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LONN Joonas
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 BeitragVerfasst am: Di Apr 21, 2020 14:32    Titel: R5 Central Diff Antworten mit Zitat Back to top

I agree that differential problem. In my opinion it is not a problem of NGP6. It is somethting that have been wrong in R5 cars since I can remember. I asked about this from Bee but as I haven't got an answer and you seems to have same kind of thoughts I paste here the main points of the text I sent to bee:

The problem is the central differential. In real life, it is "locked" / there is not a central differential in R5 cars. But in RBR it isn't correct. It works like an open central diff. Let I give some arguments:

1) If there are no central diff / central diff is locked the front and rear axle should rotate equal speeds. But in RBR during braking you can lock the front axle while the rear is still rotating. Or if the brake balance is way too back you can lock the rear axle while the front keep still rotating.

2) The power "leaks" as I like to say. If we think a simple example about differential: It directs the power to the tire / axle that has less grip. Right? Lets now call it the "principle of differential". Like if we are accelerating with FWD car and the road is more slippery below the front left tire, it start to spin as the diff directs the power to it.

And that "leaking" is happening in R5 cars because the central diff is open. Or at least the modeled lock is way too loose. Why? Because when accelerating on low grip (gravel or snow) the power leaks to the front axle. The weight transfers to back, rear tires get grip and thus the front tires are on lower grip than the rear. And according to the "principle of differential" the power leaks to the axle where is less grip which in this case is the front axle.

You can so clearly feel that. In the straight accelerations of course but also in corners. When passing the apex of the corner and getting back to the throttle the weight transfers towards the back of the car and the rear tires get more grip than the front tires. And as the central diff is open the power leaks to the front. Which causes wheel spin in the front and very little power transmission to the rear causing for example that "FWD handling".

Or if you managed to get a better grip to the front tires than rear, like if the car slides and the rear tires go on to the slippery grass, the power suddenly leaks to the rear axle according the "principle of differential."


3) The setup tuning supports that. If I tune the setup to avoid that weight transfer during accelerations, it helps. Like lowering the front ride height and raising the rear ride height to set the cars weight balance more front. Or tightening the rear bump and front rebound etc. to avoid the weight transformation.

Or if I make a really oversteerly setup where the rear tires just can't get grip enough, the problem decreases. Like relatively stiff rear springs, stiff rear ARB, high rear tire pressure, stiff rear bump etc. Then the power can be direct also in the rear as the grip levels between front and rear are about equal instead of having almost all the grip in the rear when the power leaks towards the front axle.

4) Experience about other cars. As there was too little max. locking power on the central diffs on WRC 2017 cars in NGP5, we faced exactly the same problems than with R5 cars. Now when it is fixed (max. power from 1200 Nm to 6000 Nm) those problems are gone.

You can also feel the exactly same when playing the central diff. lock of group A cars. When setting the central diff too loose all those "R5 problems" occurs that I just told. When setting it tight enouhg, which is about 70 % in my Escort Cosworths gravel setup, those "R5 problems" are gone.

I'm not an engineer and may be that I'm totally wrong. But as I have got some confirmation to that theory from other drivers it would be nice to got some answer from person who really understand those things and would told us if we are right or not with a good arguments.

I haven't driven an R5 car in real life. But that central diff thing is on the regulations so we can know how it is without driving the R5 car in real life. For example from skoda.motorsport.com: "What the rules don’t allow is the use of a centre differential, which would allow the front and rear wheels to turn at different speeds. Instead, a driveshaft with a U-joint (a cardan shaft) is used." (https://www.skoda-motorsport.com/en/what-you-need-to-know-about-fabia-r5s-drivetrain/).

And yeah on previous posts I was saying that there is nothing wrong... My point then was that the physics are ok and still I think that they are. It is just a little error in R5 that is wrong and causes problems in my opinion. But as I also said on previous posts, it is possible to handle that problem by tuning the setups and same time it is the only way to handle it as long as we will get some fix.
 
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 BeitragVerfasst am: Di Apr 21, 2020 15:14    Titel: R5 Central Diff Antworten mit Zitat Back to top

You did explain it really good. Now i understand what potentially can be a problem with the R5 (diff). Thx!
 
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 BeitragVerfasst am: Di Apr 21, 2020 16:30    Titel: R5 Central Diff Antworten mit Zitat Back to top

interesting. this might explain a lot of things.
 
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 BeitragVerfasst am: Di Apr 21, 2020 17:32    Titel: R5 Central Diff Antworten mit Zitat Back to top

I agree with Joonas. This theory would explain the weird behaviour for sure.
 
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 BeitragVerfasst am: Di Apr 21, 2020 20:12    Titel: R5 Central Diff Antworten mit Zitat Back to top

LONN Joonas hat folgendes geschrieben:
But in RBR during braking you can lock the front axle while the rear is still rotating.


