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  1. #1
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    Default Brake sizing and selection tutorial featuring Ron Sutton and Tobin of KORE3

    It seems that all too often people buy a brake "system" that isn't a system at all and wind up repurchasing different calipers or different master cylinders because the parts they initially had were mismatched.

    Let's work out the process for selecting the correct parts the first time assuming one is starting from scratch (no brake system at all). To that end I’ve enlisted the help of Ron Sutton and Tobin of KORE3 to provide the tutorial.


    The plan is that they will each from their point of expertise (Tobin on power brakes, and Ron on manual) provide the method of correctly sizing brakes to the application, and selecting the appropriate components to create a cohesive system rather than a disparate collection of parts.


    For the first example we’ll use a clean sheet of paper in the form of my car http://www.pro-touring.com/threads/4...highlight=trak . There’s a vicious rumor floating around that this project “might be” starting up again and with no brake selection yet made, it seems like a good candidate for this exercise.

    So here we go with some specifics so the guys can work their mojo.


    1968 Camaro



    Application – Auto-x, Track Day, Street (in that order of importance though total mileage may favor the latter)

    Estimated completed weight - ~3300lbs based on the “OLC Camaro” which is configured similarly…I’d like to be a touch lighter though…wouldn’t we all?

    Rear Tire/Wheel – 335x18, 220 UTQG (possible Alternate tire Hoosier A6)

    Front Tire/Wheel – 315x18, 220 UTQG (possible Alternate tire Hoosier A6)

    Rear Suspension – Lateral Dynamics 3-Link, 9” Ford Housing with “Big Ford New Style” housing ends

    Front Suspension – Let’s just say GM disk brake spindle and leave it at that for now….


    Pretty certain based on measurements that a Wilwood 140-9804 FNSL6R setup will fit in my selected wheel. No idea if this is an appropriate front brake to base the rest on, but I’m pretty sure that is the biggest I can safely go with the wheels I have planned. A 140-9803 may be more appropriate.

    NOTE: I'd ask that we let Ron & Tobin respond to this BEFORE asking additional questions so that the information is presented in a more cohesive and linear manner. After this application is sussed out, feel free to then ask questions related to your application.

    .
    Last edited by Damn True; 01-23-2014 at 03:28 PM.
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  2. #2
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    This Forum is focused on Brake Selection:
    For a thread focused on: Overall Handling & Tuning for Track Performance ... click HERE.
    For a thread focused on: Front Suspension & Steering Geometry for Track Performance ... click HERE.
    For a thread focused on: Rear Suspension & Geometry for Track Performance ... click HERE.
    For a thread focused on: Measuring & Modifying Your Front Suspension Geometry ... click HERE.
    For a thread focused on: Designing Aerodynamics for Track Performance ... click HERE.
    For a thread focused on: Safety for Pro-Touring Track Cars ... click HERE.


    ----------------------------------------------------------------------

    Great detail True.

    We should ...
    a. Get clear on intended use - DONE. (Auto-X, Track & Street)
    b. Get clear on tires being used for an idea of grip - DONE (315/335 TW220 street tires & Hoosier A6's)

    Then we should ...
    c. Decide how much total braking force we want
    d. Pick calipers, pads & rotor size with front-to-rear braking bias in mind.
    From there we'll work out pedal ratios, master cylinder sizes, boosters, etc.

    A good rule of thumb for braking force is ...
    2500# = Average passenger car
    3000# = Performance production car
    3500# = Good street & track braking system
    4000# = Track braking system with good tires
    4500-5500# = Full race brake systems
    This is just a guideline as it's a little broad and there are variables.

    Most people don't take into account the suspension set-up when selecting brakes, but in AutoX & Track Cars, it is an important factor too. The guideline above is good for conventional suspension cars with stiff springs & moderate sway bars. When running a soft spring/big bar strategy front suspension for high travel & low roll angle, we use less brake & frankly need less braking force or the car is "edgey."

    With your big street tires, I'd suggest a target of 3400-3700# total braking force if you're running a conventional suspension set-up. If your running a soft spring/big bar strategy ... with, I'd suggest 2700-3000# total braking force. Can you provide us with your spring rates, spring motion ratios (squared) & your sway bar rates?

    If yes, I can guide you better. If not, we'll proceed the best we can.

