Is Suspension Tuning Backwards? - A Test with RX-8

[Tekk]

Very, very interesting topic. But until now, I could only conclude that GT4 has an extremely complex physics engine. I was thinking if there's anyone we can contact at PD that can give us a few explanations about this matter...

 

[Vorian]

I meant to bring this up - perhaps its a flaw with the pure-racing suspension, and not the sport or semi-race?

I bought a Toyota Supra last night, and equipped it with the semi-race suspension. It understeered slightly, so I increased the front spring rate, like I had done before.

It did not fix the problem, and it may have made it worse... but I was tired & went to bed.

Ive been tuning my supra for a while now and it still understeers. I used max rear downforce and about half up front. I also set the front soft with the back stiff and that helped a little. I maxed out TCS/ASM also and set the to 1/-1. See if that helps at all.

 

[awdrifter2]

Deleted.

 

[sukerkin]

Ive been tuning my supra for a while now and it still understeers. I used max rear downforce and about half up front. I also set the front soft with the back stiff and that helped a little. I maxed out TCS/ASM also and set the to 1/-1. See if that helps at all.

Hi Vorian

I don't know if you've already tried this but to get more oversteer (less understeer) at high road speeds you need the Rear Downforce not to be greater than the Front by more than roughly twenty percent. In other words, reducing your rear downforce a tad may be of assistance to you.

This isn't really the thread for specific model tuning discussion tho' so I won't digress off topic any further

 

[Vorian]

Thanks for the tip sukerkin.

I also have a thread related question about suspension. I have read that for more rwd cars you want stiff rear and softer in the front. Would that remain the same for a fwd car or would the opposite apply for soft rear and stiff front?

 

[Greyout]

in real life, a FWD car is more prone to understeer, so FWD setups generally have softer rates up front and stiffer rates in the rear.

RWD cars understeer less, so the bias is not as strong, but some RWD cars still have a rear-stiff-biased setup.

it seems the complete opposite is true in GT4

 

[Nelsy]

i'm using the N3 Tires, and have aids off.

 

[///M-Spec]

RWD cars understeer less, so the bias is not as strong, but some RWD cars still have a rear-stiff-biased setup.

Nearly all BMWs are like this, even with their 50/50 weight distribution. A typical BMW progressive rate street spring is almost twice as stiff in the rear as in the front.


M

 

[Greyout]

keep in mind that its also a question of spring rate vs. wheel rate.

In the Strut setup in the front of a BMW, the springs/damper assembly attaches to the hub. In the rear, the attachment point is probably somewhere further up the control arm. (I'm assuming, but really don't have any idea...)

That can affect the final result of spring stiffness X.

I'm sure that GT4 didn't factor that in very accurately, if at all though (maybe just a broad compensation, but not vehicle specific)

 

[Pontiac Le Mans]

Sorry, I didn't update that post. This is my newest settings
91 Nissan Skyline GT-R N1

Mods:
Full Mod + Wing
R3 tires

Brake Balance f20/r12
spring rate f15/r5.8
ride height f76/r76
shocks f10/r1
camber f4.0/r0.0
Toe f1/r-4
stabilizers f1/r7
asm oversteer = 0
asm understeer = 0
tcs = 1
down force f30/r32
LSD Stock
Trans set
Auto set at 10
VCD 10
Weight Balance 0/0


Edit: put on stock LSD, much less understeer and ezier to drift now.

I hope that what I will say here doesn't sound to brutal. If it does, sorry, that is not my intention. But my English is rather bad (I'm a dutch and french speaking Belgian), so I don't always find the nuances in English.

When seeing this setup again, I think it doesn't permit us to come to conclusions. All setup guides insist that your settings should be consistent, without extreme differences. This is exactly the opposite of what we see above. shocks 10/1 ; soft shocks and springs r with s7 bar, etc. ;
The too heavy toe out in the rear and the (too heavy bar) is what I would put on such a car to make it deliberately oversteer.

