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Rank: C-Class Racing License
 4 users liked this post.
#1 Posted : Thursday, February 27, 2014 7:19:13 PM(UTC)
Greetings Community!
Have you ever wondered how work out your Tyre pressures?
Well hopefully with my simple formula I have designed, you'll be able to get the perfect tyre pressure for your car!
I have been creating formulas like this since FM2 and this is my first one for tyre pressures.
With only recently creating this formula for tyre pressure, I have already found an improvement within my cars ability and mine which I hope use will find to.

Tyre pressure equation (Psi) = (WD %( LBS)) * (9.8 / (USR – LSR)) + 14.7

abbreviation meanings:
WD = Weight Distribution
LBS = Weight of car in pounds (Only pounds!)
USR = Upper-Spring-Rate (Maximum stiffness the spring(s) can go)
LSR = Lower-Spring-Rate (Minimum stiffness the spring(s) can go)
9.8 and 14.7 are constants which must NOT be changed!

*Note*
When finding Front-Tyre Pressure use Rear Weight-Distribution
When finding Rear-Tyre Pressure use Front Weight-Distribution


Example:
In this example I will use a 2013 Lotus E21 (F1 car) just because it's light.
Weight Distribution: Front - 46% / Rear - 54%
Weight: 1422 lbs
Upper-Spring-Rate: 589.3 lb/in
Lower-Spring-Rate: 73.7 lb/in
Once you have got your values substitute them into the formula...
Front Pressure (Psi) = (54 %( 1422)) * (9.8 / (589.3 - 73.7)) + 14.7 = 29.3 Psi (3 significant figures) or (±0.5)
Rear Pressure (Psi) = (46 %( 1422)) * (9.8 / (589.3 - 73.7)) + 14.7 = 27.1 Psi (3 significant figures) or (±0.5)

If you want to get the perfect tyre pressure within "0.1 Psi" please follow these steps:
I will use the example F1 car setting(s) as a reference!
1. Once you have gotten your Psi set them to the nearest ±0.5 - E.g. 29.3 Put to 29.5 (Closer to 29.5 than 29.0)
2. Remember the difference between the calculated and the rounded value - E.g. 29.3 - 29.5 = -0.2
3. Once you have found the difference, at the main menu go to: FORZA PROFILE > HUD > UNITS and change to "METRIC"
4. Now in Metric go back to your car to tuning setup and adjust the tyre pressure(s) - E.g. Difference = -0.2 so tap left D-Pad twice to go down.
5. Once tyre pressures have been adjusted restore you original HUD - Unit setting and your tyre pressure(s) in Psi should be within 0.1, 0.2, 0.3, 0.4 etc.

Taking Mathematics to the game!
"The true sign of intelligence is not knowledge but imagination" - Albert Einstein

For my open source tunes please click 'here'

Hope this helps!
Enjoy,
RR

Edited by user Saturday, June 21, 2014 2:07:37 PM(UTC)  | Reason: Not specified

Rank: Driver's License
#2 Posted : Thursday, February 27, 2014 8:29:34 PM(UTC)
Awesome work thanks for contributing keep it up i will be using these tyre pressures for now on, on my E21
Rank: Driver's License
#3 Posted : Friday, February 28, 2014 1:10:06 AM(UTC)
great job,
but, I don't know how can you determinate something from the USR and the LSR. that mean, that the car tune is stiff or soft, the pressure will be the same?
and why don't you use downforces?
Rank: Racing Permit
#4 Posted : Friday, February 28, 2014 3:28:51 AM(UTC)
I get 14.7 because that's atmospheric pressure, but what's 9.8?
Rank: D-Class Racing License
#5 Posted : Friday, February 28, 2014 3:41:55 AM(UTC)
How did you test it was the best numbers for most cars and tracks ?,IRL I would have expected at least 10 more variables making trial and error easier.
Rank: C-Class Racing License
#6 Posted : Friday, February 28, 2014 3:42:23 AM(UTC)
Originally Posted by: K Steinwand Go to Quoted Post
I get 14.7 because that's atmospheric pressure, but what's 9.8?