    Last edited by Ron Sutton; 12-07-2014 at 01:59 PM.
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

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  3. #3
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    Spring rates are, going off of similarly configured cars 600lb fr & 300lb r.

    Motion ratio....er...no idea and same for the bars...but I might be able get all but the rear bar rate.

    Pedal ratio: According to notes in my totally anal retentive but never quite complete file of probably mostly useless information the ratio on a Camaro pedal assy is 6:1 on the top (manual) hole. Don't know what it is in the power brake (lower) hole. I reckon Tobin knows.

    As for setup...not sure. I've driven two cars (an M3 and a miata) that were set up with BBSS. Both were a dream on a smooth auto-x course but a bit of a mess on rougher surfaces and on a track. Could be anomalies, but at this point I'm not sold on that strategy.
    Last edited by Damn True; 01-23-2014 at 11:03 PM.
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  4. #4
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    No worries True. I just pulled the motion ratio off another Gen 1 Camaro.

    For those that care: Front MR is .54 ... so squared it is .2916 x 600# front springs gives us 175# of wheel rate. That tells me we're running a low-mid travel conventional front suspension ... around 1.5" front travel under braking ... so I'd suggest a target of 3400-3700# total braking force with the large 315/335 TW220 treaded tires.

    You can run much more total braking force with the slicks. My suggestion would be to have a more aggressive brake pad (higher CoF) for track days & install them when you put your slicks on. Put your street brake pads back on when you put your street tires on. I'd set 4000-4300# total braking force as your target ... with slicks.

    P.S. I did notice you specified Hoosier A6 tires which is a short run tire for Autocross. If you are only using this tire for Autocross, you may not want to change the brake pads, as 3400-3700# total braking force will be fine for Autocross. Drive it that way & see. You can always change out the pads with the slicks for competition events. But for road course track days ... if you run slicks ... you will want the higher braking force.

    My next post will show caliper/rotor/pad combinations.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

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  5. #5
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    Quote Originally Posted by Damn True View Post
    It seems that all too often people buy a brake "system" that isn't a system at all and wind up repurchasing different calipers or different master cylinders because the parts they initially had were mismatched.

    Let's work out the process for selecting the correct parts the first time assuming one is starting from scratch (no brake system at all). To that end I’ve enlisted the help of Ron Sutton and Tobin of KORE3 to provide the tutorial.


    The plan is that they will each from their point of expertise (Tobin on power brakes, and Ron on manual) provide the method of correctly sizing brakes to the application, and selecting the appropriate components to create a cohesive system rather than a disparate collection of parts.


    For the first example we’ll use a clean sheet of paper in the form of my car http://www.pro-touring.com/threads/4...highlight=trak . There’s a vicious rumor floating around that this project “might be” starting up again and with no brake selection yet made, it seems like a good candidate for this exercise.

    So here we go with some specifics so the guys can work their mojo.


    1968 Camaro

    Application – Auto-x, Track Day, Street (in that order of importance though total mileage may favor the latter)

    Estimated completed weight - ~3300lbs based on the “OLC Camaro” which is configured similarly…I’d like to be a touch lighter though…wouldn’t we all?

    Rear Tire/Wheel – 335x18, 220 UTQG (possible Alternate tire Hoosier A6)

    Front Tire/Wheel – 315x18, 220 UTQG (possible Alternate tire Hoosier A6)

    Rear Suspension – Lateral Dynamics 3-Link, 9” Ford Housing with “Big Ford New Style” housing ends

    Front Suspension – Let’s just say GM disk brake spindle and leave it at that for now….


    Pretty certain based on measurements that a Wilwood 140-9804 FNSL6R setup will fit in my selected wheel. No idea if this is an appropriate front brake to base the rest on, but I’m pretty sure that is the biggest I can safely go with the wheels I have planned. A 140-9803 may be more appropriate.




    .
    The Corvettes and many other cars run 20-25 minute NASA races on Hoosier A6 now, they do go through more tires but they are actually faster on track the R6 or other available slick racing tires. My understanding is that they can get a weekend out of them with proper break in, that would include quite a few miles of racing.

  6. #6
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    Wow, this thread is perfect timing for me...do you folks mind if I participate as well?
    Lance
    1985 Monte Carlo SS Street Car

  7. #7
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    Please do. But guys, can we wait to reply/ask further questions until Ron & Tobin have gone through their workflow so that their info is presented in a more linear manner?
    True T.

