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Old 16th December 2008, 09:10   #121
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Quote:
Originally Posted by RajeshK View Post
Is it so...? I belief the moment you press B-Pedal, the speed will come down, so where does the 1km comes from? Please excuse my ignorance.
I guess what he means is that "since one covers 1 km every 30 seconds at 120kph" even if you start braking hard, by the time you come to a stop is over 30 seconds and a kilometer away!

But i see your POV, which is the moment one touches the brakes, the speed reduces to less than 120kph etc
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Old 16th December 2008, 11:07   #122
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I guess what he means is that "since one covers 1 km every 30 seconds at 120kph" even if you start braking hard, by the time you come to a stop is over 30 seconds and a kilometer away!

Not really, an OHC VTEC with stock tyres can go from 100-0 in 55 meters and the newer cars with ABS (and broader tyres) do it in even lesser distance. So even a M800 should be able to do a 120-0in less than 150 mtrs.

Here are some 100-0 braking figs for cars that were tested way back in 2001.

PS : The slowest car in this test (Opel Astra) went from 0-100-0 in 336 meters.

17 CARS - ULTIMATE PERFORMANCE TEST

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Last edited by Shan2nu : 16th December 2008 at 11:11.
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Old 16th December 2008, 11:19   #123
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Quote:
Originally Posted by Samurai View Post
What? You get best engine braking in diesels. I bought diesel Jeep over petrol Jeep/Gypsy because of engine braking. I was able to drive the Jeep from Bangalore to Manipal (448Kms) with working brakes in only one wheel because I could rely on engine braking. Offroading nuts love diesel engines because of engine braking. Can you please explain your statement?
Quote:
Originally Posted by teknophobia View Post
The Engine Braking "thing" is especially applicable for diesels, try driving down a steep slope with comparable diesel and petrol cars in gear, see where you have to use the regular brakes.

Try driving in the Ghats sometime as well, you will thank yourself if you drive a diesel.
whenever I've tried downshifting to reduce speed, the engine just revs higher, and there is no significant reduction in speed, certainly not like in a petrol. But yes, when going downhill, especially on bad roads, it does keep the car in control and at the same speed.
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Old 16th December 2008, 11:24   #124
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I concur,the braking distance is not even close to one km from a speed of 120kph,even in cars without ABS.I say that from personal experience having had to brake-test my Accent a couple of times(even with its lousy brakes it doesn't take either 30 seconds or 1km).If that were true then it would be near impossible to prevent accidents for most people as IMO most amateurs would not steer the car in a different direction and keep heading straight(for disaster).
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Old 16th December 2008, 11:29   #125
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Bro!

was this statement had the necessary pun intended or were you serious!! Anywhich way I cant stop

Cheers
Shrey


Quote:
Originally Posted by bblost View Post
Practise helps.
Make it mandatory on yourself to test out a high speed sudden brake test every 6 months.
Hit the rev limiter a couple of times a year in controlled environments.

Use common sense.
Don't mess with erratic fools on wheels. They are on a suicide mission. Avoid them.

Walk around your car and inspect it every morning before take off.

Wash your car, yourself. Helps identify and spot any body problems.

Remember that at 120 kmph you are crossing a km every 30 seconds.
And if you want to stop your car it will cross atleast one km before coming to a halt.
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Old 16th December 2008, 11:34   #126
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Quote:
Originally Posted by bblost View Post
Practise helps.
Make it mandatory on yourself to test out a high speed sudden brake test every 6 months.
Hit the rev limiter a couple of times a year in controlled environments.

Use common sense.
Don't mess with erratic fools on wheels. They are on a suicide mission. Avoid them.

Walk around your car and inspect it every morning before take off.

Wash your car, yourself. Helps identify and spot any body problems.

Remember that at 120 kmph you are crossing a km every 30 seconds.
And if you want to stop your car it will cross atleast one km before coming to a halt.
Please follow both bits of advice religiously everyone.Take good care of yourself and your car
Just kidding,no offense meant
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Old 16th December 2008, 11:44   #127
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You are driving at 120 kmph.

From the time you see the kid about to cross the road till your car has come to a complete halt.
How much time and distance has been crossed.

I am not talking about brake testing.
Referring to a real life scenario on Indian highways.

But I stand corrected.
The estimate value I gave was incorrect.
It will not take so much time if you stand on the brakes and all conditions are perfect.

While thinking about this topic ran a google search.
I found this
Reaction time measurement

Note: It did not run in google chrome but runs well in IE.

