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      01-16-2018, 09:23 PM   #1
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Traction Control for HPDE

Hi All,

I am new to the HPDE scene and did 2 runs in the last 6 months with Speed Ventures. First time out was tons of fun and got hooked. The group instructor told us to run with traction control on for safety.

My second run with Speed Ventures had a different group instructor which told the group to run without traction control as it will teach us more about how to 'really drive the car'.

I have been running at the Fontana AAA track and there are parts of the track where you hit 130+ mph. Was wondering if most of the guys in the forum run with traction control on and why or run with traction control off and why. I know traction control can slow you down but is it really making that much of a difference?
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      01-17-2018, 10:02 AM   #2
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I drive with traction control off due to the interference from the system.
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      01-17-2018, 04:16 PM   #3
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Quote:
Originally Posted by Venger View Post
Hi All,

I am new to the HPDE scene and did 2 runs in the last 6 months with Speed Ventures. First time out was tons of fun and got hooked. The group instructor told us to run with traction control on for safety.

My second run with Speed Ventures had a different group instructor which told the group to run without traction control as it will teach us more about how to 'really drive the car'.

I have been running at the Fontana AAA track and there are parts of the track where you hit 130+ mph. Was wondering if most of the guys in the forum run with traction control on and why or run with traction control off and why. I know traction control can slow you down but is it really making that much of a difference?

Most run groups have different tiers of driving level. I started as a beginner and I did not have the confidence to drive with the nannies all the way off. I used to run with a "single click" which is Dynamic Traction Control. Early on I drove with everything on.

When I started getting into upper intermediate the only way to get faster was to turn all the nannies off. E-diff still works, but the car will no longer cut throttle and apply the brakes to keep the car stable. This is the "5 second" hold of the button. I also disabled some nannies, like brake pre-tension, in the cars coding. Lean ring how to use slip angles to your advantage to rotate the car mid-corner takes time. Most novices will end up putting them-self into full-on spins.

I'd like to start running advanced, but I am not there yet as a driver. I would also like to have a mechanical diff installed by then. The E-diff slows you down. It works decently enough, but it works by BRAKING tires to keep them spinning within 5% of each-other. Anytime you're braking you're losing time...
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      01-17-2018, 05:48 PM   #4
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Same as bbnks2 here. Went through running with nannies all on and later all off although I'd turn them on after a change to the car or if there were questionable track conditions, to getting a mechanical LSD, to totally defeating ABS and the stability systems so they can't be activated at all.

Earlier it became possible to tell when the stability system was mucking things up and verifying that by seeing more brake dust on one wheel than any other in the paddock afterward. Then I'd kill stability with the long button hold and go back through that point on the track to see if the problem went away and if so I left it off for the rest of the day.

After getting fast enough to need race shells and a six point harness the car's now rigid enough that stability control is a detriment and it's possible to more easily tell what's going on with the car so it's not really critical anymore.

At first? Nannies are a good idea.
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      01-17-2018, 06:20 PM   #5
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Quote:
Originally Posted by bbnks2 View Post
E-diff still works, but the car will no longer cut throttle and apply the brakes to keep the car stable. This is the "5 second" hold of the button..
This disables the E-diff on my 4/2008. One wheel will spin endlessly if not traction is available.

Quote:
Originally Posted by bbnks2 View Post
I'd like to start running advanced, but I am not there yet as a driver. I would also like to have a mechanical diff installed by then.
I usually run intermediate too but when is crowded I run in advance often and don't have LSD. Don't let that hold you back. You will do just fine. Your 335i is well sorted.[/quote]
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      01-18-2018, 06:14 AM   #6
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I see this repeated all the time and I disagree with it:

“The E Diff brakes one tire so it slows you down.” No! Not if you are applying (or simply staying) on the gas.

Not true because braking the spinning tire forces a speed increase on the non spinning tire, provided input RPM’s stay the same. If you have ever idled a car on jackstands in gear (I have a few times) and stopped one rear tire from spinning (can just grab it by hand) you will have witnessed the other tire accelerate to twice its speed. (Can also do this on a RC car with a differential.)

