As a car races forwards it punches a hole in the air as it goes along, and after the car has gone past the displaced air rushes in to fill the gap.
If you travel very close to the car in front you will notice that you can go faster than he is able to. This is known as drafting or slipstreaming. The leading car disturbs the air and does all of the work, the following car (travelling in a nice pocket with almost no wind resistance) is not inhibited and can build up speed faster than normally possible. The trailing car "gets a tow" from the car in front.
It is easy to see how drafting could be used to overtake your opponents and indeed it is a much-used overtaking technique. In some cases two cars may be so well matched that the only chance the trailing driver has to overtake is by drafting on a long straight. So obviously drafting has real benefits, but also there are hazards.
Benefits: - Your car may reach a higher top speed by drafting (once you pull out of the draft the wind resistance will steadily pull your speed back to the normal maximum for your setup. However your gear ratios and final drive will ultimately effect how well your car can take advantage of drafting).
- Drafting gives you a temporary and short-lived opportunity to gain position, but timing is important. Sometimes drafting may be the only safe way past your rival.
- Drafting can reduce lap times during a race and may have a minimal fuel-saving benefit.
Risks: - Braking is not as effective when travelling in another car's slipstream. Not only are you perhaps travelling faster than normal when you reach your braking zone but you have less resistance and slowing down will not be as abrupt as usual. The potential to shunt the leading car is great, and racers should always be prepared to adjust their braking to suit the situation.
- Shunting while travelling at full speed is also a risk. If you are very close behind the leading car then your speed may incease very rapidly in a short time. You don't want to shunt the other racer, you'll either damage both cars or even worse you may propel him forward and increase his lead!
- Cornering in the slipstream can be very tricky. Aerodynamic downforce that is generated by some types of cars (GTR, FOX, FO8) can be affected when there is no air to create downforce on the wings or spoilers. Coupled with your extra speed when drafting this can cause spin-outs in fast curves and can effect your braking too.
Considerations: Should I draft other cars in a race? Absolutely, but be wary of contact and be ready to brake earlier then usual when approaching corners or slower drivers. Is drafting a sure way to overtake an opponent? No. Often the benefit gained from drafting is not enough to make the pass. If you get close to the leading car early on to the straight then you have a real chance of winning the position, but be wary of jumping into the slipstream late, make sure you have enough room to carry out your plans. What do I do if another car is drafting me? If on a straight, hold your line but do not swerve or block, if you get overtaken, then that's motor racing, set yourself up for a well-timed attack further up the track or on the next lap and fight back when you have a real chance of making it happen. If approaching a corner you can take a defensive line to make overtaking more difficult, but swerving is still a no-no. You should only ever make one defensive movement in response to an attack. Absolutely do not brake earlier than usual if you can help it. Remember that the drafting car will brake with difficulty.