Spend the tire's grip budget on purpose
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Source path: content/lms/vehicle-dynamics-and-setup/01-weight-transfer-basics/03-friction-circle.md
Course: Vehicle Dynamics & Setup
Module: Weight Transfer Basics
Estimated duration: 55 minutes
The skill in one sentence
The friction circle is not a diagram to memorize. It is the budget you spend every time you ask the car to slow down, turn, or accelerate. Your job is to spend that budget deliberately. You do not get a separate pile of grip for braking, another pile for cornering, and another pile for throttle. You get one tire limit, and each control input draws from it.
That is why this lesson sits inside weight-transfer basics but is not just about weight transfer. The earlier lessons in this module ask you to separate static numbers from the driven car and to make your inputs move load on purpose. This lesson asks the next question: once the tire has load and is capable of making force, how do you allocate that force? On entry you trade braking force for cornering force. In the middle you protect the cornering demand from extra pedal demand. On exit you trade cornering force for acceleration by releasing steering. The whole skill is a continuous exchange.
For an intermediate driver, the breakthrough is usually not learning that tires have a limit. You already know that. The breakthrough is learning that the fastest lap is not made by visiting braking, cornering, and acceleration as three isolated rooms. It is made by moving from one to the next without dropping below the tire's useful edge and without asking for more than the tire can give.
The rule you drive by
Treat the brake and throttle pedals as if they are tied to the steering wheel. More steering angle means less brake or throttle pressure. More brake or throttle pressure means less steering angle. If you add steering while holding too much brake, or add throttle while holding too much steering, the tire has to answer two big requests at once. At some point the front tires or rear tires run out first, and the car shows you understeer or oversteer.
That rule is simple enough to say in the paddock and hard enough to practice for years. The reason is that your hands and feet are allowed to overlap, but only as an exchange. Overlap does not mean stacking full braking on top of full cornering. It means reducing one demand while building the next. Brake force comes down as steering force comes up. Steering force comes down as acceleration force comes up. The overlap is where the lap time lives.
When the tire is using all of its capacity for braking, you cannot ask it to corner at the limit too. When it is using all of its capacity for cornering, you cannot ask it to accelerate hard until you begin to release steering. When it is using all of its capacity for acceleration, you cannot still be near the cornering limit. The mistake is not using two controls at once. The mistake is using two controls at a combined level that exceeds the budget.
What the circle is showing you
The traction circle is a graph of the car's forces. Braking and acceleration sit on one axis, cornering on the other. In the examples from Bentley, those forces can be measured and graphed as the car goes through the corner. If your technique uses the tire's full potential, the trace tends to move around the edge of the circle instead of cutting through the middle.
That image matters because it changes how you think about wasted time. A driver can brake hard in a straight line, then come off the brake abruptly, then turn. That feels clean because each control is separated. But between those demands there is a short period where the tires are not doing much useful work. The car is no longer braking hard and has not yet built full cornering force.
The faster version is not rougher. It is smoother. You approach the end of the braking zone near the braking limit, then begin to ease off the brake as you add steering. The brake demand falls while lateral demand rises. That movement keeps the tire closer to the outside edge of the circle and builds force progressively instead of dumping one force and shocking in another.
This is why trail braking belongs in a friction-circle lesson, but the lesson is bigger than trail braking. Trail braking is the entry-side exchange: braking force becomes cornering force. Exit throttle is the exit-side exchange: cornering force becomes acceleration force. The same budget rule governs both.
Entry: trade brake for steering
At the start of the braking zone, the car may be almost purely longitudinal. You are using the tire for braking. As you approach turn-in, the key move is not to quit braking and then start driving the corner as a separate event. The key move is to begin steering while easing brake pressure in proportion to the steering you add.
A useful mental model is a sequence of trades. Along the straight you may be using all available grip for braking. At turn-in you begin exchanging that for cornering: first mostly braking and a small amount of cornering, then less braking and more cornering, then an even split, then mostly cornering, then finally full cornering with the brake released. The exact numbers are not the point. The point is the shape. The force should migrate, not disappear and reappear.
If you turn the wheel while the brake remains too strong, the front tires may be asked to brake and turn beyond their available grip. If the rear unloads or the rear tires reach their own limit first, the car can rotate more than you wanted. If you protect yourself from that by releasing the brake abruptly before turn-in, you create the opposite problem: a momentary underuse of the tires and a larger timing gap between slowing the car and bending its path.
