Understanding the Limit

The limit is not a scary term. Many drivers, whether online, in YouTube videos, or among friends and fellow league racers, may have used the term "limit" as something that is bad or scary. However, this perception is incorrect.

What the Limit Is NOT

The limit does not mean we're spinning, crashing, locking up, driving into walls, or wrecking the car. If you went into a wall, by definition you went over the limit or most likely went over the limit. That's over the limit - you exceeded the available grip of the tires.

What the Limit IS

The limit is simply the maximum load the tires can withstand. This is our working definition. Under the limit means not using the tires to their maximum capability.

Once we acquire the ability to drive the tires to the limit, we want to structure our corner with the goal of staying at the limit from entry to exit. Entry means the moment we're starting to roll on the brakes, and exit is basically when we're done steering and we're back in a straight line comfortably after the corner has ended.

Breaking Down the Process: Testing Tire Grip Under Straight Line Braking

Finding the limit in any situation is a difficult task - easier said than done. However, we can make this as easy as possible by dividing this into steps. We're going to test tire grip under straight line braking first.

Three Main Reasons to Test Straight Line Braking First

• It's the safest point in the corner to get to the limit: The worst thing that can happen if we go over the limit is we get a lock up. If you're trying to test the limit mid-corner and you go over the limit, you might end up spinning or understeering really heavily, making it more difficult to tell the difference between over the limit of the front or rears.

• It is the easiest point in the corner to identify over the limit: Over the limit in a straight line is a lock up - very easy to hear and see the smoke.

• It allows us to get comfortable with our cues: Because there's not a lot happening under straight line braking, it gives us more mental capacity to be able to think about our cues and get used to them.

Limit Cues: Real-Time Indicators of Grip Levels

We never want to break with the goal of achieving a specific percentage of braking pressure (like 85 percent). This doesn't account for track characteristics such as compressions, crests, camber, off-camber corners, or even temperature differences of five or ten degrees.

Our limit cues are going to be real-time indicators of grip levels. These cues essentially morph or tell us what the limit is in any given situation. For example, if you're going over a big crest (like turn six at Road America), your tire sound is going to engage at an earlier point to tell you that the limit is at a lower amount of brake pressure.

If you tell yourself that 85 percent brake pressure is the limit under straight line braking and try to brake at 85 percent over that crest, you're going to go way over the limit. If you just break to achieve the tire sound or whatever cues you're using, they act as real-time indicators of grip.

Benefits of Using Limit Cues

• Easier to replicate being at the limit consistently

• Encourages us to find the limits for ourselves instead of mimicking other drivers' telemetry

• Allows potential to exceed the performance of drivers whose telemetry you might otherwise copy

The Two Primary Cues for Straight Line Braking

1. Tire Sound (Most Important)

There is a very particular pitch or sound produced by the tires when we're in and around the limit in iRacing. We can use it to our advantage by being really precise about exactly what pitch we're looking for. We can essentially try and engage that pitch of tire sound consistently every time we go through a straight line braking phase.

2. Force Feedback

The forces coming through your wheelbase provide valuable information about grip levels.

Audio Settings Configuration

Before beginning exercises, ensure your audio settings are properly configured in iRacing:

• Navigate to the audio tab in iRacing settings

• Engine slider: approximately minus 15 decibels (can adjust to minus 18 for very loud cars)

• Tire slider: properly elevated to hear tire sounds clearly

• Reduce wind, rain, and ambient sounds

• Ensure in-car audio is maxed out

• If the engine is too quiet at minus 15, raise the master volume rather than the engine slider

Exercise One: Straight Line Braking at Centripetal Circuit

This is a 10-minute exercise using the Spec Racer Ford at the Centripetal Circuit.

Exercise Steps

1. Load up the Centripetal Circuit with the Spec Racer Ford

2. Begin against the outer wall and pick up speed heading towards the middle of the circle

3. Keep the wheel straight - we don't want any influence of steering degrees

4. Begin braking at 100 percent (you will lock up - this is intentional, as we need to find both extremes)

5. Dial down each attempt in braking pressure by roughly 5 percent, maybe a little less (3 percent) - doesn't have to be perfect

6. Gradually keep dialing down pressure until you get right below a lockup

7. The moment it doesn't lock up, connect that to a very specific pitch that the tires are producing - this will probably be a medium pitch scrubbing sound

8. Most important: If you can replicate your target tire sound five times in a row, try increasing your brake pressure by a couple of percent and identify if you begin going over the limit

If you can get to your target tire sound five times in a row, add a couple percent of brake pressure, and you don't lock up, you probably weren't targeting the right tire sound. You were probably a little bit under the limit, so go back to step two and retest with more precision.

Additional Notes

• For new people: Start with no downshifting to remove as many variables as possible (you can add them later if comfortable)

• For returning students: Feel free to downshift and experiment with how that affects the dynamic brake bias of the car

Understanding Dynamic Brake Bias with Downshifting

The cadence of downshifting affects braking. To simplify as much as possible: the faster you downshift means the higher RPMs you're getting, which also means more rear brake bias it's dynamically causing.

Key Learnings from Exercise One

Participants should notice that the sound changes significantly between being at the limit and over the limit. In a non-ABS car, it's very easy to tell when you're over the limit - when you do go over, you're probably in for a pretty rough ride with lock up. This is unlike an ABS car where, if you don't have lights, it's more difficult to tell.

The target sound at the limit is typically a scrub sound at around 85-95 percent brake pressure, though remember: we're not memorizing percentages. We're learning the tire sound cue.

