Simulators calculate how much force each tire can produce from how much it is slipping, how much weight is on it, and its temperature, pressure and wear. Grip rises as a tire slips more, peaks, then falls away. A tire also shares one grip budget between braking, accelerating and turning. Modern sims track how that budget changes lap by lap and send the resulting steering forces to your wheel.
Slip: why a gripping tire is never perfectly rolling
A tire producing force is always slipping a little against the road. Slip comes in two forms: slip ratio, when the tire spins faster or slower than free rolling under acceleration or braking, and slip angle, when the direction the tire points differs from the direction it travels while cornering (background). The slip angle comes from deformation of the tread and carcass in the contact patch (background).
As slip increases, force increases, up to a peak. Past the peak, the tire slides and grip drops, which is the difference between a car on the limit and a car in a slide.
One budget for braking, accelerating and turning
Racing schools describe a tire's capability as a circle. At maximum braking there is no cornering force left; ease off the brake and cornering grip returns. The Skip Barber Racing School notes that data systems on real cars can draw this "friction circle" by plotting lateral against longitudinal G (Going Faster! excerpt, Bentley Publishers). The same idea explains wheelspin, lock-ups and understeer in a sim: each happens when you ask a tire for more than 100% of its grip in one direction (VRS).
How sims turn this into numbers
Many vehicle-dynamics tools use semi-empirical tire models, a widely used one being the "Magic Formula" developed by Hans Pacejka of Delft University of Technology. It is fitted to measured tire data rather than derived from first principles, which is why it can describe a wide range of tires (background). A 2023 paper notes that tread depth, inflation pressure, tire temperature and road surface all significantly change tire force characteristics, and proposes adapting Magic Formula coefficients to account for them (Singh & Sivaramakrishnan, arXiv).
Simulator developers rarely publish their full tire models, but they do describe what they simulate:
- Assetto Corsa lists tire flat spots and heat cycles including graining and blistering (Steam).
- Assetto Corsa Competizione describes a mathematical model of tire grip, aerodynamics, engine, suspension and electronics (KUNOS).
- KUNOS says Assetto Corsa EVO adds a new tire model (KUNOS).
Temperature, pressure and wear
Temperature and pressure change how much force a tire can produce (see the arXiv paper above), which is why racing tires are built for specific conditions. Pirelli describes its Formula 1 intermediate as having "a wide working range" and explains that full wets are built to disperse water and resist aquaplaning (Pirelli). In iRacing, an engineer explains that telemetry tire temperatures act like an infrared sensor and change sharply through a lap, while garage readings work like a probe pyrometer, and that comparing the two helps diagnose a tire that is being loaded too quickly (iRacing).
The track changes too
Grip also depends on the surface. iRacing models rubber laid down on the racing line and track temperature that varies with sun and shade, so shaded sections can offer more grip on a hot day (iRacing). Assetto Corsa simulates rubber deposited on the track as laps are completed (Steam).
What you feel through the wheel
The self-aligning torque created by the slip angle is a large part of steering feel (background). As the front tires near their peak, that torque changes, and a detailed force-feedback wheel lets you feel it. That is why steering hardware matters; see how direct-drive wheels work and force feedback and motion simulation.
Driving tips that follow from the physics
- Do most of your braking in a straight line, then trail off as you turn.
- Be smooth with steering and throttle so you stay near the peak instead of past it.
- If the car understeers on entry, you are probably asking the front tires for braking and cornering at the same time.
Try it on a full rig
SimsForHire brings racing simulators with force-feedback wheels and SIGMA Integrale electric motion platforms to corporate events, private parties and trade shows. Delivery is free within 50 miles of Miami. See pricing or call (754) 228-5654.