Good entry overlap feels like a continuous handoff. Brake pressure falls as steering rises. The nose accepts the corner without a lurch. The car does not feel like it is waiting between the brake zone and the corner. Your hands are not trying to make up for a missed release with a sudden extra steering input. The car is still loaded, but the load is being redirected.
This does not give you permission to be heroic with brake release. The release has to be matched to the corner and the tire. The corpus describes the skill as practicing trailing off the brakes while turning into the corner. The important word is while. If your release is finished before the corner begins, you are probably leaving entry capacity unused. If your release is too late or too slow for the steering you have added, you are probably over budget.
Midcorner: know when the whole budget is lateral
At the point where the car is using the tire's full cornering capacity, there is no spare grip for meaningful acceleration. This is one of the hardest truths for drivers who want to fix every corner with earlier throttle. Earlier throttle only helps if you have freed some grip by reducing steering demand, adjusting the line, or reaching a phase of the corner where the car can be released.
The midcorner job is to protect the car from mixed messages. If the corner still requires maximum steering and maximum lateral force, your throttle pickup must be tiny or absent. If you add real throttle there, the tire is no longer just cornering. It is cornering and accelerating. If the combined demand is too high, the car will push, slide, or rotate depending on which end runs out first.
This is also where a driver can misread the car. Bentley warns that too much steering angle for the amount of braking or acceleration, or the reverse, can trick you into thinking there is a handling problem. The car may feel like it has bad front grip or bad rear grip, but the driver may simply be asking one end to do more than it can. Before you blame setup, ask whether your hands and feet are over budget.
A balanced midcorner does not mean coasting forever. It means the tire demand makes sense for the phase. If you are still at the lateral limit, you hold the car there without adding a large new longitudinal request. If the car's path begins to open, you prepare the exit exchange by reducing steering and letting the tire start accepting acceleration.
Exit: trade steering for throttle
The exit-side skill is the mirror image of entry. On entry, you release brake as you add steering. On exit, you release steering as you add throttle. The tire budget does not change just because you can see the straight. If the steering wheel is still significantly turned, the tire is still spending grip on cornering. To accelerate harder, you need to unwind the car.
That is why exit speed is not just a throttle-bravery contest. The driver who picks up throttle earlier but never releases steering is not automatically better. The better driver uses the line and steering release to create room for throttle. The car begins to straighten, the tire gives up some cornering demand, and that freed capacity becomes acceleration.
Bentley's throttle-trace comparison is useful here. Two drivers can lift at the same point and blip for a downshift at the same point, yet differ in how they return to throttle. One driver may wait and then squeeze back on later. Another may touch the throttle a little earlier, then continue squeezing toward full. Bentley notes that in most cases, though not all, the earlier pickup followed by a full squeeze is quicker and can help balance the car and improve midcorner speed.
The phrase most cases matters. The early touch is not a shortcut around the budget. It works when the touch is small enough for the remaining steering angle and when the car is ready to be released. If you are still asking for maximum lateral grip, the tire has no meaningful budget for acceleration. If you unwind the steering as the throttle rises, the tire receives the demand it can actually pay for.
Track width is part of the exit budget. If you leave the car one foot from the edge at turn-in or exit, Bentley's example shows that the corner radius can shrink by three feet and the theoretical maximum speed drops by more than half a mile per hour. That small-looking margin can cost tenths over a lap. Using the full width is not decoration. It increases radius, reduces required lateral demand for a given speed, and creates room to spend more budget on throttle.
The three exchanges in one corner
Think of a corner as three budget exchanges, not three isolated actions.
First, braking becomes cornering. You approach at high brake demand, begin turn-in, and release brake in proportion to steering. Second, pure or near-pure cornering becomes managed balance. You avoid adding pedal demand that the tire cannot afford. Third, cornering becomes acceleration. You unwind the steering and squeeze throttle so the tire moves from lateral work toward longitudinal work.
The important standard is continuity. A poor trace has gaps where the tires are below capacity and spikes where the combined demand exceeds capacity. A strong trace spends the tire budget near the limit, but it moves around that limit with progressive control. The goal is not to make every input slow. The goal is to make every input shaped.