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  8. #8
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    Hi True,

    The chart below outlines one brake system that is pretty balanced right from the get go
    , by using calipers with the right piston area front & back. Using two of the same size master cylinders, or a dual master cylinder with same size piston, creates a system that has a F/R brake bias of 67/33. Some guys shoot for 65/35, but as you track the car you'll find you want a little less rear brake bias. I find most end up around 67/33 to 70/30 with conventional set-ups.

    I have laid out a manual system here, with a proportioning valve plumbed in the rear. The first chart on the left shows the system with no proportioning adjustment. This provides 1222# of rear braking force, 2458# of front braking force & 3681# of total braking force with a 67/33 bias.

    The middle chart shows the same system but adjusted to a 70/30 bias with the proportioning valve. You'll notice the front braking force stays the same & the rear reduces. This provides a total braking force of 3512#.

    On the chart on the right, I changed the brake pads from "street performance" type BP-20 pads to "race type" pads known as "B" compound. The CoF (Coefficient of Friction) is higher, jumping the braking force up 25%. You can see the numbers are 4569# total braking force with no proportioning adjustment ... and 4354# when adjusted to a 70/30 bias. This would be a mean braking system for slicks, but simply lock up all four wheels too easily with your treaded tires.

    A few things to note:

    #1 - I have spec'ed the same pads front & rear, but they have different CoF numbers ... because the front & rear operate at different temperatures when balanced correctly.

    #2 - The front caliper is an awesome new Wilwood design called the Aerolite that should be available any day now. It has great body mass where needed, light where it can be & has 5 large bridge bolts to reduce caliper bowing. In short, it is a very good caliper.

    #3 - All of this assumes a 100# leg force (kind of a standard), 6-1 pedal ratio, 7/8" M/C & NO Booster. I have very little experience with boosters, but Tobin has tons. So let's ask him to suggest a pedal ratio, master cylinder size & booster type & size to achieve your goals.



    Name:  Trues Brake System.jpg
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    .
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

    Features: Suspension, Chassis, Cages, Brakes, Rear Ends, Engines, Transmisssions, Aero & Much, Much More!

  9. #9
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    Ron,

    That is very interesting. I wonder though what the dimensions of the Aerolite caliper will be. Their press release doesn't give any dimensions.

    The FNSL6R is super compact as can be seen in their drawings http://www.wilwood.com/Images/BrakeK...565_wcd-lg.jpg with a 4.04"sq piston area and 8.2"sq pad area
    The W6A is still pretty fitment friendly but slightly less so http://www.wilwood.com/Images/BrakeK...678_wcd-lg.jpg with a 4.04"sq piston area and 11"sq pad area

    [ninja edit] Just noticed that you spec'd the 13" rotor kits for both. That pretty much alleviates fitment concerns in an 18" wheel.....more of a concern with a 14" dia front rotor. [/ninja edit]

    I suspect the larger pad area was the driver in your selection?
    Last edited by Damn True; 01-24-2014 at 09:06 AM. Reason: Im a spaz
    True T.

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  11. #11
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    I deleted my thread derail post... Will wait to watch how the thread progresses then join in....

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    I feel like I'm tardy for class...sorry for the delay in jumping into the fray. Don't you hate it when your day job gets in the way of checking out the forums? Of course, my day job rocks, so who am I to complain?

    That said, everything so far seems to be be pretty well defined. I don't know how much of a booster expert I am, but I'll do my best, however I'm open to all opinions on the matter and am never opposed to learning something new. The first and possibly most important question is whether you need or should have power brakes, and that's not one that can be easily answered. In general, manual brakes will provide the most positive feedback to the driver and highest level of control, however it comes at the price of a longer pedal throw and higher pedal effort. Power brakes will require less pedal effort and less pedal travel. Due to the subjective nature of the question, I'll let each answer this for themselves.

    To address initial pedal ratio questions, let's assume 6:1 for manual calculations and ~4:1 for vacuum assist for most GM muscle applications. For the most part, pedal ratio is far less adjustable or easy to change than are master cylinder bore size, booster size/configuration, etc, so for this exercise I would suggest we remove that from the variable column and focus on the things that are not so inherent to the car dash/pedal/firewall design.

