| ANTI ROLL BAR TUNING FOR FORZA MOTORSPORT |
| Anti roll bar tuning is actually pretty simple in theory. The most important thing to know, in order to grasp the concept, is understanding that the vehicle itself (under the influence of centrifugal force) transfers energy. The energy is the lateral weight transfer from left to right and right to left. |
| Anti roll bars do absolutely nothing to affect vehicle pitch, which as you hopefully recall, is vehicle weight transfer forward (dive) and rearward (squat). But anti roll bars are the key tunable component for balancing oversteer and understeer when we're discussing lateral acceleration. |
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| The most simplistic understanding of ARB tuning lies in grasping the following: |
| Stiff front bar = More understeer and more tire loading Soft front bar = Less understeer and less tire loading |
| Stiff rear bar = More oversteer and more tire loading Soft rear bar = Less oversteer and less tire loading |
| The stiffer the front bar, the more the front outside wheel is loaded while cornering. The wider and stickier the front tires, the more grip they have, and the stiffer the front bar you can run. You’ll know you have too stiff a front bar when the car starts pushing (understeering) on corner entry. This means the front outside tire is overloaded and is breaking traction. |
| Softening the front sway bar transfers less weight to the oustide wheel, and reduces the load on the laden front tire during cornering. The good part of softening the front bar is that the car will turn in better. Keep in mind that softening the front bar also increases body roll (bad) and increases dynamic camber change (also bad). |
| The stiffer the rear bar, the more the rear outside wheel is loaded while cornering. The wider and stickier the rear tires, the more grip they have, and the stiffer the rear bar you can run. You’ll know you have too stiff a rear bar when the car is loose (oversteering) on corner exit. This means the rear outside tire is overloaded and is breaking traction. |
| Softening the rear sway bar transfers less weight, and reduces the load on the laden rear tire during cornering. The good part of softening the rear bar is that the car will be less tail happy when you apply the throttle on corner exit. Keep in mind that softening the rear bar also increases body roll (bad) and increases dynamic camber change (also bad). |
| MID-CORNER BALANCE |
| In mid-corner in a steady-state condition you may experience oversteer or understeer. This is most prevalent in double apex turns and long sweepers. When the steering angle is fixed and the car is on the proper racing line: |
| If the back end gets loose - soften the rear ARB If the front end starts to push - soften the front ARB |
| TUNING ARB STIFFNESS FOR TRANSITIONS |
| Once you have the vehicle in balance and you start to test and tune on different tracks, you can easily adjust the roll stiffness to meet the variety of track conditions. |
| Keep in mind a stiff car (stiff springs, stiff shocks, stiff ARBs) transfer weight faster, which means they require less aggressive steering inputs to change directions. The car is more responsive and takes a set faster (both good) but if the car is too stiff the car will understeer on corner entry (bad) and can be twitchy, slide around a lot, and be difficult to control over bumps and surface undulations (all bad). |
| A soft car (soft springs, soft shocks, and soft ARBs) transfer weight slower, which is bad for tracks that have a lot of quick transitions like esses, and chicanes. The softer springs are good for tire compliance which is essential for keeping the tires in contact with the road. But generally speaking, ARB’s that are too soft make the car sloppy, mushy, and slow to take a set. |
| This condition is most noticeable on a track that requires quick steering inputs from right to left, my favorite examples are the back stretch at Maple Valley, and the ‘esses’ at Road Atlanta. What happens with a soft set-up in these sections is pretty simple if you sit and think about it: |
| You turn the wheel right and the car responds. The vehicle is leaning left, the left side suspension is in bump, and the right side suspension is in droop (rebound). If the ARBs are soft, the body is rolling a lot and the suspension is traveling a lot, too. Now you turn left, but the car doesn’t comply to your steering input. You sit there and blame the game, maybe you throw the controller and wonder what went wrong. |
| The problem is the car is rolling too much, the suspension is traveling too far, and the softer the set-up the more time it takes for the weight to shift from the left side to the right. You need to understand there’s a delay from the instant you turn the wheel to when the car actually takes its set. Your brain is registering that you turned the wheel, but the vehicle weighs 2,500 lbs or so and it takes time to make an object that heavy traveling at high speeds change directions because of the law of inertia. |