Sub-skill 1: budget awareness
Budget awareness is the ability to know what the tire is already doing before you ask it for something else. Before you add steering, ask how much brake remains. Before you add throttle, ask how much steering remains. Before you blame the front tires, ask whether the front tires were already carrying too much combined steering and brake. Before you blame the rear, ask whether throttle or brake release asked the rear to do too much too soon.
The traction circle gives you a language for that awareness. A car that will not turn while you are still deep in the brake may not need a setup change first. It may need a release that trades braking for cornering. A car that runs wide when you squeeze throttle may not need more front grip first. It may need more steering release or a wider exit radius so the tire can afford acceleration.
Sub-skill 2: release shaping
Release shaping is the entry-side movement from brake to steering. The beginner version is simple: get most braking done before turn-in and be smooth. The intermediate version is more precise: keep some braking into the entry while progressively building cornering demand, then finish the brake release as the car reaches full lateral work.
The quality of the release matters more than the drama of the entry. A sudden brake dump can unload the front and create a gap in tire use. A brake hold that is too heavy for the steering angle can overload the tire. A good release is neither a dump nor a cling. It is a measured reduction that matches the rate at which the steering demand builds.
Sub-skill 3: steering unwind
Steering unwind is the exit-side movement from cornering to acceleration. It is easy to think of unwind as something that happens after the corner is finished. In this lesson, unwind is part of finishing the corner. You release steering to free tire capacity, then spend that capacity on throttle.
A late unwind makes the throttle wait. A fake unwind that opens the hands but leaves the car pointed at the wrong exit is just running out of road. A useful unwind is tied to the actual line. The car's path opens, the steering angle comes out, the throttle rises, and the car uses the straight rather than fighting the corner all the way to track-out.
Sub-skill 4: input diagnosis before setup diagnosis
Because the tire budget is shared, many apparent handling complaints are first input questions. Understeer can come from too much steering combined with too much brake or throttle. Oversteer can come from the rear being asked to carry a combined demand it cannot support. A lazy exit can come from waiting too long to touch throttle, but it can also come from failing to unwind and then trying to solve it with pedal.
This does not mean setup never matters. It means the driver has to clear the input question before chasing the car. If your steering and pedals are over budget, the car is telling the truth about the demand you made. Change the demand first. Only after your overlap is clean should you treat the behavior as a setup signal.
Calibration cues from the seat
The first cue is the absence of a dead zone. On a good entry, the car does not feel like it finishes braking, floats, and then begins cornering. The load transfers into the cornering phase without a pause. The brake release and steering build feel connected.
The second cue is the absence of a combined-demand shove. If the front slides as you add steering, ask whether you released enough brake. If the car will not take throttle without pushing wide, ask whether you unwound enough steering. If the rear steps out as you combine controls, ask whether one end was asked for more than the tire budget could support.
The third cue is how soon the car accepts throttle without argument. A useful early throttle touch can stabilize the car and begin the exit phase, but only if the steering is being released. If the car accepts the touch, keeps its path, and lets you continue the squeeze, you are likely moving around the circle. If the car takes the first touch and then makes you lift, you probably spent the budget too early or held too much steering.
The fourth cue is track use. If you are consistently inside the exit edge while still waiting on throttle, you may be giving up radius and therefore giving up grip budget. If you are using all the track but only because the car is sliding there, you are over budget. The good version is a car released to the exit edge by a wider radius and rising throttle, not a car shoved there by excess demand.
Calibration cues from data
If you have data, look for the shape of the trace rather than a single heroic number. In Bentley's description, a properly driven corner produces g forces that follow something like the traction circle. On entry, braking force should taper as lateral force rises. In the middle, lateral force should be high without a messy pedal conflict. On exit, lateral force should fall as acceleration rises.
A separated driver often shows square corners in the data: hard brake, drop, then lateral build; lateral hold, drop, then throttle. A rushed driver often shows spikes: brake and steering too high together, or throttle and steering too high together. The best trace is not jagged or empty. It is a controlled migration around the edge.
Throttle traces tell a similar story. A driver who waits too long may show a late rise that leaves acceleration unused. A driver who pokes the throttle too early may show an initial pickup, a correction, a lift, then a second attempt. A stronger trace often shows a small pickup when the car can accept it, then a continuing squeeze as the steering unwinds.