It has an excellent applet embedded in it. Try out the test.
It gave me a 26.64 m braking distance on dry concrete for 120 kmph.
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Old 16th December 2008, 12:04   #128
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It didn't load on my browser.

BTW is 26m the braking dist, but for which car?

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Old 16th December 2008, 12:12   #129
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It works in my IE 6.

The make of the car is not mentioned as the formula used does not involve the Mass.
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Old 16th December 2008, 12:14   #130
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Quote:
Originally Posted by bblost View Post
You are driving at 120 kmph.

From the time you see the kid about to cross the road till your car has come to a complete halt.
How much time and distance has been crossed.

I am not talking about brake testing.
Referring to a real life scenario on Indian highways.

But I stand corrected.
The estimate value I gave was incorrect.
It will not take so much time if you stand on the brakes and all conditions are perfect.

While thinking about this topic ran a google search.
I found this
Reaction time measurement

Note: It did not run in google chrome but runs well in IE.

It has an excellent applet embedded in it. Try out the test.
It gave me a 26.64 m braking distance on dry concrete for 120 kmph.
Tried it for 120 and 140 km\h: the reaction time was 25.51m.
So, after i hit the brakes the car would come to stop after 25.51 meters??
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Old 16th December 2008, 12:54   #131
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Wait a sec, are those braking distances or distance covered during rection time? Confused now....

If its reaction distance then how can it be 25.51m at 120 as well as 140kmph, when there is a 5m/s diff between the 2 speeds?

According to these results the driver in the 140kmph car reacted in 0.65 secs while the one doing 120kmph took 0.76 secs!!!

And if its braking distance, how can one conclude the distance covered without knowing the mass, tyre size/compound, braking force applied, aerodynamic resistance, rolling resistance etc......

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Old 16th December 2008, 13:14   #132
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Quote:
Originally Posted by bblost View Post
You are driving at 120 kmph.

It gave me a 26.64 m braking distance on dry concrete for 120 kmph.
Quote:
Originally Posted by deadguy25 View Post
Tried it for 120 and 140 km\h: the reaction time was 25.51m.
So, after i hit the brakes the car would come to stop after 25.51 meters??

Nothing is farther from the truth. Keeping all parameters constant, the total braking distance cannot be ~25 meters at 120kmph.

I have attached my result. Let us interpret it.

Following the dotted line, the first red vertical line signals the time when the red traffic light came on.

The second red vertical line indicates the time when I hit the brakes. The distance between the two vertical red lines, which in this case is 8.33 meters, is the time i am still covering distance at 120kmph inspite of the stopping stimulus being presented to me. Thats the reaction time which translates to 0.25 seconds, which is close to 3/10ths of a second.

After the second vertical red line, the dotted line changes its trajectory, since its a graph's y-axis depicting vehicle velocity, which obviously has started dropping as the brakes have been applied.

Total stopping distance after presentation of stimulus= reaction distance+braking distance
i.e. 8.33+70.86 = 79.19m from 120kmph.
Attached Thumbnails
Essential Guide: To driving fast!-reaction.jpg  


Last edited by doomsday : 16th December 2008 at 13:21.
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Old 16th December 2008, 13:20   #133
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We all agree that braking distance increases exponentially as speed increases. I think we can leave the debate at that and talk about other fast-driving tips.
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Old 16th December 2008, 22:30   #134
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Quote:
Originally Posted by greenhorn View Post
whenever I've tried downshifting to reduce speed, the engine just revs higher, and there is no significant reduction in speed, certainly not like in a petrol. But yes, when going downhill, especially on bad roads, it does keep the car in control and at the same speed.
I do hope you are letting go off the accelerator when downshifting

On a serious note, the fact that you can maintain a steady speed downhill without using your brakes demonstrates engine braking, on a petrol you'd have to dab on the brakes every so often.
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Old 17th December 2008, 01:54   #135
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Quote:
Originally Posted by RajeshK View Post
Is it so...? I belief the moment you press B-Pedal, the speed will come down, so where does the 1km comes from? Please excuse my ignorance.
Exactly. bblost, are you assuming that every car takes at least 30 seconds(including reaction time) to come to a stop?

Average braking distance(dry pavement) for a car traveling at 80mph is 320 feet, including reaction time, the total distance would be around 400 feet - say 130 metres. A lot lesser than a km, don't you think?

Last edited by kuttapan : 17th December 2008 at 01:55.
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