ONR RoadRunner - Test Subjects needed for new Tyre Pressure Formula

Hey guys!
Just wondering if I could get some feedback from you guys for my new Tyre Pressure Formula. I have completely revised it and hopefully it’s better!
By better I don’t mean faster. If it’s faster then great but I’m aiming for the fact of it feeling better and still being as fast.
The way I’m going to do this is I’m going to ask you guys to fill in some information and I’ll reply to you with the Front and Rear Tyre Pressures.
Please don’t bombard me with a load of cars stats! This is just a simple sampling test to see whether I have made it better.
PLEASE GIVE FEED BACK as this will allow me to know whether it’s working… or not.
Some of you guys my find it better and some of use wont, so don’t feel bad if it doesn’t work for you as it’s only a test.
Also, with that in mind some results may seem obscure (nothing ventured, nothing gained!) so don’t feel the need that you have to use them!

Info required for me to get pressures + Extra info on the car type & model:

Car Make & Model:
Front: Tyre-width/Side-wall Percentage/Rim Size
Rear: Tyre-width/Side-wall Percentage/Rim Size
Vehicle weight (in pounds): lbs

2012 Pagani Huayra
Front: 275/30R19
Rear: 355/30R20
Vehicle weight (in pounds): 3081 lbs
Front Weight Distribution: 45%

When information is inputted into into the formula…
Front Pressure: 35.3 psi
Rear Pressure: 28.6 psi

If you want to get the perfect tyre pressure within “0.1 Psi” please follow these steps:
I will use the example car setting(s) as a reference!

  1. Once you have gotten your Psi set them to the nearest ±0.5 - E.g. 34.8 Put to 35.0 (Closer to 35 than 34.5)
  2. Remember the difference between the calculated and the rounded value - E.g. 34.8 - 35.0 = -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 the 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.

Hopefully these new settings help, Thanks!

I’ll add some information later (although the car I pick will be the Gen 1 Miata).

Just a quick shout I’d like to make is that higher pressures in the tyres effectively make them stiffer springs so I find it slightly strange as to why in a car with rearward weight bias the rear pressures would be set lower? I’ll give it a go definitely but that’s just my initial observations of looking at the example car. Also, 34psi seems very high.


Front: 195/55R15
Rear: 195/55R15
Vehicle weight (in pounds): 2397 lbs
Front Weight Distribution: 52%

The RL pressures for this car are 26/26

Front Tyre Pressure: 31.8 psi
Rear Tyre Pressure: 30.5 psi

I see what you mean, but just because there is more weight in the rear doesn’t mean that the rear tyre pressures have to be higher in the rear. They’re more factors affecting the tyre pressures then just the weight. TBH, there is more factors affecting the pressures than what I require but I have tried to simplify it.
But give them settings ago and tell me what you think.

I’ll give them a shot then next time I drop out of my MP lobby, here’s what I was talking about with tyre spring rates: Hoosier Tire: Page Not Found

No, I agree it doesn’t, your ride frequency balance determines what you should set them at really but the whole thing really becomes a lot more complicated as soon as you start introducing different front/rear pressure settings and really you should revisit your damper settings since you’ve effectively stiffened/softened the system. There’s more information on this available here: http://www.optimumg.com/docs/Springs&Dampers_Tech_Tip_1.pdf here: http://www.kaztechnologies.com/fileadmin/user_upload/Kaz_Tech_Tips/FSAE_Damper_Guide-_Jim_Kasprzak_Kaz_Tech_Tip.pdf and here: http://alcor.concordia.ca/~istih/suspensn.html

Christian – in the 1st article you mention, there is mention of Motion Ratio, yet they do not describe much on it. Can you describe and provide ranges to be used, or, how to calculate? Thanks!

You can’t calculate it so to speak since it is a car property, what it relates to is how much the wheel moves in it’s vertical (approx) plane compared to how much the spring itself moves (compresses or extends), the difficulty comes in that some define it as spring/wheel and others as wheel/spring, it’s not a problem providing your equations match with it but it does matter since the equation for spring rate involves (motion ratio)^2.

For the equations i use i found wheel/spring to be the correct definition (in that, my equations give out spring rates close to known real values for a known ride frequency.

A good base to work from will be 1.00 however since this removes this issue, a lot of cars are between 0.7-1.0 for a spring/ wheel definition.

Thanks Christian! I am assuming that the 0.7 to 1.0 will depend on the type of car (i.e. from full force race [with downforce] to stock upgraded to race). I’ll analyze & test a little bit to see.

Actually not quite, you’re along the right lines only with the wrong property, what you speak of is true for ride frequencies, road car frequencies are usually around 1Hz whilst cars like Indycars are around 5Hz or more with everything else in between, in essence, the more downforce dependency, the higher the ride frequency.

