I have a few questions regarding this game that I haven't seen answered yet in any of the previews I've read and am wondering if anyone here knows the answers.  
 
-Has the driving model changed from 3?  I loved how 3 felt but there were a few problems.  The cars felt different from one another in some ways but not in others.  For example, a RWD car felt different then an AWD car.  However, I could rarely feel a difference between two RWD cars or two AWD cars.  Further, all four wheels rode on a singular plane under the cars in 3.  By this I mean that the cars didn't feel as if each wheel had a unique suspension.  Rather, they all sort of shared one universal suspension which made the experience feel a little less realistic.  Have either of these issues been addressed?  
 
-Has the collision detection and damage model been improved?  In 3, the damage model was fine and it was cool how the damage affected the driving experience.  However, bumping into walls sometimes led to some very unrealistic physics.  At times, the cars almost behaved like bumper cars.  Rather then the car compressing as it hit a wall it bounced off as if it had hit a spring.  This happened when the player's car hit other objects as well like other cars.  Is that going to be addressed?
 
-Will there be weather and day/night changes to tracks?  3 had a pretty good number of tracks and locations.  However, because the season mode is so long I eventually got tired of looking at the same tracks over and over again.  I know that the developers can't put an endless supply of track locations in the game due to size constraints.  However, by changing the time of day the race occurs and the type of weather being experienced the tracks, though exactly the same as they were before, can look and play very differently.  Will this be a feature in the new game?

So, no one knows the answers to any of these questions?

I can't say for the first one, but I believe the damage model has been changed somewhat. As for the weather and time cycles, I think they're still remaining as they are. As I said though I'm not entirely certain and I haven't really been keeping up to date so I might be wrong.

I can't say for the first one, but I believe the damage model has been changed somewhat. As for the weather and time cycles, I think they're still remaining as they are. As I said though I'm not entirely certain and I haven't really been keeping up to date so I might be wrong.

Some tracks will give you the option to play them at day or dusk but they haven't shown any night racing. Also they are working with Pirelli on there new tire physics.

Some tracks will give you the option to play them at day or dusk but they haven't shown any night racing. Also they are working with Pirelli on there new tire physics.

@JasonR86: I'm not sure I just remember in an interview they said they were redoing there tire physics.

this should answer 2 of those questions for you: 
http://forzamotorsport.net/en-us/underthehood2/