    When considering power brakes, you have two general options, vacuum assist and hydroboost in all it's various forms. For the former, you're going to need a good, reliable vacuum source to power the brake booster, and while your results may vary, we deem 14 inches Hg or more at idle to be a good starting point. We've found 12-14 inches Hg to be somewhat marginal and produce some pedal inconsistency. Less than 12 inches Hg and you tend to be fighting an uphill battle and may be better off considering manual or hydroboost options. As with anything, there are always exceptions, but these have served us pretty well as good general guidelines over the years.

    Hydroboost will require either power steering for the more conventional Bosch type units (Hydratech) or not if you're looking at the standalone type units like the Powermaster/Audi/ABS/etc type units.

    Adding a booster to a brake system will not fix an otherwise imbalanced, improperly specified, poorly maintained or otherwise flawed system, it will only reduce the pedal effort/travel required to achieve lockup, with everything else the same. This is a very important distinction, and while power brakes certainly can minimize some types of braking issues and provide more flexibility with respect to driveability, there is no replacement for starting with a well designed brake system.

    Tobin
    KORE3
    It's what I does.

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    Well, since I don't yet know what sort of vacuum my planned engine will produce (LS 376/525) it seems I should begin with a manual system and then if so desired I could then add a booster right?

    Would the master sizing remain the same for a boosted configuration vs manual?
    True T.

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    For a first gen Camaro, the brake pedal is 12.5" long, the pivot to manual brake clevis hole is 2", the power brake clevis hole is 3.25".
    Ratio:
    6.25-1 Manual
    3.8-1 Power.
    Second gen Camaros are similar but I hear around 1978 or 79 it changed.
    My number for a 1st gen Motion ratio is .5

    A 14" rotor is a good idea for a manual brake Camaro if it can clear the wheels. It lessens pedal effort which would be pretty high on a 13" manual system.
    Any manual system must be well engineered or the pedal effort/stroke will be unsatisfactory. Both stroke and pedal effort will be higher than a power brake system.
    Manual systems are more sensitive to knock back, - twice as sensitive as power brakes.
    A power brake system has half the pedal travel due to the pedal ratio & with boost, has less sensitivity to the bore sizes being slightly off, but you have less feel for preventing lockup. Hydroboost is probably the worst for feel.
    Last edited by David Pozzi; 01-24-2014 at 01:46 PM.
    67 Camaro RS that will be faster than anything Mary owns.

  15. #15
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    Quote Originally Posted by Damn True View Post
    Well, since I don't yet know what sort of vacuum my planned engine will produce (LS 376/525) it seems I should begin with a manual system and then if so desired I could then add a booster right?

    Would the master sizing remain the same for a boosted configuration vs manual?
    No. You would need a larger M/C bore with the booster, or the additional pressure from the booster would create too much braking force. What size M/C depends on how much "boost" you're getting from your booster. That varies with size, single or dual, etc. This is where my experience runs out. You would need to get with Tobin to discuss recommended boosters & M/C size.


    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

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  16. #16
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    Quote Originally Posted by Damn True View Post
    Well, since I don't yet know what sort of vacuum my planned engine will produce (LS 376/525) it seems I should begin with a manual system and then if so desired I could then add a booster right?

    Would the master sizing remain the same for a boosted configuration vs manual?
    X2 what Ron said. Adding a booster is just that, it's adding a gain/boost factor between the pedal and the master cylinder, where the magnitude of gain/boost will be determined by the power brake components chosen. Knowing that the manual system is going to be the least forgiving with respect to pedal effort, designing a good manual system is a great way to start, then you know if you convert to manual you're starting with a system that is capable of providing the same great performance, but with less effort at the pedal.

    As for master cylinder sizing, no, manual and power brake systems will not typically use the same size master cylinder for a given caliper combination. Manual systems will use smaller bore master cylinders, where a smaller bore MC = higher output pressure and less volume per inch of stroke and a larger bore MC = lower output pressure and greater volume per inch of stroke. Using a 1" bore MC as the baseline, I've included some information below showing the relative difference in output pressure between MC bore sizes for reference, keeping in mind that the pedal travel will change by the same amount.

