Season 3 brought one of the most impactful rule changes in recent iRacing memory. IMSA-licensed series now follow real-world IMSA WeatherTech Championship pit stop regulations. For iRacing IMSA endurance competitors, this means two concrete changes that affect every stop you take. First, a mandatory minimum stop time applies regardless of how much service you request. Second, simultaneous tire and fuel service is now permitted, allowing crews to refuel and change tires at the same time. Fuel burn rates also changed for several GT4 cars on the IMSA grid. Understanding how these rules interact is the foundation of competitive IMSA endurance strategy in Season 3.
Also See
➡️ iRacing Season 3 Pit Stop Rules by Series: Every Ruleset Explained
➡️ iRacing Pit Stop Strategy: Fuel Before Tires Explained
🏁 iRacing Season 3 2026 Release Notes
What Changed for IMSA in Season 3
Before Season 3, pit stop procedures across iRacing were largely uniform. Every series ran under the same basic timing rules. Season 3 changed that by tying pit regulations directly to the real-world sanctioning body for each series. For IMSA-licensed content, IMSA WeatherTech Championship pit lane procedures now dictate the rules.
Three series run under the IMSA ruleset in official competition: the IMSA Endurance Series, the IMSA iRacing Series, and the IMSA iRacing Series Fixed. The IMSA Michelin Pilot Challenge Series and IMSA Sportscar Endurance Challenge also use IMSA regulations. Several special events, including the Watkins Glen 6 Hour and 6 Hours of Road America, run under the same ruleset. If you are competing in any of these series, these rules apply to every stop you take.
For endurance racers who built strategy around iRacing’s previous default timing, the Season 3 IMSA changes require a rethink. The minimum stop time, the simultaneous service option, and the revised fuel figures all affect how you plan stints. Carry old assumptions into a Season 3 IMSA race and you will produce wrong calculations and likely lose positions.
The Mandatory Minimum Stop Time
Under the IMSA ruleset, every pit stop carries a mandatory minimum box time. This minimum applies regardless of how much service you request. Whether you take fuel only, change all four tires, or do both simultaneously, the clock runs until the minimum clears. You cannot exit the box before it does. You cannot take a splash of fuel and rejoin in seconds the way you might in an unregulated series.
The practical implication for strategy is that the minimum stop time becomes a fixed cost in every stint calculation. When you model your fuel window, you cannot assume a fuel-only stop is meaningfully shorter than a full-service stop. The floor limits how much you can differentiate stop length based on service chosen. In real-world IMSA racing, this rule exists to prevent undercutting on stops that take no time at all. In iRacing, it has the same effect. The stop costs track time, and that cost is non-negotiable.
For short stints under a full-course yellow, this matters most. The temptation under a caution is to pit immediately, grab a splash of fuel, and rejoin quickly. Under the IMSA ruleset, that splash still costs you the minimum stop time. Build your caution stop strategy around the floor, not around how fast your crew can fill the tank.
Simultaneous Tire and Fuel Service
The other major procedural change under the IMSA ruleset is simultaneous service. In Season 3, your crew can change tires and add fuel at the same time. This mirrors real IMSA pit procedure, where the over-the-wall crew works on the car while the fuel hose connects.
The strategic value of simultaneous service is significant in long-format endurance racing. Previously, a full-service stop covering fuel plus all four tires ran sequentially: fueling finished, then tires changed, or vice versa. Simultaneous service collapses that into a single window. If the fuel and tire work finish within the same time span, you get both done for the cost of one service window.
This changes how aggressively you should approach tire changes. In a pre-Season 3 endurance race, taking four tires added meaningful time to a stop. Teams sometimes skipped the change to save time. Under IMSA rules with simultaneous service, you are already sitting in the box for the minimum stop time. Any tire work that finishes within that window costs you nothing extra. The calculation of whether to take tires shifts toward: does the tire work finish before I am ready to leave anyway?
