AC's Group C cars .... Why such poor Mechanical Grip ?

[JayMonkey]

Hi Guys,

I'm confused and a bit frustrated with the Grip Level of AC Group C's cars ...

I'm working with a real life professional driver who will be driving a Group C car at Le Mans soon.
He tested in the real car a few weeks ago at Silverstone GP and although it was the first time he'd driven it he was able to achieve lap times below 1:53:00 after getting used to the car.

Last week he wanted to do some practice in a Group C car on AC ....

We tried all of the Kunos Group C cars and some 3rd Party ones but all of them seem to suffer from very low mechanical grip and would loose traction very easily in low - mid speed corners.

No matter what we did with the setup we were unable to get anywhere near a real life lap time. Even with the Mercedes C9 (which seemed to be the best of the bunch we tested) he was at least 10 seconds short of a competitive lap time.

We don't have this issue with GT3 cars (he drove one in the British GT Silverstone 500 last week) ... with a good setup his lap times were bang on what he could do in real life.

So on to my question ... is there some trick to setting up AC's Group C cars that we are missing ? Does anyone else think that the Group C cars have low mechanical grip ?

In real life these cars have huge fat sticky slick tyres .. they should have more mechanical grip than any other car in AC ... but they feel like driving a boat on a wet track ... indeed the pro driver i was working with said that the real life car was far easer to drive than the simulated one in AC ... So what gives .... any tips, setup or suggestions would be most welcome .....

I should point out that we are running AC on a custom motion simulator with OSW wheel, professional pedal set with load cell brake pedal with real life stiffness ... as good as it gets in terms of sim equipment so i don't think its anything to do with the rig itself.

Appreciate any advice on this ...
Cheers
Jay

 

[Tberg]

Didn't Silverstone get resurfaced recently with higher grip tarmac? I'll also echo again that I think these things are using 80s vintage rubber, does your friend's car have the same compound?

But then again I dont know where they got the tyre data from for the AC tyres, maybe they're just not right. I doubt the underbody airflow is modelled anything like a Group C car's venturi tunnels either - a wing is not going to be as sensitive to ride height for one and there won't be the tunnel/wing interaction you got on the later biplane wing cars.

AC's Le Mans is too long, no comparison there.

Silverstone was resurfaced in 2016, yet further parts have been resurfaced since.

What do you mean AC's Le Mans is to long for comparison? The 'No Chicane' version is shorter than any version you could possibly drive today, and AC C9 laptime on this layout is pretty damn close to the real C9 1989 no-chicane time.

Obviously you would not fit 30 year old rubber on a C9 to testdrive on Silverstone today.

 

[Richard Dastardly]

What do you mean AC's Le Mans is to long for comparison? The 'No Chicane' version is shorter than any version you could possibly drive today, and AC C9 laptime on this layout is pretty damn close to the real C9 1989 no-chicane time.

Obviously you would not fit 30 year old rubber on a C9 to testdrive on Silverstone today.

From what I'm aware of, the current AC Le Mans entire track is a little too long irrespective of chicanes. Will be happy to be proved wrong although that also means there's something further wrong if the top times at the track in modern cars are so far adrift of the real one. The layout itself even with the chicanes removed is quite different to 1989, too - corner profiles are different in many places & there's the entire new corner between the Dunlop bridge & the esses.

I'm not saying fit 30 year old rubber, I'm asking if the current tyres use a reproduction compound or a modern one.

 

[JayMonkey]

I'm quite sure the mechanical grip will be different from a real C9 with current tyres to AC's model with simulated older tyres. That goes for all the Group C cars in AC.

@Tberg,

Generally historic racing (at least in Europe) has a control tyre / compound. Tyre manufactures like Dunlop, Avon & Goodyear all manufacture race tyres that are close to period tyres specifically for historic racing which offer the same levels of period grip and tread patten if applicable.

So for example you would not be able to run a modern super slick using a fancy compound in a historic Group C race. Tyres fitted to the cars are checked by race officials during scrutineering to ensure that they conform to the race series specifications.

As such i would expect that kunos would take that into consideration when modelling the cars tyres.

Jay

 

[Tberg]

From what I'm aware of, the current AC Le Mans entire track is a little too long irrespective of chicanes. Will be happy to be proved wrong although that also means there's something further wrong if the top times at the track in modern cars are so far adrift of the real one. The layout itself even with the chicanes removed is quite different to 1989, too - corner profiles are different in many places & there's the entire new corner between the Dunlop bridge & the esses.