I tried to setup some cars this weekend (Ginetta, Alpine A 310 which both give some problems to some players as you can see in other posts here) using my GT3 experience. It's true that GT4 is more sensitive than GT3, but the base rules of tuning didn't really change. Little testing was needed to make them both behaving "correctly", although they will always keep their specific behaviour: the Ginetta is such light that jumps (Capri, Seattle) are tricky; like all RR cars, the Alpine A310 (as the A110) is "tail-happy" (especially in fast corners), just like it is in real life. You'll have to adapt your driving style, don't try to drive it like a Lancer.

The biggest change, in my opinion, is that while it was possible to obtain good lap times with "unrealistic", incoherent setups in GT3, this won't be possible anymore in GT4: nearly all posts on this setup subforum start from questions from players who have a problem with a car. If you look at their setup, you see immediately that it is incoherent.

I would say: good point for Polyphony.

And finally, to come back to the question whether a setup can be too soft on one side of the car or not. I'm quite shure that in real life, if the setup (springs and shocks is too soft), there will be too much body-roll in fast corners, which means that that side of the car looses grip. Consequence: if it's the back, there will be oversteer.

 

[///M-Spec]

keep in mind that its also a question of spring rate vs. wheel rate.

In the Strut setup in the front of a BMW, the springs/damper assembly attaches to the hub. In the rear, the attachment point is probably somewhere further up the control arm. (I'm assuming, but really don't have any idea...)

That can affect the final result of spring stiffness X.

I'm sure that GT4 didn't factor that in very accurately, if at all though (maybe just a broad compensation, but not vehicle specific)

That's a solid point. The attachment point would definately affect the effective wheel rate... but typically the mounting point for the rear spring assembly is only a couple of inches in board on a separate carrier. I doubt it'd be enough to affect much of a difference... though admittedly, I have never sat down to calculate the motion ratio, etc..

Here's a typical setup from the new 3-Series.


M

 

[awdrifter2]

Deleted.

 

[Pontiac Le Mans]

OK, I'm far from home now ( I work at about 250 kms from my home and are only at home in the weekends). So I can't really try it out now, but will do it this weekend.

 

[awdrifter2]

Deleted.

 

[Greyout]

And finally, to come back to the question whether a setup can be too soft on one side of the car or not. I'm quite shure that in real life, if the setup (springs and shocks is too soft), there will be too much body-roll in fast corners, which means that that side of the car looses grip. Consequence: if it's the back, there will be oversteer.

The body roll is limited to a certain point by suspension travel. The car will behave normally until the suspension hits that point.

even if there was a point in GT4 that something happened to the suspension, many progressive tests have been done to indicate that the physics is simply flawed.

 

[Bad760]

I had to register on this site just because of this thread.

Here is what I have found,

In all of the cars I race, M Coupe, Cleo V6(MR), & Focus I have been able to get, or get rid of a specific trait (understeer, oversteer) with the normally accepted real-world adjustments for the various drivetrain configurations.

I do limit my adjustments to 0.1-0.5 at a time for the spring rates, it only makes sense to not go overboard on the adjustment.

Seeing this 'discussion' (turned into more of a flame war) I will do some actual testing with some setups that resemble the extreme ones I have seen in this thread, I will be using the brandnew M3 GTR that I won last night (I'm never going to buy an RX8 or any other rotary).

Now looking at a real world example, I race 1/10th scale RC touring cars at a national level.

Now I can tell you that when I put the hardest springs on the front and softest on the rear I most definitely get oversteer turning into and mid corner as the rear of the car wobbles around with such soft spring rates, but bad understeer out of the corner as the car squats and loads up the rears. I can't easily explain that as my understanding of roll and pitch moments and moving roll centres and roll axis isn't 100%.

But I dare anyone to tell me that I am somehow changing realworld physics to do that.

With a stiffness bias to the front the car is very responsive to initial turnin but will push badly after that unless you put it and keep it in a slide, which is only really possible with a stiff rear swaybar.

Anyway those are just my thoughts until I do some more fiddling on GT4

 

[awdrifter2]

Deleted.

 

[Jaberwocky]

I've notice that cars dont necessarily behave textbook in GT4.

It takes more tinkering to get a car right. Slaming the ride height down usually isn't a good idea, nor is running a super stiff suspension. The game is also very sensitive to suspension changes, so a huge change sometimes have weird effects.