Building Confidence

If you're struggling to get perfectly to the limit on your initial peak pressure, apply the brakes quite a bit slower than normal. This gives you more time, reduces cognitive load, and allows you to eventually get up to the right target tire sound. Then you can hold it for whatever remainder of straight line braking you have, rather than trying to slam the brakes right up to the tire sound immediately.

Moving Beyond Percentages

While it's useful to know approximately what brake pressure gets you to the limit (85%, 90%, etc.), moving forward we should not be remembering that number or basing our braking everywhere off of it. There are so many variables that can affect how much braking pressure it takes to get to limit under straight line braking.

For example, if you're going over a crest, it's not going to be 85 percent - it will be different. We want to limit the use of percentiles as our limit indicator and instead rely on our cues.

Step Two: Maximum Rotation Point (MRP) to Exit

Now that we have straight line braking down, we move to the next easiest portion of the corner to test the limit: our maximum rotation point all the way through to corner exit.

The maximum rotation point is the point in the corner where we're just about to roll on to the throttle. The second easiest portion of the corner to test our grip limit is as we are rolling on throttle. This allows us to test lateral grip, longitudinal grip, and various other dynamics.

Limit Cues for MRP to Exit

• Tire sound: Still very important and never useless, though less critical than in straight line braking

• Force feedback: Becomes a really important cue in helping us achieve the perfect balance of staying at the limit throughout this portion of the corner

Exercise Two: Testing MRP to Exit at Centripetal Circuit

Return to the Centripetal Circuit with the Spec Racer Ford. This is a 10-minute exercise.

Exercise Process

1. Pick a circle roughly somewhere in the middle of the track

2. Start by testing both extremes: way under the limit and way over the limit

3. Way under the limit: If you turn more, do you get more rotation? If yes, you're under the limit

4. Way over the limit: If you keep adding speed and try to hold your line, eventually the front tires give up and you start drifting away (understeer). Adding more wheel just puts the front tires even more over the limit

5. Find the limit: If you add steering degrees but don't gain rotation (in fact you lose rotation and start drifting away), you're already at the limit at that speed

Force Feedback Analysis

Pay attention to the force feedback or the forces coming through your wheelbase:

• What does the wheel feel like way under the limit?

• What does the wheel feel like way over the limit?

• What does the wheel feel like at the limit?

• Notice any differences in terms of how heavy the wheel feels

• Think about how you can apply this to your regular driving on a normal track

Testing Method

The easiest way to tell if you're at the limit on the Centripetal Circuit: if you add steering degrees and don't gain rotation (or start drifting away from the circle even though your speed didn't change), you're already at the limit of the front tires. Adding steering degrees when already at the limit means you're going to go over the limit.

Key Learnings from Exercise Two

Many participants noticed they could brake harder in a straight line after learning more about lateral grip. The tire sound should be the same at the limit under braking or turning. Going back to straight line braking to hear again what the limit sounds like helps reinforce the learning.

Force Feedback Characteristics

What participants should notice about force feedback:

• Any time we're outside of being exactly at the limit, the wheel is going to be lighter in feel

• When you understeer, the wheel goes light

• When you're under the limit, the wheel goes light

• When you oversteer, the wheel goes light

• When you're at the limit, that is probably when the wheel is going to be at its heaviest

In most cars (90 percent or more), when your wheel is at the peak amount of weight (the most torque), that is when you're in a position to extract the most grip out of the tires. There are some rare cases where if you go half a percent or one percent past that peak force feedback feel, you can actually extract a little bit more grip out of the tires, but this is rare and shouldn't be worried about too much.

Force Feedback Setup Tips

For those having difficulty feeling force feedback differences:

• Ensure your force feedback is not clipping - many people max out their forces on belt-driven or gear-driven wheels to make it feel heavier, but fidelity is more important

• Be really light with your hands on the steering wheel - any force with a non-direct drive wheelbase will affect how you feel the lightness or heaviness

• Check both your software and iRacing force feedback settings

• While this exercise is easier on a higher-end wheelbase (direct drive), it is not impossible on other wheelbases

Step Three: Applying Learning to Real Track

Now we bring everything to a real track. Load up the SRF at Oulton Park International.

Exercise Three Process

1. Retest your straight line braking limit on the actual track surface

2. Bring over the procedure of how you found the limit from the Centripetal Circuit, but do NOT bring over the amount of braking pressure it took

3. Retest the limit and think about whether you gained any braking efficiency, especially in corners with very long straight line braking phases

4. Once comfortable with straight line braking, replicate step two from the Centripetal Circuit

5. Ensure you are at the limit from MRP to exit (the second easiest point in the corner to bring the tires up to the limit)

6. While you can do this in all corners, three corners where this will be easier to test are Turn 3, Turn 5, and Turn 12

Transitioning from ABS to Non-ABS Cars

For drivers coming from cars with ABS, this process is definitely different. You'll need to put more mental focus into finding the tire sound and trying to hold the tire sound all the way to the actual turn. It's a different thought process, but the control it provides is very beneficial.

Eventually, we want tire sound monitoring to become more of a subconscious thing - something we can use as a form of double-checking, whether that's while driving or after we drive (through recording or replay). The tire sound is a real-time indicator of the grip limit of the tires.

Common Observations During Track Application

When applying these techniques to a real track, drivers often notice:

• Significantly more braking performance when closer to the limit under straight line braking

• They were previously over-slowing in certain corners

• The mental process requires more focus initially but becomes more natural with practice

• Losing the limit slightly at the end of corner exit - adjust throttle application timing to maintain tire sound throughout the exit phase

The goal is to maintain the limit cues (tire sound and force feedback) consistently from the maximum rotation point all the way through corner exit.