ONR RoadRunner - OLD Tyre Pressure Formula!

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[/h]
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

4 Likes

Awesome work thanks for contributing keep it up i will be using these tyre pressures for now on, on my E21

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

I get 14.7 because that’s atmospheric pressure, but what’s 9.8?

Gravity

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

Genius

okey, thx, we will try that :wink:

Physics. Nice. I was wondering why your tire pressures were lower than others…now it makes sense. Thanks for sharing!

in your example for the lotus are your wd’s % the wrong way around

No…
Read it, don’t skip!

Ah, yeah I didn’t read it.

Thanks RR

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.

you did a fantastic job with the tire pressure formula. Taken my cars handling to another level.

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,

double post