If RPM’s stay the same at the diff input (pinion) then braking one wheel speeds up the other wheel. If you have say a 3.15 diff then the drive shaft spins 3.15 times for 1 rotation of 2 rear tires. That means if you hold one tire steady, like lock it down, then if you spin the driveshaft 3.15 times then the locked (100% braked) tire will spin 0 times and the free tire (no brake application) will spin 2 times. All the energy coming into the differential has to go out of it. 3.15 input rotations must always equal 2 tire rotations in some form of split between the tires.

So the ediff has the capability (in theory if it can 100% brake a tire) to drive the tire with traction up to twice as fast as it would be spinning at the same input revs normally.

Ediff will cook the brakes. No doubt about it. I’d much rather have a LSD but please stop saying ediff slows you down it’s not true.

If you are applying throttle and the revs are increasing then you definitely should accelerate if the ediff effectively brakes a spinning tire because the tire with traction will spin faster than it was. I think the limitation is we don’t know how much braking the ediff can apply maybe it’s not powerful enough to really stop a full throttle tire spinning. (Like Feuer’s reference above seems like the Ediff can’t apply enough braking.)

Last edited by Biginboca; 01-18-2018 at 06:29 AM.
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      01-18-2018, 09:38 AM   #7
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Quote:
Originally Posted by Biginboca View Post
If you are applying throttle and the revs are increasing then you definitely should accelerate if the ediff effectively brakes a spinning tire because the tire with traction will spin faster than it was. I think the limitation is we don’t know how much braking the ediff can apply maybe it’s not powerful enough to really stop a full throttle tire spinning. (Like Feuer’s reference above seems like the Ediff can’t apply enough braking.)
With DSC on I can hear and feel the brakes engaging. With DTC on (just one press on the button) I can still hear and feel the brakes engaging but less abruptly. With DTC off (long hold press on the button) I don't feel and hear the brakes engaging. I track my car and rear pads are lasting me twice as long as the front. That and one wheel spinning all the time makes me think that DTC off (long hold press on the button) disables the E-diff. Now some people say that this can be done via coding and that BMW changed the coding through out the years. They say 2007/2008 were the switch years. I would say that isn't accurate. My 335i MT is build 4/2008. My mother in-law 335i AT is build 2/2007. They both behave the same. She is in the 60's so definitely didn't alter the coding. Both the car new. I haven't mess with mine either. Regarding comments that DSC/DTC is slowing you down,I do would agree with. I can't predict when DSC/DTC will kick in, apply brakes, cut throttle ect etc when I go fast around the track. So when it does, the system will throw you and the car out of balance, you aren't in sync anymore. It will try to compensate to much. Too many corrections. Every time it does this is like you are stating all over again to gain speed, momentum, etc, etc... With out the interference is just lot easier to go faster given you know you car and you are familiar with the track.
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      01-18-2018, 09:54 AM   #8
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Quote:
Originally Posted by feuer View Post
With DSC on I can hear and feel the brakes engaging. With DTC on (just one press on the button) I can still hear and feel the brakes engaging but less abruptly. With DTC off (long hold press on the button) I don't feel and hear the brakes engaging. I track my car and rear pads are lasting me twice as long as the front. That and one wheel spinning all the time makes me think that DTC off (long hold press on the button) disables the E-diff. Now some people say that this can be done via coding and that BMW changed the coding through out the years. They say 2007/2008 were the switch years. I would say that isn't accurate. My 335i MT is build 4/2008. My mother in-law 335i AT is build 2/2007. They both behave the same. She is in the 60's so definitely didn't alter the coding. Both the car new. I haven't mess with mine either. Regarding comments that DSC/DTC is slowing you down,I do would agree with. I can't predict when DSC/DTC will kick in, apply brakes, cut throttle ect etc when I go fast around the track. So when it does, the system will throw you and the car out of balance, you aren't in sync anymore. It will try to compensate to much. Too many corrections. Every time it does this is like you are stating all over again to gain speed, momentum, etc, etc... With out the interference is just lot easier to go faster given you know you car and you are familiar with the track.
On my Ď09 if I do an aggressive start DTC off the rear end will slide sideways. I know both tires are spinning for sure.
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      01-18-2018, 10:13 AM   #9
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Quote:
Originally Posted by feuer View Post
This disables the E-diff on my 4/2008. One wheel will spin endlessly if not traction is available.
[/quote]