Brake traces can reveal the same skill from the entry side. A release that falls off a cliff before turn-in may create the unused gap Bentley describes. A release that stays high while steering rises may overload the front or destabilize the car. A useful release tapers while the car starts to rotate into the corner.
How to recover when you overspend
If you overspend the tire budget, do not add more of the same demand. If the car is understeering while you are still on the brake, adding more steering usually asks even more of the front tires. Reduce the demand that is overloading them. That may mean easing the brake a little more, reducing steering slightly, or waiting to add throttle until the car is released.
If the car runs wide on throttle, do not assume the fix is a bigger throttle squeeze. The tire may already be cornering at the limit. Unwind if the track and line allow it. If not, hold or reduce the throttle until the car's path opens. Then resume the squeeze as steering comes out.
If the rear rotates more than you intended during entry overlap, the recovery is also budget based. You reduce the combined demand and regain a shape the tire can support. That usually means stopping the escalation: do not keep adding steering and do not keep a brake release or brake hold that is upsetting the car. Settle the car, point it, and rebuild the exchange more progressively next time.
The safety version of the lesson is this: the same rule that makes you faster also gives you a way to back out. When the car complains, ask which demand you can reduce. The tire does not care whether the demand came from your hand or your foot. It only responds to the total.
How this lesson connects to the rest of the module
This lesson does not replace weight-transfer control. It sits on top of it. Load transfer helps create the tire state you are using, but the friction circle tells you how to spend that state. You still need to make inputs that move load on purpose, and you still need to read balance before changing the car. The friction circle keeps those lessons honest by asking whether the tire was given a possible job.
It also cross-references directly to trail braking and throttle-control lessons. Trail braking is not just late braking. It is the entry exchange from brake to steering. Throttle pickup is not just confidence. It is the exit exchange from steering to acceleration. If you separate those lessons, you can become tidy but slow. If you combine them without respecting the budget, you become busy and unstable. The skill is disciplined overlap.
What good looks like at your next event
Pick one corner where you are comfortable and have margin. Do not choose the fastest or most intimidating corner first. Your goal is not to find a new personal best on lap one. Your goal is to feel the exchange. On entry, brake with purpose, begin turn-in, and release brake as steering increases. In the middle, resist the urge to add throttle while the car is still at full cornering demand. On exit, unwind the steering and let the throttle rise with the release.
After each lap, ask three questions. Did I leave a gap between braking and cornering? Did I ask for throttle before I gave the tire steering relief? Did the car's balance problem appear exactly when I combined too much hand and foot? Those three questions are enough to turn the traction circle from a classroom drawing into a driving tool.
The final standard is not that every corner feels dramatic. The best laps often feel less dramatic because the tire is never ignored and never ambushed. You are still near the limit, but you are moving around it on purpose. That is what it means to spend the tire's grip budget well.
Worked example: the 1.1 g entry exchange
Start with Bentley's braking-to-cornering example. The car reaches the end of the braking zone at about 1.1 g of braking. The separated approach is to finish the brake, come off the pedal, then turn and build toward about 1.1 g of cornering. That sequence feels orderly, but it creates a short period where the tires are below their potential. The car is no longer braking hard and has not yet built full cornering force.
The budget approach is to keep the tire working while the job changes. As you begin turn-in, the brake release begins. At first the tire is mostly braking and only lightly cornering. Then the exchange continues: less braking, more cornering; then roughly half and half; then mostly cornering with only a little brake left; then full cornering with the brake gone.
The exact percentages are not meant to be recited while driving. They teach the shape. The brake trace should not end as a cliff before steering begins. The steering trace should not spike while brake pressure stays too high. The exchange should feel like one force being handed to another.
If the car understeers in this example, diagnose the budget. Did you turn while still holding too much brake for the front tires? Did you add more steering after the front already said no? If the car feels lazy and coasts into the corner, diagnose the opposite budget error. Did you release all braking too early, leaving the tire below the useful edge before lateral force built? Both drivers can claim they were smooth. Only one kept the tire working.
A good attempt feels quiet but connected. The car stays loaded into the turn. You do not wait for the chassis to settle after a brake dump. You do not need a sudden steering correction to make the apex. The entry is faster because the tire was never unemployed during the transition.
