I have a good overall understanding of tuning in Forza. I’m not an expert but I understand the concepts and equations to get a balanced base set up. I could use some help on dampening.
I am seeing open source tunes and calculator tunes setting the bump very low in the 2-3 range and the rebound around 6 and some tunes going as high as 11.
When I use those settings on most cars there seems to be too much roll and weight transfer. My tunes seem more stable with the rebound between 6-8 and the bump at 66% of the rebound. So if my rebound is 7.8 the bump would be 5.1.
There’s roll because the suspension offers little resistance during compression. But most people do “overall” tunes to account for all tracks in the game, including bump hells such as Rio. This can make cars much softer, more grippy and they roll much more as a result.
Dampers affect balance in transitions. Springs/ARB’s affect balance steady state. The most difficult thing I find is diagnosing what is really going on especially on tight turns when you are never at steady state. Sometimes I need to save a replay and watch the acceleration vector on telemetry to figure out which way the weight is really moving. It is easy to miss diagnose and tune the wrong direction. It is also easy to end up with a car that actually understeers but is too difficult to drive because the dampers, differential, and brake bias all make it oversteer terribly in and out of the turn.
Once I get a good feel I do use math to keep things the same when I want to modify the build or take it to a different track. I tend to run bump 70% of rebound on rough tracks with lots of elevation and down to 30% on flat smooth tracks. I found that estimating ARB’s as a percentage of spring works fairly well. A 40 rear ARB seems to have the roll stiffness of 40% of Weight/2. It’s a guess but seems to work well with a 6.2 damper being 620 in English units. I usually start with damping ratios matched front an rear so the car doesn’t change character running through a slalom course ( average bump+rebound around 0.34 but sometimes as low as 0.29 and high as 0.54). I don’t go by the number like rebound 8 and bump 2 since a heavy car with maxed out springs/ARB’s for Daytona will actually required max 13 rebound and bump over 10. A 1,000 lb car with 200 lb springs may only need 3 rebound and 1 bump.
But in general I find FM7 takes more bump than FM6 and way more then FM5 where everyone was running -3.5 camber and bump of 1.0.
The best cookie cutter approach for me has been to have bump at about 33% of rebound, but IMO that never really works great without some tweaking.
With bump the thing to keep in mind is that it’s very closely linked to ride height. The lower you go, the more bump you’re going to need to not bottom out over bumps on the track. The higher you go the less bump you need to prevent bottoming out. Of course, higher center of gravity can limit peak grip, but going from peak grip to zero grip in a corner because the tire left the pavement after ramping over a curb isn’t so great either.
So with dampers there’s a window you want to stay in. Too little bump means bottoming out and no grip, too much bump upsets is basically the same exact effect.
To set bump open the suspension telemetry screen and do some laps. If the bar quickly fills or completely fills, you need more bump damping. If it moves slowly or doesn’t get close to the edge, you can reduce it and keep watching. If not excessively lowered many cars will feel like they’ve picked up a noticeable amount of grip as you reduce bump and get closer to the sweet spot.
When you lower it too much the car is going to start to feel crashy and uncontrolled in transition. However, this s also a symptom of not having enough rebound.
To set rebound the best advice I can give is to read the in game menu and go from there. It’s a good place to start learning. Not enough rebound will feel crashy and uncontrolled, but too much will make the car feel stiff.
No problem. Just play around with it and see what you like. Damper tuning is a bit of an art, even on real cars. My approach is typically to set the bump split based on weight balance with the overall level being what effectively absorbs bumps at the ride height I have set. Then I use rebound to fine tune how the car enters and drives out of corners.
For example, preparing last week’s GT Racing Reborn ghost league I was having a difficult time getting my RX-7 power out of corners. The rear wanted to fly away without much throttle input. I noticed that I had a lot more rebound up front than at the rear, so I started reducing rebound stiffness up front which tightened it up nicely and really made the car a lot of fun to drive. It still doesn’t rocket out of corners like the Lancia or Ferrari, but good enough for a car with the engine up front.
It’s so much of an art that it’s the part most people are clueless about. Even from reading your post I didn’t understand why softening front rebound would result in taming exit oversteer. The way dampers work is a little complicated to mentally visualize.
However, dampers are key to a good tune.
Speaking of the league, the Ferrari seems very fast and balanced, a difficult car to win against no doubt. I was in the Porsche and had a lot of trouble against the Ferraris because the gearing is not optimal in the 935. In the Lancia it was definitely much easier, it may lack top end but acceleration is much faster.
Yeah sorry, I try to avoid going down the “why” path because that leads to even longer posts. But also because if you run out and try to research this you’ll find guides that’ll tell you to increase front rebound to solve the same problem.
In my example I believe lowering front rebound tamed the oversteer because less rebound allowed for quicker transfer of load to the rear tires, for more grip. Also, that’s what the in game adjustment guide said to do which I took as a clue that this was how the programmers made the dampers work in Forza.
The moral of the story is… make an adjustment and do a lap.
Here’s a very simplified way of visualizing bump and rebound.
Bump = how the ROAD affects the car. Bumps, curbs, dips etc.
Rebound = how YOU affect the car. Dive, squat, roll etc.