without slipping. Now, half way through the day, the tire has 20% less grip. The ECU will deliver the same amount of power, but now the tire will be slipping and - get this - the traction control will intervene in a balanced way based on lean angle.

So, here's the key question: How does BMW know how much grip my tire delivers, and how does it control how much power the ECU delivers? The answer to control is... the throttle bodies! That's right, you give it a 100% throttle at 40 degrees of lean, it believes the tire can take 80% throttle, it keeps the throttle at 80%. Crazy right?

What's the answer to "how do they know?" Another mystery called "modes." Here's what BMW/Bosch did:

First they built a number that corresponds to grip level. So a tire that has a grip of 1.5 has much more grip than a tire that has 1.3.



Then they built a map called reduction pre control, the grip level is applied to the map:



The result of grip + reduction_map = the tables the "tuner" sees with their "tuning" software. BMW even gave you a really handy way to tune this, by using those mode buttons. Slick mode is actually only good in the real world for the beginning of a slicks life on a race track, meaning the bike delivers too much power in most cases. In fact the bike opens the throttle bodies too much in slick mode.

See, in a perfect setup this use of "torque control" would supply the exact ft-lbs that the tire can take across all scenarios, and you'd never see that little DTC light come on. But the one time you hit a little patch of dust with the rear tire you'd have 10% less grip then you should have (for the tire), and the DTC would take away 10% power for a brief moment and amazing things would result.

The fact that we all see our DTC light flashing regularly when we're on the gas at a track tells you something key: the ECU already opens the throttle bodies too much in slick mode.

What does torque control look like on a track? Glad you asked:

Let's look at a 1:26.08 lap at Laguna Seca with throttle traces and a brand new Dunlop slick



Remember blue line is throttle bodies, green line is your hand turning the throttle.

Let's zoom in



You'll notice the blue line never goes flat, that's because the S1000RR doesn't have a bypass to the throttle bodies so the ECU has to always hold them open enough to idle the bike.
 
#223 ·
Hi,

I don't have RCK yet but I downloaded the manual of RCK2 to study.

There is one thing I don't understand about how ReductionPreControl works in different gears. In the manual it says,

"The applied values are only completely effective in 1st gear. In gears 2-6 the values are reduced by the available relative overall gear ratio. In second gear the reduction value of the value table is multiplied by factor 1.27. In third gear it is multiplied by 1.53.......Values above 100 are interpreted by the system as 100 % (maximum)."

If I multiply the values in the table by 1.27, every number is greater than 100....

Does that mean Torque PreControl is only effective for 1st gear, and mainly for smooth launch?

In RCK1 manual torque reduction values are calculated in a different way. Nevertheless the torque reduction values become all 100 in 3rd gear.

Dagor6 seemed to imply that TorquePreControl affect all gears?
 
#5 ·
Torque control sets up how the bike delivers power, traction control handles what happens after it's delivered. Let's take a look at that system too, because that also controls the throttle bodies.

First up is a TC map, this controls how much slip you should allow before intervening at all.



There is one map per mode (rain through slick) and each one is tuned the best it can be. This controls how far back the ECU throws back the throttle bodies when you start slipping too much.

Some people complain that TC is holding them back too much in the corners, this is how BMW controls the rate at which it closes the throttle to get the bike back under control. If you think it's holding you back too much, this is one area to tune:



But get this, all of this stuff turns off at a pre-defined lean angle setting, which is different for each mode. So usually the answer is to just stand the bike up more



And what does it all look like, well here's a trace from Road America in Wisconsin. I've included lean angle in red this time, and you can see when it hits the target of 30 degrees, it stops controlling the throttle bodies.



If you look carefully at the the blue/green throttle traces on the left side, around 15:26.25 through 15:27.75. What you see is the line sweeping up at the max rate it will (blue line = throttle bodies) until the tire slips, then you see what looks like rapid static in the blue trace even though the green trace (hand on throttle) stays solid. This is DTC taking over for a tire slipping, again too much power was delivered. And at exactly 30 degrees of lean, you can all of this stuff deactivate.


