How to read iRacing telemetry: the five traces that matter
The first time you open a telemetry tool, dozens of channels come scrolling past: tyre temperatures, ride heights, yaw rate, suspension travel, things you’ve never heard of. Thankfully nearly everything useful for going faster comes from five of those channels. Learn to read speed, brake, throttle, steering and gear and you’ll spot most of the time you’re losing.
I ignored telemetry for my first couple of years in iRacing because it looked like an engineer’s job. When I finally sat down with it, the thing that surprised me was how little of it I needed. The other channels matter for setup work, but for driver technique those five do almost all the talking.
Why you need a faster lap to compare against
A trace on its own tells you what you did. It doesn’t tell you whether that was any good. Your brake trace at Turn 1 might look perfectly tidy, a sharp spike and a smooth fade, and still be 15 metres too early. You can’t see that until there’s a second line on the graph showing where someone quicker started braking.
So the first rule is to compare against a faster lap in the same car at the same track, ideally in similar conditions. Same car matters more than people think. A GT3 lap at Spa and a GT4 lap at Spa brake at different places, carry different minimum speeds and use different gears, so overlaying them teaches you nothing useful. The reference doesn’t need to be an alien’s lap, either. Something a second or so quicker than you is often more helpful than a record lap, because the differences are ones you can realistically copy.
Most tools line the two laps up by distance around the track, with speed, brake and the rest stacked vertically so you can drop a cursor anywhere and read every channel at that point. There’s usually a delta trace too, showing time gained or lost as the lap goes on. Use the delta to find where the time goes, then use the five traces below to work out why. When the delta line tilts steeply in one section, that’s the corner to study.
Speed: your map of the lap
Think of the speed trace as the map of the lap. Every dip is a corner and every climb is a straight. After a while you’ll recognise tracks from the shape alone. Lime Rock is a handful of dips close together, while Monza is flat plateaus broken by deep chicane holes.
When you compare against the faster lap, look at three things in each dip. First, the lowest point, which is your minimum corner speed. A faster driver will often carry 2 to 5 km/h more at the apex, and because they start the exit from a higher speed they keep some of that advantage all the way down the next straight. Second, where the trace starts dropping. If your speed falls away earlier, you’re braking earlier. Third, how quickly it climbs out. A shallower climb after the apex usually points to a late or hesitant throttle.
Of those, minimum speed is the one most drivers underrate. It’s tempting to hunt for later brake points because braking feels like the brave, measurable part of a lap, but in my experience a couple of km/h more at the apex is worth more than braking five metres later, especially in low-power cars like the MX-5 or a Formula Vee where you can’t just power out of a mistake.
The shape of the bottom of the dip tells you something too. A sharp V means the car is slowing to a point and then accelerating straight away. A long flat bottom means you’re coasting through the middle of the corner, often because you over-slowed the car on entry and are now waiting for it to rotate. If your dip is flatter and lower than the reference, you’ve found the classic “too cautious on entry” pattern.
Brake: how you apply it and how you let go
The brake trace shows pedal pressure from 0 to 100%. Good braking in most cars has a fast, near-vertical rise to peak pressure, a short hold, then a smooth taper as you approach and pass turn-in. Think of it as a steep cliff followed by a gentle slope. What you don’t want is a cliff on the way down as well.
If pressure builds slowly to the peak, you’re wasting the first part of the braking zone. The tyres can take the most braking force at the top of the braking zone, particularly in cars with downforce, so that’s where you can hit the pedal hardest. A lazy ramp up means you have to brake earlier to make the corner. I see this a lot in drivers who are nervous about locking up.
The other end is the release. If the trace falls from 60% to zero in a blink right before turn-in, you’ve unloaded the front tyres at the exact moment you asked them to steer. The car pushes wide, you wait, and the minimum speed you saw on the speed trace suffers. Compare the slope of your release against the reference. Faster drivers usually have a longer, softer tail that overlaps with the start of the steering input. Our trail braking guide goes through that release in detail, and the brake points guide covers finding where the cliff should start.
Watch for a bumpy plateau as well. Wobbles in the middle of the braking zone usually mean you’re modulating for lock-ups, or your foot isn’t settled on the pedal.
Throttle: pickup point and commitment
On the throttle trace, check two things after each corner: where you first pick up the throttle, and how long it takes to get to full. The pickup point tells you when the car was settled enough to accept power. The ramp tells you how confident you were once it was.