So long as both wheel speeds are within 5% of each-other the E-diff will let them spin all day. You can still get 1-tire fires with the e-diff. There is a limit on how much brake line pressure it is programmed to apply... An abrupt loss of traction can easily overpower the slight application of the brakes by the e-diff.

Or, the programming is just different on older cars
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      01-18-2018, 10:20 AM   #10
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Quote:
Originally Posted by Biginboca View Post
I see this repeated all the time and I disagree with it:

“The E Diff brakes one tire so it slows you down.” No! Not if you are applying (or simply staying) on the gas.

Not true because braking the spinning tire forces a speed increase on the non spinning tire, provided input RPM’s stay the same. If you have ever idled a car on jackstands in gear (I have a few times) and stopped one rear tire from spinning (can just grab it by hand) you will have witnessed the other tire accelerate to twice its speed. (Can also do this on a RC car with a differential.)

If RPM’s stay the same at the diff input (pinion) then braking one wheel speeds up the other wheel. If you have say a 3.15 diff then the drive shaft spins 3.15 times for 1 rotation of 2 rear tires. That means if you hold one tire steady, like lock it down, then if you spin the driveshaft 3.15 times then the locked (100% braked) tire will spin 0 times and the free tire (no brake application) will spin 2 times. All the energy coming into the differential has to go out of it. 3.15 input rotations must always equal 2 tire rotations in some form of split between the tires.

So the ediff has the capability (in theory if it can 100% brake a tire) to drive the tire with traction up to twice as fast as it would be spinning at the same input revs normally.

Ediff will cook the brakes. No doubt about it. I’d much rather have a LSD but please stop saying ediff slows you down it’s not true.

If you are applying throttle and the revs are increasing then you definitely should accelerate if the ediff effectively brakes a spinning tire because the tire with traction will spin faster than it was. I think the limitation is we don’t know how much braking the ediff can apply maybe it’s not powerful enough to really stop a full throttle tire spinning. (Like Feuer’s reference above seems like the Ediff can’t apply enough braking.)
That is all nice theory, but that is NOT how the e-diff ends up working in real life.

Torque still gets delivered to the wheel being braked by the e-diff. You can physically feel the car slow down mid-corner as the e-diff applies the brakes. There is no denying it. The e-diff cannot manually lock the rear axle to deliver the torque to the wheel with more traction. Energy is wasted any time you apply the brakes. Other manufacturers use "electronic torque vectoring," but it is more advanced and is done through the use of mechanical clutches and not the brake pads.

Also, everything you said ignores one huge problem. WEIGHT TRANSFER. Applying the brakes in a turn, whether it's the e-diff doing it or the driver, upsets the car. E-diffs are fantastic for FORCING A CAR TO ROTATE for this reason, which is how brake biasing has been used on race cars with the driver in control over when it happens. Manual control over individual wheel braking was actually considered cheating and banned from being used in some Motorsports. That is not how BMW is using it though.

With the E-diff you end up with a squirmy rear-end under hard acceleration as the e-diff pulsates the brakes back and fourth. The car sometimes even ends up launching out of corners in odd directions. It's hard to accelerate out of a corner when the e-diff is DRAGGING the inside wheel to keep both wheels at the same speed.

Also, please go outside and jam a bar through your rear wheel. Then go try to accelerate down the street. YOU WONT GET VERY FAR. The free wheel will not double in speed. The motor will bog as torque is wasted through the locked wheel.
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Last edited by bbnks2; 01-18-2018 at 10:39 AM.
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      01-18-2018, 10:42 AM   #11
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I’m not looking to argue the effectiveness of the LSD vs Ediff. Obviously LSD is superior hence its inclusion on M cars that already have Ediff. And cooking rear brakes can’t be good too.