The moral of the story, your throttle bodies are doing a lot more than you thought, go to slick mode, you don't want a 1:1 throttle mapping or anything else like it, straight line or on a curve.
 
#13 ·
Hands down the best write up I've seen soo far this should be a sticky!.. dagor you don't happen to live in Canada?
 
#14 ·
If I get my old ecu back that has a alpha flash on it can you study it and see why it went bad and never performe on a dyno what George claim and after my bike would also get VDS code with no start at times? Send me a pm if yes also nice write up very informative and straight to the point
 
#18 ·
I also get the VDS ! code on my bike if i stop and turn the ignition off and turn it back on again the VDS ! goes onto the dash and won't start i have to turn it off and wait about a minute before i can turn it back on again which seems a long time when you are waiting for it, I also have the flash kit on my hp4 but to be honest i don't feel any more power, i had a 2010 s1000rr before my hp4 with power commander and a custom map set up on dyno and that was more responsive and faster than my hp4,
Kevin (from the u k)
 
#20 ·
Thanks for the great write up!

So slick mode, on slick tires at the track is bad?

Shawn Dwyer said he went faster on his 2010 s1000rr at Jennings GP in race mode than Slick mode, due to the abrupt behavior of slick mode.

I have always run Race mode on slicks rather than Slick mode, based on his advice .... but i don't have any other reference points.
 
#21 ·
Sean Dwyer raced my bike at Macau the next year on the kit ECU, I know his preferences well. He really didn't get on with the S1000RR in general though, and switched back to the Suzuki the next year IIRC. He's a great guy though.

Sean likes smooth power to feed in, which a lot of pros prefer. Maybe all of the pros. Slick mode was probably too aggressive for him at Jennings.

But yes, there's another data point telling us slick mode can be violent for sure.

Really what he's saying is it didn't have enough reduction pre control for him, it fed the power in too fast and then he had to deal with the TC and the surges.
 
#27 ·
Another Possible Option For ECU Tuning

I had a thought today and wanted to throw it out here and see what the local tuners think.

First a couple of statements and questions.

1. When doing an ECU flash, various tables have to be located and modified. I'm under the impression that there might be some tables that no one has found yet, and if this is the case, could it be possible that there is an interaction between these and the ones that are currently being modified during the flash?

2. The ECU's have built-in error correction. This checksum verifies presumably all tables, both independently and as a complete code set?

3. Part of the flash process, both bench and hand held, is to make sure there is a valid checksum. If changes to one table affects another hidden table, would the checksum have to be somewhat dynamic? If the ECU learns or adapts with time, the checksums would have to be dynamic, correct?

My questions obviously revolve around possible ECU failures.

What if the ECU was flashed using a different procedure? Could you send in your ECU, dash, and ignition/key/antenna ring. Hook those up to a test bike or mock-up system, with all sensors and such to simulate a complete bike. Then, use the BMW calibration kit to perform the tune. I know that the calibration kit is tied to a specific serial number, but I have also heard that it is possible to override that link using some software tools.

If the flash could be done this way, it seems that the chance for problems would be eliminated.

I know that this is a little different direction from the first part of the thread, but it seems that what Dagor6 is implying is that the calibration kit gives full access to the ECU and there would be benefits to that. The vendors offering bench flashes would still flash the ECU's using the settings they have already developed. They would just use different tools.
 
#29 ·
Bmwian, what year model is your bike?
Just wondering if there is a huge difference between 2010 - current T/C, throttle etc.
I have to run in slick. I've tried running in race and much prefer the throttle but just can't due to abrupt power cut when the front wheel lifts and no power until the thing is upright. It costs me 3 secs avg a lap!
 
#30 ·
I started with the early 2010 with the lightweight crank, then had another 2010 with the heavier crank, now i have a 2012. Across all three bikes with various mods and Pirelli slicks or Dunlop NTEC slicks, my best times are within 3 hundreds of a second.

I load the throttle and anticipate when the power will come in, you should not need to do massive wheelies on the bike, if you do you are in the wrong gear!

