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Race Driving Fundamentals: Trail Braking

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Trail Braking


00:00 - While the way we apply and hold brake pressure is important, the way we release the brake pedal at the corner entry is often overlooked or misunderstood.
00:09 Done correctly it achieves two crucial things, first it allows us to brake later since we'll be continuing to slow the car as we simultaneously turn into the corner.
00:21 Secondly by manipulating the brake pressure as we turn in, we can control the weight transfer and therefore the balance of the car.
00:29 This can be used to help overcome an inherent chassis imbalance that may be resulting in a natural tendency to either oversteer or understeer at turn in for example.
00:39 Before we cover the process of trail braking, let's just come back to our traction circle and refresh our memory on what's happening as we go through the braking sequence.
00:49 Remember that in order to generate maximum braking force there's no extra grip available to turn the car.
00:56 To put it another way, when we get to the turn in point we're going to need to reduce the braking force in order to allow the car to turn.
01:04 Conventional thinking when it comes to braking on the road is to brake in a straight line, get completely off the brakes and then begin turning into the corner.
01:12 This all makes sense in light of the available grip from the tyres and it's a safe technique on the road.
01:19 On the racetrack however it creates two problems that are going to cost us a lot of time.
01:24 First of all, if we want to get all of our braking done before we start turning into the corner, we're going to need to brake earlier.
01:31 Secondly, if we plot what this technique would look like on the traction circle, we can see that we're doing a horrible job of exploiting grip from the tyre.
01:40 If we take the concept to the extreme, we're only ever applying braking force or cornering force but never a combination of both.
01:49 Remember that ideally we want to ride the rim of the traction circle as we transition from braking to cornering.
01:55 To do this we want to still do the majority of our braking in a straight line, however as we approach the turn in point, we'll begin to release the brake pressure.
02:03 We're not going to completely release the brakes so we'll still continue to slow the car.
02:09 Since we're reduced the brake pressure, we're now asking less from the tyres and this will free up the grip that's required that'll allow us to turn into the corner.
02:18 As we approach the apex we'll require more steering lock which generates more lateral force and this of course means that the tyres won't be able to generate as much braking force so we need to further reduce the brake pressure.
02:31 If we look at the relationship between the brake pressure and steering angle, it'll look something like this.
02:38 We still have an initial drop off in brake pressure as we're nearing the turn in point but then the brake pressure tapers off much more slowly as the steering angle is increased.
02:48 Finally as we get closer to the apex we'll be completely off the brake again.
02:53 Done correctly, the GG diagram should look more like this.
02:57 Although it's not perfectly following the rim of the traction circle, you can see how much more of the tyre's potential grip is now being used.
03:06 You may be wondering what the correct amount of brake release is and exactly when this should be done.
03:12 Unfortunately there's no one solid answer for these questions, it's dependent on our vehicle, the circuit and the conditions and getting a feel for it is something that can only come with practice so the question then is, how do we start practicing this technique? To give you a ballpark to aim for the brake release generally starts just before we reach the initial turn in point and you should be completely off the brakes before you reach the apex.
03:38 A good rule of thumb here is the relation between steering and brake.
03:42 The rate at which we're reducing steering lock should be similar to the rate at which we're releasing the brakes.
03:48 Trail braking is also a great tool to help you manipulate the handling of the vehicle.
03:54 By adjusting the amount of brake pressure you're using, this will also alter the weight transfer front to rear which will affect the available grip.
04:02 So where would this be useful? Well if we've got a car that's suffering from understeer at turn in, trail braking will help keep additional load on the front tyres during turn in, which will increase the available grip.
04:14 This is a fine line of course because if we're still demanding too much braking force at turn in, there won't be enough grip to turn the car.
04:22 In some instances, we can take advantage of this weight transfer that results from trail braking to purposefully create some oversteer and help rotate the car into a tight corner.
04:34 It's also worth understanding that we don't necessarily need to trail brake into every corner.
04:40 This is a technique that's most useful for slower corners where we're spending more time on the brakes and we want to help rotate the car into the corner.
04:48 On the other hand, with faster corners where we don't need to reduce speed so much, we'll usually trail brake less as this will transfer less grip away from the rear which can result in the car feeling more settled and predictable, exactly what we want in a high speed corner.
05:04 This is all a fine balance and something that's a constantly moving target over a race weekend depending on the grip levels of the track.
05:12 These levels can change due to anything from track temperature, track condition or tyre condition.
05:18 This requires us as drivers to constantly explore these limits and think about how the brake release went on any given corner and whether we were too fast or too slow at the apex..
05:29 We should also be thinking about the balance of the car during this time and whether we can help improve these characteristics with the rate we bleed off the brake pedal.
05:38 In summary, trail braking is a fine art that allows us to both scrub off speed and turn into a corner simultaneously.
05:45 If this wasn't an option, we'd have to do all of our braking on the straight much earlier before we could turn in.
05:52 This way, we can save time by combining the two inputs.
05:55 The key to this technique lies in an equal balance between both inputs in order to ride the rim of the traction circle, As the brake pedal pressure is bled off, more grip is freed up to be utilised by more steering lock as we approach the apex.
06:10 More than that it's also an extremely effective way of controlling the handling balance of the car by manipulating the weight transfer front to rear as we enter the first phase of the corner.

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