[exDM69]

Aero models are actually much simpler than racing tyre models.

Most older flight sims used a lookup table for aerodynamic forces, which is gives a pretty decent model for most of the flight envelope. Newer sims do model the airflow around the wings but it's still relatively simple.

Tyre models have similar history, most models are empirical and based on the Pacejka tyre model with some adjustments, not quite a lookup table but some very basic math formulae with no physics behind it. Notable exception is iRacing which has a physically based tyre model based.

But the physical phenomena going on in a deforming, elastic racing tyre are much more complex than a wing cutting through air.

[lloeki]

Not sure about the details, Forza Motorsport 4 has completely redeveloped the tire model at some point, with fresh intel from (IIRC) Pirelli, and they only improved since then.

I could be wrong but it seems to go way beyond Pacejka in my experience (including sidewall deformation). On old cars it's night and day.

[exDM69]

I assume most sims have moved beyond vanilla Pacejka model by now, but they are generally still empirical models with their roots in Pajecka. The standard model doesn't account for dynamically changing pressures and temperatures, for example.

When tyre manufacturers provide data, it is usually in the form of coefficients for the Pacejka model or some variant thereof, the model being the de facto standard in the automotive industry.

But I admit I don't know the specifics about Forza 4 tyre model.

At least a few years ago, the iRacing tyre model developers said in their dev log videos that their model is unique in being physically based and not an empirical model. But that may have changed.

Empirical models are generally considered "better" feeling for sim racing, iRacing's model is criticized for being bad in handling extreme slip angles and ratios (read: drifting).

[magicalhippo]

Project CARS described their tire model that they developed for the first game[1], based on three coupled simulations for the carcass, threads and heat. They describe it as a fully dynamic model.

Not sure what the state of the art is though, I just recalled this post from way back.

[1]: http://www.wmdportal.com/projectnews/inside-project-cars-set...

[lloeki]

> The standard model doesn't account for dynamically changing pressures and temperatures, for example.

Forza definitely accounts for these, there are three thermal bands exposed in the telemtry UI: outer, middle, and inner. Pressure is a tunable, and it varies with heat.

There is also axial and radial deformation. Like, on small rim/big wall tires accelerating produces a tire twist along its rotating axis, as the wall itself is elastic, which creates a lag in tire reaction, followed by a tightening (and even a bounce) when it reaches elasticity limit. Same on turns when the tires deform laterally and depress, which creates some additional lag/bounce back effects that tally up to create interesting situations at the limit. This all matches up with my (completely anecdotal and limited) real life experience.

Most people play the cars tuned up to a given perf class slot, which often includes rim/tire upgrades by default (there's an auto-tune feature) when handed by the game for the cars to be sort of competitive in that perf class, so they probably don't get to feel that to the full extent. I myself don't care about the perf, I like to restore the car parts and settings to stock condition and enjoy the "original" feel of cars I will probably never drive or ever come near, and lap the car by myself or with a couple of like-minded friends.

> Empirical models are generally considered "better" feeling for sim racing

Yeah, theory has this way of matching reality, save for the corner cases that are the ones being interesting. I god honest don't know what Forza is using, and certainly don't claim it's a super accurate sim, but they did a fantastic job to make it feel realistic to great detail, and gracefully degrading from a full-fledged sim race setup to a gamepad (where it still manages to convey a ludicrous amount of info given the device limitations)

[exDM69]

Live for Speed also had tyre deformation, temperature, pressure etc but it was still based on Pacejka model, applied to different parts of the tyre separately.