Axle or wheels? The wheels of one axis can rotate at different speeds, as well as the wheels of different axes can rotate at different speeds relative to each other. You are confused somewhere.

LONN Joonas hat folgendes geschrieben:


The power "leaks" as I like to say. If we think a simple example about differential: It directs the power to the tire / axle that has less grip. Right?



No! Not right. What force (power) are you talking about if one of the wheels rotates in the air? What force do you use to lift 0 kg of cargo?


LONN Joonas hat folgendes geschrieben:

The weight transfers to back, rear tires get grip and thus the front tires are on lower grip than the rear.


That's right, and this happens on any surface, and the higher the adhesion of the wheels to the surface, the greater the redistribution of weight. (on asphalt, weight redistribution is much more pronounced than on slippery surfaces)

LONN Joonas hat folgendes geschrieben:

When passing the apex of the corner and getting back to the throttle the weight transfers towards the back of the car and the rear tires get more grip than the front tires. And as the central diff is open the power leaks to the front. Which causes wheel spin in the front and very little power transmission to the rear causing for example that "FWD handling".


With a hard-locked central differential, it will be one to one as you described.


LONN Joonas hat folgendes geschrieben:

If I tune the setup to avoid that weight transfer during accelerations, it helps


you cannot avoid weight transfer, but only reduce weight transfer (decrease ground clearance), or change the time it takes for this weight to move.

LONN Joonas hat folgendes geschrieben:


I'm not an engineer and may be that I'm totally wrong. But as I have got some confirmation to that theory from other drivers it would be nice to got some answer from person who really understand those things and would told us if we are right or not with a good arguments.



Hang in the air the front wheel of the R5, having previously loosened the front differential lock to zero. If you are right, the car will remain in place, furiously turning the hung wheel, if the central differential is locked, the car will start.
(Google translator)

PS: I also get the impression that there are problems, but in my opinion, the problems are most likely with weight transfer formulas and inertia
 
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 BeitragVerfasst am: Di Apr 21, 2020 22:12    Titel: R5 Central Diff Antworten mit Zitat Back to top

Yea for sure I'm little confused as writing in english is difficult for me as is all those technical aspects of a differentials too. Sorry for that. As I said "you can lock the front / rear axle" I meant that you can lock both the wheels of that axle. Locked front axle = locked front left and front right tire.


By power I meant the power that comes from the engine to the tires. I know that the "principle of differential" wasn't right from theoretical aspect but that is how it seems to occours in practice. Here is a video where you can see what I mean: https://www.youtube.com/watch?v=U0c0z0W6aEE

And yea, I meant that you can reduce but not totally avoid the weight transferm .. Wrong choise of word there.

"Hang in the air the front wheel of the R5, having previously loosened the front differential lock to zero. If you are right, the car will remain in place, furiously turning the hung wheel, if the central differential is locked, the car will start.
(Google Translator) "

I see it almost like that in RBR. Like if you are stuck in the ditch and your rear wheels are on the bottom of the ditch (touhcing the ground) and the front tires are hanging in the air or touhing the ground just for a little load. The car will remain in place as the power leaks to the front where there is little or zero grip, the front tires start to spin and rear tires do nothing.

That was an extreme example... But that happens on a smaller case also in almost every time when you drive over a crest that is big enought to lighten the car but too small to set the car in to air. Especially if you have a setup that tends to lift the front of the car more than the rear when jumping, like the default setup of the Fabia R5. And if that crest happens to be in the middle of a corner, you can feel how the power of the engine leaks to the front tires when the front of the car lightens at the crest. And at the same time that massive "FWD-style" understeering occours as all or most of the power goes to the front tires and zero or just a little to the rear tires.

And that happens also for example with WRC2017 cars if you set the central diff open or too loose. And when tightening it enough that problem dissapears and you can do a beautiful controlled drift over that crest.

I'm not sure if the central diff of the R5 are totally open in RBR. Or is there just a very loose lock. Which doesn't really matter as there should be a solid axle instead of any kind of differential ((https://www.skoda-motorsport.com/en/what-you-need-to-know-about-fabia-r5s-drivetrain/).

The fact that in the setup menu the central diff lock values are zero may be telling us that the diff is just totally open. As for example on group A Escort, where is some kind on solid brake lock at the rear differential, the value is constant 45% if I remember right. So inferring from that if the there is a some kind of solid lock, there are some solid value in the setup menu also but in R5 case the central diff value is 0.0000% = open...

Just hope that Workerbee would answer and tell he's opinion. And if I'm wrong, maybe he can give some explanation why those thing happens that I and other drivers are feeling right now.
 