But Ediff always accelerates the tire with traction. Always! Braking the spinning tire must force the traction tire to move faster. Always. Probably not enough to ever equal a true LSD. It may negatively affect handling dynamics. But it never would slow the tire with traction, provided input revs stay the same.

The input revolutions of the diff always equal a fixed output over both tires. The sum output always stays the same, slowing one tire speeds the other if input revs stay the same. Always.

Ediff affect on handling might slow a lap time (due to affects on handling) but it never slows the car.

Note: Perhaps in Feuer’s example a rear brake upgrade would make the ediff more effective

Last edited by Biginboca; 01-18-2018 at 10:52 AM.
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      01-18-2018, 10:42 AM   #12
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It's very simple, replace the open diff with a clutch type LSD and the car will be obviously faster through a corner, it's impossible to not notice. The BMW e-diff only approximates an LSD by dissipating power in heating up the brakes rather than steering it through clutches, big difference.
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      01-18-2018, 10:55 AM   #13
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Quote:
Originally Posted by justpete View Post
It's very simple, replace the open diff with a clutch type LSD and the car will be obviously faster through a corner, it's impossible to not notice. The BMW e-diff only approximates an LSD by dissipating power in heating up the brakes rather than steering it through clutches, big difference.
I agree, power is being lost by applying the brakes. That is simple physics. Why do you think the brake pads produce heat? energy is being transferred.

Also, the rear axle is not 100% open like the theory is suggesting. If you lock one wheel the motor bogs. It's just harder to see on a jack stands because there is 0 resistance on the wheels.

My rear right caliper was frozen the other day. I can assure you the rear left wheel did not run 2x as fast and I did not end up driving in really fast circles. The motor bogged and the car went NOWHERE. Energy was lost.

I won't pretend like I understand more about differentials than I do, but I do know what I've experienced first hand and the e-diff kills autocross times. Not to mention the car taking off in random directions toward curbs.. Rcomps and race pads exasperate the issue for sure. Am I over-exaggerating it now to make a point? Yes. It actually does work pretty well for intermediate drivers like myself.
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Last edited by bbnks2; 01-18-2018 at 11:50 AM.
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      01-18-2018, 12:45 PM   #14
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Quote:
Originally Posted by justpete View Post
It's very simple, replace the open diff with a clutch type LSD and the car will be obviously faster through a corner, it's impossible to not notice. The BMW e-diff only approximates an LSD by dissipating power in heating up the brakes rather than steering it through clutches, big difference.
You do not think clutches dissipate power into heat? They both work through friction and generate heat when they slip.

I’m not a track guy but I’m a differential guy having had many diffs apart and they all work the same. Input and output have a fixed relationship. I can’t comment to the lap times and handling quirks. If the ediff bogs the motor and the input revs to the diff drop then yes the car will slow for sure, obviously. If the motor doesn’t bog and diff input revs stay the same, then the tire with traction will accelerate when the loose tire is braked by the ediff.

What’s strange is Feuer’s post hints that the ediff cannot apply enough braking to be effective. The loose tire gets smoked.

Others are saying the ediff applies too much power and bogs the motor.

So apparently the ediff programming must be off cause you have too little braking in one scenario and too much in another.

Last edited by Biginboca; 01-18-2018 at 12:58 PM.
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      01-18-2018, 12:55 PM   #15
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Quote:
Originally Posted by Biginboca View Post
You do not think clutches dissipate power into heat? They both work through friction and generate heat when they slip.

Iím not a track guy but Iím a differential guy having had many diffs apart and they all work the same. Input and output have a fixed relationship. I canít comment to the lap times and handling quirks. If the ediff bogs the motor and the input revs Drop then yes the car will slow for sure. If not then the tire with traction will accelerate when the loose tire is brakes.

Whatís strange is Feuerís post hints that the ediff cannot apply enough braking to be effective. The loose tire gets smoked.

Others are saying the ediff applies too much power and bogs the motor.

