Vehicle tuning help

I have my modified 200BX that can brake straight and has some slight turbo lag, but not enough to instantly overpower the rear wheels and spin out. if I turn under braking or under throttle, and I turn the wheel slightly, the car tends to want to spin out really quickly. Can somebody help with the vehicle stability problem I'm having?

 

How's your suspension setup ? There might be something wrong with it.

 

Well... spinning out under breaking and under throttle sounds more like your just being a bit to aggressive with your inputs, but I think I can help make it better anyways. Warning... there will be much fiddling involved so be prepared for that.

So first thing first... you have to asses what kind of car you are building as different racing disciplines require wildly different suspension setups (even with all the same parts) So like Race track racing, street racing, autocross, drifting, gymkhana, rally, rallycross... so on and so forth. Once you know exactly what your aiming for (which I am sure you already do, but this is for other people reading this) the fun can begin.

Now I will be starting here assuming that you are running 0 camber, 0 toe on all wheels... just keep that in mind.

Step one: Set your Ride Height.
In Beam this only really effects Roll Center and Center of Gravity height and (to my knowledge) doesn't really play a part in aerodynamics like it does in the real world (yet). So what you will want to do is set the car as low as you can while still clearing all of the bumps on the circuit at a moderate to high speed (roughly 60mph). If the car bottoms out at any point (other than maybe hitting large curbs) your going to want to lift it up a little bit. Keep doing this until you find your ride height. Take a mental note of the cars height, and then take it a few more adjustments up... this will make sense in a second.

Step two: Set your Spring Rate.
Now what your going to want to do is to lower your spring rate by as much as possible until you hit your desired ride height and the spring rate is just enough to hold it there. (this is probably gonna take some more laps around the track to make sure you don't bottom out) Tires are rather soft and can take a lot of the impact, but also have minimal damping in them. Soft springs allows the tires to move about while not upsetting the car. They also allow the suspension to soak up bumps rather than bounce over them keeping both the tires in contact with the road, and while applying as low force to launching the car upwards as possible. This may sound like it flies in the face of every race car you have ever known, but remember... most race cars are running a few centimeters of ground clearance (or less) around very smooth, well maintained circuits, so to maintain their ground clearance they have to crank up the spring rates to be very stiff. More than likely (unless your on a very rough track) you are going to be doing the same. If you decide to run even stiffer springs than this process gets you, you can actually lower the car even further (usually) and still be ok... remember to make sure you don't bottom out though as that takes weight off the tires and can cause you to lose grip very easily.

Step three: Set your Damping Rate.
Depending on what kinds of parts you are using, you may just have Damping... or you may have several different kinds of damping. I will speak purely from an overall damping perspective here.

In general you want your damping to be what controls the majority of the suspension movement and weight of the car in general. You want the suspension to absorb as much of a hit as possible, while still limiting the recovery speed of the suspension back to its intended ride height to limit or totally eliminate oscillations. Oscillations in the suspension can just as bad (or worse) as hitting bumps in the road... just your hitting bumps that aren't even there.

The general rule of thumb is lower damping will allow the suspension to react faster to bumps. Overall this means more grip (to a point) but if you really start pushing the car (much harder than 60mph) then you may not be able to cut enough energy out to actually absorb the bumps properly. Higher damping will absorb your bump energy much better, but it will act almost like a stiffer suspension. It will improve suspension reaction times, but will cause the car to skip about if you go with too high a setting. Again, will require some fiddling.

Something to follow though, lower front damping should help with turn in grip, higher front damping will help with turn in speed. Lower rear damping will help reduce oversteer snap (or in general) while higher rear damping will again improve handling response, but will make the car lose grip much more abruptly.

Step four: Set your Toe.
Now this is mostly going to be to your preference. I recommend no more than + or - 0.5 degrees total on any of these.

Front toe in will cause straight line stability, but when you go to turn in, its more likely that the car may understeer. Front toe out will make the car start to wander, but will increase turn in response.

Rear toe in will also cause straight line stability, but in a very different way. When you turn into a corner with rear tow in, it will feel like your rear is also turning with you (slightly) and helping you corner and keeping the car from oversteering as bad. Rear toe out will cause the rear to walk about and will induce oversteer when entering corners.

I usually run 0 degrees up front and 0.2 degrees toe in in the rear.

