I’ll get internet again next month and install FM7… I’m confident about what works in FH4 (1k hours), less so of FM7.
From the Help page:
Anti-roll bars, springs, and dampers are all balanced separately. That is to say, the various stiffness rows for springs don’t correlate to the rows for damping.
They aren’t related. The damper values are weighty^0.5*[scaling factor] with a spread of 4x. I don’t tune for 100% critical damping, but for reference, squaring (4x) the spring rate causes a 2x increase in critical damping, whatever the mystery units are, and doubling the weight (2x) only increases the critical damping point 1.4x. Assuming the min and max balanced damper values extend beyond ideal settings for the range of spring rates, there is enough spread to choose from, and specific amount and balance should be done by test driving.
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I was just curious, it’s very similar to what it should be irl in terms of rebound especially.
Also of note, when increasing spring rates, critical damping coefficient increases by the square root… if 400lb spring and 4.0 rebound works for you, 800lbs and 5.7 rebound should feel equally bouncy. The lack of actual units on Forza dampers make them impossible to set without test driving. In both FM7 and FH4, the tuning menu is annoyingly far from the initial pause menu state, compounding the inefficiency of setup.
Hey, I just realized I applied the weight correction factor on the damper balancer incorrectly, resulting in more damping than should be on the light end of the car. It’s fixed now.
I only noticed as I was adding a second damper section, with inputs for current spring rates. The new, “Ratio-matched” column, reads the weight distribution and chosen spring rates to output balanced damping ratio values. If your ride rate is balanced front to rear, at 100% scale on the new dampers, they should read exactly the same. If the rear ride frequency is lower, the rear dampers will scale down accordingly. If you try this, and flatly correct your rear damper rate like this
frontdamper/frontspring*rearspring=reardamper
You’ll find the table gives a touch more rear damping. This is because the weight of the vehicle is equally a factor in effective damper stiffness as spring rate.
With race suspension you can use the exact same spring rates both in Forza 7 and Horizon 4 just with a different scaled damping since they employ different damper ranges.
Forza 7 has Race and Drift suspension only, no rally. The spring range for Race/Drift in Horizon is 2.01 to 4.50hz on a 50% car. The spring range for Rally suspension is 1.42 to 3.18hz on a 50% car. The max ride height for Rally is around an inch more than Race suspension.
I’m confident the damper units are the same–try the same springs and dampers on a car with rally, then race suspension. See if it turns different lap times.
Do you pay attention at all or do you just come onto the forum and say things?
I tried the damper calculator with Horizon 4, which has imbalanced springs by default. As long as the car’s weight distribution is unchanged from stock, if you input the correct frequencies to match the stock springs, and the correct average damping and bump ratio, my calculator gives the same numbers. It’s interesting they applied equal damping ratio to the front and rear… at such high damping ratios, the balance doesn’t matter much.
Thats great and all but it comes up with numbers similar to stock. May be correct for irl, but its not going to make a good tune for forza physics. Its too middle of the road and not at the extreme enough for bump or rebound. Most of my setups have always been around 9-11 rebound and 1-3 for bump.
You’re missing the point. The numbers the damping calc put out inside the game would be what you would assume to be critical damping. You would then tune to the % of critical you want. You actually do not want a ton of damping, you also want as little spring as possible too.
And once again in one of these damping threads. I dont care what rl theories and practices say thats just not as good or fast in forza. Tune to the game, this game is way too far off to be tuning to real life perameters. Min/max or max/min works quite well in forza in most situation and is better than mid tier numbers. Do with that what you will, but with the limited information this game gives you are still using arbitrary numbers to come up with even more arbitrary numbers.
Neither ratio nor coefficient are necessary to create a table of equal-ratio front-rear damper coefficient value pairs. It’s probably possible to generate velocity/time traces for each wheel using data out. Yes, it appears they are linear without adjustment.
Mike has the Spring Rate as k = (2πf)²w / 2g
where f is the frequency, w is the corner weight (with down force), and g is gravity (32 in imperial units). This produces sensible looking answers in imperial if you just assume the final units are in lb/in, but I don’t know why gravity is in there.