 

[Bad760]

This is what I found in GT4 also. Stiff front/soft rear = oversteer. How did you get rid of the understeer during exit of the corner in your RC cars? Thanks.

I don't actually run very stiff front and very soft rear springs on my RC car, I was just giving an example to show that wild oversteer can happen using that kind of setup.

The only setting to change to get rid of the on-power corner exit understeer in the RC car that you can change in GT4 is to stiffen up the rear springs.

The other adjustments on the RC car are (assuming relatively realistic spring rates front to rear), tighten up the front diff (they are 4WD), increase front toe-in, decrease rear toe-in, use some anti-squat in the rear, and raise the rear roll centre.

The setups that Maturin and others have posted with the rear way softer than the front most definitely will give oversteer, as I have confirmed with my real-world example, but these wildly different spring rates are way outside what would normally be used on a car, except for the odd exception and weird circumstance, which usually means that what we normally expect to happen quite possibly won't.

Now i won't say anymore on the subject until I have done some tinkering myself on GT4 least i put both my feet in my mouth

 

[awdrifter2]

Ok, thanks for the reply.

 

[sukerkin]

It's good that we're getting some opinions for the 'Traditionalist' School of tuning in this thread now. It makes for more of a balanced discussion and hopefully will assist in making the point that sometimes with suspension tuning there is no "Right" answer, only what works for you.

I'm particularly pleased to read Pontiac's and Bad760's contributions as they have voiced opinions that I personally hold (it's always hard to be objective when someone is using an arguement you agree with ).

Because I'm busy with work right now, I've not been able (still ) to wield a spanner in anger on GT4 but it's looking hopeful that my hard-won tuning 'expertise' (such as it is) will not be null and void with the GT4 physics engine after all :sigh of relief:.

Oh and a final point, M-Spec, the Installation Ration (which is what makes the Wheel Rate and the Spring Rate different measurements) can actually be quite significant - however, in-game, I've always worked from the assumption that the IR is 1. This was for two reasons:

1) We just don't have the necessary data to calculate an IR for a GT car
2) It makes the equations easier

 

[///M-Spec]

Oh and a final point, M-Spec, the Installation Ration (which is what makes the Wheel Rate and the Spring Rate different measurements) can actually be quite significant - however, in-game, I've always worked from the assumption that the IR is 1. This was for two reasons:

1) We just don't have the necessary data to calculate an IR for a GT car
2) It makes the equations easier

I trust you and Greyout on this. But given the typical BMW has progressive rate springs twice as stiff in the rear as in the front, I'd be surprised to find that the effective wheel rate ended up being the same or with the front being stiffer... but then again, most BMWs are tuned to understeer and have signifigantly stiffer front bars, so perhaps you guys are right.

EDIT: I ducked under my car last night just for grins and giggles and visually noted the rear spring carrier is maybe an inch or so from the hub. (couldn't get a tape measure in there... stuff is packed too tight) So if you want to plug it into the formula and prove me wrong, go ahead


M

 

[sukerkin]

Mmm ... Installation Rations ... yummy

That should, of course, be Installation Ratio .

The very stiff rear springs on a BMW are probably to rein in the massive camber changes that occur in (some of) their rear suspensions during cornering.

 

[///M-Spec]

You are thinking of the older E30 style semi-trailing arm suspensions, my friend

Camber and toe control is quite excellent with their modern multi-link (4 and 5 links.. one just for toe) rear suspensions. They are practically unequal length a-arms at this point.


M

 

[sukerkin]

Astutely observed sir - yes, that is indeed the suspension type I was referring to.

As an aside (nearing OT so my apologies) here's a very interesting, if short, discourse on suspension types and characteristics:

http://forums.autoweek.com/thread.jspa?forumID=16&threadID=8032&start=15&tstart=60

 

[///M-Spec]

It's not often I prove myself wrong. But it happens on occasion. I did some looking around and discovered amoungst club racing circles, the ratio of spring rate to wheel rate for a typical E36 chassis running stock geometry is agreed to be roughly 46%. Thus makes the effective wheel rate for front and rear very, very similar... on the E36, which is about as typical BMW as you can get.

Color me surprised.


M

 

[Duke]

It may fit the formulas, but I think assuming an MR of 1 is a bit messy. Spring rates can vary hugely by car, when one would assumes a fairly consistent range of ideal wheel rates for a given type and weight of car.

