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#1 30-07-09 01:14:09

dog
Verified Member
Registered: 29-10-06
Posts: 813

Braking distances and the highway code

After noticing some discrepancies with the details a user on another forum posted about his recent crash, me and a friend set out to do some real world tests.

Technical bits:

weather conditions - dry
front tyres - 195/50/15, 4mm tread
rear tyres - 195/50/15, 7mm tread
front brakes - 266mm vented disc with ABS
rear brakes - 247mm solid disc with ABS
vehicle weight with driver and fuel - 1168kg
level road.

***note: these tests were done on an industrial estate on a sunday evening with no other cars around***

The highway code states the following braking distances:

30mph - 14 metres
40mph - 24 metres
50mph - 38 metres

Allowing 5 minutes in between tests for the brakes to cool so that brake fade wouldn't mitigate the results, we recorded:

30mph - 7.05 metres (49.6% shorter than HWC)
40mph - 15.55 metres (35.2% shorter than HWC)
50mph - 23.92 metres (37.1% shorter than HWC)

Which is pretty interesting as these tests were done in a 10 year old car, WITH ABS which increases stopping distance in the dry.

Have videos of all three if anyone would like to see what it looks like dropping the anchors from 30, 40 and 50 miles per hour.

Hope this is of use to some people.

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30-07-09 01:14:09

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Re: Braking distances and the highway code



#2 30-07-09 05:17:31

daz6215
Verified Member
Registered: 07-06-08
Posts: 449

Re: Braking distances and the highway code

What is interesting is that with a 10 mph hour increase your stopping distance has more than doubled! :police:

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#3 30-07-09 05:21:27

daz6215
Verified Member
Registered: 07-06-08
Posts: 449

Re: Braking distances and the highway code

***note: these tests were done on an industrial estate on a sunday evening with no other cars around***

So were you speeding ? lol  :police: :police: :police:

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#4 30-07-09 07:05:33

Freedom Phil
Verified Member
From: Sunderland, North East UK
Registered: 31-03-09
Posts: 342
Website

Re: Braking distances and the highway code

Before I became an instructor I had lots of driving jobs and was a very experienced driver (with lots of bad habits tongue ), so when I began studying for part 1 I knew the braking distances just weren't right.  I have a friend who is a design engineer at VW and I asked him about it.  He said the highway code was written in the 1950's and the braking distances were set then, and since the 50's advances in breaking technology have advanced dramatically and this has substantially reduced braking distances. 

I don't know if thats true or not, but it does sound right.  My feeling is this:  if people think the braking distances is reduced, they may drive closer to the car in front than thy should, but if they think it's further away, hopefully they will drive further back and give themselves more space, which cant be a bad thing.

.phil.
smile


DIA diploma in driving instruction.  DSA registered fleet trainer.  ORDIT registered trainer part's 1, 2, 3 & ORDIT premises inspected.  SAFED trainer and assessor.  RoSPA approved tutor.  Diamond registered advanced instructor.  Diamond qualified advanced examiner. City & Guilds 7303 PTLLS teaching certificate.  IAM advanced test, Diamond advanced test, Diamond special test, Cardington special test, RoSPA gold

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#5 30-07-09 07:08:04

ExAdiNigel
Member
From: Plymouth, Devon
Registered: 13-12-04
Posts: 4,739

Re: Braking distances and the highway code

ABS increases stopping distances?  Since when?  An expert may be able to stop a car quicker without using the abs but that doesn't apply to the general public.

What's teh important thing here?  Not that you have been able to outbrake the Highway Code, to a great extent who cares what the braking distance is?  The more important thing is the comment by Daz.

When I do controlled stop practise with my pupils, we find that an extra car length is needed to stop between 30 and 35.

The much more variable figure is the thinking distance.

What would be much more worrying would have been if you took longer to stop that that suggested by teh Highway Code.

Nigel


National Standards Cycling Instructor, Ex Adi

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#6 30-07-09 07:11:29

driverpete
Verified Member
From: Nottingham
Registered: 06-02-06
Posts: 457

Re: Braking distances and the highway code

But just think what would happen if Joe Public (who I know hasn't a clue about stopping distances anyway) took this info on board. Your mirrors would be even more full of tailgaters than they are now!


RoSPA Gold
Retired RoSPA Approved Tutor
Retired NDAC & NDAS trainer
Retired ADI

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#7 30-07-09 07:47:38

DampDog
Verified Member
From: Staffordshire.
Registered: 04-02-06
Posts: 1,538

Re: Braking distances and the highway code

Thing is though you knew you wanted to do an emergency stop (where and when) in normal driving it always comes as a surprise.. big_smile

The reason why the likes of Mercedes and others are bringing in "Brake assist" is that most drivers don't apply maximum braking force when doing an emergency stop. They typically brake "Hard" then a bit more! But not as hard as they can from the off. Not giving it everything could easily add several metres.

It's nice to know modern brakes have progressed, but it's better to give it an extra metre or two than drive to the edge.


ADI (car)
1st CT (5)

I used to be a compleat idiot, until some bits fell off...

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#8 30-07-09 08:09:11

kjs
Verified Member
From: Rossendale Lancashire
Registered: 20-05-06
Posts: 976
Website

Re: Braking distances and the highway code

Think it was top gear did a test on the stopping distances a few years ago using very modern cars. They to found that new cars will stop well within the distances in the H/C. So, do we now have them changed, or keep them as the same ? At least we know the car will stop safely with in the prescibed distances now.
kevin

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#9 30-07-09 09:32:16

reddragonbus
Verified Member
From: Edinburgh
Registered: 05-02-06
Posts: 1,656

Re: Braking distances and the highway code

At least we know the car  MAY stop safely with in the prescibed distances now.
kevin

The distances in the highway code are "typical" stopping distances, based on an average driver with an average car.

No one ever suggested that these are the true distance taken to stop by a given vehicle.

The average car is not maintained to the highest standard, the average driver is not concentrating fully on the driving task.


LGV PCV Instructor DVSA ADI Fleet

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#10 30-07-09 17:49:44

kjs
Verified Member
From: Rossendale Lancashire
Registered: 20-05-06
Posts: 976
Website

Re: Braking distances and the highway code

Don't forget though Jonathan, the H/C stopping distances have never been upgraded since the H/C came into being so I'm lead to believe, meaning that they were devised for pre WW2 vehicles. If I couldn't get a pupil to stop my car, given that what I 've written is true, and that braking systems are supposedly far more efficient, then some one at Peugeot will have some explaining to do.

Not saying your wrong either by the way.

kevin

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