Here is fun idea that also saves time
If you have all DLC my mod below should activate
www.dropbox.com
Go offline run mod, set up conditions, select only 14 AI
In opponents select GT3 and GTE only that will give you 15 models in list
run room once to save and Close rF2
Set up dedicated sever should not need ports for you to see the room
Join your room select first car you want to test and do laps
In garage you will see tab to select car
click and select any of 15 cars
all lap times are kept for all cars you drive just reload a car you already drove
People complain rF2 takes too long to load I have to agree
So if you only have a hour to drive 1/2 your time is spent loading the room 15 times to drive the 15 cars
This way it is instant swap
and you don't get any lag or other effect from doing this or lose rubber or time of day or lose lap times like you do reloading for a new car offline
Pick out your favourite 15 skins and tracks and make your own mod same way
even add Prototype you can have up to 25 different models
at least that was limit from first builds don't know about now probably 25 still
Also you notice there will only be 1 of every model no matter what you drive , that is why you have to select only one skin for each model or you will get random duplicates
As far as I am aware this is unique to rfactor2
If you wanted to drive 15 cars in any other sim all the loading time will take longer then this no matter how fast they load !
MORE TIDBITS
Of course one of the prime mods for this is ASR single cars
make mod the same as above, pick one skin for each, if you have 23 ASR models select 22AI
At Italy 66 you can do hotlap for that many F1 in under a hour ie: esc for cool down lap
Normal way would take longer just for the 22 reloads
Any sim will be slower reloading 22 times then rF2 is 1 time