So apparently the ediff programming must be off cause you have too little braking in one scenario and too much in another
Obviously not nearly as much. I've never seen diff clutches get so hot the diff smokes.

I am a track guy and my logger tells me my sector times got faster with a Salisbury type LSD and that's without induced rotation in either case.

The e-diff is a half assed implementation that in the real world keeps half assed drivers out of the kind of trouble they would otherwise be adept at avoiding, like most of the crap on consumer vehicles.
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      01-18-2018, 01:44 PM   #16
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Quote:
Originally Posted by justpete View Post
Obviously not nearly as much. I've never seen diff clutches get so hot the diff smokes.

I am a track guy and my logger tells me my sector times got faster with a Salisbury type LSD and that's without induced rotation in either case.

The e-diff is a half assed implementation that in the real world keeps half assed drivers out of the kind of trouble they would otherwise be adept at avoiding, like most of the crap on consumer vehicles.
That’s not obvious to me that diff clutches do not generate the same heat as ediff. I don’t know if they do or not but it’s not obvious to me.

I’ve seen many diffs that get so hot you can’t even touch them.

In your track scenario the brakes are being used to slow the car for turns and to accelerate on the straights (ediff engages), so the brakes in this scenario are taking twice the heat input (generalized) of a diff clutch that only sees friction on acceleration. So obviously you see the brakes get very hot, they are in essence working double duty with ediff. Also let’s not forget you are looking for hot brakes and monitoring it. Try checking your diff after some hot laps I guarantee it’s too hot to touch.

Ediff or LSD there is friction in both, probably similar amounts with similar heat generation too when they engage. (M series LSD diffs have cooling vanes. There would be no real added cost to add those to all models if they needed them, but open diffs don’t generate that kind of heat. The new camaro ZL1 1LE, or whatever they are called, even have diff coolers for their LSD’s with their own oil pumps.)

Anyway I appreciate your input and this discussion. You bring up some good points and I appreciate your personal experience. I still insist Ediff doesn’t “slow the car”. It might lap slower than a LSD but it does not decrease the cars speed. If anything it seems like maybe some guys aren’t powering through enough, like keeping their revs up. Only way the car can slow is if the engine bogs. I’ve not experienced this with my car, but I’m not gentle on the throttle when my ediff engages it’s always on a launch full throttle (drag race scenario).

I doubt the ediff can engage strong enough to bog a motor during that instance.

Last edited by Biginboca; 01-18-2018 at 02:01 PM.
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      01-18-2018, 01:49 PM   #17
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Quote:
Originally Posted by justpete View Post
The e-diff is a half assed implementation that in the real world keeps half assed drivers out of the kind of trouble they would otherwise be adept at avoiding, like most of the crap on consumer vehicles.
There are more sophisticated e-diffs than what we have in our BMWs and we are going to see more and more of them in the future. Is cost saving for manufacturers. Is also simple. Is faster. Easy to modify/calibrate to end user preference. Same goes for the e-diff locks found on the new M cars. We like it or not the "e" is the future and if you drive car with superior e-diff than what we have you might change your mind
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      01-18-2018, 01:49 PM   #18
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Quote:
Originally Posted by Biginboca View Post
Thatís not obvious to me that diff clutches do not generate the same heat as ediff. I donít know if they do or not but itís not obvious to me.

Iíve seen many diffs that get so hot you canít even touch them.

In your track scenario the brakes are being used to slow the car for turns and to accelerate on the straights (ediff engages), so the brakes in this scenario are taking twice the heat input (generalized) of a diff clutch that only sees friction on acceleration. So obviously you see the brakes get very hot, they are in essence working double duty with ediff. Also letís not forget you are looking for hot brakes and monitoring it. Try checking your diff after some hot laps I guarantee itís too hot to touch.

Ediff or LSD there is friction in both, probably similar amounts with similar heat generation too when they engage. (M series LSD diffs have cooling vanes. There would be no real added cost to add those to all models if they needed them, but open diffs donít generate that kind of heat.)