I'm not saying fit 30 year old rubber, I'm asking if the current tyres use a reproduction compound or a modern one.

My point was just to question the logic of even trying to compare the real C9 to AC's C9, albeit I failed in that

I could've just said that the tyres emulated in AC (soft slicks 90's) are not the same as Jay's friend drove 1:53 in at Silverstone. Even though, RSR has a WR at 1:54 recorded, so it's still possible to go pretty fast on the old vintage emulated tyre in AC.
I'd say the 90s tyre emulated in AC is the sole reason Jay+friend are 10sec off real contemporary laptimes.
My Le mans reference was a crippled shot at saying the times match up better when taking rl laptimes from the correct timeperiod.

 

[Tberg]

@Tberg,

Generally historic racing (at least in Europe) has a control tyre / compound. Tyre manufactures like Dunlop, Avon & Goodyear all manufacture race tyres that are close to period tyres specifically for historic racing which offer the same levels of period grip and tread patten if applicable.

So for example you would not be able to run a modern super slick using a fancy compound in a historic Group C race. Tyres fitted to the cars are checked by race officials during scrutineering to ensure that they conform to the race series specifications.

As such i would expect that kunos would take that into consideration when modelling the cars tyres.

Jay

Cool, thanks for explaining. I knew this from the historic races I've attended, sneaking around the garages in the pits. Still not sure how identical tyres made today with the "specs" are as back in the day, synthetic rubber being used today regardless. I'm not trying to defend AC as such, I'm just trying to seek out the factors that could be the reason you guys are 10sec off pace in AC compared to rl. Could be hundreds of reasons.

 

[Pawel Ziolkowski]

"loose traction very easily in low - mid speed corners"

This got me thinking... if we are looking at it too narrowly, yeah tyres are very important for mechanical grip but just adding enough grip to feel "ok" at low speeds would make the car much much faster overall. And while low speed means low downforce, it's not "no" downforce - AC group C cars have a distinct "turn on" speed range just around that low speed. For example C9 downforce doubles when going from 100 to 135km/h , and (speaking from sim experience) at that point every kg of downforce can actually mean a lot.

I can't add any useful knowledge on the topic but after messing around with the cars a bit, running +10% tyre grip does not fix the low speed issues while making the car 5s+ faster already at Silverstone (and that's with super low downforce package - more downforce would only increase the difference).

So while tyres are definitely important there might be just as much black magic with low speed aerodynamics.

 

[JayMonkey]

I'm not trying to defend AC as such, I'm just trying to seek out the factors that could be the reason you guys are 10sec off pace in AC compared to rl. Could be hundreds of reasons.

@Tberg,

The gap between period correct tyres and modern tyres would never be as much as 10 seconds, ether simulated or in real life hence the reason for my initial post.

Since starting this topic I've had a few conversation's with people in the know ... not going to say who or exactly what is wrong and why but basically it seems that quite a few of Kunos high down force cars such as the group 'C's do indeed have an inherent issue when it comes mechanical grip, largely as many of us have suspected to do with the way the tyres are defined within the model.

I would think that its possible to fix most of these issues by editing the data files using AC Car Tuner but its going to take a bit of investigating and development work to so see exactly what needs changing.

However all that aside one thing I've learned from starting this thread is that a few talented AC developers are working on a new Group C add of for Assetto Corsa, If done right and they have access to real life data i see no reason why these future add on's will not be superior to the Kunos Group C cars.

Its really great to know that Dev's are still working with AC ... which IMOH is still the PC best race car simulator platform in terms of physics and car simulation if done right.

Cheers
Jay

 

[Tberg]

@Tberg,

The gap between period correct tyres and modern tyres would never be as much as 10 seconds, ether simulated or in real life hence the reason for my initial post.

Since starting this topic I've had a few conversation's with people in the know ... not going to say who or exactly what is wrong and why but basically it seems that quite a few of Kunos high down force cars such as the group 'C's do indeed have an inherent issue when it comes mechanical grip, largely as many of us have suspected to do with the way the tyres are defined within the model.

I would think that its possible to fix most of these issues by editing the data files using AC Car Tuner but its going to take a bit of investigating and development work to so see exactly what needs changing.

