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Old 15th January 2008, 19:18   #1
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Arrow Safe Braking Distances

Hai Tech Gurus,

I did a serch on safe breaking distances here and found many variations but not a clear thead to this question. If its already there, Mods, please merge this thread there. My quiery:

1. What would be a safe breaking distance for my 2.5 ton behemoth (Scorp CRDE), no ABS? On hard breaking, it feels as it the beast will fly over the front wheels as it nose dives forward.

2. Some thumb rules we can use in India, most of what we read are on ideal conditions and on test tracks. Most of the figures they come out are breaking distances without giving calculations for thinking time which can be critical.

3. What is the experience of different cars in actual emergency breaking, specially those without ABS, ppl with ABS are indeed lucky.

I've done a research on the web and have read all about the 2second, 4 second 10 second rule on this but would love to learn from actual experience of people who drive in India where no driving condition is ideal.

Thanks in advance,

--Ramky
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Last edited by ramkya1 : 15th January 2008 at 19:20.
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Old 15th January 2008, 19:41   #2
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Is there a 'single rule' for this? Braking distances vary depending on the condition of the road surface, incline, speed, load in your vehicle, condition of your brakes and tyres and so on. It's your feel of your vehicle capabilities (after getting used to it) that should guide you to drive leaving sufficient room between yourself and the vehicle ahead
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Old 15th January 2008, 19:45   #3
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I guess the ideal would be allow as many feet as the speed you are traveling and then add 50% to be on the safe side. That is if you are traveling at 100 then 100 feet is minimum, plus 50 feet for unforeseen circumstances, people darting in front of you, road conditions ETC. Gurus please shed some light.

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Old 15th January 2008, 20:09   #4
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Like Jeep quoted, no fixed formula for this, depends upon so many parameters around you and the within the vehicle itself.
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Old 15th January 2008, 20:15   #5
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The safe braking distance depends on a number of factors (as noted by Jeep). I don't want to specify any numbers, but here are some important considerations.

1. The vehicle you drive, its speed and condition of its brakes/tyres.

2. Ditto for the vehicle you are following.

3. Visibility. Night/rain/fog reduce visibility and hence increase the reaction time required. Straight and wide roads afford greater visibility, since you have enough width to see ahead of the vehicle in front of you and also to swerve if necessary. E.g. following a bus closely at high speed on a narrow road is asking for trouble, big time. Give greater distance on ghat roads, because visibility is poor due to narrow and curving nature of roads. Hard braking at speed on curving ghat roads may cause your vehicle to skid out of control.

4. Condition of the road surface (wet/snow/muddy/bumpy).

5. Your driving skills. Good anticipation and correctly positioning your vehicle to afford maximum visibilty are vital. Skilled drivers can follow more closely at speed, but inexperienced ones will need greater braking distance. I was following an L-board Santro Xing lady driver in my own Santro on a narrow lane with a number of apartment gates on the sides. I immediately realized that the lady was driving too much to the left, very close to the gates and asking for trouble (idiot instructor did not apparently correct her). Sure enough, a two-wheeler guy cut into the road from an apartment gate in characteristic style and the lady stood on her brakes. Fortunately I had given her some distance *and* saw the bike cutting into the road ahead of her, and still had only just enough time to avoid rear-ending the Xing (which has superior brakes to my old Santro).

6. Driving skills/style of the driver whose vehicle you are following. Some drivers will follow the vehicles in front of them very closely at high speed and then frequently brake hard. Buses are notorious for this, but so are some SUV-taxi drivers, van drivers, etc. You can anticipate trouble in these cases because these are big vehicles attempting to go too fast on narrow roads. You should either quickly overtake these guys or follow them at a safe distance.

Some drivers will brake too early and unnecessarily hard as a matter of habit. Ladies, I hope you don't mind my putting you in this category. I don't mind rear-ending a lady while walking on a crowded street (just kidding, just kidding), but I don't want my car to rear-end hers. Follow them closely at your own peril.

Last edited by rks : 15th January 2008 at 20:19.
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Old 15th January 2008, 20:45   #6
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Arrow Jeep Is Right

Quote:
Originally Posted by Jeep View Post
Is there a 'single rule' for this? Braking distances vary depending on the condition of the road surface, incline, speed, load in your vehicle, condition of your brakes and tyres and so on. It's your feel of your vehicle capabilities (after getting used to it) that should guide you to drive leaving sufficient room between yourself and the vehicle ahead
I also agree with Jeep and others; there's'nt a single rule, many variables come into play, including the age/ reflexes / conditioning of the driver. What I am trying to get here is some common rules, even general ones, collated in one thread and experiences of drivers on emergency braking conditions.

I also came across a site which said its best to pump in the break and the clutch pedal, the logic being you don't want to be in a dead stop in an emergency with an engine-stall and may still want some steering power to roll in the direction of safety. I always thought gear-down+ using the brake would be a better solution? Here I guess the technique is also important. I'd love to learn........

--Ramky
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Last edited by ramkya1 : 15th January 2008 at 20:49.
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Old 15th January 2008, 20:57   #7
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I remember seeing a video on Edmunds,where the person presenting a 'Test Drive' report,said that not only do you have to consider the car's braking system,the effectiveness of the brake pads,the speed of the car etc, you also take into account every single parameter such as road conditions,even weather conditions for that matter.
As always,a car's braking distance is checked under ideal conditions at the test facility.
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Old 15th January 2008, 21:22   #8
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I follow the 2 second rule.... Keep a 2 second gap with the vehicle in front. So far I never ever had to do panic braking where on I had to slam the brakes.
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Old 15th January 2008, 21:36   #9
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Quote:
Originally Posted by ramkya1 View Post
I also came across a site which said its best to pump in the break and the clutch pedal, the logic being you don't want to be in a dead stop in an emergency with an engine-stall and may still want some steering power to roll in the direction of safety. I always thought gear-down+ using the brake would be a better solution?
Note that you should only pump the brakes if your vehicle does not have ABS. If it does have ABS, the computer will do the pumping and you should refrain from doing so (and confuse the computer in the process).

One reason you may need to pump the brakes is to prevent the tyres from locking up in an emergencey braking situation. If tyres lock up, then you will lose steering control, the braking distance may (but not necessarily will) increase and tyre life will come down. I personally make it a point to avoid braking too hard and whenever possible I pump the brakes to make the maximum use of available braking distance. This will increase the life of your brake pads as well as give enough time for the guy behind you to react and avoid rear-ending you. It is better to pump the brakes (especially when going down-hill on a ghat road) rather then continuously pressing the brake pedal. This will prevent excessive wear on the brake pads and avoid over-heating them.

Pressing the clutch is not so crucial and in fact should be done to prevent stalling only after the car has slowed down sufficiently, in order to make maximum use of engine braking. As for gear down, you can do this if you have time, but you should also keep an eye on your speed. Going to very low gear at too high a speed can damage your engine and should not be done except in emergencies (like brake failure).

Last edited by rks : 15th January 2008 at 21:38.
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Old 15th January 2008, 23:15   #10
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The Best practice in a non -abs car is to press only 80%of brake above 75-80kmph so not to lock up severly leading change in direction,and apply brakes with full force below this speed.But it depends on vehicle,road and driver.It worked well with my accent.
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