Anyway I appreciate your input and this discussion. I still insist Ediff doesnít ďslow the carĒ. It might lap slower than a LSD but it does not decrease the cars speed. If anything it seems like maybe some guys arenít powering through enough, like keeping their revs up. Only way the car can slow is if the engine bogs. Iíve not experienced this with my car, but Iím not gentle on the throttle when my ediff engages itís always on a launch full throttle (drag race scenario).

I doubt the ediff can engage strong enough to bog a motor during that instance.
Adding an LSD took six seconds off my lap time. Pretty sure I didn't become a miraculously better driver over the few months it was in the shop and getting broken in. Also, I've seen very hot rear brakes using minimal entry braking while I've seen relatively low temp rise of the diff fluid although the diff cooler is a recent add and hasn't been tracked but the logged temps and pump/fan operation cycles will be interesting once it gets back on the track.

Regardless, luckily the entire ABS and stability systems are completely disabled now so it's all moot in my application.
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      01-18-2018, 01:59 PM   #19
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Originally Posted by feuer View Post
There are more sophisticated e-diffs than what we have in our BMWs and we are going to see more and more of them in the future. Is cost saving for manufacturers. Is also simple. Is faster. Easy to modify/calibrate to end user preference. Same goes for the e-diff locks found on the new M cars. We like it or not the "e" is the future and if you drive car with superior e-diff than what we have you might change your mind
Absolutely! Ordering an M6 today and I'm pretty sure it has a more advanced e-diff (MDM maybe?)
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      01-18-2018, 04:19 PM   #20
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Quote:
Originally Posted by Biginboca View Post
Anyway I appreciate your input and this discussion. You bring up some good points and I appreciate your personal experience. I still insist Ediff doesnít ďslow the carĒ. It might lap slower than a LSD but it does not decrease the cars speed. If anything it seems like maybe some guys arenít powering through enough, like keeping their revs up. Only way the car can slow is if the engine bogs. Iíve not experienced this with my car, but Iím not gentle on the throttle when my ediff engages itís always on a launch full throttle (drag race scenario).
I think you underestimate a few variables. Like, driver input. A driver is always going to lose this battle. You think your right foot can react by adding gas faster than the e-diff can engage the brakes? By the time you push the gas down to power through the corner the damage has already been done in a matter of milliseconds. These milliseconds add up to 1-2 seconds a lap when you multiply them by 10+ corners. Just a thought...

Then again, you're trying to say the e-diff doesn't slow the car. I'd argue against that too. The inside wheel of a car is always rotating at a different speed than the outside wheel. Mechanical diffs don't lock 100%. Clutch types usually don't lock more than 60% on acceleration and 40% on deccel, depending on how you have set up the ramp angles. A wavetrack claims it can distribute up to 50% torque on accel/deccel I believe. A clutch type lsd doesn't ride the friction material to bias the torque like you're suggesting it does...

E-diff is basically aiming for a 95% lock in ALL situations. You might as well weld the differential...

Slow speeds and tight corners I feel like the e-diff oiver-reacts. High speed roadcourse work I've spun the inside tire trying to accelerate out of corners so it's not working well enough in those instances. It's not an ideal unit for more advanced drivers and it shows in lap times.
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Last edited by bbnks2; 01-18-2018 at 06:22 PM.
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      01-18-2018, 08:34 PM   #21
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Quote:
Originally Posted by bbnks2 View Post
I think you underestimate a few variables. Like, driver input. A driver is always going to lose this battle. You think your right foot can react by adding gas faster than the e-diff can engage the brakes? By the time you push the gas down to power through the corner the damage has already been done in a matter of milliseconds. These milliseconds add up to 1-2 seconds a lap when you multiply them by 10+ corners. Just a thought...

Then again, you're trying to say the e-diff doesn't slow the car. I'd argue against that too. The inside wheel of a car is always rotating at a different speed than the outside wheel. Mechanical diffs don't lock 100%. Clutch types usually don't lock more than 60% on acceleration and 40% on deccel, depending on how you have set up the ramp angles. A wavetrack claims it can distribute up to 50% torque on accel/deccel I believe. A clutch type lsd doesn't ride the friction material to bias the torque like you're suggesting it does...

