"When you're in the back of the pack, you can gamble a little bit more"

This quote by Michael Andretti is describing the technique of racing. When a chauffeur remains in the back of the pack, they have more flexibility to take threats and try various methods. This is because they are not in contention for the win and can pay for to take a couple of risks. For instance, they may attempt a different line on the track, or take a rest stop earlier than anticipated. This can be a dangerous relocation, however if it settles, it can help the chauffeur move up the field and get some positions. This is why Andretti recommends that drivers in the back of the pack can "bet a bit more". It is a way to make up ground and possibly finish higher than anticipated.