Gravity

Rank: C-Class Racing License
#7 Posted : Friday, February 28, 2014 3:45:22 AM(UTC)
Originally Posted by: freakinout1969 Go to Quoted Post
How did you test it was the best numbers for most cars and tracks ?,IRL I would have expected at least 10 more variables making trial and error easier.


tested on about 6 cars all different. FWD, RWD and AWD, also light, medium and heavy weights. All of them found to be better.
Rank: C-Class Racing License
#8 Posted : Friday, February 28, 2014 3:53:17 AM(UTC)
Originally Posted by: BAM Osef Go to Quoted Post
great job,
but, I don't know how can you determinate something from the USR and the LSR. that mean, that the car tune is stiff or soft, the pressure will be the same?
and why don't you use downforces?


The springs are measured in lb/in which is similar to Psi lbf/in^2
So what I have done is used them values to find the range because there is a limit with the lb/in thus why i use them... if you get what i mean.
This formula isn't fine tuning, its a simple way to get the expected "perfect" pressure required by your car! Downforces do obviously make a difference but the formula would be even longer!
RR

Edited by user Friday, February 28, 2014 4:02:01 AM(UTC)  | Reason: Not specified

Rank: B-Class Racing License
#9 Posted : Friday, February 28, 2014 4:27:48 AM(UTC)
Rank: Driver's License
#10 Posted : Friday, February 28, 2014 4:28:46 AM(UTC)
okey, thx, we will try that ;)
Rank: D-Class Racing License
#11 Posted : Friday, February 28, 2014 4:31:32 AM(UTC)
Originally Posted by: ONR RoadRunner Go to Quoted Post
Originally Posted by: freakinout1969 Go to Quoted Post
How did you test it was the best numbers for most cars and tracks ?,IRL I would have expected at least 10 more variables making trial and error easier.


tested on about 6 cars all different. FWD, RWD and AWD, also light, medium and heavy weights. All of them found to be better.


I'll give it a go ,like the unit switch idea by the way.
Rank: C-Class Racing License
#12 Posted : Friday, February 28, 2014 4:55:14 AM(UTC)
Originally Posted by: freakinout1969 Go to Quoted Post
Originally Posted by: ONR RoadRunner Go to Quoted Post
Originally Posted by: freakinout1969 Go to Quoted Post
How did you test it was the best numbers for most cars and tracks ?,IRL I would have expected at least 10 more variables making trial and error easier.


tested on about 6 cars all different. FWD, RWD and AWD, also light, medium and heavy weights. All of them found to be better.


I'll give it a go ,like the unit switch idea by the way.


It's to do with the weight transfer... XD
RR
Rank: R-Class Racing License
#13 Posted : Friday, February 28, 2014 5:58:59 AM(UTC)
Physics. Nice. I was wondering why your tire pressures were lower than others...now it makes sense. Thanks for sharing!
Rank: B-Class Racing License
#14 Posted : Friday, February 28, 2014 1:03:45 PM(UTC)
in your example for the lotus are your wd's % the wrong way around
Rank: C-Class Racing License
#15 Posted : Friday, February 28, 2014 1:56:01 PM(UTC)
Originally Posted by: ToOSk3tChY Go to Quoted Post
in your example for the lotus are your wd's % the wrong way around


No...
Read it, don't skip!
Rank: B-Class Racing License
#16 Posted : Friday, February 28, 2014 3:14:09 PM(UTC)
Ah, yeah I didn't read it.

Thanks RR
Rank: Racing Permit
#17 Posted : Saturday, March 1, 2014 9:26:47 AM(UTC)
Just wanted to say thanks for these threads. I tried your formulas on 3 cars and set PBs in all of them. I really appreciate it.
Rank: B-Class Racing License
#18 Posted : Sunday, March 2, 2014 4:15:38 AM(UTC)
you did a fantastic job with the tire pressure formula. Taken my cars handling to another level.
Rank: B-Class Racing License
#19 Posted : Sunday, March 23, 2014 3:24:19 AM(UTC)
Hi Roadunner, thanks for sharing. When applying your formula to Mustang 69 D class I get very low front tyre pressure (27,4) resulting in a warm front tyre pressure around 30psi which is lower than the suggested range of 32-35, the handling seems to be ok though. Any thoughts? I have no such issue on the rear tires with your formula getting a perfect 33.x psi there when warm.

Best regards,

Edited by user Sunday, March 23, 2014 3:27:52 AM(UTC)  | Reason: Not specified

Rank: B-Class Racing License
#20 Posted : Sunday, March 23, 2014 3:24:34 AM(UTC)
double post

Edited by user Sunday, March 23, 2014 3:25:53 AM(UTC)  | Reason: Not specified

Rank: S-Class Racing License
 1 user liked this post.
#21 Posted : Monday, March 24, 2014 4:49:17 AM(UTC)
The formula requires a factor for compound. There is as much as 2PSI cold difference across Stock/Street/Sport/Race compounds to arrive at the same hot temp.
Rank: Driver's License
#22 Posted : Tuesday, April 22, 2014 10:46:36 AM(UTC)
thanks for your formula, I'll give it a go.