I have ridden at Jennings GP, Barber Motorsports Park and Daytona (times good enough for top 30 in Daytona 200), and never had the bike wheelie enough to engage the TC in race mode!

I met Nico Ferreira, a local racer in FL, and he is friends with Carlos Checca, who told him that what made Stoner so fast on the Ducati was that he would apply the rear brake thru the corner and grab a handful of throttle, then gradually release the rear brake while already having plenty of throttle, which would give him much more control but make him much faster on the Ducati than Rossi.

I think the ideal compromise would be a couple of extra TC modes between the current Race and Slick modes, because neither mode is ideal!
 
#37 ·
There was a question on tire size in another thread I'll answer here:

Dela said:
Regarding The race ECU 2, can anyone explain why the tyre radius is set as it is?
For me, this value doesn't correlate with the entire radius of a wheel, front or rear regardless.

In my software the radius is set rear at 327,3mm, which is not even close to the radius of the wheel.

Anyone care to explain how the value is measured out? I might need to change from the Dunlop settings to Pirelli for next season!

Thanks
Here is the setting you are referring to:



Yes, the tire diameter size is critical to knowing the amount of actual slip. The slip is measured as a percentage of speed difference between the front and rear wheel, so front wheel is going 200 kph, rear is going 220 kph, 10% slip roughly. That's mapped in the traction control table by lean angle and front wheel speed:



The ECU needs to know the correct tire size front and rear (differs by manufacturer and profile) so that in a straight line, the front and rear tire are going the same speed. Then they use some math to figure out as you lean over how that differs as well (it changes with each degree based on profile and lean).

Here's the issue, at 20 degrees of lean, you might be 10-20-30 kph different front and rear just from tire profile difference, i.e. no slip occurring at all. The ECU will see slip. The traction control slip setting needs to at least allow that amount of "slip" just to keep a smooth drive off of a corner.

In other words if my tire profile shows 10% wheel speed difference at 30 degrees of lean, no actual slip occurring, and I allow a maximum of 8%, then my bike will be engaging TC just opening the throttle.

Stock is set up for Pirelli, with the Dunlop you need to change your values to match.

One of the ways to safely tune big changes in the ECU is to change the tire sizes in some dramatic way, that way the ECU always thinks there is slip, then you can back it off to reality.
 
#47 ·
There was a question on tire size in another thread I'll answer here:



Here is the setting you are referring to:

As seen above, the value for the rear is set at 321.2mm - this equals 12.6" and I really don't understand how this length is measured out on the rear.

Dagor, can you elaborate on this? Sorry for being such a persistant piss-ant ;)
 
#38 ·
Also, 321 mm for a radius doesn't send that wrong, diameter would be close to 24 inches, and that sounds right.

Either way, you bum the settings of someone who knows, or use a logger to get the right by checking front and rear wheel speed equal in a straight line down the pit road before entering the track.
 
#46 ·
Dagor, my entire ECU is right now set up for Dunlop by the BMW technicians at IDM. I bought the bike from a rider who only used the bike briefly.

I want to source a map for the Pirellis, preferably from the same level of rider as the map I have, so they behave similarly.

However, I still don't understand the value itself. As I read the input, it is the entire rolling circumference you put in, but that value is somewhere around 189cm for a Dunlop tire - so Why is this value so low? Is it measured across the tire surface or what?

I understand the lean input and slip difference, I just don't understand the input for the radii.

Btw, Slipcor Mod 1 to 4. - they just correlate to riding mode, correct?

Thanks for picking this up so fast! :D
 
#45 ·
Thanks dagor6, for some very interesting info.
 
#49 ·
Of course, sometimes it is required to understand what is written….

They ask for the radius. RADIUS. In the manual they just wrote you could find the radius by rolling your bike forward and measure distance required for one rotation.
In this, I understood circumference. No, it is radius. You have to use the circumference and compute the radius.

For you other guys it’s simple trigonometry. L = 2*pi*radius => radius = L/(2*pi) (just if you or not experienced in finding values like this).

