iRacing Season 4: NASCAR 26 launch, three track rebuilds, Aston Martin Valkyrie and Caterham cars
iRacing has announced major updates arriving with Season 4, headlined by the September 18th launch of NASCAR 26 alongside significant physics engine improvements and a substantial roster of new and refreshed content.
Tracks
Three classic circuits receive complete rebuilds based on fresh laser scans captured in 2026. Road America, part of iRacing's original 2008 lineup, has been fully reconstructed and will gain two new configurations featuring the Turn 5 bypass road (East and West variants). Mid-Ohio Sports Car Course, added in 2010, has been rebuilt to emphasise its variable terrain and sweeping layout. Milwaukee Mile also receives a complete overhaul and introduces a new Road circuit configuration in Roval style. Existing owners of these tracks will receive the updated versions automatically at no cost; older versions will be retired.
Two additional tracks receive visual refreshes. Summit Point Raceway undergoes a complete art upgrade with rebuilt models, textures, curbs and scenery throughout. Jefferson Circuit receives the same treatment. Road Atlanta gains new track surface textures, 3D curbs, foliage, trees and upgraded scenery.
Cars
The Aston Martin Valkyrie AMR-LMH arrives after over a year of development, incorporating telemetry, engineering data and direct collaboration with the manufacturer to capture the V12 hypercar's power, downforce and chassis dynamics.
iRacing has partnered with Caterham Cars to deliver two open-wheel sports cars: the Caterham Academy and Caterham 420R. Both vehicles will be sold as a single package. The Academy, designed for novice racers, emphasises lightweight mechanical grip and pack racing dynamics, positioned in Class D series. The 420R offers increased power-to-weight ratio and will compete in Class C.
The Mazda MX-5 receives a complete re-engineering covering suspension kinematics, engine tuning, damper specifications, tire model integration and aerodynamics. The update aims to deliver more intuitive handling and closer door-to-door racing. The Gen 4 Grand National stock car joins the existing Gen 4 Cup package, positioned just below the premier division with high-momentum racing characteristics. Both Gen 4 cars receive drafting model updates. The pavement Sprint Car undergoes a front-to-rear rebuild with increased power, broader low-end torque, new tire model, overhauled suspension geometry and updated braking, developed in partnership with real-world and sim community drivers.
Sim Systems
The physics engine receives its first major milestone from a multi-year overhaul initiative called 'Physics Islands'. The core physics update loop has been refactored and multi-threaded, distributing calculations across available CPU threads. In full-field races and crowded multi-car battles, CPU physics overhead drops by 50% or more across a range of hardware, with gains unlocking future improvements to physics tick rates, input sampling and force feedback loops.
A new multi-class, multi-pace car system launches for Season 4, deploying dedicated pace cars for each class and independent green flags for every category. The feature initially rolls out on select tracks with full support in official IMSA series, aiming to eliminate chaotic grid stacking and improve turn-one racing fairness.
Season 4 also introduces updates to the Sim UI engine, retiring legacy architecture to unlock long-planned interface advancements. NASCAR 26 includes a new Chase mode allowing players to jump directly into championship racing, alongside new burnout celebration animations.