Pre season test / team progress.
I think it would enhance the game if their was a pre season test.
A three day test. Each day is 10/15 laps on the different tyre options. At the end of the test you see the fastest lap times. Thus you can see if your team is developing or going backwards. If you are unhappy with your team an option to jump ship during the season or replace an injured driver on a short term contract could be more appealing if you are at the back of the grid. This gives you an opportunity to create a bigger driving pool of test drivers ect, as well as a driver market and contracts.
I would like to the teams levels of performance go up and down over the years as guide of who to sign for as after two / three seasons you know who is the fastest car and the game becomes easy. It would make it more fun for long term players if you had to monitor the progress of certain teams to chose your offer for next season.
I will be a long term player, at current say I want to do a ten season career I have pretty much done it all by season 4. A few peaks and troughs will keep me in interested.

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Thanks Ross - I agree this will add a lot more "longer term" depth.