| SHOCK TUNING FOR FORZA MOTORSPORT 3 |
| |
| The two main adjustments for our dampers are as follows: |
| 1- Tire Compliance |
| 2- Balance (oversteer and understeer) |
| |
| TUNING BUMP AND REBOUND FOR TIRE COMPLIANCE |
| |
| Tuning our dampers for tire compliance is the easier of the two types of adjustments we can make. I like to break down tire compliance into two scenarios: |
| 1- Compliance over bumps: When our vehicles go over bumps, our springs compress (damper - bump) on the way up the incline. As they go over the peak of the bump they begin to expand (damper - rebound). |
| |
| 2- Compliance in the corners: The second scenario is on a flat road at the point where we begin to turn in. The dampers react differently here because the inside wheels are in rebound (damper- unloaded) and the outside (laden) wheels are in bump (damper- loaded). |
| |
 |
| |
| When the wheel goes over a bump as shown, the spring compresses on the upslope of the front side, and then expands as it passes the peak of the bump and rolls down the back side. Although the suspension is in a constant state of motion, a properly tuned damper should compress enough to allow the spring to absorb the bump, then return in one rebound stroke to equilibrium....all while maintaining maximum wheel to road contact (as illustrated by the contact patch). |
| |
 |
| |
| If the wheel hits the front of the bump too hard, the damper is not allowing the spring to compress fast enough. If the resistance is too great the impact from the bump can bounce the wheel off the ground. |
| |
 |
| |
| The same thing can happen on the downside of the bump if the rebound is too stiff. The resistance of the damper will not allow the spring to unload fast enough to push the wheel down. The wheel will hang up too long inside the wheel well and lose contact with the road. |
| In both cases, tire compliance is compromised. |
| A good rule to follow is if the wheel is losing grip on the up side of the bump then the shock's bump setting is too stiff, if the wheel loses grip on the down side then the shock has too much rebound. |
| The other extreme is when the dampers are too soft. You'll know this is the case when the car feels like it's 'bouncy', 'floaty', rolls too much, and is slow to take a set in transitions. |
| When the bump damping is too soft you'll know because the initial reaction to the bump has a soft 'mushy' feel. The car will have too much pitch under brakes (dive) and acceleration (squat). Under extreme circumstances the nose of the car may scrape the road under brakes, and from dips in the road. |
| When the rebound is too soft you'll know because the wheel will oscillate after it hits a bump rather than returning to its state of equilibrium. Basically the car will feel 'bouncy'. |
| |
 |
| |
| With our car turning left, the inside wheels are in rebound, the damper and spring are extended in 'droop'. Meanwhile on the other side of the car, the outer wheels are in bump; the damper and spring are compressed. |
| If the rebound is too stiff, the spring will not extend fast enough and the unladen wheels will pull off the ground in the corner. |
| If the bump is too stiff, the car may feel like it wants to slide going through the corner and the power may be difficult to put down on exit as the driven wheels may hop or 'patter'. |
| If the dampers rebound is too soft, it may also be difficult to put the power down. |
| If the dampers bump is too soft, the car may feel like it's rolling too quickly; the body feels like its rolling over the front tire on corner entry, and over the rear tire on corner exit. |
| |
| DAMPER TUNING FOR BALANCE |
| |
| I'll state right from the beginning that I'm not a big fan of balancing oversteer/understeer issues by adjusting the dampers. Personally, I tune my shocks to maximize tire compliance and leave the balance issues to my ARBs, springs, and aero. If I need the car to turn in or exit turns better, for example, I'll make adjustments to my alignment (camber, caster, toe) before I go playing around with my dampers to fix the problem. |
| Another reason I feel this way is because lack of tire compliance leads to balance problems in the first place. In the example above, if we're turning in and the inside wheels are pulling off the ground, we probably need to soften our rebound to keep those wheels gripping the road. But the symptom of the wheels pulling off the ground is that the car will understeer. Fix the compliance issue and you fix the understeer. |
| Another example that is common on 'wavy' tracks with a lot of elevation changes is when we have a turn at the top of a hump. The car gets 'light' much in the same way we get a feeling of weightlessness at the top of a hill on a roller coaster as we descend on the other side. When we put the power down on turn exit, we can't because our driven wheels are lacking grip and we get 'power on' oversteer. The problem is most likely the dampers are too stiff and we're lacking adequate suspension travel to maximize our contact patches as the car traverses the hump. Once again, if we fix the tire compliance, we fix the oversteer. |
| Adjusting dampers for balance is more about adjusting the slow bump/rebound characteristics than the faster ones. Damper pistons are velocity sensitive because the cylinder is filled with a viscous oil. Velocity sensitive meaning the faster you try to push the piston in, the more the piston will push back. So when the car hits a bump, the shock will apply more resistance here than it would if we were turning the car in for a slow speed corner. |
| In the case of hitting a bump, the suspension is taxed with a lot of force from the sudden jolt of the impact. The slow speed corner affects suspension travel much differently as the inside springs are unloaded more gradually and the outside springs are loaded more evenly as well. This is the impetus behind the 4 way adjustable damper. |
| To the best of my knowledge, we don't have 4 way adjustable dampers in Forza Motorsport 3. |
| But damper adjustments for balance/handling have more to do with how the car responds to turn in, and turn exit. It needs to be noted that dampers effect on handling is contingent upon the suspension being in some state of transition. Once the car takes its set (ie: in a steady state sweeping turn) the dampers have no affect on handling until we supply a steering input that gets the suspension moving again. |
| As the car enters a turn, the bump stiffness on the outside wheels determines the rate at which the body rolls and the resultant change in dynamic camber. The rebound rate on the inside wheels determines how quickly/slowly the inside springs will unload. |
| As you can see, the balancing act between bump and rebound is a potentially complicated dynamic that requires knowledge and a lot of experimentation with the car. |
| My personal slant on the issue is that there's 400 cars in FM3, so you need to decide how many cars you want in your garage and how much time you want to spend tuning any one car. If you like to have a lot of cars in your garage and don't want to spend too much time tuning any one vehicle, my advice is don't play around with the damper balance too much. Set the dampers to maximize tire grip, and use the other adjustables that are easier to work with to balance the car. |
| If you're really into damper tuning, there's a great article on the subject that can set you in the right direction: |
| http://www.smithees-racetech.com.au/theory/shocktune1.html |