Here's why, and where, slow-in, fast-out, late apex cornering works

A wide entry and late corner apex saves time down the following straight. Photo: Shutterstock.
A wide entry and late corner apex saves time down the following straight. Photo: Shutterstock.

Having discussed various advanced car control techniques including load transfer, as well as some other factors like tyres, road surface, steering geometry and the basics of aero, let's now begin to look at cornering techniques.

If you want to start with vehicle control before worrying about the racing line, here are the links to make it easy:

There are four stages to cornering; the approach (positioning ourselves to the outside of the track before a corner), the entry (turn-in), the apex (the furthest point reached towards the inside of the corner during our cornering arc), and the exit.

For this we're going to concentrate on the exit, and only where it leads onto a straight.

The old expression is, slow in, fast out, and that is a very good mantra to have. It will also involve a late apex, and we'll get to that.

The reason it works is you get a better rate of acceleration onto a straight, and the better your rate of acceleration from your lowest speed in a turn (or from a stationary start) the sooner you reach the next braking marker, or the finish line on a drag strip.

Actually, drag racers know the launch (the time it takes to cover the first 60 feet or 18.288 metres) makes more of a difference to the elapsed time (ET) than does the terminal (or trap) speed at the finish line.

Gamers and sim racers meanwhile, get to witness the effect of getting better acceleration at corner exit when paying attention to the ghost car (or the time delta display) when they're hotlapping against themselves.

Back in 1991, a club-level motorsport enthusiast named Brian Beckman, PhD, started writing a series called The Physics of Racing, initially in 13 parts. Years later he expanded on it and you can find it online in a couple of different forms if you just search for it.

In Part 9, Straights, he gives a couple of mathematical examples of a hypothetical Corvette entering a 200ft (61m) straight at different speeds, and again with a 500ft (152 metre) straight. The most extreme examples he calculated were 25mph and 50mph (he's American) at the start of the 500 foot straight, and the result was 81.12mph vs 85.83mph at the other end, so not even a 5mph difference there. However, the time taken to cover that 500 feet was 5.811 vs 4.875 seconds, a whopping difference of nearly a second.

Now, before we go any further we need to avoid thinking this means simply attacking a corner with higher speeds is better. It can actually make us slower onto a straight (Dr Beckman also explained this in 2000 with parts 17 and 18, Slow in, Fast out).

Just concentrating on the driving line for now (not modifying the car at all to improve its cornering performance), if we think of the 500 feet as starting where the straight is actually straight, we've still got some room to accelerate up to that point. This is where the slow-in, fast out, late apex mantra comes in.

A cornering line with a late apex before a straight is taken when you're not having to defend for position on the way into that corner (which will also explain why a car defending their line loses time to the leader), and the purpose of it is to begin accelerating again from as far back as possible.

At some point between the initial entry and the (late) apex, the speed of the car needs to dip (just momentarily, and we're probably using the effect of load transfer to briefly put more grip on the front tyres) as we change direction and point the car towards the exit. Then we want to get back on the power without experiencing any unmanageable levels of understeer or oversteer that would cause us to back off in order to make a correction.

The resultant line from this, in relation to the track, is a wide entry, turning in what sometimes feels like slightly late (and the slower the corner, the later this is likely to be; it can be quite late for hairpins) but also a bit sharper than the road's actual arc, and then accelerating through the point where we apex the corner (which is where we go nearest, or occasionally over, the inside kerb).

This section from changing direction to where our straight measurement would begin, is what's critical for lap times. And so, if we think of this section as our equivalent to a drag racer's 'launch', we'll always save as much time as possible down the straights.

Sam Hollier is an ACM journalist and a motoring fanatic who builds cars in his shed in his spare time.