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Thread: Finally, the truth about speed bumps and low speed limits

  1. #46
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    Quote Originally Posted by Fleet 500 View Post
    Wait a minute... alllow me to make a correction. There are some cars that get better mileage at 50 mph than at 30 or 40 mph. Like the Pontiac I posted before:

    '68 Pontiac Catalina (400-cu-in engine, 290 hp, 2.29:1 axle ratio, 4,133 lbs curb weight)

    MPG @ steady:

    30 mph------------ 19.5
    40 mph------------ 21.5
    50 mph------------ 22.0
    60 mph------------ 19.0
    70 mph------------ 17.5
    and of course you have no idea why that it? Because at 30-40 the autobox is constantly thinking what gear to be in...while at 50 the engine delivers enough torque to make the gear box think it can stay in top.
    "I find the whole business of religion profoundly interesting, but it does mystify me that otherwise intelligent people take it seriously." Douglas Adams

  2. #47
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    Quote Originally Posted by henk4 View Post
    and of course you have no idea why that it? Because at 30-40 the autobox is constantly thinking what gear to be in...while at 50 the engine delivers enough torque to make the gear box think it can stay in top.
    I don't think so. That Pontiac has the same trans as the one in my Cadillacs (Turbo-hydramatic).
    These transmissions shift into third (with regular acceleration) at about 25 mph and won't drop back into 2nd until the car speed is below about 20 mph.
    In other words, 3rd gear is used from 20-25 mph up to the car's top speed, unless the the throttle is opened up enough for it to downshift which doesn't happen with steady 50 mph driving.
    '76 Cadillac Fleetwood Seventy-Five Limousine, '95 Lincoln Town Car.

  3. #48
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    Quote Originally Posted by Fleet 500 View Post
    In other words, 3rd gear is used from 20-25 mph
    will the revs be constant? or will the torque converter try to compensate for the low revs?
    "I find the whole business of religion profoundly interesting, but it does mystify me that otherwise intelligent people take it seriously." Douglas Adams

  4. #49
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    Quote Originally Posted by henk4 View Post
    will the revs be constant? or will the torque converter try to compensate for the low revs?
    Not sure... my cars don't have a tach. I think the torque converter does compensate.

    ... I forgot to reply to the original subject of this post (speed bumps).
    There are two kinds here- the ones in the parking lot and the "humps" on some residential side streets.

    I don't mind the ones in the parking lots much, although some are unnecessarily high and peaked.

    I don't like the ones on the streets because the residential streets have a speed limit of 25 mph and the humps force you to slow down to 15 mph. I think it's a waste of fuel and brakes to force drivers to slow down and speed up again. And the residential streets have anywhere from 2 to 5 or 6 "humps."
    I try to avoid driving on streets that have those; fortunately, there are none on my street because it ends in a cul-de-sac.
    Last edited by Fleet 500; 02-05-2008 at 03:58 AM.
    '76 Cadillac Fleetwood Seventy-Five Limousine, '95 Lincoln Town Car.

  5. #50
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    Quote Originally Posted by Fleet 500 View Post
    I don't like the ones on the streets because the residential streets have a speed limit of 25 mph and the humps force you to slow down to 15 mph.
    that's why I suggested to use a "big" Citroen (one from the top range with the hydropneumatic suspension...) no waste of energy, just carry on

    (and it does not necessarily have to be this one, mine will do fine as well)
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    "I find the whole business of religion profoundly interesting, but it does mystify me that otherwise intelligent people take it seriously." Douglas Adams

  6. #51
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    just did some experimenting. First thing I found is that the actual fuel consumption is not registered on my computer for speeds below 30 kph.
    Second I have been shifting around a little and using 4th and 5th gear for speeds between 30 and 50 kph and let the revs drop to idle, (without stalling the car). Fuel consumption did not differ much whether I was in 5th or 4th (close to 40 and close to 30 respectively). Furthermore it is difficult to maintain constant speed at this range and the influence of the wind will show nice fluctuations as well. Actual results were something like between 78 and 94 mpg for speeds between 30 and 45, but indeed not very scientific.
    "I find the whole business of religion profoundly interesting, but it does mystify me that otherwise intelligent people take it seriously." Douglas Adams

  7. #52
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    Quote Originally Posted by henk4 View Post
    that's why I suggested to use a "big" Citroen (one from the top range with the hydropneumatic suspension...) no waste of energy, just carry on

    (and it does not necessarily have to be this one, mine will do fine as well)
    Most people (including me) drive down residential streets at 25-30 mph. While it is possible to stay at those speeds when driving over the humps, it is easier on the suspension to slow down to at least 20.

    That is what I do... slow down to 20 or 15 mph, but sometimes when I'm lazy I'll stay at 25 mph.
    Of course with my cars, the humps don't bother them much.
    '76 Cadillac Fleetwood Seventy-Five Limousine, '95 Lincoln Town Car.

  8. #53
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    The ones that irritate me are the ones you virtuall have to stop, get out and push your car over. Speed bumps should be deisnged so that they can be comfortable driven over at the speed limit. Sadly many in 30mph zones require 10-15mph and possibly lower, 20mph zones require 2-3mph. Ridiculous, this things are practically just kerb stones cemented to the asphalt.

    My personal solution is to buy a WRC type car, Evo, Impreza etc, and tune it to WRC spec suspension settings. That way you can fly over them without the slightest worry, whilst maintaing a steady, and envionmentally friendly 60mph.

  9. #54
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    All vehicles are different. A speed hump that limits a 4WD to 15kmph will limit a smaller/lower car to 5kph. There is no good solution to limiting all vehicles to the same speed with a speed hump.

  10. #55
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    why should they have a speed hump that you can comfortably drive over at the speed limit? does that not defeat the purpose of slowing the traffic down?
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  11. #56
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    Quote Originally Posted by whiteballz View Post
    why should they have a speed hump that you can comfortably drive over at the speed limit? does that not defeat the purpose of slowing the traffic down?
    The point of speed bumps are to discourage traffic from breaking the limit. If you're driving at or just below the limit, why should you have to slow down unnecessarily? As previously mentioned, all that does is waste fuel and increase suspension wear.
    "This is hardcore." - Evo's John Barker on the TVR Tuscan S

  12. #57
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    Perhaps I dont quite follow because I dont think australia has the same problem as you guys in terms of numbers of these humps, But I imagine a design to keep all happy is pretty easy..

    Such as one wide raised burm, then as you drive up that a sensor reads your speed, and if your going faster, it raises a second hump ontop that would suffice to slow people down?
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  13. #58
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    Oh the expense and litigation of that type of thing....

    We have a deterrent for this type of thing already called a speed camera.

  14. #59
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    I skipped from the first page to the fourth, but I must say I agree with most of what I've seen Clivey remark. Speed cameras are bollox too.

    Just to add more fuel to the flame: eliminating speed limits lowers the number of accidents, cameras increase the number of accidents. If you try to tell the government different Nazis riding on dinosaurs will steal your children.

  15. #60
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    I'm sorry, while I all up for scrapping speed limits, I want that because I personally want to drive like a loon everywhere and not get done for it. I cannot see in any way how eliminating the speed limits would reduce accidents.

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