Come on Turn 10! We need to access to set up when entering the pits on test drive. So we can Change car set up instead of quitting the game. Going back to set up then start all over again losing old lap times and setting new laps.
Having in game option we could then compare lap time after car adjustments. Not having this option is short sighted from you guys. Get that up date out please! 
I use Test Drive in Free Play to tune my cars - I access Tuning by pausing the game.
If you’re looking for realism i.e. fresh tyres to go with your changed settings, why not adjust your settings as you approach the pit entry, then pit. You have fresh tyres and a full tank to go with your new settings.
I’m not looking for realism here, tuning the car by pausing the game works well enough for me. My issue with this is if I’ve done a bunch of laps and have new parts to put on the car, the intuitive thing to do is to come in to the pits to put those parts on. Instead, i always end up needing to select tyres (same) and fuel (same), rejoin the track, then pause and exit to the garage (where I just was). If there was some sort of prompt on pit entry to “End run” (hold B or something), it’d save save the pain of needing to leave the pits and then go back in via menu.
It’s a decent idea. I like it. Where can I vote on it?
It would be a nice quality of life thing. I ran that Challenger Demon race and couldn’t get the back end from coming around. Once I found out that the car was on Drag tires as stock tires… I wanted to rip them off and toss on some Sport tires ASAP. Too bad I had to quit the event to do it.