Aerodynamics Fundamentals: Downforce & Drag Effects on Lap Times
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Downforce & Drag Effects on Lap Times
03.59
| 00:00 | We've discussed how aero forces are generated, and what those aero forces do to the tyres, brakes, and engine. |
| 00:06 | But what does that mean for our actual lap times? There's a few important bits of information to follow. |
| 00:12 | Generally speaking, the more downforce we add to the car, the faster we corner and the faster our lap times will be. |
| 00:19 | There's a theoretical upper limit to the amount of downforce that can be generated before we start to overload our tyres. |
| 00:25 | But a standard club level car won't be anywhere near that. |
| 00:28 | So basically, we always want more downforce. |
| 00:31 | From our earlier discussions, you'll remember that drag requires the power from the engine to overcome. |
| 00:37 | So more drag is bad for speed. |
| 00:40 | But drag is a more complex thing to assess with respect to lap time compared to downforce. |
| 00:46 | The power required to overcome the drag force is proportional to the speed of the car cubed. |
| 00:51 | So it really starts to ramp up a lot as the speeds get higher. |
| 00:55 | However, for most cars, the car only approaches its top speed for a very small part of the lap. |
| 01:01 | Most of the lap is spent well below top speed. |
| 01:03 | As a result, for most of the lap, the effects of drag on effective power output of the car are low. |
| 01:10 | When we further consider that at higher speeds we're covering ground faster, so less time is spent there, typically we're not as heavily punished for drag as we may expect just looking at the raw end of straight speeds. |
| 01:24 | I'd take a 10km per hour hit at the end of straight drag any day of the week if I could have a 5km per hour gain in low to medium speed corners. |
| 01:33 | As discussed before, the optimum balance between downforce and drag will vary from car to car and circuit to circuit. |
| 01:40 | So, for example, a track with long straights like Monza or Le Mans requires an efficient car without much drag. |
| 01:47 | While at the other end of the scale, for low speed courses like autocross, drag is almost irrelevant. |
| 01:53 | To contextualise this, at Le Mans, I may consider a part and aerodynamic gain if it produces 5 points of downforce for every point of drag it makes. |
| 02:02 | Whereas for an autocross circuit, I might consider a part of gain if it produces 1 point of downforce for every point of drag it makes. |
| 02:09 | We can see that the average speed, max speed and speed of the corners will play a large part in what the optimums are. |
| 02:17 | More power on a car can allow us to run less efficiency and higher mechanical grip may require us to run more efficiency. |
| 02:24 | At the professional level, lap time simulation is relied upon heavily to determine drag and efficiency targets. |
| 02:31 | But with that said, even at this high level, we'll still often need to refine these targets using on-track testing. |
| 02:38 | At the club level, simulation is less accurate and useful and we tend to rely entirely on track testing, using the stopwatch and running through different drag levels, say by adjusting the rear wing. |
| 02:51 | This will help us understand where the optimum efficiency lies for each track, and don't worry, we'll be covering testing methodologies in detail further into the course. |
| 03:01 | Most touring cars at the club level are overpowered and overweight with the amount of aero on them. |
| 03:07 | So 90% of the time they benefit most from having a higher drag level and more downforce on board. |
| 03:13 | It's very rare that I come across a club level car that will gain lap time by prioritising reduced drag over increased downforce. |
| 03:21 | That wraps up our discussion around downforce and drag effects on lap time. |
| 03:25 | So let's review. |
| 03:27 | Adding downforce generally improves cornering speed and lap times, but it also introduces drag, which can slow the car down on straights. |
| 03:34 | The impact of drag is more significant at high speeds, but since high speed sections are often brief, the trade-off can be worthwhile, especially if downforce gains dramatically improved performance in the lower speed corners. |
| 03:47 | The optimal balance between downforce and drag varies depending on the car and the circuit, and is best determined through methodical on-track testing. |
