Porsche 935/78 understeers a ridiculous amount.

[Kondor999]

Yes, I realize this car has a locked (100/100) diff and so it suffers from initial understeer IRL, however - as depicted in AC - it borders on the truly ridiculous. Even with a cazy setup (maxed-out stiffness in the rear, with maximum softness up front and brake bias at 51/49), you still can't get the car to turn in worth a damn.

Example: At the Michael Schumacher S's on the Nurburgring GP track, I have to slow down to **80-84 miles per hour** to avoid pushing off with more understeer than your typical FWD family sedan. By comparison, even meager machinery like the Nismo 370z has a higher entry speed (88-89mph), though its exit speed is only 90mph (I can get the 935 to rocket *out* of corners just fine).

I'm just finding it real hard to believe that a 935 can't take corners or turn in as well as a 370z.

The Raceroom Fabcar 935 has some serious turn-in understeer as well, but it's nowhere near as bad as this.

Lastly, how come I can't use negative toe-in (that would be toe-out) on the front of this car? That's a pretty common cure to turn in problems for race cars using these stiff (75%/75% and tighter) rear diffs. But in AC, all you can do is zero out the toe.

Disclosure: I run a 2013 Audi TTRS as my track-day car, and I use 0.04deg of negative toe on the front (meaning 0.04deg toe out) to subtsantially cancel out my car's tendency to understeer. Works great. If my street car has this level of adjustability, why doesn't the 935/78 - a friggin' Le mans-winning race car?

[INDIANA ELI]

it's a game

[Talkie Toaster]

Do you mean the 917/30? I have a big issue with the understeer of the 917/30 but I quite enjoy the 935, I can wrestle the thing through turns and have more fun in the process than with that can-am beast.

[kazereal]

Originally posted by Kondor999:

Yes, I realize this car has a locked (100/100) diff and so it suffers from initial understeer IRL, however - as depicted in AC - it borders on the truly ridiculous. Even with a cazy setup (maxed-out stiffness in the rear, with maximum softness up front and brake bias at 51/49), you still can't get the car to turn in worth a damn.

Example: At the Michael Schumacher S's on the Nurburgring GP track, I have to slow down to **80-84 miles per hour** to avoid pushing off with more understeer than your typical FWD family sedan. By comparison, even meager machinery like the Nismo 370z has a higher entry speed (88-89mph), though its exit speed is only 90mph (I can get the 935 to rocket *out* of corners just fine).

I'm just finding it real hard to believe that a 935 can't take corners or turn in as well as a 370z.

The Raceroom Fabcar 935 has some serious turn-in understeer as well, but it's nowhere near as bad as this.

Lastly, how come I can't use negative toe-in (that would be toe-out) on the front of this car? That's a pretty common cure to turn in problems for race cars using these stiff (75%/75% and tighter) rear diffs. But in AC, all you can do is zero out the toe.

Disclosure: I run a 2013 Audi TTRS as my track-day car, and I use 0.04deg of negative toe on the front (meaning 0.04deg toe out) to subtsantially cancel out my car's tendency to understeer. Works great. If my street car has this level of adjustability, why doesn't the 935/78 - a friggin' Le mans-winning race car?

There's a couple of things here.. LeMans has that Mulsanne straight which has pretty large effect on car design, there were only few tight corners on the track when 935 was used there (they've changed some things later).

Toe-in/out is limited suspension geometry and what kind of adjustment it allows. If the real car has limits, that's what you get.
Note that you INCREASE toe value to get it negative due to way the geometry works.

I advise increasing suspension stiffness at both ends: higher spring-rate at both ends allows better weight transfer. Leaving front too soft might not have enough capability to force load on front tyres.

Also reduce front ARB/increase rear ARB instead of changing suspension balance to change under/oversteering tendencies.

Old race cars used very different design than what is these days used for road-going cars. For example, large turbo in 935 means you have to compensate for that in other parts of design so it won't get too tail-happy.

These days tracks have more chicanes to keep maximum speed down at some places (look at tracks like Monza, Imola..). Tracks in the 70's did not have that much limitations and were faster to drive, cars were designed for that back then.

Steering in 935 is not as "fast" as more modern cars, you might have turn it more than you are used to. Tyres in this car are modelled after those it originally used too.

Remember that it is nearly four decades since the car was introduced, things have changed a lot since then. To put that into perspective: the difference from Ford Model-T to Chevrolet Corvette is roughly four decades..

[Kondor999]

I already know those things, but thanks for the input.

What I'd like to know is:

1. Why you can't give the 935 (or the 917) some toe-out on the front? Did they really not have that level of adjustability? This is normally a cure for a car that won't turn in, especially if it's due to a stiff rear diff.

2. Is it at all realistic for a 935/78 to have less corner entry speed on racing slicks than what can be achieved by a humble Nissan 370z on semi-slicks?

3. Would a 917/30 really have been unable to negotiate the Mercedes Arena S-curves or the Nordschleife Hotzenbach at anything over 40mph? That's substantially lower than what I've seen a bone-stock Honda S2000 manage in the exact same areas.