It is so simple I can’t believe that I failed to read what was written. *FAIL*
Haha.

Now I just need to make - or find - a slip map that fits the Pirellis!
 
#50 ·
Ah, I see the confusion. Each tire has two key characteristics for dimensions, the total circumference in a straight line and then at each degree of lean angle it's different. BMW uses this chart in the Kit ECU manual to describe the difference:



The two lines show two different tire sizes. over each lean angle. So a Dunlop and a Pirelli will have two different profiles as well, the software just lets you set the variable for straight riding, put another way at a lean angle of zero.

The full range of rolling circumference for each tire at each lean angle degree is way too complex for us to add them in as users. They made it so it doesn't matter in general, they consider up to 10% "slip" to be normal.

What is slip? it's the difference - in the mind of the bike - between the front and rear tire speeds. If the two circumferences are off front and rear, it'll look at that as slip, and then the map allows a certain amount of slip. This isn't actual slip, it's just the difference in tire circumference.

Which is the reason the system has a lot of wiggle room in it. Which is why you don't need a custom Pirelli map, or a custom Dunlop map. Just get the tire size as close as possible.

I've attached an additional image that shows this concept:



It's entering the front straight at Miller. The blue/green traces are throttle, the red trace is front wheel speed, purple is rear wheel speed. Notice they are virtually never identical.

The trace starts on the left, with the rider turning and the throttle closed and you can see that the purple trace is higher than the red, the ECU believes the rear tire is spinning faster than the front. They're not, that's just the confusion in the tire profile.

When the rider opens the throttle, the tire spins and you'll see the purple line get spiky, so do the throttle traces and that's slip and the TC intervening.
 
#52 · (Edited)
Which is the reason the system has a lot of wiggle room in it. Which is why you don't need a custom Pirelli map, or a custom Dunlop map. Just get the tire size as close as possible.
I was just told, that the entire map I have right now is the map that the technicians from BMW loaded on to the bikes competing at IDM, if requested, in 2013.

I will try and alter the tire radius only and see how it goes in September at Brno.

Just to double check, can anyone else confirm that Pirelli is 300F/329r?

My map for Dunlop says 298,4mmF/327,3R. In case anyone needs them!
 
#54 ·
It means HP4 set on zero is the same as whatever map you're in now, like slick, race or whatever. It's never been clear to me if the HP4 has a less restrictive TC map, I don't think so because the engine is the same and those guys tend to think of the engine and tire as driving the map settings.

As for whatever the percentage is, it really does indicate that it's only 3.5% but I'm not sure if I believe it, the Germans have a hard time with translations and parts of the ECU use unusual terminology. Either way, with the kit ECU or I guess a flashed ECU, you can change what those steps are.

I would probably set it up for me so that -/+0-4 were tiny changes and then 5-7 were big steps, that way I knew I could use the button to get whatever result I needed.

For a racer, on a race track, you probably want 0-6 to be even tinier changes then what BMW has to account for minute loss of grip or increase in grip (tire/track coming up to temp) and then you want 7 to be a massive jump in case the tire chunks of melts in some way to totally screw up your grip.
 
#56 ·
These offset values are only working in slick mode and you can change them on the handlebar :rolleyes:

Like the manual clearly says: "The system starts engine intervention when wheel slip reaches approximately 10 % of the computed value."

So with these 15 steps from -7 to +7 you can put an offset to these standard 10% slip:
-7: 10%-3.5% = 6.5% so DTC kicks in much earlier
-6: 10%-3% = 7%
...
0: 10%-0% = 10% so DTC is like standard
---
+4: 10%+2% = 12% so DTC kick in later
...
+7: 10+3.5% = 13.5% so DTC kicks in much later

You can define whatever positive or negative offset from the standard 10% slip you want as long as it makes sense to you. But having +5% somewhere will cause black lines coming out of each turn and -5% will let the DTC light flashing all day long :p

You can also have something like this - every 15 values in a increasing order - the gaps are defined by you:
-5 -4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 0 +.5 +1 +1.5 +2
or
-5 -4 -3 -2 -1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
 
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