ACC drops FPS at race starts because the processor suddenly has to calculate physics, collisions and AI for a full grid at the same time. In rain and at night, the graphics card gets extra work on top of that: spray, raindrops, wet reflections and dozens of headlights. The fix is to lower the settings that load the CPU, such as visible cars, and the settings that explode in the wet, such as mirrors and shadows.
The good news is that you rarely need new hardware. You first need to know which part of your PC runs out of breath.
What makes ACC heavier in the wet and at the start?
Two different problems look the same on your screen, so it helps to split them.
Race starts load the processor
In free practice you drive alone. At the start of a race, 20 to 30 cars sit within a few hundred metres of you. ACC then calculates physics and contact for every car near you, and the AI drivers make decisions every frame. That work runs on the CPU. When the CPU cannot keep up, the graphics card waits, and you feel stutter and input lag right when you need precision most.
Rain and night load the graphics card
Rain adds spray behind every car, raindrops on the screen and wet reflections on the track. At night, every car carries its own headlights, and each light source costs extra work. Add mirrors, which render the scene a second time, and the load almost doubles. ACC improved the spray and raindrop shaders in update 1.8, but wet races with a full grid stay the heaviest moments in the game.
How do you see which part is the bottleneck?
A quick check with an overlay tells you where to look.
Read CPU and GPU usage side by side
Open an overlay such as the one in your GPU driver and start a race with a full grid. If one CPU core sits near 90 percent or more while the graphics card stays well below its maximum, ACC is CPU bound. If the graphics card runs at 95 to 100 percent, the GPU is the limit.
SIMGASM | Pro Aluminum Sim Racing Cockpit - White
Test the worst case, not an empty track
Many drivers tune their settings in a dry hotlap and then wonder why the race feels different. Always test with a full grid, in rain, at night, from the start. That is the moment your settings need to survive. At SIMGASM, we follow the same thinking with hardware: every product is tested as part of a complete simulator under real loads, not as a loose part.
Settings that fix drops at the start
These settings take load off the processor without making the game look worse from your seat.
Lower visible cars
Visible cars decides how many opponents ACC fully renders around you. Setting it to 15 or 20 instead of all keeps the cars you race against on screen and cuts work on cars far away. Setting it lower than 10 makes cars pop up in your mirrors, which is not safe.
Cap your frame rate
Set the frame rate limit to your monitor refresh rate. A stable 120 frames feels smoother than a number that jumps between 160 and 90. It also leaves headroom for the heavy first corner.
Tidy up Windows
Close browser tabs, recording software and RGB tools before a race. Use a high performance power plan and keep your GPU driver up to date. Our sim racing latency checklist lists the rest.
SIMGASM | Hobby Aluminum Sim Racing Cockpit - Black
Settings that fix drops in rain and at night
For wet and dark races, the graphics card needs relief in the right places.
Mirrors first
Lower rearview mirror quality and resolution to medium or low, and set mirror distance to about 100 metres. A mirror frame rate limit around 30 also helps a lot. You still see who is behind you, which is all a mirror needs to do.
Shadows second
Shadows are one of the heaviest settings in ACC. Medium often looks almost the same from the cockpit. Turn contact shadows off, because they cost a lot and add little in a race car. If you still miss frames, try DLSS or FSR. Our comparison of DLSS or FSR in ACC shows which one suits your card.
Keep the rest of the setup quiet
A heavy wet race is also when your rig works hardest, with long braking zones and lots of steering corrections. Founder Johan Akkerman won real championships in the DNRT BMW E30 Cup in 2023 and 2024, and he raced the Alpine A110 Cup in wet conditions at Nogaro. His view is clear: consistency over a long session matters as much as stiffness. A screen that shakes in the rain makes a drop in frames feel even worse.
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Questions about FPS drops in ACC
These short answers cover the most common follow up questions.
Why does ACC run fine in practice but stutter in races?
In practice you drive alone. In a race, the CPU must handle physics and AI for many cars, which often makes ACC CPU bound at the start.
Which setting helps most in the rain?
Mirror quality, mirror distance and shadows. Lower those before you touch resolution, as our ACC video settings guide explains.
Does a faster graphics card fix race start lag?
Not if the CPU is the limit. Check usage with an overlay first. A CPU with strong single core speed helps more in that case.
Do force feedback settings affect FPS?
No, but heavy stutter makes force feedback feel rough. Our Fanatec ACC settings guide helps you tune the wheel once the frame rate is stable.
Want to learn more? The SIMGASM experts are happy to help.
