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Braking G's of different race cars
Last Post 09 Aug 2002 09:44 AM by Tony Shepherd. 7 Replies.
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06 Aug 2002 08:56 AM
    I was just wondering how many G's different cars ahieve while braking. Cars like spec Miatas clear up to F1.

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    '98 2.5 RS
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    06 Aug 2002 10:41 AM
    According to my G-analyst, my ITA MR2 peaks at about 1.2G with Hoosiers.

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    Norm Floyd ITA #55
    Arkansas Region SCCAForums Image [url="http://www.alltel.net/~jberry"]Tree Frog Racing's Homepage[/URL]
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    06 Aug 2002 05:16 PM
    Braking forces heavily depend upon downforce. Vehicles with little to no aerodynamic downforce typically generate about 0.8 to 1.3 Gs, depending upon the interaction of the surface and the tires. With more downforce, braking G-forces can be virtually limitless. Typical F1 cars can generate close to 5 Gs of deceleration from higher speeds. The *real* limits start to become biological: the driver can start to black out with high enough loads! G-suits required in F1? Perhaps someday . . .



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    Marshall (yes, my last name really is Cone)
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    06 Aug 2002 07:52 PM
    My g.analyst says that I can hit 1.10g peaks in my 95 Honda Accord EX. That's with Kumho V700s and with ABS kicking in hard. The g.analyst can display an average of the last full second (10 readings), which I think is more accurate. Using averages, I can see between 1.00 and 1.05g in deceleration for several seconds at a time.

    My old 1987 Honda Civic Si could hit 1.17g peaks with 1.08g averages on Yokohama A-008R tires. But without ABS, they could easily turn into 0.70g slides. I think ABS trades slightly higher peak deceleration in exchange for a lower, steadier, more contolled stop. I would not be surprised at all if a Z-06 or 911 Turbo could pull 1.2 - 1.4g

    I don't know how much an F1 car can pull, but 5g sounds too high. Downforce all put dissapears at lower speeds, so I imangine that an F1 car looses braking ability rapidly as speeds quickly decrease. While an F1 car can pull 3g+ laterally, that is done using relatively steady ground speed. Perhaps an F1 car can pull 3g+ in deceleration at peak moments, but not for very long.Three G in deceleration is losing (someone check my math) 65mph PER SECOND.

    If I remember correctly, some F1 tests in Road & Track magazine revealed stopping distances from 70mph that were 20-30 feet shorter than the best street cars. Impressive, but 70mph just isn't fast enough to see an F1 car's real ability.

    [This message has been edited by bky (edited August 06, 2002).]
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    06 Aug 2002 08:40 PM
    Thanks guys, that's what I was looking for.

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    '98 2.5 RS
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    07 Aug 2002 06:33 PM
    [QUOTE]Originally posted by bky:
    [b]

    My old 1987 Honda Civic Si could hit 1.17g peaks with 1.08g averages on Yokohama A-008R tires. But without ABS, they could easily turn into 0.70g slides.

    I don't know how much an F1 car can pull, but 5g sounds too high. Downforce all put dissapears at lower speeds, so I imangine that an F1 car looses braking ability rapidly as speeds quickly decrease. While an F1 car can pull 3g+ laterally, that is done using relatively steady ground speed. Perhaps an F1 car can pull 3g+ in deceleration at peak moments, but not for very long.Three G in deceleration is losing (someone check my math) 65mph PER SECOND.

    [/b]


    bky,

    Your numbers sounds spot-on. You are correct: F1 cars only hit loads close to 5G for brief moments. For one thing, with this sort of braking ability, the aerodynamic downforce quickly dwindles as the car slows down and the braking/cornering ability lessens. At low speeds, an F1 car's abilities are not that much better than a typical street car as far as braking/cornering loads: it is just dependent upon the coefficient of friction between the tires and the road. Of course, F1 cars spend virtually none of their active lives at these sort of humdrum speeds! Your numbers from your Civic also sound almost exactly like the numbers I've gotten from my G-Tech Pro on Kumho V700s on my '87 CRX Si: 1.15-1.18G spikes with about 1.03-1.05G steady-state cornering and similar braking numbers. If only I could get straight-line acceleration numbers like that!



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    Marshall (yes, my last name really is Cone)
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    07 Aug 2002 06:52 PM
    A Stock 89' vette on Kumho's 1.27 with Geez.

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    Jason "RX7 KLR" Isley
    Tony ShepherdUser is Offline
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    09 Aug 2002 09:44 AM
    Coeffiction of friction is the answer. You could have your F1 with hugh G stopping power fail to stop at all on ice as an example. Remember stopping includes both the tire and road or track surface. Your numbers will change with track surface changes (blacktop, concreate), rain, ice etc.

    FWIW, can you tell I have just completed a drivers instructor class. SCCAForums Image Now I need to go to english class!
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