BrakeTorque figures

Discussion in 'Technical & Support' started by philrob, Jan 20, 2025.

  1. philrob

    philrob Registered

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    I am working on the Jaguar lightweight built in 1963. The Brake Torque parameters have me beat.

    Homologated at 960kg dry 1040kg with fluids and fuel

    Disk size 11.25 F 284mm 11.25 R 284mm 12.7mm thick

    DS11 pads

    Single pot calipers

    No servo

    Brake distribution 62.5 37.5

    Brake cooling was only on the rear

    i am having trouble finding master cylinder sizes, parts from the Etype were used throughout so 5/16’ ?
    Does anybody have any idea how you work out the "BrakeTorque= " figures ?
     
  2. 8Ball

    8Ball Registered

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  3. philrob

    philrob Registered

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    Thanks 8Ball, i try and get it right to start with and then you have to start tuning. The link i had not seen before in my research, even things like the colour of his stripes was new to me. So that skin will be gaining some go faster stripes.
     
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  4. DanRZ

    DanRZ Registered

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    I think there is some sort of calculation that can help fo BrakeTorque value.
    Mass, max speed, can give you the kinetic energy you need to stop the car.
    Use some "conservative" energy formula. Energy to brake = Energy of the moving car.
    The grip must be taken in account too i think.

    E = (1/2) m V ² (linear kineatic) = (rotational kinetic) : 0.625 kinetic Front + 0.375 kinetic Rear.

    Find some median value for torque, that can help you "round" some value and adapt accordingly on feeling by iterating.

    There is some complex calculation to find the moement of inertia from torque, not that easy.

    Best option is to find another equivalent mod and use the same baseTorque value i guess,
    and adjust on feeling or litterature on behaviour.
     
  5. philrob

    philrob Registered

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    DanRZ,
    thank you for your input, i feared it would be some complex maths involved. I have done what you suggested in the past regarding borrowing other cars values . Making a small list of real ife cars brake/disc sizes and comparing with ISI/S397 torque figures for the same or similar cars.
    Not many lightweight E types around though, unfortunately.
    Normal E types are a good starting point.
     
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  6. Emery

    Emery Registered

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    Ignoring Coombs' prototype and only going with the 11 "production" versions, Phillip Porter's "Jaguar Sports Racing Cars" has the brake specifications on pages 145-146:

    Mark IX saloon calipers 11-1/4" diameter discs in front and 10-3/4" in rear, 1/2" thick solid. Pedals, pedal boxes, and front master cylinders were all production items. A Kelsey Hayes brake booster from production E-Type were fitted to the earlier Lightweights (Qvale and Cunningham), but not the later ones (Atkins, Lindner, and Jane). Pedal load for the cars with brake booster was not given, but the unboosted brakes required 150 lb (68 kg) for a 0.9G stop. Front/rear brake bias was 64.5/35.5.

    On pg 144, while giving brake specifications for the Coombs Lightweight, the Mk IX saloon calipers are said to be 2.5" in front and 1-5/8" in rear. It's not clear if the master cylinder had a balance bar, but the Coombs' car had one with a pair of production 5/8" master cylinders.

    A quick Google says 7/8" master cylinder for the Mk IX.

    Coefficient of friction for DS11 was 0.3. The BrakeResponseCurve=(-95,340,575,1080) from the Howston is reasonable as the Lola T-70 was originally designed to use DS11 brake pads.
     
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  7. philrob

    philrob Registered

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    Emery,
    thanks for the great info, i have porter and pages later book " Jaguar Lightweight E-type" and so far i can not find those specs in it.
    So i am glad you posted them.
     
  8. Corti

    Corti Registered

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  9. Emery

    Emery Registered

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    Plugging numbers into the physics spreadsheet suggests each front BrakeTorque=1160 and each rear BrakeTorque=550 as a starting point.
     
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  10. philrob

    philrob Registered

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  11. philrob

    philrob Registered

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    Those figures are lower than i expected, then again the Jag did have braking trouble. They fitted Jaguar X brakes to the later cars, but i will put them in today and test drive the car.Thank you again for your assistance.
     
    Last edited: Jan 22, 2025
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  12. philrob

    philrob Registered

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    Emery, i have been testing with your suggested figures.They make for a very different car. It now feels more like an earlier sports car, were you have to think more about your braking. Prior to these new Torque figures the E type felt like a modern Historic racer with modern brakes and suspension.So it is definately on the right path.
    Thank you again.
     
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  13. Emery

    Emery Registered

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    I probably should state that by "starting point", I mean that's where the brakes will stop the car without skidding. Maybe increase the BrakeTorque about 10% so you have some room for locking them and dealing with any brake fade. If that doesn't allow you to lock the brakes, then the tires might be too grippy.
     
  14. philrob

    philrob Registered

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    Emery,
    just got hold of the book you mentioned and it seems to have far more interesting information than the later version i had. And yes i did use the
    " Starting Point " as my base figures. Again many thanks for your help.
     
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