Can you clarify one thing please - should these 'perfect' pressures be aimed for, once the tyres are warm?

Or should the tyre pressures be applied when the tyres are cold?

Rank: D-Class Racing License
#23 Posted : Wednesday, April 23, 2014 5:46:12 PM(UTC)
These are cold pressures bud. But to be honest I believe this formula is total nonsense. I got stuck on it for a bit then figured out that dropping both pressures by 1.5 to 2 pounds and tuning from there was somewhat faster, unless you are bad at math then it can be daunting I suppose lol. And not only faster but I found it to be better for me. You will find cars at 35 pounds and cars at 25 pounds with this. Think about it. Atmospheric pressure and gravity. Its a game. Don't get stuck on tire pressure believe me.
Rank: D-Class Racing License
#24 Posted : Wednesday, April 23, 2014 5:55:48 PM(UTC)
Originally Posted by: WearyMick Go to Quoted Post
The formula requires a factor for compound. There is as much as 2PSI cold difference across Stock/Street/Sport/Race compounds to arrive at the same hot temp.


I totally agree Mick. And also if you look into how this works it really is nonsense. It is numbers pulled from real life physics measured in the standardized system and translated into a tire pressure on a car in video game. You can pick a number like 28 and make all kinds of equations involving the weight and distribution of that weight from video game car stats and add your own variations to them.

Like the bump equation that has you add 1 at the end... If 2.5 worked better then 1.5 on most cars then it would say add 2 at the end. To each their own.

Drive a car with just a build on it. A smart build. Really drive it. Then go 28/28 tire pressure. Raise camber to 3.0/2.5. Even out toe. Raise caster to 6 for front engine RWD and lower caster to 2.5 for mid engine. Raise rebound to front 10.5 and rear 11. Lower bump to 1.4 front and 1.9 rear. Tool with your diffs and aero after you take it for a spin as you need to. <-- Thats a formula for tuning to work with.
Rank: B-Class Racing License
#25 Posted : Thursday, April 24, 2014 4:19:32 AM(UTC)
Sorry guys, his formula works & is accurate. You would know that if you knew how & were tuning your negative camber. When checking inside/center/outside tire temp, you would know his formula is the truth. Center tire temp is directly related to tire pressure. My center tire temp is dead on with his formula. I also use Forza 5 tuning app. I enter alignment from Forza 5 app. Then adjust negative camber because the app is to excessive with negative camber (however, the apps Toe & Caster are spot on). After I finish addjusting negative camber in relation to inside/outeside tire temp, this is what I see (depends on tire compound for actual tire temp, but all 3 will be the same degrees).

Examples

Inside 229.7
Center 229.5
Outside 229.1

Or

Inside 210.9
Center 210.6
Outside 210.3

Or

Inside 222.8
Center 222.4
Outside 222.0

Now this would be the case after 4/7 laps of normal hard racing & not excessive unnecessary sliding/tire spinning. That's when your tire pressure & alignment is dead on, you do achive perfect uniform tire temp inner/center/outside. Vehicle response is precise & turn in is great. Doesn't matter what type of tire compound it is. Evenly heated tire grips & can get it done with in limitations of the Lateral G's the tire compound can handle!

Do not doubt this guys formula. When racing in real life, all 4 tires are not set to same tire pressure. Now Forza only lets us do front/rear. This formula along with Forza 5 app has my builds dead on. I do use my own settings for differential (RWD I use 20/5 or 35/15 or 30/10) & brakes. I don't suffer from terrible oversteer that some people say they have. I totally enjoy driving RWD with no issues on Forza 5. The Forza 5 app is dead on for springs, damping, alignment (base for negative camber & I use apps toe/caster) & anti roll bars. If everything is set right, any car is easy to drive (with in limits of tire compound you choose to run & width. Can't push stock compound like sport compound). You can't expect 14" tires to perform as good as 19" in relation to side wall height. If it's not set up right completely ugly oversteer, understeer, skitish over the track will happen. His tire pressure formula completed my puzzle.

Edited by user Thursday, April 24, 2014 4:39:08 PM(UTC)  | Reason: Not specified

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