Khan Academy was my next stop for a high school refresher.
Ah yes - the period of an mass driven oscilating spring is given by: T=2π√m/k
So we can turn that around and solve for k:
k = 4mπ²f²
where the mass is in kg, and would be the corner (sprung mass) of the car, f is the frequency, and k will be the spring rate in Nm⁻¹ or equivalent english units.
The display units in Forza are Kgf/mm, so /9807 to convert. Which gives stupidly small results.
https://eibach.com/us/p-101-suspension-worksheet.html was next.
They seen to just ignore the 2 pi, and throw in a strange constant: 187.8. wtf is that? Investigation reveals its √G*60. Only problem is: thats metric G, not english G, which means, OMG the guys over at Speed Academy - that Blog that we both found and referenced - just tuned a RL vehicle with maths that was out by a factor of ~2. Oops.
Then theres Dr Tuned: Spring Rates and Suspension Frequencies - Plus Frequency Calculator! — DRTuned Racing
Now here are some proper physics looking formulas, on a racing site. No dodgy constants thrown in. A calculator. Tables of expected frequencies. But applying these calculations to Forza produces cars with stupid / out of band frequencies.
Its at this point I am leaning strongly to the idea that frequency analysis of the tlemetry stream is the only way to determine if the spring values in ForzaX are in fact at all meaningful at all.
OMG!
Ive been working in metric units. And I don’t know if this is FH4, or FM7 or the entire series, but, the car I am looking at as a set of springs that when I look at their min and max are: 277.2lb/in and 1386/2lb/in in English units, and when I switch to my default (English), the same min and max are: 49.5 kgf/mm and 247.5kgf/mm.
But, if I google the conversion ratio: 0.0178579673 … then FH4 should be displaying 4.94 kgf/mm and 24.75kgf/mm. Which is where my spring calculations kept on landing me, making me think I’d missed a conversion from Newtons to kgf (why oh why does motor sport still use kgf!?) and/or generally mistrust the source of the equations.
Its been a Forza display issue all along. With a factor of 10 change to my spring rates, my frequencies are probably going to end up in range. But smudge it. I’m going to play. Enough time wasted on this for one weekend.
The conversion between kn/m and kgf is less than 2% difference iirc. Every other game I’ve tuned in uses newtons or kn/m, agree it’s strange Forza chose kgf.
It is heartening to see others interested in the subject of using using using math and science to assist with tuning.
I have some questions as I come from an entirely FH4 background,
I made optional fields in my spreadsheet take the min and max values from the ring rates so it calculates and displays the min and max frequencies available to select in the car you are trying to tune.
I chose cpm rather than Hz as it seems more of a standard in motorsports, and the numbers are more usable (30 and 60 vs .5 and 1 etc).
Display units aside, when I enter the mass and min, max spring rates available to cars like the Mosler in FH4, I get a tiny range of Hz values: 2.5 to 4 - All crazy high.
I don’t think we can directly compare real-world frequencies with in-game frequencies, at least in FM7. Up the thread a bit NumberlessMath and I got into a discussion about the discrepancy. I personally don’t worry about it; I just use the calculator to jigger the numbers around until the car drives the way I want it to, and whatever that puts the frequencies at is whatever it puts the frequencies at. The calculated frequency just gives me a nice, easy-to-remember number to quantify how much adjustment I want to make while tuning.
Well, what we don’t know is how the ForzaTech engine deals with
Sprung vs unsprung mass - do tires count?
Downforce transfer onto springs at different speeds
weight transfer onto corners while covering, accelerating and braking.
what are the hidden parameters such as downforce on components that are not unlocked for manual turning.
Given the use of real units and the general fidelity if the rest of the simulation I suspect if we had access to the proper way of dealing with these things our numbers would start to make more sense.
Almost for that alone, I exclusively use rally suspension. On cars where stiffness isn’t as much an issue (like the Mosler) I still use rally, for the extra travel–Maximum Race rear spring rate and ride height on the Mosler or F1GT less effective at keeping off the “bumpstops” than max rate/height with rally.