Hello,
The weight ballast that is added to some teams in the Rookie and Pro tiers is an automatic measure in an attempt to balance the fields.
The following quotations is taken from the iGP Manager Rules and Regulations:
"Ballast is used in leagues to handicap teams which exceed the regulated performance for the tier (see 3.1 below for more on levels). In leagues, ballast is added as 1kg per level exceeding the tier level cap plus one additional kilogram. For example: a team that is 3 levels over the tier level cap would carry 4kg of ballast (3x1+1), a team that is 7 levels over would use 8kg (7x1+1) and so on."
The level caps per tier are as follows:
Rookie - Level 10
Pro - Level 20
Elite - Level 30
The iGP Manager Rules and Regulations can be found
here.