Tag: tutorial

3.3: Fundamentals: Car control

Posted on by David Williams

A fundamental skill required to drive around a race track as quickly as possible, along with following the optimal racing line, 3.2, is having the ability to carry the maximum speed on that line. This essentially boils down to one thing: car control.

To have good car control means you are comfortable driving a car on the limit of its grip (and sometimes a little bit over it), where the behaviour of the car is very different to that of driving below this limit.

Below the limit, a car will steer to follow exactly the cornering path and radius to which you demand. Yet driving on the limit presents a much bigger challenge, and is where a competent racing driver operates.

How do we know when we’ve reached the limit of grip?
Two behaviours can occur when we exceed the maximum speed for a particular cornering radius. One of these is known as understeer, the other is known as oversteer.

Understeer
Understeer occurs when the available grip at the front tyres is less than at the rear tyres, and as a result the front of the car begins to push wide of the desired cornering radius when the limit of grip is exceeded.

 

Oversteer
Oversteer is the opposite and occurs when the available grip at the rear tyres is less than at the front tyres, and as a result the rear of the car begins to slide wide and the whole car rotates in the steered direction more than desired. When left uncorrected, this typically results in a loss of control and a spin.

 

Typically a car will exhibit very mild understeer or oversteer just below the limit of grip and the maximum possible speed for a given cornering radius. This is usually accompanied with a slight scrubbing sound from the tyres. In a simulator it’s difficult to feel the onset of under or oversteer, but it’s definitely possible to hear how hard you are pushing the tyres, and therefore how close you are to the limit of grip.

If you avoid exceeding the speed which results in these subtle cues from the car and tyres, you will also avoid putting yourself in the situation where you are forced to make a correction for either pushing wide from understeer, or over rotation due to oversteer. However, achieving this without ever exceeding the grip limit is an unrealistic expectation, and as a result it is very important to learn how to make corrections to deal with excessive understeer or oversteer to regain control of the car and bring it back within the limit of grip.

Generally a car will have an inherently built in bias towards either understeer or oversteer, but even a perfectly setup and balanced car can exhibit either characteristic depending on how it is driven.

Correcting for understeer
Understeer is certainly the easiest over-the-limit behaviour to make a correction to. The most effective method is to simply reduce throttle input, and if understeer persists, gently press on the brakes until the car ceases to run wide of the desired cornering line. The most common mistake a driver makes when experiencing understeer is to steer further into the corner. This will never reduce understeer (since you’re already over the limit of grip) and most of the time further reduce the grip at the front tyres, which in turn worsens the understeer.

 

Correcting for oversteer
Oversteer is significantly more difficult to deal with. If it’s felt or observed early enough, it can be fully corrected by doing the opposite to that which created the oversteer in the first place. For example, oversteer can be caused by using too much throttle in rear wheel driven cars, overwhelming the rear tyres and robbing them of lateral grip. Clearly, reducing throttle input in this situation will help reduce the oversteer.

 

There are however, other ways in which oversteer can be induced. There’s so called “lift off oversteer” whereby a driver abruptly lifts off the throttle whilst the car is loaded up mid corner, which causes a sudden deceleration due to engine braking and the car experiences a forward weight transfer shift, which adds grip to the front tyres whilst simultaneously reducing it at the rears. This effect can be even more severe if the driver squeezes on the brake pedal. The best method to correct for this is to quickly reapply some maintenance throttle to shift the weight transfer back to its original balance.

 

Opposite lock or countersteer
Generally, when oversteer occurs, it very quickly escalates beyond the point at which the above methods offer an effective correction, and a further measure is required.

This is known as countersteering, but also goes by the name of opposite lock, or steering into the slide. It is the act of steering in the opposite direction to that which the car is rotating.

 

Common mistakes
One of the most typical situations experienced by drivers who attempt to countersteer when presented with oversteer is overcorrecting. This happens when the correct amount of steering input is applied to begin to reverse the rotation of the car, but the driver is too late at straightening the steering wheel and as a result the car continues to rotate beyond the desired direction and continues into a “spin”.

