Braking Distance
Discussion
cptsideways said:
Interesting even if its not very scientific, clearly shows we all have room improvent or maybe we really should trust ABS after all. I'm a big ABS fan, even on trackday car.
A well trained right foot can be a very effective means of stopping quickly, however if your are that good then your ABS will very rarely kick in, if it does it simply meant it's beaten you.
This was a test, I was prepared for a lock up & yes I got a lock up, yet I dealt with it ok'ish. Many others would & do simply carry on at .58g. Brake assist takes care of this & of the ABS & will haul you up regardless of foot pressure at probably 0.8g or more consistently.
I noticed something very interesting, I tried this on some very newly laid super smooth tarmac & with no lock ups I left a hoofing great skid mark, this was the new layer of tar overheating I assume yet if it was an accident scenario I think that might have been calculated as a lock up? what the criteria do you look at the pattern stretch?
NEW? How new? What type of surface? Most modern surfaces take a while to bed in. This is because all the chippings have a decent coat of bitumen to help them bind. When SKIDDING, this is rapidly melted and then acts as a lubricant between stone and tyre. Thus in the dry deceleration rates equivelent to those in the wet can be experienced. Bedding in can take months depending on traffic use and wether. Back in the late 80's there was a multi on the M4 somewhere near Newbury and a lot of peeps were killed. A large portion of the blame was put on the new road surface as its skid resistance in the dry (it was dry at the time of the crash) was no better or worse than it was in the wet!!
Because ABS braked wheels don't lock, you don't get the heat, and therefore the bitument won't melt and .... So ABS vehicles are largely unaffected by new surfaces. In the wet, the effect is far less significant or even inexistent.
ps. 'smooth' and 'rough' surfaces by appearance are not a guide to their skid resistance.
Who's got a brake assist car then??
Intersting that the time it takes to cadence manually effectively eliminates the gains in increased G when you do get peak G's eventually. As you say may as well carry on with it locked & start saying your hail mary's then bother cadencing unless it's a tree your heading for in which case hurry up!
I'd like to do an ABS avoidance test/demo & show that you can pull 0.6g plus whilst driving around things, most people have no idea just how amazing this is. I think it should be part of the test.
PS managed 3.3 secs stopping without a lock up on the chippings stuff, mind you it digs the stuff up a bit
Intersting that the time it takes to cadence manually effectively eliminates the gains in increased G when you do get peak G's eventually. As you say may as well carry on with it locked & start saying your hail mary's then bother cadencing unless it's a tree your heading for in which case hurry up!
I'd like to do an ABS avoidance test/demo & show that you can pull 0.6g plus whilst driving around things, most people have no idea just how amazing this is. I think it should be part of the test.
PS managed 3.3 secs stopping without a lock up on the chippings stuff, mind you it digs the stuff up a bit
If you can get 0.6G braking, then you can get it cornering. If you can get .8G braking, then you can get it cornering. If you can get .9G braking, then you're on a track.
But you can't get .7G braking AND .7G cornering at the same time. Something has to give. That's why if you're going round a bend with the tyres squealing, you're at max G and you've got no more friction available to brake. Dab the brakes and you've either got to straighten up a bit or you'll lock the wheels.
However, if you're on a road where you can brake at .7G, you can get .5G braking whilst cornering at .5G!! That's why by leaving just a small amount of friction available to brake whilst cornering, you can still brake pretty hard in a bend. Try it. On a track!!
But you can't get .7G braking AND .7G cornering at the same time. Something has to give. That's why if you're going round a bend with the tyres squealing, you're at max G and you've got no more friction available to brake. Dab the brakes and you've either got to straighten up a bit or you'll lock the wheels.
However, if you're on a road where you can brake at .7G, you can get .5G braking whilst cornering at .5G!! That's why by leaving just a small amount of friction available to brake whilst cornering, you can still brake pretty hard in a bend. Try it. On a track!!
You can't usually pull quite the same lateral G as braking G in a 2wd car, this is why people refer to the elipse of friction rather than the circle of friction. I don't generally get more than about 0.9G lateral but can get up to about 1.15G under braking. (Road tyres on a normal tarmac surface.)
GreenV8S said:
You can't usually pull quite the same lateral G as braking G in a 2wd car, this is why people refer to the elipse of friction rather than the circle of friction. I don't generally get more than about 0.9G lateral but can get up to about 1.15G under braking. (Road tyres on a normal tarmac surface.)
I would have thought that with a non-ABS car you could get marginally higher lateral acceleration rates than SKIDDING to stop deceleration rates. I would base this argument on the fact that with lateral acceleration you are achieving results closer to PEAK grip than you are with MEAN skidding to stop braking (road imperfections aside that is!)
What car are you driving and has it got aerodynamic modifications to increase the downforce? I must say that my opinions and experiences are all based on normal street mass produced cars.
cptsideways said:
Who's got a brake assist car then??
Mine's got ABS if that's any good?
Figures for my 1993 Vauxhall Cavalier are:
Start Speed 60.0mph
mph s g ft
50.0 0.54 0.83 43
40.0 1.09 0.84 79
30.0 1.63 0.84 107
20.0 2.17 0.84 127
10.0 2.72 0.84 139
0.0 3.26 0.84 142
Peak G: 0.0mph 3.26s 142ft 0.84g
--------------------------------
Start Speed 60.0mph
mph s g ft
50.0 0.47 0.94 37
40.0 0.99 0.87 72
30.0 1.51 0.87 98
20.0 2.04 0.86 117
10.0 2.56 0.87 129
0.0 3.08 0.87 132
Peak G: 50.8mph 0.43s 34ft 0.95g
These are 2 runs on the same bit of road, but in opposite directions so the average is 3.14secs and 137ft.
(measured using an AP22 as well)
>> Edited by danhay on Sunday 16th May 18:04
Wotabloke said:
cptsideways said:
Who's got a brake assist car then??
What is one of those?!!
www.conti-online.com/generator/www/us/en/continentalteves/continentalteves/themes/products/brake_actuation_folder/brake_assist_en.html
It's an overide system and very simply monitors the speed the pedal is applied if it senses a fast application (not actually hard) it applies full on braking inc ABS until you fully remove your foot from the pedal.
Quite a few cars are now fitted with it Merc's, Laguna's, Mondeo etc.
Fitted becuase its been found 90% of people when encountering an ABS moment don't make max use of the ABS & continue on way passed the potential stop point.
Having tried an Merc E class with it fitted its suprisingly easy to fool. A fast but gentle dab will have it going off (full on mega stoppy time) so after some experimentation & passed experience with Citroen brakes I tried my old trick
not on a public road I hasten to add. Reach down with your hand & push the pedal by hand, sure enough you can set it off by hand pressure only all be it with a very quick dab. It works very well by the way having come down a semi-snowy mountain pass & having to do a bit of a stoppy it does definately work.
So those lemming driving drivers on the motorway who don't look ahead & have to contantly brake all day long are those most probably frequently rear ended as they stop far sooner than expected due to their quick dab on the brakes. Would be interesting to see some accident data on the cars rear ended the most?
>> Edited by cptsideways on Sunday 16th May 19:14
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