car.rb

class Car < ActiveRecord::Base
  has_many :drivers, :inverse_of => :car
end

class CreateCars < ActiveRecord::Migration
  def self.up
    create_table :cars do |t|
    end
  end

  def self.down
    drop_table :cars
  end
end

driver.rb

class Driver < ActiveRecord::Base
  belongs_to :car, :inverse_of => :drivers
end

class CreateDrivers < ActiveRecord::Migration
  def self.up
    create_table :drivers do |t|
      t.references :car
    end
  end

  def self.down
    drop_table :drivers
  end
end

gistfile3.txt

>> c = Car.create
=> #<Car id: 1, created_at: "2010-06-20 17:39:26", updated_at: "2010-06-20 17:39:26">
>> c.drivers.create
=> #<Driver id: 1, car_id: 1>

>> Car.find(1).drivers.first.car
  Car Load (0.3ms)   SELECT * FROM "cars" WHERE ("cars"."id" = 1) 
  Driver Load (0.2ms)   SELECT * FROM "drivers" WHERE ("drivers".car_id = 1) LIMIT 1
  Car Load (0.2ms)   SELECT * FROM "cars" WHERE ("cars"."id" = 1)

I still have this problem with rails 3.2.5