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 BeitragVerfasst am: Di Apr 21, 2020 23:02    Titel: R5 Central Diff Antworten mit Zitat Back to top

LONN Joonas hat folgendes geschrieben:
I know that the "principle of differential" wasn't right from theoretical aspect but that is how it seems to occours in practice.


I understand what you mean, but you are slightly mistaken.


LONN Joonas hat folgendes geschrieben:

And at the same time that massive "FWD-style" understeering occours as all or most of the power goes to the front tires and zero or just a little to the rear tires.


In order to talk about power (force) - it must be realized. If the wheel rotates in air (on bare ice), the required power for its rotation will tend to zero. A symmetrical differential distributes 50/50 torque. And if, as you say, an open symmetrical differential is realized, in this case, in the situation described above with unloading the front wheels, the power does not flow to the wheels of the front axle, but decreases on the rear axle. If the rear wheels can realize 100 Nm of torque, and the motor can give out 800 Nm, then the front wheels can only have 100 Nm of torque, and the exact opposite.

And if really one pair of wheels may not rotate relative to another, then the lock does not work. (Google translator)
 
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 BeitragVerfasst am: Mi Apr 22, 2020 13:31    Titel: R5 Central Diff Antworten mit Zitat Back to top

Zitat:
But in RBR during braking you can lock the front axle while the rear is still rotating.
my experience from my brake tests (during the brake balance of R5 discussion) says thats not right. if i braked straight on same suface for all 4 tires. they all slow down in same speed. if ou would be right, with braking, you load the front and the rear should be blocking first (but it doesnt)


Zitat:
You can so clearly feel that. In the straight accelerations of course but also in corners. When passing the apex of the corner and getting back to the throttle the weight transfers towards the back of the car and the rear tires get more grip than the front tires. And as the central diff is open the power leaks to the front. Which causes wheel spin in the front and very little power transmission to the rear causing for example that "FWD handling".

maybe the other possible reason is, that the front lift up and get less grip?


Zitat:
Hang in the air the front wheel of the R5, having previously loosened the front differential lock to zero. If you are right, the car will remain in place, furiously turning the hung wheel, if the central differential is locked, the car will start.

he is right with this statement, if the the theory means a 100% open differential. if it is also a little bit locked you cant prove it in this way. i dont know as good you would see then the turning speed differences.

Zitat:
By power I meant the power that comes from the engine to the tires.
name it torque wink

Zitat:
I see it almost like that in RBR. Like if you are stuck in the ditch and your rear wheels are on the bottom of the ditch (touhcing the ground) and the front tires are hanging in the air or touhing the ground just for a little load. The car will remain in place as the power leaks to the front where there is little or zero grip, the front tires start to spin and rear tires do nothing.
you have to check both sides of the axle. it can happend, that right front tire spins, right rear tire is not moving (but if it is working right, than rear left tire must also spin).

Zitat:
That was an extreme example... But that happens on a smaller case also in almost every time when you drive over a crest that is big enought to lighten the car but too small to set the car in to air. Especially if you have a setup that tends to lift the front of the car more than the rear when jumping, like the default setup of the Fabia R5. And if that crest happens to be in the middle of a corner, you can feel how the power of the engine leaks to the front tires when the front of the car lightens at the crest. And at the same time that massive "FWD-style" understeering occours as all or most of the power goes to the front tires and zero or just a little to the rear tires.

it must not be wrong, if you go uphill, your front will compressed, if you on the middle of crest, first your front will decompressed it will increase if you accelate in same time. so its normal, that you have less grip for steering on crests


Zitat:
And that happens also for example with WRC2017 cars if you set the central diff open or too loose. And when tightening it enough that problem dissapears and you can do a beautiful controlled drift over that crest.
for comperatin with R5 cars it is better to use old WRC like Escort WRC. They also have a center differential but they are more close to R5 than WRC2017

Zitat:
The fact that in the setup menu the central diff lock values are zero may be telling us that the diff is just totally open.

you can not be sure that this parameter are used for equalations on R5 cars. we all have no information how Workerbee programmed it. forget the idea, that workerbee only play with some values, there was written complete new codes and only he knows, how they play together.

maybe a test for you, take a escort WRC and set it similar than your R5 car but set center differential at mapping allways to 0% and the force to maximum. this should simulated a car as you think the R5 are, isnt it?

if you be right you should feel the same problems as with R5 cars

(thats also not a prove, thats all right or all wrong, or one right or the other wrong)
you dont know if the problems caused by only R5 cars (i dont think so, other different car classes have the bad behavior too but some more, some less)

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 BeitragVerfasst am: Do Apr 23, 2020 00:15    Titel: R5 Central Diff Antworten mit Zitat Back to top

Yea other possible reason could be that the front do lift up both during a smooth corner and a corner over crest when going back to thottle. And the point was that because this happens we can observe that the central diff is open.

