Good afternoon fellow iRacers,
This question has been getting asked a lot, so we are going to add it to our FAQs. Many of you are wondering why we limit the number of different car types per session. See below for a thorough explanation!
(Currently we limit to 6 different cars types, not to be confused with cars in a race field, in which we can have race fields of about 60 cars, if not limited by pit stalls).
Historically, when we have increased the number of car types we have run into compatibility issues with customer’s systems. Each additional car type in a session uses about 150MB of video memory, and 275MB of system memory. So six car types easily consumes about 1GB of video memory, and 1.6GB of system memory, that is just for the car types. When you add on all of the car paint jobs for a full session, a large track and all of its objects and textures, graphical frame buffers for the main display, post process effects, anti-aliasing, mirrors, cube maps, etc, it pushes many systems beyond their limits. And on windows, we don’t even have full use of the GPU or system RAM, it is shared across apps and the OS.
Next, there is an issue of stability. The more memory the simulator requires, the more chance there is problems with the GPU device drivers and or operating system that share the available resources. As things approach unknowable limits, the more chance there is of some sort of a memory-related failure, such as failing to resize the screen, or the GPU reporting itself removed to the application. Just using more memory is a risk, as memory is not 100% accurate all of the time, especially when overclocking. Additionally, although a fairly rare issue, whole different stability issue can occur relating to the car physics. With each additional car type, there is more chance of a race session being exposed to an undetected minor physics issue in one of the cars. If any of the car types in the session has a very minor bug, such as a numerical stability issue during collisions, the session is more prone to crashing out.
Finally, but not inconsequential, the car limit helps control load times. Each car type can require can require more than 10 seconds to load, so 6 car types are already over 1 minute of load time, just for the car types, on a fast system.
Simply put, our experience at this time is that the sessions with the most stability issues and longest load times are large multiclass races, particularly at large tracks, for the reasons above. Although our goal is to have everything possible and every feature possible we need to proceed taking everything into account. Our policy is that stability, speed, etc. and overall experience takes precedence over feature sets like having unlimited types of cars in a session. Our plan is to keep increasing the allowed number of car types as systems improve and as we continue to improve the efficiency of the sim. It was not all that long ago that we only allowed three or four car types and we have kept inching it up. It will not be that long until we increase to seven car types, etc.
