Help with the nissan gtr gt3

[Kek700]

although i love my nissan for gt3 racing and will probably always stick with it ,
mainly due to the fact that i find it easy to drive.
But Donington has high lighted its short coming somewhat for me, making me
reassess its short coming , but i have found this quite difficult, having multiple
offs during practice which is very unusual for me.

I did not know about the negative squat and had always assumed front wheel
drive meant engine weight bias to the front as represented by brake bias.

Also that most of all cars are considered mid engined ( assuming i understand
the statment correctly )

 

[Kek700]

I have always had the impression that it could be at a disadvantage to
the other Gt3 cars on certain circuits, but never sure how the quality of the
driver can mask this.

Just an uneducated guess. As i have never drivern another gt3 car in a race.

 

[Pawel Ziolkowski]

I did not know about the negative squat and had always assumed front wheel
drive meant engine weight bias to the front as represented by brake bias.

To clear that one up, it does not matter where engine is. "Anti squat" is a feature of special suspension geometry that just limits how much the car pitches under throttle. If cranked to eleven (like with gtr), anti squat causes rear to lift.

Here you can see it in action:

Note how rear lifts when power is being applied to rear wheels and how it stays up after launch. On normal cars (including many racecars) rear goes down during acceleration.

I have always had the impression that it could be at a disadvantage to
the other Gt3 cars on certain circuits, but never sure how the quality of the
driver can mask this.

If you drive default setup a bit yeah i think. GTR is quite fast gt3 when set up properly, but default setup is probably the worst out of the whole gt3 filed.
Not that it's bad setup, it's good compromise for AI and drivers that never change it, so it is drivable on difficult tracks in any conditions. But to bring it's full potential the car needs to be lowered down, and different tracks or even weather will need different settings to get it right.

Just for example how much ride height is important for GTR - i think with optimal setup it might loose up to 0.2s per lap when server prohibits tyre blankets - only because of lower pit lane tyre pressures forcing higher ride height to adhere to regulations.

 

[Richard Dastardly]

What matters is that as much of the mass of the car is as near the centre of mass as possible.If all the mass is at the ends of the car then it'll still not want to change direction even if it's 50:50 distribution. You'd have to make sure the centre of mass at each end is the same height for it to have no effect at all, but in general terms where the engine is between the axles doesn't really matter.

Most GT3s are mid-engined ( most GT cars that allow you to move the engine are too ). The only real difference is whether the driver is in front or behind the engine.

 

[Kek700]

Most confusing, are you saying that the gtr has anti squat programmed into to
It’s software and other gt3’s don’t.
And why is the brake balance set at 69% (approximately) if it is a mid balanced car.

 

[Neilski]

Most confusing, are you saying that the gtr has anti squat programmed into to
It’s software and other gt3’s don’t.
And why is the brake balance set at 69% (approximately) if it is a mid balanced car.

Well, anti-squat is created by suspension geometry, and if AC is modelling that geometry correctly then the anti-squat should just "happen" I suppose.
As for brake balance, I may be misunderstanding your question, but even a car with 50/50 weight distribution will still have its optimum brake balance much higher than 50% front, because (depending on aero!) the weight transfers to the front under heavy braking, simply by virtue of the fact that the centre of mass is well above the contact patches.

 

[Pawel Ziolkowski]

Most confusing, are you saying that the gtr has anti squat programmed into to
It’s software and other gt3’s don’t.
And why is the brake balance set at 69% (approximately) if it is a mid balanced car.

Nothing is "programmed" there. The anti squat is just a result of how suspension linkages are set:
Here is a normal rear suspension for gtr (street):

Here is how linkages of anti squat that stops all pitch from acceleration looks like (100% anti squat):

Can you spot the similarity? Its the pitch of the linkages that decide what the rear will do on acceleration, that's it. Other cars just have less angled linkages, and most of them has some anti-squat as a result. GTR just has the most.

As for "mid balance", if you look at wheel loads the gt3 gtr, we can see it has around 54:46 front weight distribution (fully fueled it's 52:48), that's not far from 50:50... if you'd tell a kid to sit on the rear wing it would make gtr into a rear weight biased car, just like porsche.
Brake balance depends on center of mass height just as much as weight balance, and for GTR it's a bit higher than other gt3's so the brake balance is more toward front from that.

 

[Richard Dastardly]

Brake balance is only initially 68% in the default setup, you can make it what you want. Under braking weight will transfer forwards, so it's not 52-54% on the front wheels *at that moment* - it's true of any car because the centre of mass of a car is above the road & it pivots around the tyre contact patches. Understanding weight transfer is essential to setting a car up.

 

[Kek700]

Most confusing, are you saying that the gtr has anti squat programmed into to
It’s software and other gt3’s don’t.
And why is the brake balance set at 69% (approximately) if it is a mid balanced car.

 

[Kek700]

Forget the above.

 

[Kek700]

Forget the above posted by mistake, my ipad pad is having hissy fits at the moment

 

[Kek700]

i have always had problems with traction out of slow corners, even sacrificing all other
settings to acheive this has not improved it at all. I have to use low power in the diff
to achive lower electronic traction control settings. This is the only way i have found to maximise
accelaration out of the corners.
Have tried other gt3 cars, none of them seem to have this problem.