Motion Ratio is just one of those properties that comes from the original suspension design and is usually arrived at either because of:

  1. A desire to have a specific motion ratio (in order to match a specific shock, etc, there’s also a theory that dampers work better at higher speeds hence higher motion ratios to move them faster, this is explained in the KAZ link)
  2. Packaging, the most likely for a production car, simply put, pushrods and rockers are impractical for most cars hence, the motion ratio is dicatated not by what you want but by where your chassis designer wants to put the hard pad for the upper spring mount (criminal in itself really that a chassis design is done before a suspension design but that’s another story!) for example, this is the first link from googling ‘motion ratio diagram’ http://yw1015.tripod.com/worksheet.html it gives an OK idea of what I’m talking about.

Hope this helps.

Thanks Christian, this really helps me understand better these dynamics and interdependencies. The doc I read through (I’ll check the KAZ link) did not really go into a lot of detail, thus, your explanation is very helpful.

lol about the chassis design prior to the suspension…brings back (not so) fond memories about some of my past jobs where Industrial Designers would take the lead on “concept” and the engineers would still be closing out the previous cycle of products, thus, a little late to the “picture” resulting in a “design around” the ID…

I see what you mean. Up to now it’s been positive results for my cars and my mates too so I thought expanding this into the community I might see if anyone else is improving with the feel/time or both.

Also Christian, on this game, the damping settings 13 /13 / 1 / 1 is actually the best setting! The only time this needs changing is when a track is glitched like Long Beach or the track is really bumpy like Sebring!

What would you consider at the Indy Oval? Thanks!


Not sure tbh, don’t run Oval. Probably 13 / 13 / 1 / 1 or 1 / 1 / 13 / 13

I guess I missed the memo, how is Long Beach glitched?

On the exit of the fountain, the cars squat and sink under the track.

I’m not arguing it wont give positive results, sorry if it came across as a dig it wasn’t meant to, I just thought given that you’re interested in formulas for things you might find those interesting given that those show the basic start points for real cars :).

I know that the damping setting is messed up, it’s really annoying to me as those settings would be deadly in real life.

I actually find the links you presented really interesting and hopefully I’ll use them to see if they improve results on Forza, thanks for providing the links to me! Tyre pressures don’t really mess around with damping apart from frequency distribution but that’ll change depending on the track. I couldn’t really get the right formula for Tyre pressures because this game isn’t really the best simulator and it doesn’t provide valid information but anyway…
No probs,

I managed to get them to work for me so hopefully you do too! :slight_smile:

I ran some times at TTAF (D400) (each time I ran 3 laps and took the best lap)

So with my pressures(28/28) and damping: 1.06:870
Your pressures and my damping: 1:07.113
My pressures and crazy 13-1 damping: 1:07.730
Your pressures and crazy 13-1 damping: 1:07.628

Why did I pick the Miata? I’ve been using it a lot recently so I’m familiar with it.

Interestingly, your pressures made the car almost 2 tenths faster up until the first sector line suggesting that they’re probably better for high speed fast corners, all the time was lost though when it came to the 90 right and the hairpin, I found the car less willing to turn in, effectively, it had less response and more understeer (possibly why it was quicker in S1 as my setup was sliding slightly and losing time?). The car to me also felt slightly vague at the front end (as though the car was floating above the track).

I chose TTAF because it is one of the few where the broken damper settings are caught out, as you can see the time lost at both large bumps isn’t small and the launches at both points illustrate why these damper settings are just plain wrong.

Using your pressures with the broken dampers did give a slight time improvement though so maybe if you’ve derived your formula from setups using these settings that might be why it doesn’t work with my setup but works with one similar to yours?

And yes exactly! they alter the effective spring rate and frequencies which alters the damping you need! The game does lack in information though which is disappointing, if you can find enough information from the real car though you can get a good setup underneath the car using real world formulae.

Edit: The way I see it is that the difference between mine and your pressures altered the balance (stiffening the front in relation to the rear and stiffening the car as a whole too) which explains why the handling balance was pretty much ‘reversed’ between the two setups.

TTAF is TestTrack AirField right?
If so, that track is definitely one I would never run those damping settings making your test Bias (for the damping test).
Also, 3 laps isn’t enough. Especially when your use to just running your tune it takes more than 3 laps to get use to another.
But as I said in the OP, for some people it would improve them and for some it wont…

Yeah, I know it was biased for the damping test, it was intentional in that it’s one of the few tracks where obscene damper settings don’t work, similarly, if you read the KAZ link you’ll see he recommends compression biased damping in the cases of racecars, if you try that on forza you get a truly awful car.

3 laps was enough, the tune was identical aside from pressures, if anything the laptimes were largely irrelevant given that I’m not the best driver so 0.2 seconds I would consider reasonable variance, I’d have thought my observations were more relevant? I can see how it can work for others but setting the car up that way just isn’t for me.