However all that aside one thing I've learned from starting this thread is that a few talented AC developers are working on a new Group C add of for Assetto Corsa, If done right and they have access to real life data i see no reason why these future add on's will not be superior to the Kunos Group C cars.

Its really great to know that Dev's are still working with AC ... which IMOH is still the PC best race car simulator platform in terms of physics and car simulation if done right.

Cheers
Jay

Yeah, possibly easier to ask Stefano and Aris what they had in mind when doing the "90s" tyres in AC. They probably did not try to emulate the exact Michelin tyre that the C9 supposedly drove back in the day, but more a close-to-period overall one.

 

[Trezoitao38]

How was possible to Stefan Bellof do 6:11 at Nordschleife with a 956?

These cars were fast.

 

[F_B]

How was possible to Stefan Bellof do 6:11 at Nordschleife with a 956?

These cars were fast.

Because it was Stefan Bellof, he was crazy.

 

[Glaurung]

Because it was Stefan Bellof, he was crazy.

Definitely a talented driver, but the shorter layout plays also a role.

 

[F_B]

Definitely a talented driver, but the shorter layout plays also a role.

Ah, thanks for the info, didn’t know that.

 

[Tberg]

Definitely a talented driver, but the shorter layout plays also a role.

Wiki says Stefan drove the same layout as the present one, it was changed just the year before.

 

[RasmusP]

T

Wiki says Stefan drove the same layout as the present one, it was changed just the year before.

Then Wiki seems to be wrong, at least in the language you used.
Here's a quickly found article saying that the layout was only once used in that shortened configuration because of constructions.
LINK

 

[Tberg]

T

Then Wiki seems to be wrong, at least in the language you used.
Here's a quickly found article saying that the layout was only once used in that shortened configuration because of constructions.
LINK

I don't see anything wrong, other than saying Stefan drove a shorter layout than what can be driven today. The official record for current nordsleife layout for all cars is still his.

Edit: checking further, Stefan even drove the longer version of 20.832 meters, without todays 200m safety cut.

 

[Tberg]

I think what is missing from the discussion is, that since Stefans lap, no racing car in competition has been able to run the Nordsleife layout, only legal and non-legal roadcars has. Still impressive that not even todays super/hypercars in whatever figuration they come with has been able to break that record, regardless if they have 200meters less to go.

 

[Trezoitao38]

I think what is missing from the discussion is, that since Stefans lap, no racing car in competition has been able to run the Nordsleife layout, only legal and non-legal roadcars has. Still impressive that not even todays super/hypercars in whatever figuration they come with has been able to break that record, regardless if they have 200meters less to go.

That is my point. With a 956C is a superb lap.

 

[Kek700]

I would be amazed if a fully up to temperature 1980' s slick tyre was that much less "grippy"
than a modern equivalent, if at all.

I am prepared to be amazed

 

[AccAkut]

I would be amazed if a fully up to temperature 1980' s slick tyre was that much less "grippy"
than a modern equivalent, if at all.

I am prepared to be amazed

I have worked briefly in tire development in ~2012 and the leaps it did in just the last few years were big. I did not have direct contact with race tire manufacturing, but with "vintage replica" street tire production, which in essence was modern tire compounds, patterns and layering in old formfactors with white sidewalls and all that. You could even order special one-off tires if you offered enough (order for a Benz Patent Motorwagen went through while I was there. They used a modern standard car tire compound).

Peak grip of race tires may be similar to old stuff, but modern tires of all types offer more stability (in its chemistry and structure). Like modern "medium" tires offer grip levels only possible for three lap supersofts in the 80s.

 

[Kek700]

Porsche is set to attempt to beat the long-standing lap record around the Nurburgring Nordschleife with its upgraded 919 Hybrid Evo LMP1 car this month.

It will be interesting if it comes off
( maybe it has already)
Another 300 bhp plus modern tyres.
I am not sure if this can be done on
the shortened circuit that Stefan Bellof
Used

Porsche has turned its attention towards bettering the 6m11.13s recorded by Stefan Bellof in a Porsche 956 in qualifying for the 1983 Nurburgring 1000km.

Two-time Le Mans 24 Hours winner Timo Bernhard took the Nordschleife for a test on Monday at the wheel of the 919 Hybrid Evo, equipped with special Michelin tyres.

Anyone got any info on this.