| When it comes to tuning for transitions ARBs are your best friend. We can do it with springs and shocks but that’s not the best option. Stiffening the spring/shock combo messes with tire compliance and dynamic camber. |
| Let’s say you have the ARBs in balance: the front is set to 12 and the rear is set to 22. If the car is rolling too much in transitions and lacks responsiveness, you want to stiffen both ARBs proportionately to not disrupt the oversteer/understeer characteristics. Increase the front 10% to 13.2 and the rear 10% to 24.4 or you can try to move them in unison buy increasing the front bar from 12 to 14 and the rear bar from 22 to 24. Try it both ways and see which one works for you. Then take it out to Maple Valley and run it on the back stretch. Keep stiffening the ARBs until you can run the car through the chicanes coming down the hill WOT (acronym) without having to lift. |
| TUNING ARBs FOR HIGH SPEED CORNERS |
| Shaving time off laps is about figuring out spots on the track where you can run WOT without lifting. Stiffer ARBs aren’t just good for reducing body roll for transitional response, but can be used to maximize the tires’ cornering force in the high speed turns. If there are certain high speed corners that you feel you should be taking at full throttle but find yourself running out of track and having to lift off, stiffen both bars in proportion to transfer more weight to the outside wheels. This will increase your grip and maximize the amount of cornering force your tires can generate. |
| Turns that come to mind that you can use to test and tune on, are: |
| Turn 1 at Sunset Peninsula 'The Kink' at Road America (Turn 11) Turn 14 at Suzuka Circuit (the legendary 130R) The Nurburgring (Too many fast corners to list) |
| BALANCE - TUNE THE END THAT NEEDS IT |
| Basically, there’s really no such thing as corner entry oversteer (at least that's what Carroll Smith says). If you're lifting off throttle and the back end is stepping out as you roll into the turn, the decel on your LSD is too low, so it's not your sway bars. And generally speaking, if corner exit understeer is is an issue under power, you can probably fix it by increasing the acceleration setting on the LSD. |
| That said, we're usually dealing with understeer on entry and oversteer on exit, and this is where the ARB can be your best friend. if the front end of the car is pushing into the corners, tune the front of the car and soften the front bar to get the turn in you want. If the rear end of the car is loose and stepping out in the back, soften the rear bar. |
| The moral of the story is this: If Carroll Smith says fix the end of the car that's giving you trouble, who are we to argue? |
| INITIAL SETTINGS |
If you're looking for hard and fast rules in regard to initial settings for sway bars, sorry, I can't help you. The best I have is a philosophy which I 'borrowed' form the experts who wrote the books I've read. My personal preference is medium to medium-soft springs and a lot of sway bar. Right now I've been working on tunes for lightweight A and B Class cars since picking up Forza 4, and my initial observations are that these light cars like a lot of ARB, which makes sense. Heavy cars load the tires with their weight, while light cars don't load the tires as much, especially cars like the S2000, Lotus Exige/Elise, and the MX-5. So we're relying on sway bars to load the tires to compensate. I know that last time around (Forza 3) I was using vehicle weight distribution as a baseline, and at this point I'm not sticking to it as a hard and fast rule because it doesn't always apply. As far as tuning calculators go, I'm not buying into that either. I've been dealing with real cars the last few years, and the general rule with RWD cars is more spring and/or sway bar in front, regardless of weight distribution to keep the back end happy when applying power out of the corners. The Exige, for example has a 43%-57% weight distribution and if I were to go the 'math' route, if I were running 1000in/lbs of total spring, it would be 430 / 570 front-rear. I'd also be running less sway bar in the front as well. Well, I'm doing noe of that. My 1000in/lbs of spring I'm running 650 /350 and 37/37 on the ARBs and the car feels amazing driving with no assists. People have said the Exige is a pain to tune, but not really. I tried going the math route and the car felt like dogshit. My advice is build your car up to whatever PI index you want, and then run the default settings. Put in some laps, get a good feel for the car and then use your knowledge to make the adjustments you need. |