Worked example: Driver A, Driver B, and the exit squeeze
Bentley's throttle-trace comparison gives you a clean exit example. Two drivers approach the same corner. Both come off the gas at the same point. Both blip the throttle for a downshift at the same place. The difference is how they return to throttle.
Driver A does a clean squeeze back onto throttle later. That is not automatically bad. It may be tidy and safe. But Driver B touches the throttle a little earlier and then squeezes fully on. Bentley's point is that this second shape often produces the quicker lap because it begins the acceleration phase sooner and can help balance the car.
The trap is to copy the early touch without copying the budget logic. Driver B is not simply mashing the pedal earlier. The early touch has to fit the remaining steering angle. Then, as the steering unwinds, the squeeze can continue. If you touch throttle early while the car is still at maximum cornering demand, the tire has no room for the extra acceleration request.
Use this example in your own data. A late throttle trace with a clean steering release may show caution or delay. An early throttle trace with a lift afterward may show over-ambition: you asked for acceleration before the tire could afford it, then had to give it back. A strong trace shows a first touch the car accepts, followed by a steady rise as steering angle comes out.
The seat-of-the-pants version is just as useful. If the early touch makes the car settle and lets you continue opening your hands, it belongs. If it makes the nose run wide or the rear demand correction, it was not free speed. It was an overdrawn budget.
Worked example: the one-foot track-width tax
The track-width example is a reminder that the friction circle is tied to line choice. Bentley gives a simple case: keeping the car even one foot away from the edge of the track at turn-in and exit reduces the corner radius. In the example, that one-foot miss reduces radius by three feet and lowers theoretical maximum corner speed by more than half a mile per hour.
That may sound small until you connect it to the budget. A smaller radius means the same speed requires more cornering force. More cornering force leaves less room for throttle. If you are inside the exit edge and still waiting to accelerate, you may be paying twice: once with a tighter radius, and again with delayed acceleration.
The correction is not to throw the car at the edge of the track. The correction is to release the car there. A good exit uses steering unwind, rising throttle, and the available width together. The car arrives near track-out because the radius opened and the tire budget shifted toward acceleration. A bad exit arrives there because the car slid or pushed beyond the demand it could support.
This example also protects you from a common setup mistake. A car that will not accept throttle while you leave unused track may not be short on power or front grip. You may simply be forcing it through a tighter radius than necessary, then asking the tire to accelerate before you have reduced the cornering demand.
Drill: the grip-budget overlap ladder
Use this drill in one familiar medium-speed corner with good runoff and a consistent reference point. Do not choose the fastest corner on the circuit. The purpose is to feel the exchange, not to prove bravery.
Session 1 is entry only. For four laps, keep your normal brake start point and normal turn-in reference. Your only assignment is to make the brake release and steering build overlap smoothly. On lap one, make the release conservative and early. On laps two through four, carry a small amount of brake closer to turn-in while reducing pressure as steering increases. Success is not a later brake marker. Success is a continuous entry with no float between brake release and cornering and no front-tire protest from holding too much brake while adding steering.
Session 2 is exit only. For four laps, ignore entry improvement and focus on the hand-to-throttle exchange. At the point where the car's path begins to open, begin unwinding the steering and add a small throttle touch. Continue the throttle squeeze only as steering comes out. Success is a throttle trace or felt input that rises without requiring a lift. If the car runs wide immediately, you added more throttle than the remaining steering angle could afford. If you are still waiting until the car is nearly straight before any throttle, you may be leaving exit capacity unused.
Session 3 links the corner. For six laps, drive the full budget arc: brake at the limit you can repeat, trade brake for steering on entry, protect the tire at midcorner, then trade steering for throttle on exit. The success criterion is repeatability. You should be able to describe after each lap which exchange was clean and which was not. If you cannot tell, slow the drill down and exaggerate the relationship: more steering, less pedal; more pedal, less steering.
Use one correction at a time. If the entry is messy, do not chase the exit. If the exit is messy, do not move the brake marker. The drill works because it isolates the two exchanges before asking you to link them. Once the shape is reliable, speed can come up without changing the rule.
Common mistakes
Mistake 1: the separated-control habit. This driver brakes, releases completely, waits, turns, waits, then accelerates. It feels neat because each control has its own space, but the tire trace cuts through unused capacity. Good looks like a managed overlap: brake force falls as cornering force rises, then cornering force falls as acceleration rises.