Step five: Set your Camber.
Setting your camber is all about cornering grip. Basically you always want the tires with grip to be leaning into the corner. Ideal camber will roll the car outwards just enough that the tire stands mostly vertical, but still slightly leaning into a corner as to place as much pressure on the contact patch of that tire as possible.

Again... I don't recommend more than + or - 2 degrees on either of these unless you are doing some EXTREAM cornering with some REALLY grippy tires that can take it.

Basically the more camber you use, the more grip you will get in a corner, but the less grip you will get in a straight line. That may sound kind of silly, but when you get into higher power cars, you need that grip in a straight line. You need everything you can get.

Remember though, if you use more camber than cornering ability that your car can produce, you will likely not roll all the way onto the contact patch while taking a corner and you will actually have less grip than with less camber.

Step six: Set your Sway Bars.
Now, other than tires, THIS will have the largest effect on how your car will handle and you may have to go back and tweak a few things after you adjust these.

The simple of it. The softer the front sway bar, the more turn in you have and more turn in grip you have. The stiffer the front sway bar, the more responsive your turn in will be, but the more understeer you will have. It will be very obvious. For the rear, the softer the rear is, the more grip you will have while turning. The stiffer the rear sway bar is the more likely the car will oversteer in a corner, but it will react quickly. Again, it will be VERY obvious.

You will want to run as soft of sway bars as you can while still keeping your vehicles roll under control. This will maximize your grip, but the car will want to lean. The further the car leans, the more grip it has, but it will only have that grip while it is leaned. On a track with long sweeping corners that don't have any chicanes, this isn't an issue as you can turn in slower and control the suspension through the steering wheel rather easily and response time isn't really an issue. On a very twisty track, you are going to need quick response times to go from left hairpin to right hairpin. This will require stiffer sway bars to keep the car from leaning and keep its weight under control. This will reduce your grip, but the overall response time will more than make up for it.

That was probably way more in depth than you wanted, but there you go.

 

I will mention that I am using a controller, and the car just doesn't like to turn at higher speeds, always resulting in sliding and oversteer, which becomes even more pronounced when downshifting and steering under light throttle (around like 10-25% throttle with turbos producing 5-9 lbs of boost at 5600 or so rpm) and braking (it brakes fine when going straight, but any sort of braking input upsets the balance. I lowered the tyre pressure from 30 PSI to 18 PSI, and that helped a bit.

I kinda want it to be a more street-focused car that can be taken out on track, so mostly for around medium speed or so corners.

yeah, is slightly confusing. I'm running the stock race suspension right now, should I adjust the differential too to help combat some issues like spinning out during downshifting?

 

If you are using sport tires like i always do, then the stock race suspension is actually too stiff. Like atv_123 said, try fiddling around with the suspension, make it softer, more "daily drivable".

 

Alright, so simpler explanation. For a race suspension to become a street suspension, do this.

1. Raise the ride height a little to deal with the bumps.
2. Soften the springs a bit (possibly a fair bit). This will help deal with uneven surfaces and help keep the tires on the ground. Remember, the more you soften the springs, the more your gonna need to raise the ride height.
3. Lower the damping rates a little. If oversteer is your issue, lower the damping in the rear a little more than you do in the front.
4. Set your toe to something around front 0 to 0.02 degrees toe in (will help with straight line stability and lessen sharpness on turn in) and rear 0.1 to 0.2 degrees toe in (or even more possibly... wouldn’t go over 2 full degrees though or else you will start to get wandering)(will help to keep rear from stepping out and will guide it back to straight)
5. Camber, as a street car, anything over 1.5 degrees in the front and 1 degree in the rear is probably excessive unless you got some fat sidewalls on your tires. So I would probably run something like 1.1 front and maybe 0.7 in the rear.
6. Sway bars. This is where you make or break everything. If you want less oversteer, soften the rear sway bar... potentially a lot. If you want more turn in, soften the front. Remember, this will reduce response due to increased weight transfer distance, but it will massively increase turning grip. If you want the inverse of these then just stiffen the sway bar, simple as that.

edit: I forgot to mention... there is an advanced wheel debug app where you can get your live camber and toe readings down to the thousandth of a degree. I recommend using that when setting your camber and toe settings as usually the sliders units don’t even get you close to what you actually want.