    ⌀1.125" bore -> A=.994 square inches [-26.6%]
    ⌀1.063" bore -> A=.886 square inches [-12.9%]
    ⌀1.031" bore -> A=.835 square inches [-6.4%]
    ⌀1.000" bore -> A=.785 square inches [BASELINE]
    ⌀0.938" bore -> A=.690 square inches [+12.1%]
    ⌀0.875" bore -> A=.601 square inches [+23.4%]
    ⌀0.813" bore -> A=.519 square inches [+33.9%]
    ⌀0.750" bore -> A=.442 square inches [+43.8%]

    Tobin
    KORE3
    It's what I does.

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    Ok, you guys lost me.

    F=PxA right? So why does more P (by virtue of boost) applied to larger A not result in more F?
    True T.

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    Force and Area are independent variables from each other, related by pressure, so let's look at it one variable at a time. You are 100% correct that Force = (Pressure)*(Area), or F = P*A. Since the system output is pressure, not force, then we should solve for pressure resulting in the following form of the same equation, P = F/A. This should make sense given the units of pressure, pounds per square inch or force per unit area. Now, based on the formula noted, an increase in F results in an increase in P. Similarly, since A is in the denominator, a decrease in A will also result in an increase in P and the inverse is true for both as well.
    It's what I does.

  19. #19
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    Tobin,

    Can you share with us a good method to figure out how much pressure a booster will add?
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

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  20. #20
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    Quote Originally Posted by Ron Sutton View Post
    Tobin,

    Can you share with us a good method to figure out how much pressure a booster will add?
    The short answer is that most boosters provide a gain factor somewhere between 2-4 times, however that's not very exact and doesn't really begin to explain some of the deeper mysteries of modern vacuum boosters. The most definitive way to determine how much gain/boost a booster will add to any given system would be to measure it either directly or indirectly. The direct method would be to apply a vacuum to the booster, apply a force on the input side and measure the output force. Indirectly tends to be easier, where you could install a master cylinder and measure the output pressures for a giving input force, one with vacuum and one without, as this would give you the most accurate and real world numbers as anything. That said, we're here for the theory too, so here we go.

    The basic principle behind a vacuum boosters is to utilize a pressure differential in order to aid in the application of the brakes. Control of this function is through a control valve assembly connected to the input rod and attached to the pedal, effectively controlling the condition on the firewall side(s) of the diaphragm(s). At rest, there is vacuum on both sides of the diaphragm, essentially cancelling each other out and resulting in zero net gain. There is a return spring inside the booster (and MC for that matter) that returns the pedal after brake application. When the brakes are applied, the control valve assembly closes the vacuum supply and allows air into the chamber on the firewall side(s) of the booster diaphragm(s), reducing the vacuum level and creating a net gain/boost towards the master cylinder proportional to the diaphragm area, vacuum level supplied and control valve position.

    For those gluttons out there wanting a more complete and thorough mechanical description without all the math and theory, there's a decent article here.

    We're going to simplify things for the moment and ignore the internal losses and inefficiencies involved with vacuum boosters, at least for the time being, and do a relative comparison as an example. Below are the approximate effective diaphragm areas for a few common booster sizes for reference:

    Dual-7" -> A(D7) = 77 sq inch -> [608 lb]
    Single-10.75" -> A(11) = 91 sq inch -> [716 lb)
    Dual-8" -> A(D8) = 100 sq inch -> [790 lb]
    Dual-9" -> A(D9) = 127 sq inch -> [1003 lb]

    If you were to then assume a typical engine vacuum level of say 16 inches Hg, about 7.9 psi vacuum, then you can calculate the maximum level of force multiplication or gain that the booster can supply as noted in the brackets above. Please note that this is purely theoretical and the maximum level (referred to as runout when the valve is fully open with full vacuum on the one side and full atmospheric pressure on the other) based solely on the relative diaphragm areas assuming the control valve is wide open (aka panic stop, locked up type braking), but it gives you an idea of relative performance between the units. Just a side note, however smaller diaphragm units tend to be less efficient than larger diaphragm units, so while the ratios above can be useful for comparison, a dual-7" booster is actually worse than the numbers might indicate in actual practice.

    Another interesting tidbit is that the reaction force of the booster is generally only about 20%-40% of the force applied by the booster depending on the design of the reaction disc/plate or lever, and is there to provide a more accurate pedal feel. More modern booster designs tend to do a better job of providing good brake feedback to the driver, which can make precise modulation and threshold braking much easier.
    It's what I does.

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