 

Snap oversteer is another problem inexperienced drivers tend to suffer with, and is characterised by a sudden transition from understeer to oversteer. Typically when the car is understeering, the driver makes the mistake of applying more steering lock, further reducing the front grip. In this situation if the car loses rear grip (which could be caused by an abrupt throttle change, braking or a change in track surface), the car may begin to transition to oversteer whilst the driver maintains steering input. At this stage, if the driver attempts to countersteer, he/she must first unwind the extra steering lock which momentarily results in even more front grip before they can countersteer. Unsurprisingly, this almost always results in a terminal spin before the driver can react properly.

Drifting – sustained oversteer
Oversteer can be deliberately sustained in many cars, and the act of doing so is known as drifting. Drifting involves intentionally provoking oversteer, and then modulating the throttle and steering corrections in a way which prevents the car from spinning out of control but doesn’t fully arrest the slide. It can be a very helpful technique to learn, as it forces you to very quickly learn excellent car control which can help balancing the car on the limit of grip and saving potential spins and / or crashes. Of course we don’t recommend intentional drifting as a means for driving fast!

 

Balance
The ultimate goal here is a word you hear often in top level motor racing circles such as Formula 1, and that is balance. When the car has good balance, it means that you’re equally likely to experience either under or oversteer above the limit, resulting in the most neutral cornering behaviour which is usually the most efficient – and the fastest.

Up to you

We recommend taking the MX-5 out to the centripetal circuit within iRacing and having a play with the car at and over the limit, much in the same way as the demo videos in this article. We’re sure it will help you handle the car better at the limit and improve your overall car control. Aim to sense early cues for under and oversteer, both visually and aurally through tyre noise to recognise when they are nearing their limit of grip. Then apply that to the racetrack!

 

3.2: Fundamentals: The optimal racing line

Posted on by David Williams

Let’s apply the traction circle from 3.1 to the racing line, and combine it what we learned in 2.4, Driving Basics. Simply put, we want the tyres as close to the limit of grip as possible, and we want to carry the largest possible radius through a corner. See the following illustration.

The maximum speed we can carry through a corner is dictated by the size of the radius of the line taken, and as such, in the above corner, the green line will allow for the highest cornering speed for a given grip level.

racing-line

Sequences
Corners vary greatly in shape and style, and often tracks contain closely connected sequences. A good example are turns five to eight at Summit Point Raceway, where the ideal exit of turn five isn’t at the edge of the circuit because you want a wide entry into turn six, where you tighten up before running wide and bringing the car back in again for turn seven and finally turn eight. Notice how when treated as an interconnected sequence, the ideal line still follows the largest radius possible at all times, whilst being a compromise at an individual corner scale.

summit-point

Chicanes are treated in the same way: a combination of two corners with the route of straightest line through both, as seen here at Donington Park National.

donington

Entry vs exit
The ideal line isn’t always symmetric. Driving around a track isn’t a corner-by-corner thing. With each one you should consider what comes before and after. It’s worth, for example, compromising the entrance of a corner for a faster exit if you have a long straight after, as more time can be gained since exit speed is carried for the duration of the straight.

To achieve this, your turn-in point will be later and from a wider position, and therefore the radius of curvature is going to be tighter before returning to a late apex, resulting in a straighter line on exit, allowing for earlier throttle application as a result.

The reverse is also true. If you have a slow corner immediately following the one you’re taking, you can sacrifice the exit for a faster, more direct entry. The slow exit of the corner doesn’t matter, because you’ll spend very little time before the next one which requires a slow apex anyway.

Each corner requires prioritisation between entrance and exit, based on what comes before and after.

Here’s an example. The first corner of the Nürburgring Grand Prix layout has an early apex, where you compromise the exit because a slow corner follows.

nurb-gp

A good example of a late apex is the last corner at Road America, where the straight follows. Keep the car wide on the brakes and have a late turn-in. Your minimum speed should be well before the apex. Once you’re there, the car is already accelerating hard, carrying more speed onto the straight.

rd-america

Other factors
A final thing to note about the optimum racing line is that there are often exceptions caused by track and corner specific characteristics, such as bumps, camber (positive or negative), and curbs. Consider the racing line F1 cars use at Monaco after “Casino”, where they jink to the right then left to avoid the bump which would otherwise unsettle the traction and balance of the car, costing time. The racing line as described above assumes a circuit where grip levels are uniform throughout the racing surface, but when these other factors come into play, it’s worth modifying your line to where the extra grip is provided and vice versa.