I've already tried the tuning tricks you mentioned, but I'll be happy to play around with it a bit more in the hopes that I can get this 935 to behavor somewhat like the ones I've used in rFactor and Raceroom. The problem I see is that, unlike in those sims, you have limited options in terms of geometry. Do any cars in AC have toe-out? I need to check, but it seems like all of them just have varying degrees of toe-in.

My opinion: Something is badly wrong with the suspension setups on these cars. We already know that, if everything is properly modeled, AC can spit out some fantastically realistic cars. Every single car in the Japanese Pack was dead-on in this regard.

Look at this footage:
https://www.youtube.com/watch?v=1SigpkdFZCQ

The guy is barely able to creep through the Hotzenbach section of the Nordschleife in the 917/30 at what looks to be around 30-40mph! Even FWD hot hatches can do far better than that. This cannot be realistic.

[Drisq Kivuli]

ahem....

https://www.youtube.com/watch?v=jycYKFJKcng

[Drisq Kivuli]

I would imagine if some of you had the 935/78 in real life you'd still have something about the car to complain about. hahha!

The Moby D1ck was only intended to be driven at Le Mans, thats it!! Also, why are you comparing a race car from 1978 to a modern sports ?

Look up the the 1972 to 1978 layout of Le Mans. The largest uninterrupted section ie; the Mulsanne straight is 3.7 miles long. You dont need to turn when you're just drag racing for 24hrs which is what Le Mans is.

http://www.maisonblanche.co.uk/circuits.html



https://en.wikipedia.org/wiki/Porsche_935

quote:

For 1978, a third and final version of the 935 was developed, the 935/78, intended only for Le Mans.

Before being retired to the museum, the Moby D1ck was also entered at Vallelunga and at the Norisring, the annual highlight of the DRM series, but the twisty track around the Nuremberg Reichsparteitag grand stand is quite the opposite to the Le Mans circuit the car was made for, including being run counter-clockwise around two narrow lefthand turns. The car did not finish there.

[quf]

The 917/30 has a spool rear axle. Which means both rear wheels will rotate at the same speed. Is not like cars with differentials where to help cornering you have one wheel rotating less than the other. Is like this in the 917/30 to help better with traction when you pull out of corners. The problem with this is that if you coast the car at lower speed corners you'll suffer understeer, since both rear wheel spin at the same speed, so there's one only direction they can go.

Imagine a person in a wheelchair. If he rotates both wheels at the same speed with his hands, he will go forward. If he rotates one less than the other, he will turn the wheelchair. The 917/30 is like the first situation. So to compensate for this, don't coast much the car, then the car doesn't have turning power and will understeer in one direction. Give it some throttle in lower speed corners and maybe a bit of coast, and then you'll turn better the car.

The porsche 935/78 in AC has rear semi-trailing arms suspensions. These aren't used in modern cars any more, or just in few occasions. Is because they don't offer a good ride and handling compared to multi-link and double wishbones suspension, which come in your typical vehicles and can indeed corner faster in some corners because they have better stability and are more planted, due to the suspensions and other components of modern cars.

Read this about your 2013 audi ttrs:

"First and foremost, you have Audi’s famed Quattro system keeping the wheels at their optimal traction levels through the twist. Up front, you have a 5-link independent steel spring suspension and on the rear, you get a trapezoidal-link independent steel spring suspension. This suspension setup is a little dated, but toss in the Audi magnetic ride with Sport button and 10 mm (0.39 inch) lowered chassis and you get a car that sticks to the road like week-old road kill – yeah, that’s a good thing."

Now you tell me after that description if it doesn't make sense your modern car handles better and safer than 40yo racing car technology, built for the high speeds of LeMans.

[Erik]

Originally posted by Kondor999:

Look at this footage:
https://www.youtube.com/watch?v=1SigpkdFZCQ

The guy is barely able to creep through the Hotzenbach section of the Nordschleife in the 917/30 at what looks to be around 30-40mph! Even FWD hot hatches can do far better than that. This cannot be realistic.

https://www.youtube.com/watch?v=YHocr7zF1rc

The 917/30 can easily do better than that if you now how to drive it. Like quf said, don't go coast too much. Also moving the brake balance to the rear helps a lot.

[Kondor999]

Originally posted by Nakadai:

ahem....

https://www.youtube.com/watch?v=jycYKFJKcng

Are you joking? That video *exacty* proves my point. The guy is understeering off the road all over the place, even in high-speed sweepers. Sure, the Moby ♥♥♥♥ is optimized for straight-line uber alles, but Le Mans has plenty of twisty sections as well that this car, as currently modeled, couldn't negotiate faster than a family sedan.

[Kondor999]

Originally posted by quf:

The 917/30 has a spool rear axle. Which means both rear wheels will rotate at the same speed. Is not like cars with differentials where to help cornering you have one wheel rotating less than the other. Is like this in the 917/30 to help better with traction when you pull out of corners. The problem with this is that if you coast the car at lower speed corners you'll suffer understeer, since both rear wheel spin at the same speed, so there's one only direction they can go.

