Racing line basics: apexes, track width and why late apexes win
The racing line is the path around the track that lets you carry the most speed. Simple enough on paper, yet if you’re a second off the pace, some of that second is almost certainly coming from your line. It’s the first thing most of us learn and the first thing most of us stop thinking about, which is exactly why it’s worth going back over the basics, even if you think you’ve got them.
The three points of a corner
Every corner has a turn-in point, where you start steering; an apex, where you’re closest to the inside; and an exit, where you finish the corner, usually right out at the edge of the track. Get those three points right and the bit in between mostly takes care of itself.
The classic shape is outside, inside, outside. You start wide, clip the apex and let the car run out to the edge on the way out. Doing that makes the corner’s radius as big as it can be, and a bigger radius means more speed for the same amount of grip. A car can only generate so much sideways force before the tyres give up, so the gentler you can make the curve, the faster you can go round it.
The turn-in point is the one people get wrong most often, and it’s the one that decides the other two. Turn in a car length too early and you’ll arrive at the inside before you meant to, which pushes everything after it out of shape. Turn in too late and you’ll miss the apex by a metre, which costs less but still makes the corner tighter than it needs to be. When you’re learning a corner, pick a physical reference for turn-in, like a marker board, a change in the kerb colour or a crack in the tarmac, and use it every lap. If you want a method for building those references at a track you don’t know yet, learning a new track goes through it.
From the cockpit, a well-judged corner feels calm. You turn in, the car settles onto a steady arc, you touch the inside kerb without having to reach for it, and the car drifts out to the exit kerb under power without you having to force it there or hold it back. If any of those moments involves a correction, the points aren’t quite right yet.
Use the whole track
Every bit of width you use makes the corner gentler. If you leave half a car width at the apex, or don’t let the car run out to the kerb on exit, you’ve made the corner tighter than it is and you’ll have to go slower to get round it. Half a metre doesn’t sound like much, but on a medium-speed corner it’s often worth a couple of km/h of minimum speed, and that carries all the way down the next straight.
Pull up a fast driver’s onboard and watch how close they get to the edges. Most of us leave a lot more room than we realise. It’s partly self-preservation (nobody wants to drop a wheel on the grass and spin) and partly that it’s genuinely hard to judge where your car’s wheels are from the driver’s seat. In a single-seater like the Skip Barber or the Ray FF1600 you can at least see the front wheels. In a closed car like the MX-5 or a GT4, the corners of the car are guesswork until you’ve done a lot of laps.
A practical way to find the edges is to deliberately overdo it in practice. Pick one corner and spend three or four laps putting the car right onto the apex kerb, then a bit further, until you’ve found the point where it becomes unsettled or you get a track limits warning. Then do the same on exit, letting the car run wide until it’s genuinely at the edge. Now you know where the limit is, and you can back off to just inside it. Most people discover they had a full car width they weren’t using.
Kerbs deserve a mention here. Some can be used freely, some will throw the car into the air, and the same kerb can behave differently in a stiff GT3 car and a soft Formula Vee. Test each one in practice before you rely on it in a race. The flat, low kerbs at a lot of modern circuits are part of the racing line. The tall sausage kerbs at chicanes usually are not.
Early, geometric and late apexes
Geometric apex and late apex
The geometric apex sits in the middle of the corner. If you drew the largest possible circle that fits between the track edges, the geometric apex is where it touches the inside. That gives you the largest single arc, so it’s the line with the highest possible minimum speed through the corner itself. On paper it’s the fastest way through a corner in isolation.
A late apex means you turn in later and clip the apex further round. Your minimum speed drops a little, because the first part of the corner is tighter, but the car is pointing straighter at the exit, which means you can get on the throttle earlier and harder. You’re doing more of your turning early, at lower speed, and less of it late, when you want to be accelerating. The Andretti Hairpin at Laguna Seca is a good one to try both on in the MX-5. Take a geometric line and you’ll feel the car still turning as you try to pick up the throttle for the run to turn 3. Turn in later, get the car rotated early, and you’ll be on the power sooner with the wheel much straighter.