Up to you

Analyze your lines carefully, keeping the biggest radius in mind and the sequence of corners and straights. Combine it with the knowledge of the traction circle, for the fastest way through corners.

If you’re struggling, remember you can compare your lines at any time with telemetry from datapacks on the VRS app. Follow it up with reading 3.3, on car control.

3.1: Fundamentals: The traction circle

Posted on by David Williams

untitled-3Welcome to season two of the VRS Academy — let’s dive into racing on a more technical level. We’ll start off with the traction circle, which is a key element used to understand the grip available from the tyres.

Back in article 2.4 Driving basics, we summarised how the optimal lap is a combination of carrying the maximum speed on the best racing line. The best drivers can achieve this by understanding how to fully exploit the grip available at all times during a lap.

The traction circle
Tyres are responsible for providing a connection between the car and tarmac, and it’s through this connection that the driver is able to accelerate, brake and corner. The most important thing to recognise is that there is a finite limit to the amount of grip or force which can be produced in any direction.

To define this, we can visualise a diagram called the traction circle.

traction-circle-copy

The axes represent g-forces experienced in the car as a result of tyre grip in a single direction. At rest and when coasting in a straight line, the resultant forces are effectively zero and thus we are in the centre of the traction circle. During acceleration, the tyres produce grip in a forward direction, translating into a rearward g-force and propelling us along, whilst the opposite happens under braking when the tyres produce rearward grip, slowing us down. It’s a similar story when cornering, and this is when we see the tyres produce lateral (side) forces.

The limit of force the tyres can produce is defined by the red circle in the diagram which represents 100% of grip available. It is the goal of a racing driver to operate as close to this as possible, but to never attempt to go beyond it.

Looking at the circle, it’s very easy to understand that wheelspin in a Formula 1 car is caused by reaching the red line in the acceleration direction. It’s also easy to see how braking too hard would cause the wheels to lock up trying to exceed the red line, and finally obvious to visualise how going too fast for a given corner would cause us to demand more than 100% from the tyres in a lateral direction and cause understeer or a slide.

It’s more difficult however to understand when on track how the combined relationship between braking or acceleration, and cornering at the same time works, and this is where the traction circle helps us.

Using the full traction circle in all directions
Again back in 2.4 Driving basics, we recommended that the beginner driver entirely separates their braking, steering and throttle inputs. Whilst this is a good approach for the novice, it is clear that this driving style does not fully exploit the full limits of the traction circle and the diagram instead will look more like the following.

2

We can see here that the driver reaches the outer limit under braking, but then comes off the brake fully before then steering, once again reaching the outer limit but this time laterally.

A driver can better exploit the grip available at the tyres by combining braking, steering and acceleration, however first picture the following scenario. You’re approaching a right-hand corner, and you’re braking to 100% of the available grip, on the edge of the circle. You begin to turn into the corner whilst maintaining the same brake pressure, the front tyres then lock up and you immediately begin to run wide.

traction-circle-1

 

Looking at the diagram, we can see that since you were already on the red line in the braking direction, as soon as you turned the wheel you tried to demand some lateral force from the tyres, which would put your car outside the circle (if it were possible).

traction-circle-2

The correct technique is to reduce braking pressure as you begin to steer, so that you remain inside the outer extent of the red line. As you reach the apex (middle) of the corner, you should be using 100% of the lateral grip available with little to no pedal input. From this point onwards you can feed in the throttle so you remain on the outer circle up until you reach full throttle (and are no longer limited by the grip available).

 

Using telemetry within the VRS software
The driving analyzer on the app includes a traction circle which can be displayed by choosing the “driving style” tab, which reveals the following diagram:

This diagram represents “g force” in the direction in which the driver feels it. Braking is at the top, acceleration at the bottom and lateral g force at the sides. The above data is from turn 4 at Okayama with the MX-5, and we can see that the full extent of the grip available is well used throughout braking, transitioning to cornering, and finally acceleration – until full throttle. The MX-5 only has 2 driven wheels and isn’t very powerful which is why the car has so much more braking potential when compared to acceleration.

