ONR RoadRunner - Tyre Pressure formula CONCLUDED!

@RR i appreciate all the work you have put in on this project. even if people complain i would like to see the math behind it .

It’s still a working progress but what I have now is the closest I have ever been to getting pressures which I have tested and beaten my LB times!
The Maths that has gone into the formula is quite a bit and unfortunately I’m keeping it a bay until I’m satisfied with it as well as the community is satisfied as well hence why I’m doing this.
Once I’m happy with it I might try to publish it, for free, on a program. I have currently done this formula on a program called visual basic but hope to expand on to formulas for springs and damping etc. This is before publishing…
RR

Hey RR,

Happy to help you out…

Here you go:
1981 BMW M1
W = 2349 lbs
Front = 265/45R16
Rear = 325/35R16

Output: tire pressures in PSI

Let me know what you’ll need back. Thanks for your efforts!

PRKid

So no factor for weight distribution or tyre compound? I’ll be interested to see the results of this.

Great points on both fronts! I am thinking the wight distribution (esp. for heavy bias to F or R) might be of higher criticality than the compound, yet, not sure. What do you think?

RR - just a quick note to let you know that awhile ago during one of my internet searches I came across a person that was actually calculating Tp’s based on the Wi/WaRRim information, and in addition, using the weight distribution. I tired it out and it work for a couple of cases, yet, for the majority these were off by a significant amount especially when one introduces very wide tires in the rear (i.e. not even between F/R). He assumed a patch/contact area, which there are some docs out there with research (20-35 in^2) yet was still in need of some work.

In addition, at speed one would introduce the add’l downforce of the aero onto the tire changing the patch. And, to WearyMick point no coefficients were used for compound. Anyway, just thought I share that. With all that been said, I am hoping you come up with a great equation. Thanks!

Front Tyre Pressure: 26.1 psi
Rear Tyre Pressure: 24.7 psi

The info I need back is just the general feel whether it was better or not and why. Also, with that information I’d like to know whether you improved or not. If so, what track and by how much.
Remember these are settings for Circuit!

Weight distribution when looking up real formulas wasn’t really a factor. The gross weight was the main factor which was used in all. When looking at different cars and their tyre widths, the weight distribution has been incorporated into them hence why it must not be as much of a factor than what it may seem… my guess, but this is the best formula I have done up to now so oh well, as I said in another reply, this is only a working progress but hopefully I’ve hit the head on the nail, or at least touched it!

Well… I have tried stupid settings on this formula and found that it doesn’t give stupid settings. My formula actually contains a lengthy bit of code to work out the contact patch which took ages but it works really well.
The downforce though is a bi product of weight which unfortunately I haven’t used, hence why I didn’t ask for it, as like I said it’s a bi product of weight which varies in all straights and corners! Hopefully that backs up my case for not using it =P
Thanks for doing some research and telling me!
RR

OK, so here is my quick update. The car did feel better and running pretty smooth I must say, I ran the car at the Catalunya National track, short though a little challenging. At set the tire pressures per your instructions (F 26.1, R 24.7), and, when I looked at the telemetry after running about 8 laps I saw that the pressure on the front tires (31.5) were 2.5 psi higher than the rear (29), and, not within the recommended range of 32-34psi. I also was under the impression that one needs them about even after warm-up!! Not sure if it needs to be if car feels good, yet, just reporting back.

My original tire pressures were set at 28 F and 28.5 R and closely match (at about 33.5) when warm. If you notice where I started with mine and your settings the ending pressures after the car being warm make sense.

I did not get a better time, yet, my driving is somewhat inconsistent yet so I would not worry about that part for now.

Hope this helps!

p.s. DO you try to land your warm tire pressures to that described by many in the Forum and guides?

As far as I know, there isn’t really a recommended pressure on this game. It’s really what ever feels beat and goes the fastest!
But, if it’s more smooth and your running the same time, I’ll take that as a positive =]
RR

hmm i have been thinking about the compound idea , when you install new tires there is a grip % gain that is shown on each compound upgrade. i wonder if this can be applied to achieve different results

Grip doesn’t really have any relevance of psi value… It’s only a % Grip gain and doesn’t really specify any units so… yeah, anyway. =]
RR

Hey RR, glad to help bud.

Car: 1968 Alfa Romeo 33 Stradale
Weight: 1423lbs
Front: 265/45R13
Rear: 325/45R13
Pressure in PSI please

Front Tyre Pressure: 23.8 psi
Rear Tyre Pressure: 22.6 psi

Hey RR, here’s some feedback. First overall impressions, the car felt more sluggish and less responsive from my previous settings of 28.5 a piece. Also, I’m like 24th or something on LB East with this car so when I say it slowed me down by over a sec, that’s a lot. I started bumping both front and rear pressures up by .5psi until I got the sticky feeling back and that ended up being exactly 4 psi higher on both ends.

I would like to think that these pressures feel a lot less responsive due to the tune on the rest of the car, but that would take a while to work back out, so this is the best I could give you for now. Also, do you tune around your tires to begin with? That could be the biggest factor with your formula here.

Yes, I tune everything around my tyres as they’re the first part of contact with the road.

HI RR, here’s the caterham stats I spoke last night

Car: Caterham
Weight: 1333 lbs
Front: 195/45R13
Rear: 325/45R13

50% Distribution

Front Tyre Pressure: 25.8 psi
Rear Tyre Pressure: 22.3 psi

Are you sure those tyre stats are right? Because the front tyre is a lot thinner than the rear!.. But anyway… see how they feel.
RR

Yep sorry, was a late night and don’t know what happened, or where I got the tyre sizes from

195/45R14 FR
255/45R14 R
1333lbs
50% Distribution

Lets try again :smiley:

Thought those widths were crazy =P
Anyway,
Front Tyre Pressure: 25.4 psi
Rear Tyre Pressure: 23.4 psi

Hopefully these are better, thanks,
RR

I will throw something in here a little later. Very interesting read so far. I noticed right away in FM 5 that the lower pressures give a little better grip on some cars. I will be back to post some stats, and give it a go.