Fuel Burn Rate Changes in Season 3
Season 3 adjusted fuel burn rates for three GT4 cars that run in IMSA-licensed series. iRacing made these changes as part of the BoP update, and they directly affect how you calculate fuel stints in endurance races.
The Mercedes-AMG GT4 received a 3.0% increase in fuel burn rate. This is the largest adjustment of the three cars. If you ran the Mercedes-AMG GT4 in Season 2 IMSA competition, your previous stint calculations are no longer accurate. A car that reached the end of a fuel window with margin will now run short. Do not carry those numbers forward. Recalculate your fuel window using current burn data before you race.
The Porsche 718 GT4 and BMW M4 GT4 Evo each received a 2.5% increase in fuel burn rate. Like the Mercedes-AMG GT4, both cars burn more fuel per lap in Season 3 than they did in Season 2. The 2.5% change is meaningful over a long stint. Across a 30-minute fuel window, the difference compounds enough to matter. It affects how many laps you can complete before a mandatory stop. In a three-hour-plus IMSA race, a miscalculated burn rate can force an extra pit stop. Your competitors may not need that stop.
GTP class machinery running in IMSA series did not receive fuel burn rate changes in this update. Any cars not listed in the Season 3 release notes are unchanged. If you race a GTP car in the IMSA Endurance Series, your Season 2 fuel numbers are a reasonable baseline. Adjust for track and conditions as needed.
Building Your Stint Plan Under IMSA Rules
The combination of a mandatory minimum stop time, simultaneous service availability, and revised fuel burn rates means endurance strategy in Season 3 IMSA racing requires updated inputs. Start with your per-lap fuel consumption on the specific track you are racing. Use in-race telemetry or practice data from Season 3. Numbers from a previous season or a different car configuration will not be accurate.
From there, calculate your maximum fuel stint length in laps. Subtract a buffer of one or two laps as a safety margin against fuel reading inaccuracies. Then anchor your stop timing to the minimum stop time as a floor. If your fuel window calls for a stop at lap 28, check whether stopping at lap 26 or 27 costs you anything extra. If the minimum stop time covers the gap, stopping early and taking fresh tires simultaneously is worth modeling.
Full-course yellows are a separate planning layer. Under IMSA regulations, a caution is still a potential pit window. The mandatory minimum stop time limits how quickly you can cycle through. If pitting costs more than continuing when the caution drops, the minimum stop time factors into that math. A caution with two laps before your planned stop forces a decision. Pit now and spend the minimum stop time under yellow, or stay out and green-flag stop. In a long-format race, that decision has real points implications.
Tire Compound Selection Under IMSA Regulations
Simultaneous service changes the calculus for tire compound strategy. When tire work overlaps with fuel service at no additional time cost, the penalty for harder compound tires changes. Harder tires typically need a longer warm-up to reach operating temperature. Under IMSA rules, that cost is the track time of the warm-up itself, not additional stop time.
If you will be in the box for the minimum stop time regardless of service, there is limited reason to skip tires. The exception is a tactical position battle where one more lap on current rubber gives you an advantage. For most iRacing IMSA endurance competitors, the Season 3 default should be clear: take tires unless there is a specific tactical reason not to.
For races where tire wear matters, the simultaneous service option opens up mixed strategies. On tracks with high degradation, partial tire changes become worth modeling. Changing two tires while fueling can be worth exploring when one axle has not yet reached the degradation point where a full change is clearly optimal. Under older iRacing rules, a partial tire change carried a time penalty that often made it uncompetitive. Under IMSA rules with simultaneous service, partial tire changes within the stop window are a legitimate option.
The Season 3 IMSA changes raise the ceiling on how much endurance strategy matters in iRacing competition. The mandatory minimum stop time, simultaneous service, and revised fuel burn rates give teams more variables to optimize. There are more ways to differentiate from competitors who have not done the homework. For anyone who takes iRacing IMSA endurance racing seriously, these are not minor patches. They are the new foundation. Build every stint plan around them.