A late pickup usually means the entry went wrong. You turned in, the car didn’t rotate, and you spent the middle of the corner waiting for it. That’s why a throttle problem is so often fixed at the brake pedal. Lots of on-off-on is a different story: the car’s unstable, or you’re reacting to wheelspin or oversteer. In a GR86 or a GT4 car at somewhere like Summit Point you’ll see this at the slow corners where the rear gets light, and the telemetry makes it painfully obvious how much time the hesitation costs.
A smooth, committed ramp is what you’re after. Getting to full throttle a car length earlier than before is often free time, and it compounds down the following straight. The throttle control guide has drills for feeding it in without spinning the rears.
One trap: don’t copy a faster driver’s throttle trace if you haven’t copied their entry. If they’re at full throttle 20 metres before you, it’s usually because their car was pointed straighter at the apex. Try to match the throttle alone and you’ll just have a bigger slide.
Steering: the trace that exposes understeer and corrections
The steering trace shows how much lock you’re using and how smoothly it goes on and comes off. Ideally you’ll see one clean hump per corner as you turn in, hold, and unwind. The unwind should roughly mirror the throttle going on: as you open the wheel, you add power.
Saw-tooth wiggles mid-corner are corrections, and every correction scrubs speed. Some are unavoidable, especially in cars with a lively rear like the Skip Barber or the Ray FF1600, but if yours has five wiggles where the reference has one, the car is doing something you’re fighting. Look back at the brake trace at the same point. Often the rear stepped out because the brakes came off too late and too hard mid-corner, or the front washed out because they came off too early.
Compare peak lock with the faster lap at the same point. If you’re using noticeably more steering, that usually means understeer: the front tyres have run out of grip and extra lock isn’t turning the car any more. An early brake release or too much entry speed is often the cause. Using less lock than the reference and still being slower can mean you’re taking a wider, straighter line, which is worth checking against the track map.
Steering is also where you see turn-in timing. If your hump starts well before the reference, you’re turning in early, which usually leads to an early apex and running wide on exit.
Gear: the easy wins
The gear trace is the simplest of the lot, a staircase going up and down the lap, but it catches easy mistakes. Look for shifting too early on exit, sitting a gear too high through a slow corner, or bouncing off the limiter on a straight because you didn’t grab the next gear. Pair it with the speed trace and you can see whether an early upshift is costing you acceleration.
Downshifts are worth checking closely. Compare where each downshift happens in the braking zone and how many gears the reference driver drops. In a GT3 car at Watkins Glen, taking the Bus Stop a gear higher than the faster driver can feel smoother but leave the car bogging on exit. Our guide to downshifting and gear choice covers when a different gear helps.
If the gear trace looks identical to the reference and you’re still losing time, that’s fine. It rules something out, and the other four traces will have the answer.
Putting it together: one corner, then the next
With all five channels in front of you, go through the lap one corner at a time against the faster lap. At each corner, ask whether your minimum speed is lower, and if so let the brake and steering traces tell you why. Then check whether you’re braking earlier, by comparing where the brake trace starts and where the speed begins to drop. Finally, check whether you’re slower on exit, by looking at throttle pickup and any steering corrections.
As a worked example, take the MX-5 at Laguna Seca and the Andretti hairpin at Turn 2. Say the delta shows you losing two tenths there. The speed trace shows your minimum is 4 km/h lower than the reference and the dip is flat at the bottom. The brake trace shows you started braking in roughly the same place, but your release drops off a cliff just before turn-in. The steering trace shows more lock and a couple of corrections through the double apex. That’s one story: the front unloaded on entry, the car pushed, you added lock, then waited. The brake point was fine. What needs work is a softer, longer release.
A practice routine that works for me: pick the single corner with the biggest loss and give it 10 laps of focus while driving the rest of the lap at 90%. Save a lap, compare again, and if the gap has shrunk, move to the next corner. Trying to change everything at once rarely works, because you can’t tell which change did what. Once a lap feels right, run 10 more to see if it holds, since a fix that only works once isn’t a fix yet. If you want a structure for that part, the consistency guide has one.
Reading traces by hand is a skill worth having, but the slow part is interpretation, working out why a trace looks the way it does. That’s what Sim Sense is built for. Its desktop companion records your laps and compares them against a reference lap for the same car and track, then scores 26 driving skills corner by corner, such as brake release and throttle application, and ranks your weaknesses with a lesson and drill for each. The telemetry analysis is part of the free tier, and it’s in early access now.