A few minutes with the gear down in the air is equivalent for getting onto an hour of ground cooling just sitting still with a very minor draft blowing through the undercarriage, or flying with the gear retracted (very poor air circulation). As a result, some short legs with quick turnarounds can cause the wheel brakes and tyres to start getting really hot. For the Classic 747, hot brakes are quite a problem. A landing at max landing weight alone can easily cause very hot brakes, and that is only using light braking.