Mistake 2: the stacked-input habit. This driver hears overlap and adds everything at once. Brake stays high while steering rises, or throttle rises while steering remains high. The tire budget is exceeded and one end of the car gives up. Good looks like a trade, not a pileup. One demand grows because the other is shrinking.
Mistake 3: setup blame before input diagnosis. This driver feels understeer or oversteer and immediately wants to change the car. Bentley specifically warns that too much steering for the amount of braking or acceleration, or the reverse, can trick the driver into believing the car has a handling problem. Good looks like clearing the driver input first: compare steering angle, brake release, throttle rise, and track use before treating the balance as a setup conclusion.
Mistake 4: early throttle without steering release. This driver tries to copy the earlier throttle pickup from the throttle-trace example but keeps the wheel turned. The result is push, correction, or a lift. Good looks like a small throttle pickup that the car accepts, followed by a continuing squeeze as the wheel unwinds.
Mistake 5: late unwind and unused track. This driver waits to accelerate because the car still needs too much steering, then also leaves room at track-out. The tighter radius increases lateral demand and delays throttle. Good looks like using the available width to open the radius so the tire can shift from cornering to acceleration.
Mistake 6: chasing a number instead of the shape. This driver wants a later brake point, a bigger lateral g peak, or an earlier throttle point as a standalone goal. The friction circle does not reward isolated hero numbers if the transition is empty or overdrawn. Good looks like a complete force path: strong braking, progressive release, full cornering when appropriate, steering unwind, and full acceleration onto the straight.
When this principle changes shape
The tire-budget rule does not disappear, but the best-looking overlap changes with the corner and car. Bentley's throttle example says the earlier pickup is quicker in most cases, not all. That caution matters. Some corners may not reward an early touch if the car is still committed to lateral grip. Some entries may not reward deep trail braking if the steering demand rises faster than the tire can accept with brake still applied.
The principle stays the same: the combined demand must fit inside the available grip. What changes is the path around the circle. A longer corner may spend more time near maximum cornering before the exit exchange begins. A corner leading onto a long straight may reward opening the exit earlier so full acceleration starts sooner. A car with more willingness to rotate on entry may need a more careful brake release. A car that resists rotation may need the driver to preserve useful front load without overloading the front tires.
The corpus does not provide a named-corner map for these variations, so do not turn this lesson into a universal corner recipe. Use it as a diagnostic frame. If you are below the limit during transitions, connect the exchange. If you are beyond the limit during overlaps, reduce one of the demands. If the car accepts the overlap and the trace moves around the edge, keep refining the shape.
Author Review
No quiz questions are attached to this lesson.
Sources
| # | Document | Chunk | Pages | Score | Collection |
|---|---|---|---|---|---|
| 1 | Ultimate Speed Secrets - Ross Bentley | 0e9afb29-0479-7aba-8645-6fe4c4b7c2de | 105 | 1 | uio_books_raw_v1 |
| 2 | Ultimate Speed Secrets - Ross Bentley | f07eac14-7af2-b3d9-e1eb-35595db1e999 | 103 | 1 | uio_books_raw_v1 |
| 3 | Ultimate Speed Secrets - Ross Bentley | 450ecd19-9241-590a-137b-e6341558212c | 104 | 1 | uio_books_raw_v1 |
| 4 | Ultimate Speed Secrets - Ross Bentley | b273f365-45a7-575b-405a-c6e136b56c1f | 107 | 1 | uio_books_raw_v1 |
| 5 | Ultimate Speed Secrets - Ross Bentley | c3d90f02-7442-89a6-a131-b0e5e0638701 | 107 | 1 | uio_books_raw_v1 |
| 6 | Ultimate Speed Secrets - Ross Bentley | 617555a5-5a94-7190-3b48-655ac006bba6 | 110 | 1 | uio_books_raw_v1 |
| 7 | Ultimate Speed Secrets - Ross Bentley | 40874004-9e22-9b52-ff4e-b66fe894c0db | 214 | 1 | uio_books_raw_v1 |
| 8 | Speed Secrets Professional Race Driving Techniques Ross Bentley | 128552b0-78f3-e195-cfb3-e4f329c5e956 | 31 | 1 | uio_books_raw_v1 |