Sorry about the iPad delay problems.

 

[Pawel Ziolkowski]

Yeah slow speed corners will always be a problem. It's a combination of several factors, including peaky power delivery, problematic diffuser and mechanical balance.

To fight power delivery, setting gearing right can do a lot good. You want the gear ratio of the gear you use in corner to be fast (high max speed in this gear) enough so that the power isn't peaking immediately, but importantly you don't want to be too slow either so that the power comes from boost mid corner.
So try to have it as fast as possible but without any lag in power from the moment throttle is pressed.
In fact if you are using TC it's better to have slower, high power gear and lean on TC, than trying to "short-shift" the issue.

Normally for good exit traction you'd want to have understeery mechanical balance (stiff front ARB and springs, soft at rear) but that makes the car understeery in general.
So to counter that you want pretty low coast differential (i often use 15-25%), front balanced aerodynamics (from 2 to 6), and no excessive rear camber (use camber extravaganza app or similar).
Then make sure sure you don't loose traction on bumps. Try running as low as 0 rear rebound and mild fast rebound (especially with softer rear springs).

Depending on your skill thou, you might get better results with more oversteery balance. Sounds counter intuitive, but if you manage to keep apex speed high, you can get away with gradually adding throttle. Allowing the car to clear any mid turn bumps, gain speed so aerodynamics start helping, and being in better stance to straight the car out while giving full acceleration.

Lastly on power differential setting, in general it should be somewhere around 20-40%. Generally higher settings coupled with more understeery mechanical balance would be better for driver with aggresive inputs, and lower setting and oversteery balance would be faster for smooth driver.

 

[Kek700]

Most of what you have said is how my car is setup.

I have a real problem with feeling the car, but i seem to overall prefer stff front and soft rear
setup.

I can either run TC at 2 with diff power at 30 to 40%
or i can run diff power at 10% and TC at 3 or 4. But I cannot run TC at 3 or 4 and power at 40%
if i do it becomes difficult to stop snap oversteer, which constantly spoils average lap times.

So far it seems best for me to run TC at 4 and power at 10%. This seems to give best lap times
with a stable rear grip.

I will try the low rear rebound, this is at 6 at the moment; i run 115 rear springs so
maybe i can afford to run it softer. It is probably not a combination i have tried.

Sometimes it feel’s like changing the setup by big amounts gives me positive results with
negative counter effects. I just then seem to end up with the same lap times without
any conclusions.

Also slowly changing a setting slowly, produces no gains, then all of a sudden it produces
a drop in lap times when the setting becomes excessive.

I do not seems able to achieve a fine balance for all circuits, then just change tyres and gearing.
I am having to constantly manage setups for each circuit which becomes excessively time
consuming. ( This combined with learning the new circuit, then over driving the new circuit
can cause quite a lot of problems when i am having to attempt to set the car up as well )

Also one other aspect you mention is gearing, are you suggesting raising the gearing
for each slow corner exit rather the running the exit at near peak power.

 

[Pawel Ziolkowski]

I do not seems able to achieve a fine balance for all circuits, then just change tyres and gearing.
I am having to constantly manage setups for each circuit which becomes excessively time
consuming. ( This combined with learning the new circuit, then over driving the new circuit
can cause quite a lot of problems when i am having to attempt to set the car up as well

Yeah that's GTR in a nutshell. You have picked yourself a really demanding wife Gotta man up or divorce!

Also one other aspect you mention is gearing, are you suggesting raising the gearing
for each slow corner exit rather the running the exit at near peak power.

It really depends on how (and where) you drive, experiment with both short and long. As long as the turbo gap won't form, long (raised) should be better.

Also you can try throwing the setup my way and we can see if there is something simple to do about it. (do mention on what track)

ps: The reliance of TC on power diff is a bit curious thou, never saw that much impact from it, you might be running some excessive toe or camber or something... idk.

 

[Kek700]

Also you can try throwing the setup my way and we can see if there is something simple to do about it. (do mention on what track)

My setup appears that it is almost the same as
your suggestions.
This Sunday I am at Donington, so I will see how I
get on then send you my setup. ( many thanks )

I just need to soften the rear
With the fast and slow rebound lowered.

I run about +0.1 rear toe and -0.03 front toe

Have not had too much success with toe.
Although for Donington I run +0.02 toe in an attempt
To get the rear turning on some bends.

Funny about TC and diff for me it has a marked
effect but in truth it is much more about controlling
snap overseer rather than performance ( lap times )

 

[mclarenf1papa]

Well, anti-squat is created by suspension geometry, and if AC is modelling that geometry correctly then the anti-squat should just "happen" I suppose.
As for brake balance, I may be misunderstanding your question, but even a car with 50/50 weight distribution will still have its optimum brake balance much higher than 50% front, because (depending on aero!) the weight transfers to the front under heavy braking, simply by virtue of the fact that the centre of mass is well above the contact patches.

There's actually an issue with the force calculation in AC...the GTR should be squatting under acceleration.