Corner Entry Speed

Publication: Total Magazine Article 2009

The summer is a busy time for us at CAT, lots of track day and race tuition. With the benefit of longer evenings and the hope of nicer weather the diary is always full. The motor racing calendar at this time of year is in full swing, championships are taking shape with a natural pecking order being established. Drivers often look to find an advantage over their competitors through vehicle set up, and improved driving skills.

Coincidentally over the last few weeks I have found my self working on the same subject with several different drivers running in different championships, all looking to find a tenth or two. All 4 drivers found they could reduce their lap time by focusing on their corner entry speed. It seemed a natural choice for the focus of this feature for me to share my thoughts on circuit braking & corner entry speed with you.

We have covered Threshold Braking in a previous feature. Let’s recap just in case you missed it. To find true speed throughout a circuit lap, we should be feeling comfortable braking as late as possible and over the shortest piece of tarmac – a technique known as Threshold Braking. It requires practice and a degree of commitment on behalf of the driver.

Our 4 competitors had a good feel for their vehicles braking efficiency and levels of retardation, but had missed one key element: true threshold braking and it’s effect on corner entry speed. Constructing a safe fast lap requires discipline and a systematic approach. Consistency is the key, if you can drive to a process and with repeatable lap times, you can then begin to work out where time can be saved. One of my favourite sayings is “the corner begins a long way before you turn in”. Imagine you are braking for a corner from 140 MPH down to a corner entry speed of 60 MPH. By nature of the speed you have attained on the straight, your braking technique is critical to achieve the desired speed at turn in, and optimised G throughout the corner.

Reference points can aid your braking technique as you learn a circuit. If you brake at a known point each lap it will assist the mapping of the circuit. If you are braking too early, you can extend your braking point one or two meters at a time from your original reference – this will help you to find the optimum place to brake. Reference points are a contentious issue amongst instructors and a subject of debate amongst all of us who drive on circuit. The counter argument is that they focus your attention away from the approaching corner and are therefore counter productive. My opinion is once you have settled into driving on a particular circuit and feel confident with your braking points, they tend to become redundant. This is because your brain has started mapping the peripheral view and speed sensing takes over. I therefore use them to my advantage as and when required.

Why is it so important to threshold brake? If you are braking consistently to threshold you can add a degree of predictability to the speed you approach a corner at. Imagine braking from high speed and not using all of the tyres available grip – in effect wandering in and out of optimum G. If you use data logging it is very simple to see this on a line trace. Try to visualise the effect it may have on your corner entry speed. If you are running on track day tyres we could confidently expect to pull 1.2g under braking and laterally through a corner. My line trace should read 1.2g throughout the retardation/braking phase as I approach the corner. In effect a flat line at optimum G. But what if my threshold braking requires a little practice and I am not holding my braking at optimum G? My line trace will now show peaks and troughs extending my stopping distance, adding a degree of inconsistency to my corner entry speed.

If each time I approach the corner my braking G trace varies, my turn in speed will vary provoking an unnecessary input on the controls. Unwanted use of the accelerator, brake or steering at this critical phase in the corner will now reduce available grip as the tyre fights to cope with the unwanted adjustments. In order to drive in, through and out of the corner at the tyres limit of adhesion I must be focused on threshold braking in the braking zone, optimising corner entry speed.

As I brake the front of the vehicle dives, the tyre is compressed into the road surface. We feel the effects of braking through our body as we ease forward in the seat, and experience the dipping of the nose of the vehicle. If it is safe to do so, take a look in your rear view mirror and watch the effects of the braking on the vehicle platform. In a softly suspended car the horizon changes dramatically. So we can sense quite happily the body of the vehicle diving as we brake, but let’s not forget how hard the road wheel is working underneath us. As the wheel is excited by the road, it is momentarily relieved of its spring pressure – the result a slight screech/chirp from the tyre before the spring forces the tyre back onto the road. Audible confirmation that I have optimised braking effort and used all of the available grip. Try to avoid wheel lock or intervention of the ABS if fitted as it will extend your stopping distance and as importantly induce fluctuations in your corner entry speed.

With braking zones in mind I can begin to map the circuit. Identify the corners that require high speed, high G retardation with all of my attention and focus on my braking technique. By contrast note those corners that require a dab of the brakes with a following high speed apex, recognising where the apex speed may present me with more of a challenge than the braking.

Before pushing for the ultimate lap time the circuit and its complexity can be broken down and structured into bite sized manageable challenges. If I ask myself have I achieved optimum apex speed and sector time throughout the lap, it is often the braking zone that yields the biggest gains. At the risk of being repetitive “the corner begins a long way before you turn in”.

Until next time

Regards

Colin Hoad

COPYRIGHT CAT DRIVER TRAINING LTD. JULY2009

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