Up to you

Continue reading with 3.2, where we explain the ideal racing line, which you can combine with your knowledge of the traction circle!

 

2.6: Driving basics

Posted on by David Williams

untitled-1The optimal lap is easy to describe, but difficult to achieve. It’s a combination of two basic things: utilising the full grip of the tyres through the perfect line. In other words: optimal racing line & optimal speed.

Sounds simple? Mastering this is in fact extremely challenging due to the complex layout of a typical circuit and the behaviour of a racing car at the limit of grip. This is why the following fundamentals are so important to achieving your maximum potential, not only as a beginner but also as a seasoned veteran.

Importance of solid basics, an analogy:
Several months after struggling to learn the guitar, I learned that I’d been holding the pick incorrectly. I stumbled across my mistake randomly whilst browsing internet tutorials, where I discovered the widely accepted, correct grip. Initially the change made my playing worse, however a few weeks later and I’d made massive progress over my previous level.

Racing line
The most fundamental thing a racing driver can learn is the correct line, so we’ll start with the basics for this first. Generally speaking, the optimum line through a single corner is that of the largest radius, as it allows for the highest speed possible for a given amount of grip. Essentially, the goal is to reduce the tightness of a corner as much a possible, which can be achieved by using all of the track.

All of the track
Take for example a 90 degree corner on a circuit roughly five times the width of your car. The line of largest radius is going one which starts from the outside of the corner on entry, sweeps to the inside at the apex, before then tracking out to the outside once again for the exit. This is illustrated in the following image:

screen-shot-2016-10-09-at-20-08-45

Often the track will either tighten or open on exit. Sequences of corners often require a compromised line, and the length of the straight following a corner will strongly determine if you are better off sacrificing a wide entry for a tight exit, or vice versa.

We strongly recommend referring to the datapacks provided on the VRS app to gain a good understanding for the best line on a particular circuit with a given car. If there’s no datapack, search your car, track and season combination on the iRacing forums or YouTube.

Limit of grip
Generally speaking, the limit of grip is the speed at which a car begins to no longer follow the line on which you intend to stick to. Your goal should be to drive at a speed close to this, but to not exceed it, so that you can follow the best line around a circuit. If you drive too fast, you’ll find the car either runs wide (understeer), or you risk having the rear step out (oversteer).

Common mistakes
The most common errors the average beginner to race driving or sim racing make are the following:

  • They enter slow corners too quickly, and enter fast corners too slowly
  • They brake too late
  • They attempt to brake and turn at the same time
  • They carry too little speed out of corners

A phrase you often hear in racing circles is known as “slow in fast out”. This is a generalisation, but it’s used to reduce the likelihood of the either of the above mistakes from occurring. It’s also much easier to make a correction to your driving when you’re not going fast enough and there’s more grip still available. Focus on carrying more speed out of corners, rather than trying to carry too much speed in. Pay attention also to the type of corner; is it quite shallow or very tight? Adjust your entry speed accordingly.

Brake in a straight line
When braking hard, it’s highly recommended to travel in a straight line. This comes down to something known as the “traction circle”, whereby a tyre only has certain amount of grip in any direction. This means that in order for a tyre to produce any sideways grip required for cornering, it will have less grip available for braking or accelerating.

As such, we recommend to a beginner driver that they deliberately separate braking and turning completely. Combining braking and turning is a more advanced driving technique which definitely has it’s rewards, but it requires more skill and will feature in a future article.

Brake hard enough so you can sense the wheels would lock up if you braked harder, and smoothly release the pedal as the turn in point approaches. You should be turning the car hardest in the middle of the corner (the apex).

Commit to full throttle when you know you don’t need to lift
After driving through the apex, smoothly unwind the steering whilst carefully applying throttle as the exit of the corner approaches. Avoid applying too much throttle too early and then lifting again later, as this will greatly reduce your exit speed and momentum on exit. Exit speed is very important, especially when a long straight follows a corner as you will carry that speed all the way until the next braking zone or lift.

iracingsim64dx11-2016-10-11-23-40-46-03 

Up to you:

We recommend that you come back to this article several times in between practice sessions to refresh your understanding as it is a lot of information to process and too much to remember and apply in one session.

As we said: the optimal lap is easy to describe, but difficult to achieve!