For instance, the Neon ACR's Mopar Performance hi-rates are around 225#f / 185#r, with extra-hi rates at 310#f / 230#r. A Mk III Golf might run 300#f / 350#r spring rates for a good handling setup. On a Civic Si Coupe the going rate can be as high as 500#f / 600#r.

These are all ~2500-pound FWD cars with ~150 hp. I'm simplifying quite a bit, of course, but obviously the motion ratio can vary widely due to the suspension geometry.

 

[sukerkin]

I quite agree Duke but thinking in terms of how a programmer would go about coding the IR (Motion Ratio is a synonymous term), in a game where you have no control over the suspension geometry, it was not unreasonable to assume that they would 'Black Box' it (that the output of the IR (if modelled) was reflected in the Spring Rate). However, I also had to assume that all suspensions were modelled as McPherson Struts and that only Linear (non-Progressive) springs were used :faints:.

In other words, if you want to apply real world suspension equations to GT cars then you had no option but to simplify and assume that the Spring Rate is equal to the Wheel Rate (i.e. that the IR is 1).

Of course, in the end, I abandoned my work on trying to mathematically model the GT physics engine due to there being far, far, too many unknowns.

 

[Pontiac Le Mans]

Hi Bad760, welcom on GTnetwork.

I think you make a very important point in your first contribution: setup changes shouldn't be very "huge": 0,1 to 0,5 changes at a time are much better.

Another thing I'd like to say is that the most important thing is the "coherence" of the different settings. I'm not surprised you observed in "real life" that a car with a too soft rear suspension oversteers: a spring setup is the search for an compromise between stiffness and softness. To stif: your wheels won't stay on the ground, so you loose grip: bad. To soft: in corners (especially in fast corners), too many weight will be transferred to the outside to the outer tyres: so you loose grip again. The best compromise to find is the one where (i) the wheels stay on the ground (means: not too stiff) and (ii) there doesn't go too many wheight to the outer wheels (means: not too soft).

When I say "coherence", I also mean that you should avoid settings of the kind f10/r1.

I must say also that I'm very pleased with the comments of Sukerkin. I consider him as one of my "teachers". The over 150 printed pages workshop on gtbythenumbers made me understand what tuning is. The confrontation between different opinions in that guide was very positive. On many occasions, I had to find it out myself. So, I went to other websites to find more information, etc.

If you read French, have a look at my website, where I put my GT3 tuning guide.

http://perso.wanadoo.fr/plmgt

Oh yes: it needs an update. Don't look at the toe-in / out part: I mixed it up, but the GT-value recommendations are correct.

 

[Shoes_98ls]

The body roll is limited to a certain point by suspension travel. The car will behave normally until the suspension hits that point.

even if there was a point in GT4 that something happened to the suspension, many progressive tests have been done to indicate that the physics is simply flawed.

this is what im starting to think as well. I believe that PD may have used a pendulum style phycics engine...

why do i say this?

well it all has to do with that damn G-meter at the bottom of the screen, which i might add is TOTAL inaccurate compared to RL. If you go into a corner, lets say a right turn for the sake of discussion, the ball in the meter will swing wildly to the left of the screen... ok thats true to real life, other than the fact that you can pull 1+Gs on almost any stock car with N1-3 tires.

I THINK what im starting to see is the car acts like a little weight on the end of a string. you turn the car in, the "string" will swing to one side, and stay there regardless of how fast or slow you are going.... however, once you get on the gas to rotate some thru the corner the "string" will stay in the same spot.. why it does this im not sure, and it seems to do it more with rwd, vs fwd, for some reason.

really the only way to consistantly get the rear end out on a car is to feint into a corner... regardless of entry speed, or the angle of the turn.

this, to me, shows the pendulum style physics engine. Think of the "string's" movement, agian in a right turn, if you were to feint into the corner. It would swing to the right (towards the apex of the corner) and then accelerate all the way thru the neutral (strait up and down) and left most position it would reach. perhaps this is how the decided to emulate weight transfer?

agian, im not to sure of this myself, so im going to go test it out some more...

please feel free to call me an idiot