| TIRE TUNING FOR FORZA MOTORSPORT 3 |
| This ought to be a riot to try and figure out. The marketing propaganda coming from Turn 10 talks about improved tire physics and tire deformation. But we've been promised additional info about the subject that has not arrived yet. |
| The one bit of newness in regard to tires is the confirmation that in Forza Motorsport 3, we'll finally be able to mount tires independently of each other front and rear, as opposed to the tires being a package deal. This is an excellent feature for tuners to have at their disposal. |
| Basically, when choosing a tire, wider means more grip, so you'll probably want to mount the widest tires the P.I. will allow. But considering the 'points' limitations we're working with, regardless of the class we're running our car in, going as wide as possible is only part of the equation that needs to be considered. If you wonder why a C6 Corvette has 295mm tires on the back, while you'd never put that much rubber on the rear wheels of a Miata, is because we need to match tires with available wheel torque. |
| Not enough tire relative to available power is going to result in wheelspin, and an unstable car in the corners and on turn exit, but too much tire with a lack of available power is actually worse because it kills your car's acceleration since there's too much friction between the tire and road and not enough horses at the wheels to utilize all that grip. |
| The best news about our ability to choose tire sizes is we're not completely reliant upon our Anti-roll bars to dial out oversteer and understeer. |
| If we have a car that is understeering and pushing into the corners, and we want better turn in, we can go with a wider front tire. If we have a car that is breaking loose on turn exit, we can go with a wider rear tire. In the case of AWD, we pretty much want a squared tire set-up which is the same size tire on all four corners. |
| We should note the relationship between Anti-roll bars and tires: |
| Anti-roll bars regulate how much lateral load is placed on the outside tires when we corner. Tire width and tire compound determine how our lateral loads are utilized on the road surface. |
| Springs transfer loads laterally as well, but to a much lesser extent. ARBsare our primary source of regulating load transfer because they directly connect the lower control arm on the left side to the lower conrtol arm on the right side without any damping. |
| The stiffer the Anti-roll bar, the more load is transferred to the outside, laden wheel when we're cornering. Lateral load transfer is bad, but it's a necessary evil because our ARBs main function is to reduce body roll. The more load we transfer laterally, the more capable a tire we need to absorb that load and use it to generate cornering force, be it a wider tire or a more aggressive compound. |
| First things first, we're going to set up our car around the tire we choose. As always, we're looking for balance. |
| Let's say we have chosen a tire and then we set stiffness on our ARBs. When we finish our initial tune, we take it to the track and observe the results. Let's say we have corner entry understeer, which may mean two things: |
| 1- We're overloading the outside front wheel beyond its tractive capacity. 2- We don't have enough load on the inside front wheel, so it's not giving us enough grip. |
| I say 'may' because possibility #3 is the car could be rolling up on the front tire excessively which is giving us too much positive camber, reducing our contact patch and our tire is losing grip. But that's another story for another section.... |
| Let's assume the problem is laod transfer and not body roll: |
| One fix would be to soften the front ARB to reduce the lateral load transfer, keeping the load more evenly distributed between the front wheels. But my first choice would be to go with a wider tire or grippier tire if I could work it into the build. A tire change would be a better choice because it'll increase our track width slightly, and give us more overall grip. Keep in mind however, that more tire means more cornering force, so we need to monitor our tire compliance on the inside, front wheel, which runs the risk of being lifted off the ground during hard cornering. |
| In this instance, we could soften the front ARB, to try and keep the front wheels more evenly laden, but at the expense of increasing body roll. So a logical first choice might be to look at our suspension instead, and soften the front shocks in the rebound direction to increase suspension travel and keep the inside wheel in compliance with the road. |
| If we have oversteer on corner exit, we're probably overloading the rear outside wheel. A wider rear tire will give us additional grip, again, if we can tweak our build to fit a better tire within the allotted P.I. Softening the rear ARB may help here, to try and even out the loading of the rear wheels. The stagger that we choose with our front/rear tires is a great tool we can use to balance our car's handling. |
| As stated in the tuning Basics section. When we have a problem with one end of the car, we should work on that end without touching the opposite end of the car as a fix. If we need a wider tire in the rear, we shouldn't compensate (if the PI will allow for it) by increasing rear tire size and decreasing the front. If we do this, we're reducing front tractive capacity and why would we want to do that? |
| There's not much more I can elaborate on until we either get more info from the developers, or the game is released in October. |