Imagine a person in a wheelchair. If he rotates both wheels at the same speed with his hands, he will go forward. If he rotates one less than the other, he will turn the wheelchair. The 917/30 is like the first situation. So to compensate for this, don't coast much the car, then the car doesn't have turning power and will understeer in one direction. Give it some throttle in lower speed corners and maybe a bit of coast, and then you'll turn better the car.

The porsche 935/78 in AC has rear semi-trailing arms suspensions. These aren't used in modern cars any more, or just in few occasions. Is because they don't offer a good ride and handling compared to multi-link and double wishbones suspension, which come in your typical vehicles and can indeed corner faster in some corners because they have better stability and are more planted, due to the suspensions and other components of modern cars.

Read this about your 2013 audi ttrs:

"First and foremost, you have Audi’s famed Quattro system keeping the wheels at their optimal traction levels through the twist. Up front, you have a 5-link independent steel spring suspension and on the rear, you get a trapezoidal-link independent steel spring suspension. This suspension setup is a little dated, but toss in the Audi magnetic ride with Sport button and 10 mm (0.39 inch) lowered chassis and you get a car that sticks to the road like week-old road kill – yeah, that’s a good thing."

Now you tell me after that description if it doesn't make sense your modern car handles better and safer than 40yo racing car technology, built for the high speeds of LeMans.

Ok, to be clear, I know exactly what a spool/locked diff is, and how it affects handling. My complaint is that the 935 doesn't allow you sufficient adjustability in the suspension geometry to mitgate the low-speed understeer this causes. I refuse to accept that the real 935 didn't allow toe-out (or "negative toe-in"). I think it's an oversight by the devs in this case.

I also know exactly what a semi-trailing arm rear suspension is, since I've had a 1980 BMW 320i, a 1981 323i and a 1983 318i that all used it. I've also driven a Porsche 944 with this type of suspension.

And...I have no idea why you're mentioning it, because this type of suspension (which is basically an improved swing-arm type with less camber change) actually tends to produce snap lift-oversteer (believe me, I've experienced it first-hand). Which has precisely nothing to do with the AC 935's unbelievable understeer.

The car, as modeled, feels totally different to the excellent Fabcar 935 in Raceroom, for instance. Yes, that car too has a locked diff and Yes, it too has pretty bad understeer. But you can adjust the suspension in ways that AC doesn't allow. And before you try to impugn that cars versimilitude, it turns laps that are within just a few tenths of the real Fabcar 935.

I've since talked to a friend who has a 1979 930 Turbo (he's a surgeon lol), and he confirms that he can adjust toe-out on the front suspension, Given that the 930 is a vastly less sophisticated road-going cousin of the 935, and they both have the same front suspension type (struts), I'm just *not* buying that a Le Mans-winning race car doesn't have suspension that's as adjustable as the road car it was derived from.

[quf]

What do you mean the in game 935 moby doesn't allow toe change? In the setup for the front it allows -0.28 to 0.22 and for the rear -0.42 to 0.31. These are live values, so it won't be a fixed toe degree, maybe depends on what surface bumps the car is positioned in.
And it does have oversteer, but on acceleration.

[Cheese is Life]

Originally posted by INDIANA ELI:

it's a game

Bad bad answer.

[Kondor999]

OK, nevermind. This was all my fault. Despite owning AC for well over a year now, I never realized that the settings for alignment were reflected in the box on the right of the setup screen. As a result, what I thought was negative toe-in (ie toe-out) was actually maximum toe-in!

In other words, I was exacerbating the understeer by dialing in a lot of front toe-in. I thought that, by clicking (-) for Toe, it would give me greater negative toe-in (confusing, I know). Instead, clicking (-) actually results in greater positive toe-in. Which is the last thing this car (or any other with a locked diff) needs.

Bottom line, I just went in, set my Front Toe to about 20, which results in Front Toe of -0.17. And Guess What: Car handles way better now, pretty much just like the Fabcar 935 in Raceroom.

Suffice to say, I've never been more happy to get something wrong!

[Drisq Kivuli]

Glad you realized your mistake. You should be a pro, if you can navigate Racerooms complicated FFB menu then setup up a 40 year old race car shoud be a piece of cake! j/k

I like the Raceroom demo alot although I am still trying to dial in FFB. I am amazed how in depth the FFB setup is, very interesting.

[Simon said EAT DUST PLAYER_1 !]

Originally posted by Kondor999:

In other words, I was exacerbating the understeer by dialing in a lot of front toe-in. I thought that, by clicking (-) for Toe, it would give me greater negative toe-in (confusing, I know). Instead, clicking (-) actually results in greater positive toe-in.

been there, done that!

Which is the last thing this car (or any other with a locked diff) needs.

Bottom line, I just went in, set my Front Toe to about 20, which results in Front Toe of -0.17. And Guess What: Car handles way better now, pretty much just like the Fabcar 935 in Raceroom.

Suffice to say, I've never been more happy to get something wrong!

what's better than free stuff?
useful free stuff!
thx for the heads-up on locked-diff setup-basics :D