And because that "open central diff thing" doesn't happen for example with group A or WRC2017 when the central diff is locked to its maximum, it shows to me that the open diff of R5 cars is the main problem. Not the up lifted front of the car. Lifting up the front is just a one situation where it is easy to observe if there is a lock in the central diff or not.

I see that group A is a very good point of reference as in them you can set the central diff fully locked (100%). And that fully locked central diff should work just or almost like that solid shaft that there should be in R5 cars in place of an open central diff. With those two cars, the R5 wiht open diff and group A with 100% locked diff, the observing of this thing is as simply as it can be. Like black and white. Lock or open. Citroen or Ford? To be or not to be?

I haven't driven those 1.6 WRC cars where should have a same kind of central diff than R5 cars if I'm right. Just checked and at least the values ​​of the setup menu seem to be the same as in R5 cars. But it doesn't matter for me right now. If there is a problem in R5 central diff, at least Bee has now been informed about it. That is all I can do, that is all I wanted. If there is the same kind of problem in some other cars, he can fix it like he can fix that R5 problem.

I don't see it helpuf to contiue the depate about how the diffs works. I'm not an engineer, I don't have all the right words and I guess there is a little language barrier also. All in all it lead to nothing in the case of fixing this possible problem. I have my theory about the problem, I have the support from many drivers and the only thing we need now is the answer from Bee as he is the man behind the physics.

And yea I know that those parameters can be what ever. That was just a small extra to confirm my thoughts which don't really depend on if the parameters are right or not. And for the same reason we can't be sure if the problem is the diff or what ever as we don't have any idea how the coding and everything is done. Or at least I don't have. But as I said, we do have a feedback, therories and ideas about what might be wrong and hopely some day some answers too.

And if there is not a problem then I just hope that he has some good answers for me and all of those who think and feel that the diff is open.
 
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 BeitragVerfasst am: Fr Apr 24, 2020 12:48    Titel: R5 Central Diff Antworten mit Zitat Back to top

try the ford escort cosworth and subaru impreza 555

for me the handling feels totaly different on snow. i also dont know why the escort have no differential lock setting for brake situation?

i also dont want discuss about workwise of differentials. But the differential thing is a big new part of NGP. Im sure Workerbee prove the general funktion of it not only few times. The workwise is theoretical clear with no room for a greyzone!
so i would say, it is not wrong to check it again in your way, but the probability is in my opinion very less.

Im more by AlDrive, something in direction of inertias, suspension geometry in combination of surface/tire. Thats all areas with a higher chance of grayzones.

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 BeitragVerfasst am: Mi Mai 06, 2020 22:06    Titel: R5 Central Diff Antworten mit Zitat Back to top

I tried the group A cars when selectin my favourite one to compete in our local serie. And I noticed too that the Escort feels different. Not only in group A, but also when comparing to every other car that I can remember. I supposed it due to the front geometry and when wathing replays it seems that the turning of front wheels is different than usual. I don't have words to tell it better. But it must also have an effect that there is no "brake lock" on the front diff at all.

But that doesn't change my opinion about the point of this topic. I can feel the "R5 problem" on every 4wd car where I can set the center diff open and then tighten it to see how the "problem" dissapears. It happens with escort, other group A cars, WRC2017... As I have said.

I also tried the WRC1.6 car where should have a same kind of solution on diffs than on R5 cars. I picked up the Fiesta RS WRC 2014 and did my testing on gravel. I tried many kind of setup variations for hours and I didn't feel the "R5 problem". I have told how I think the problem occours and I didn't notice any of them.

I want to make my setups looks as realistic as possible which in WRC1.6 gravel setups means relatively soft suspension. And if you watch videos of the Fiesta it really have a soft suspension. And moreover, the setups seems to be quite tail heavy too.

Those two things, soft suspension and tail heavy setups are things that are toxic on R5 cars when trying to minimize that "R5 problem". But those were both all ok with WRC1.6 car.

Also the fact that WRC1.6 has more power should contribute the "R5 problem" to occour. But it didn't. So I would say, only based on my observations and in the absence of information from the creator of the physics, that the diffs are not modeled to similar between R5 and WRC1.6. As they should be considering the regulations of those groups: mechanical diffs at front and rear and no center diff.

I just can't believe it is suspension, geometry, inertias or anything else than the diff. Those may play a small part of this problem but for me the main problem seems to be the central diff. Why? As I can make the problem to happen in many different cars that have many different suspensions, geometries etc. But just setting the central diff to open, the "R5 problem" occours and setting it tight enough, it dissapears. No matter how the setup of suspension or anything else is. For me its still clear.

But as long as we dont have answers I just quote Grönholm: "Sitting here and quessing I don't know."
 
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