Early apex
This is the one you want to avoid. Turn in too soon and you reach the apex early, then run out of track on exit and have to lift or wind on more lock. It’s almost always slower, and it’s the mistake I see more than any other in public practice sessions.
It happens for understandable reasons. Turning in early feels like it’s getting the corner done sooner, and when you’re nervous about braking late, turning early is a way to feel like you’re attacking. There’s also a visual trap: the apex kerb is the most obvious thing in your view, so you head straight for it. The tell is on exit. If you regularly find yourself running out of road, dropping a wheel off, or adding steering after the apex, you’re apexing early. Moving your turn-in point back by half a car length is usually enough to fix it.
Why late apexes usually win
Most corners lead onto a straight, and whatever speed you bring out of the corner stays with you all the way down it. Giving up a bit of minimum speed for a much better exit is a trade worth making, which is why a late apex is the default for most corners before a straight. A few tenths of a km/h lost at the apex, spread over a short stretch of track, is tiny. A couple of km/h gained on exit, carried along a 700 metre straight, is not. Our throttle control guide goes into exits in more detail.
The exception is a corner that flicks straight into another one going the other way. In that case you might give up the first corner to set yourself up for the second. The esses at Watkins Glen are a classic example: what matters is being on the right part of the track for the last part of the sequence, because that’s what leads onto the long uphill run to the Bus Stop. Take each bend on its ideal line and you’ll arrive at the final one out of position. Chicanes work the same way. Usually you compromise the entry so the exit is straight and fast.
There’s also the slow corner after a straight, where the late apex shows up in a slightly different form. Braking in a straight line and then turning in late lets you brake later and harder, because you’re not asking the tyres to turn and slow at the same time for as long. Trail braking blurs this a little, since you’ll carry some brake into the turn, but the geometry is the same. Our guide on finding your brake points covers how the braking zone and the turn-in fit together.
Different cars, different lines
A low-power car like the MX-5 is all about momentum, so it wants a smooth, wide line and a high minimum speed. There isn’t enough power to make up for speed you scrub off mid-corner, so you tend to use a rounder line with an apex closer to geometric, and you look to roll as much speed as possible through the middle. The Formula Vee and GR86 reward the same approach. If you drive the MX-5 like a GT3 car, pinching the entry to get a straight exit, you’ll often find the exit gain is smaller than the minimum speed you gave away.
High-power cars with plenty of grip reward a later apex and a straighter exit so you can put the power down. In a GT3 or a car with real downforce, the exit is where the lap time is, because the car can accelerate so hard that every metre of earlier full throttle pays off. These cars also tend to have a different shape through fast corners, where aero grip lets you carry a surprising amount of speed on what looks like a geometric line, while the slow corners get the much more V-shaped, late apex treatment.
When you watch onboards, pick ones in the car you’re actually driving, not just any car at that track. A GT3 lap around Lime Rock and an MX-5 lap around Lime Rock will have noticeably different lines through Big Bend, and copying the wrong one will only confuse you.
Check your line with data
Your line is hard to judge from the cockpit. You can think you’re touching the apex when you’re half a metre off it, or that you’re using the full exit when you’re leaving a car width. The data is less forgiving. On a speed trace, a pinched corner shows up as a lower minimum speed than the reference and a slower ramp back up afterwards. An early apex tends to show a higher speed at turn-in followed by a dip, or a lift, on exit where you ran out of road. Our guide on how to read iRacing telemetry explains how to compare these traces against a faster lap.
Sim Sense scores apex accuracy, track width usage, line consistency and minimum corner speed for every corner against a reference lap for the same car and track, so you can see where you’re pinching a corner or leaving track on the table. That analysis is part of the free tier.
A good practice routine is to pick two corners per session and leave the rest of the lap alone for now. Do five laps on the first corner experimenting with turn-in, one car length earlier and later each time, and note which lap gives the best speed at the end of the following straight. Then five laps finding the edges on the apex and exit. Then five laps on the second corner doing the same. Finish with ten laps at race pace without thinking about the line, and check the data to see whether the changes stuck. Once your line is sorted, braking and throttle get a lot easier to work on, because you’re no longer fighting the corner’s geometry at the same time.