Ackerman

[Gustav]

For a good visual example,take a look at a mini or a london taxi cab on full lock.Both these cars use a lot of ackerman to give their tight turning circles and it's very pronounced .

Basically,take any car (one of your RCs) and turn to full lock.You'll notice that the inside wheel turns tighter than the outside.This is because the outside wheel has further to travel than the inside so ackerman reduces how much they fight each other (scrub) particularly when turning tightly.Think of it as having a similar effect to your front diff(diff allows outside wheel to spin faster than inside as it has further to travel).Without the diff and ackerman the front tires will fight each other to turn and turn in and turning circle will be poor.