How to combat terminal oversteer/understeer?

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Hello everyone, I need some advice for how to combat terminal oversteer and understeer.

Currently I’m building a Porsche 911 style car using the 1975 coupe body. It’s a rear engine, RWD 3.0L boxer 6.

But, I have this consistent problem. Usually, at medium to high speeds (~50-100MPH+); my car terminally oversteers, wobbles side-to-side and I lose control.

At low speeds even with the throttle floored and the wheel turned all the way, the car has extreme understeer to the point of where I have difficulty going around a small corner in the West Coast USA map without understeering into the sidewalk.

I have tried using the engineer’s advice in the game and increase rear grip by increasing rear tyre width, but it only barely makes a difference with the oversteer; and actually makes my understeer much worse. It feels too linear.

I have not tried messing with any other handling settings because I don’t know what will work.

Does anyone know how to fix this?

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Tyre Stagger, Suspension tune, Aerodynamics.

There’s a bunch of ways to go about it. It’s just experimentation

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A boxer6 is a pretty heavy engine layout, and mounted at the rear of a short wheelbase fairly light car is very hard to tune for. The flip side of the coin however is more even brake loads front to back, and if your rear wheel drive more traction to accelerate.

The thing that will have the biggest impact is your tyres, wider at front will increase oversteer, wider rear will increase understeer. 40% profile provides full traction, and there is a increasing reduction in forwards\braking grip as you go lower, however lower profiles will improve cornering grip slightly.

Next Suspension, the tooltip “I” on the far left of the lower bar will explain this, Killrob also has a decent recent youtube video if you want more details. As a note not covered in that video, keep your beamNG car springs and dampers reasonable or even a little soft, being very hard will result in highly elastic body flex. There is also currently some minor issues with solid axles, but I don’t think your car is likely to be anything but independent.

Finally if you can make it handle right at low speed, but not at high speed, adding aero can allow you to tune the high speed handling in alone, but adds drag. A more front llps\wings or higher front angle will increase oversteer, more rear wings\wing angle the inverse. The actual size of lips, spoilers and wing fixtures used makes no impact, so you can keep it subtle and still get the handling you want.

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Rear-engined cars are quite different to the other formats due to the extreme rear-biased weight distribution. Most of the early Porsches were what we’d consider now a real handful to drive, particularly due to the rapid jump in engine performance and mass, and most of their advantages lay in the mastery of the lift-off -> power oversteer. They were particularly hairy under hard braking.

One of the issues here is that while the handling model for most cars within reasonably common limits is quite good, it’s hard to say how accurate they are at the extremes of power, weight distribution etc… If you compared this to another car at low speed without absolutely caning the throttle, does it feel similar or does it feel that the front is too light and there’s not enough friction in the front wheels? What’s the low-speed corner speeds really like? High tyre stagger will definitely make the car understeer more at low speed, but to really test what its limits are, since effective friction actually reduces when the tyre loses traction, you’ll have to find the balance where there’s no understeer to really test how fast it can corner.

As for high speeds in a rear-engined car, I’m also at the point where I can’t tell whether it’s the model or it’s my tuning or a combination of both that limits me from being able to consistently tune an MR car that can turn both slow and fast. As a general rule the stiffer your suspension the twitchier and more responsive it is but depending on the geometry and the tyre and the loading, too stiff and the wheel will either be overwhelmed or lose contact with the ground and that will limit grip (front) or make the car very nervous (rear). Not going overboard with rear swaybars and rear spring rate helps keep the car a bit slower and more predictable (within reasaon).

I haven’t worked out the relationship between the downforce and cornering performance or the high speed graph in Automation. IIRC downforce in Beam has been iffy up to this point and my impression is that it’s still not fully working yet, or the model is too simple and reacts funny in certain situations. I’m no expert on the actual code, though, so don’t take my word for it, but what I do know is that the values given in Automation and the behaviour at high speed in Beam still don’t match sometimes.

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One particularly helpful tip I found: reducing front camber and/or increasing rear camber induces understeer, while increasing front camber and/or reducing rear camber causes oversteer. However, excessive camber will lead to a significant increase in tire service costs.

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This may sound counter-intuitive, but try narrower tires. I was able to fix the dreaded “high speed death weave” on my fast MR cars by doing this (oh god! it’s weaving under throttle at speed! i’ll just ease off the throttle… woops. now I’m pointed backwards, or spinning wildly towards certain doom). I’m not sure why this is going on, maybe a tramlining effect?

Any RR car will understeer at full throttle unless it has enough power to instantly blow the tires off or the rears are already sliding. So part of your problem may be understanding weight transfer and vehicle dynamics? And part of it may just be the car’s natural dynamics, I’m having a hard time adjusting my 3.5V8 RR not356, too…

Generally speaking, increasing roll stiffness (shocks, springs, antiroll bar) will decrease grip at that end.

This is probably a different animal, but I have a 1600cc boxer 6 in that (75 not911) body style. Handling preferences are personal, but I like the way this one drives. (I drive on a wheel, no idea how it will do with other input types). It’s completely analog (no ABS, TCS), I’ll post it here if you’d like to try it for comparison.

NG Rallysport - street v2.car (22.9 KB)
road car
edit: woops. this one’s not analog, but I like it better with the tcs off.

NG Rallysport - street turbo.car (22.9 KB)
road car with turbo

NG Rallysport - test.car (22.5 KB)
dirt version
edit: also has tcs, my bad. I like this one with tcs off, diff locked. This would make a car awful in RL, but not in BeamNG

edit to add: My method: Hard on the brakes before the corner, get your downshifting done in a straight line. Still off the throttle, or lightly trail braking, tip it in towards apex. Control rotation with throttle/brakes as necessary. If it’s oversteering, add throttle to shift the weight back to the rear. Once the car is mostly rotated (hopefully near apex if you’ve done it right), roll back into the throttle. No amount of throttle will unstick the rear at this point, but the front will go lighter the more throttle you add. When it’s pointed where you want it to go, let 'er eat.

Hope that helps.

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Narrower tyres overall helps: the wider the tyres (at low profiles especially) the more sensitive they are going to be to: 1) changes in load 2) tyre wall deformation. I’m with Obfuscious here in that I’m not sure that the sensitivity is yet appropriate (this was adjusted somewhat so funnily enough between the initial release and the patch the behaviour actually improved). Especially since hypercars like the LaFerrari are apparently really understeery at high speed, which they ought to be, and that has 335 rears.

I actually replicated a 1991 NSX: sure it only has 276hp for 1330kg or so, but it also has 225 rears and 205 fronts (at around 45-50 profile). It responds very predictably at all speeds and is wonderfully stable at 260km/h. Get much beyond that and things deteriorated significantly.

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Faster way: tyre width. Add more width in the axle that has problems.

Other way is playing with the suspension setup, and with the power layout (FWD, RWD or AWD)

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Thanks everyone for the responses so far, it’s been really helpful. I also just found the Youtube video that the devs did on handling and suspension; so I’m sure that will help a lot as well.