E-diff is basically aiming for a 95% lock in ALL situations. You might as well weld the differential...

Slow speeds and tight corners I feel like the e-diff oiver-reacts. High speed roadcourse work I've spun the inside tire trying to accelerate out of corners so it's not working well enough in those instances. It's not an ideal unit for more advanced drivers and it shows in lap times.
Those are great points! It seems like you guys are all talking lap times. So you all agree that the Ediff equipped car is slower in lap times than an open diff car? Is this what you mean by “Ediff slows the car down”? As I said I’m not a track guy and can’t speak to the nuances of handling and track times, etc but I just can’t see how an Ediff will rob power from a wheel with traction and slow a car down when it brakes a spinning wheel. That’s a tough pill to swallow when you understand how differentials work.

I do notice Pete is saying his LSD made him 6 seconds faster. I doubt anyone is surprised or would even question this because we all agree mechanical LSD is ideal. I’m not making any argument that Ediff is in any way better than (or even equal to) a mechanical LSD.

I don’t see how Pete’s example supports the ediff “slowing cars down” statement. My issue is with that statement. In his example Pete added a LSD (which is superior to the ediff he had) and the car was faster around a track. This example doesn’t mean the ediff was slowing the car down (as in it would be faster with a true “open diff” vs the Ediff he had.). This example only means a LSD made the car faster it doesn’t show an Ediff slowing a car (vs having No Ediff.)

“Ediff slows cars down” means (to me and maybe not all of you) that a car with ediff will be slower than a car with open diff, or that the ediff somehow robs power from a tire with traction and you’re speedometer will slow when ediff engages and it would have stayed the same speed with ediff off.

You guys all know that the input and output revolutions in differentials are ALWAYS fixed ratio right? There’s no way to lose revolutions inside the diff. What goes in must come out in the fixed ratio. (Sorry to keep repeating this but I want to make sure we all agree 3.15 input always equals 2 tire rotations between the 2 outputs. Unless the engine slows when Ediff activates, the non braked tire will pick up speed (torque) while the braked tire is slowed.). I can’t see how and when this becomes untrue, the gears can’t slip inside the differential.

My argument is still that Edif cannot slow a car down. This is the statement I’ve seen repeated on this site maybe 10 times by various posters. (Basically saying in my mind that having Ediff is a liability that takes away speed.). The quote above by @bbnks2 does speak to the limitations of the Ediff but doesn’t show how “Ediff slows the car down”. (I assume meaning slows the car down vs an open diff or slows the car down as a speedometer decrease when it engages.)

Again I would never compare our Ediff to a LSD for efficiency and effectiveness they aren’t in the same ballpark but maybe they will be someday.

Last edited by Biginboca; 01-18-2018 at 09:50 PM.
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      01-18-2018, 10:48 PM   #22
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E-diff will slow the car down. Absolutely. Not only around the track. When DSC is on the e-diff is on and it will over power the engine, it will cut throttle and the engine will bog. When DTC is on by short press on the button the e-diff is on doing the same as above but is less severe and less abrupt intereference. It will not completely cut throttle but it will cause it to basically flactuate mostly depending how the wheel is gaining traction on the surface. When DSC and DTC are off by long press hold on the button the above intereference no longer happens. Like I said I can spin one wheel endlessly given no traction. Some people say e-diff is on non stop and can't be turned off by the long press hold on the button. I think if that is true then when DSC and DTC are off the brake forse the e-diff is applying is significantly reduced so that it can bog the engine and won't cut throttle. Regarding LSD allowing faster track time I don't know what to say since I'm on open diff and 2-3sec behind cars that have LSD, more power, lighter weight, and etc. so if I pick up 5-6 buy installing a LSD I will be the fastest, heaviest and least powerful car in my group. Now I don't think I'm that good of a driver lol. So probably drivers that gain that much time by going to LSD weren't really comfortable pushing the car in the corners and I know why as I find myself saving the car from a spin out often....
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