How is the PI calculated? They make no sense to me anymore. e: Now I get them and also hate them

So every vehicle in your garage has got a set of numerical values bind to them, speed, handling, acceleration… you know them, which may or may not change when parts are changed.

I thought I had a pretty good idea about their meaning but now I know, I didn’t know jack.

For example one of my cars, BMW XDRIVE50 (A800) has been given a 3.5 for speed. I tuned it in a way that it has got some acceleration also and it can do 286km/h max now. For 3.5 I think that’s no short of amazing.

I decided to test another car, not so amazing Wuling Sunshine (C600) but it has got a speed value up to 4.3 and tuned to go as fast it can with its current parts. It can’t break even the 200km/h mark.

This left me in a state where I no longer have any clue about the meaning of those numbers.

If you understand them better, please share your wisdom and help me figure them out.

You are forgetting to take back one kadam to honor the dev coder, whose game this is.


If there is a rhyme or reason to it I’m not sure anyone has truly cracked it. At times I felt like maybe it was all internally relevant, so a “Speed” (whatever the heck that is anyway) of 3.5 for Car A does not mean the same as a “Speed” of 3.5 for Car B. Across the board. At times though I see evidence that the numbers mean absolutely nothing in reality.


They were always a bit questionable at best.

That reality hit me hard today as they were usually at least somewhat useful figures but now I learned that it has been a lie. The discrepancy is the biggest I’ve ever witnessed and I thought the numbers were my friends :cry:

Pretty sure it’s class based… With 10 being best possible of class (stock twinmill A798 getting 8.6 for reaching 375km/h)

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The class theory kind of went out for me for good when the 3.5 value BMW told me that it should barely be able to overtake the freeroam NPC cars. Obviously that’s not the case.

…I have never really given the PI stats much thought, but generally agreed they made little sense.
This comment was def a eureka moment for me, NGL. Makes better sense now.

It’s another of the things about game play and mechanics, and tuning that are not exactly intuitive about the games mechanics that they seemingly make no effort to educate people on.

It’s really a rather simple mathematical algorithm.


The variable is which Mustang or Cobra is used in the equation.


I forgot the most important part of the equation



You forgot to factor the slope of the driveway leading away from the cars and coffee parking lot and multiply that by the HP then divide by height of the curb and the number of people on the shoulder that have to run away.


If the numbers are class based then each class from D to X would be able to attain 10s in each category. I don’t really believe that.

I don’t put much attention towards them. Often they seem arbitrary and are only based on the car with the parts installed rather than including how it’s tuned. Gearing and aero drag affect the speed and acceleration yet don’t affect the values of these ratings. I’ll sometimes use them when comparing tunes of the same/similar PI on one car at a time but that’s mostly to make an opinion on the intent of the tune. With the prevalence of rally tires in road tunes some of the ratings are even less relevant.

Best is to test.


I agree they seem to be worthless. I do runs in rivals events with some nice people on these forums and the first few times I tried I couldn’t even come close to the bottom of the leaderboard. Then I start using their tunes, which had the same or even worse number than the tunes I got off the list and yet the cars performed waaaaay better. Maybe once they introduced the more detailed tuning they didn’t bother to adjust the numbers? I don’t remember the numbers being worthless in FH4, but I could be wrong.


Six days the FM!!!

How will the typical Horizon player cope when they find out they get penalized for ramming and can no longer wall ride!


some notes:

  1. the numbers only represent the build, not the tuning

  2. even then, they are only a rough average. it’s hard to compare 800 very different cars with one system.

  3. off-road value is one of the only useful ones. FH4 had no off-road rating, this was huge improvement

  4. focus on your lateral g’s - that is affected by fine tuning, and is the best final value to judge “handling” - sometimes tires have a surprising affect on lateral g’s that pi value doesn’t indicate

  5. speed value is one of the least correct, because it doesn’t take gearing into account


Better not make it a Fox-Body Generation and throw a third “amminal” in there lol

But I have a few NSX’s with various engines and their performance ratings are way off compared to true acceleration and top speed between each other. The SC V6 is rated with a higher top speed and accel than the 6.3L with a “race” cam in it, but its not.

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Yes. Since the tuning doesn’t affect the numbers I thought it must be the potential given for the build but it’s not that either. Now it’s just a number that indicates that there are numbers.

The rough average doesn’t seem to apply anymore in all cases. And when picking a car for the next race that’s the info player is given if the values aren’t useful I guess I need to have spreadsheets ready for all the cars with their respected info. That if you can’t remember all your cars true performance by heart.

Along with off-road tires it was a welcome addition.

Goes to tell more how broken the value system is.

The logic behind it is so fuzzy that even Fuzz Fuzzerton’s fuzzball hamster doesn’t get it.

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I agree with your points, it’s a strange system and there’s a million exceptions I haven’t even gone into. like why does the 10 gear transmission have such better launch numbers than 6 gear, when you can gear them the same for almost the same exact performance. there are ways of making s tune look stronger than it is, for sure.

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Ok, so… I spent some time in the lab and I think I finally got some grasp to the matter. It doesn’t exactly fix the issue with the values but at least there’s something consistency with them now.

Car class is irrelevant to them and don’t share anything directly other than raising PI raises the class and as mentioned before, tuning not affecting the PI causes problems only for those who actually do any tuning.

The first mentioned XDRIVE50 is actually super slow car with stock tuning, hence the low PI and by this it renders the number completely irrelevant to tuners as it has got nothing to do with reality.

Now I see only two ways out of this. You either need to have a separate list of your cars at hand, with their real performance figures or just remember them, all of them.

Do people even tune their cars in general or does only Forza nerds do it? I would bet on the latter and PG can’t be bothered.

Thanks everyone, this was fun either way. Time to fire up good ol Excel.

Typically; I drive the car stock for a while on my test areas of the map.
I toss a standard set of upgrades on all my cars to max their current class (typically)
9 times out of ten, I adjust the gearing and that is about it. I might soften it up a little depending on what I’m doing with it. My builds are always handling builds.

…you really don’t have to do very much tuning in this game, and there is a old school gamer voice in my head that literally thinks that you can complete the entirety of the single player side of this game on Highly Skilled in stock cars.

This is to say: because this game is about accessibility E For everyone, they wouldn’t exactly make the game “require” tuning to play at the intended levels for completion.

For example: Last series they gave away a Ferrari F40 as a reward for one of the challenges, then required that same car to complete 3 PR stunts.

So we have this set up: Complete easy challenge that you can use almost any car for, and win a car you need to do other challenges - you don’t even need to tune this car, the car can do it stock.

…it’s just basic game design really, they aren’t trying to make the game harder than it needs to be, and while I am one of those nerdy forza tuners (I’m embracing this term BTW, thank you) I don’t feel like I’m forced to be some elite tuner to complete the game. Competing online, Rivals, well…that’s different.

I think also that tuning shouldn’t be a requirement to make good enough in the game, as many players don’t want to hassle with that stuff.

The game does however have its deep end (for the nerds) to it where a single zone of single tire gets simulated data of its temperature and the data can be brought up anywhere when driving but then denies the players to have access to vital data in the car selection screen. PG really does have the means to offer even the most trivial info of the car if they want to but in PI they just don’t.

I just wish the PI had additional after tune value visible. Just a general QOL improvement, a simple convenience… [sighs in finnish] It’ll never happen, I know.

At least I got to vent about it.

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