Safe Speed Forums

I'd doubt it... Aero drag is a square function, so the "tea tray" would have to be huge to get any effect at 30-or-so mph. About the size of an "America's Cup" sailing yacht mainsail at a guess!

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"Politicians are the same the world over... We build bridges where there aren't any rivers." - Nikita Kruschev

...EBA ?

No. That's been done. Nearer ESP. I've PMed Paul. He thinks Volvo have this one nailed. If he's right I'll put my take in here for discussion/evolution. If not, I'll lodge the patent and then drop my take in here after the first round of searches.

...roger?

Bigger discs.

firing two anchor bolts down into the tarmac which are attached to steel rope on a friction release drum mounted under the passenger
The bolts would fire down deep enough to cover the head of the bolt and at a slight forward angle to prevent tearing out. The cable would have flanges fitted to prevent the bolt firing through the surfice just in case it was fired on a bridge to prevent it going too deep and hitting the traffic below...

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Speed limit sign radio interview. TV Snap Unhappy
“It has never been the rule in this country – I hope it never will be - that suspected criminal offences must automatically be the subject of prosecution” He added that there should be a prosecution: “wherever it appears that the offence or the circumstances of its commission is or are of such a character that a prosecution in respect thereof is required in the public interest”
This approach has been endorsed by Attorney General ever since 1951. CPS Code

as discussed earlier in the thread (i think) most current brakes are more than capable of locking the wheel.. so how does bigger discs help?

That's right, you can make wheel brakes as powerful as you like - bigger disc surface area, 8-pot calipers, even multiple discs. The problem is the limit of adhesion between the tyres and the road. The maxiumum retardation force that can act on your vehicle under braking is the maxiumum friction generated between tyres and road surface plus whatever aerodynamic resistance you can muster.

You therefore need to increase tyre/road friction somehow, or use aerodynamic methods. The aerodynamic one is tricky. Aircraft use aeordynamic brakes to great effect after landing, but they have a huge surface area (the wings) over which to deploy the braking flaps. The small mounting area you have on a car for spoilers etc. limits how much aerodynamic braking you can employ.

A jet engine on reverse thrust produces huge aerodynamic retardation force, but this just isn't practical on a car.

So, where you really need to look is at tyre/road adhesion. You need to do as many of the following as you can:
1) increase the adhesion of the tyres
2) increase the adhestion of the road surface
3) increase the tyre-road contact area

Tyre-road contact area is the big one. A tracked tank can stop on a sixpence, but you wouldn't want to drive one of these to work every day!

Perhaps you could have a second pair of wheels inside your existing rear wheels which are dropped onto the road and braked when required. It wouldn't matter if these wheels locked, since the main wheels doing the steering would still be turning. These "braking wheels" could be fitted with special tyres, optimised for maxiumum braking friction without consideration for road noise, fuel economy, longevity and lateral traction like normal car tyres are.

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“For every complex problem, there is a solution that is simple, neat, and wrong.” - H. L. Mencken

Or even a large rubber friction pad 1m X 3m as you say fitted with the optimum tread and soft rubber with vacum pumps sucking the pad to the road.

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Speed limit sign radio interview. TV Snap Unhappy
“It has never been the rule in this country – I hope it never will be - that suspected criminal offences must automatically be the subject of prosecution” He added that there should be a prosecution: “wherever it appears that the offence or the circumstances of its commission is or are of such a character that a prosecution in respect thereof is required in the public interest”
This approach has been endorsed by Attorney General ever since 1951. CPS Code

What are you after here though, a standard braking system,
say with good brakes and ABS. Then on top of that you want
something to stop the car quicker in extreme emergencies?

I don't think this is possible. You have ABS to allow
you to steer whilst braking, that alone must improve
safety far more than anything else that has ever been
invented so... how can you improve on that? You want
to cut the braking time right down but this is almost like
you are trying to replicate the same conditions caused by
an actual crash.

Like the time my granded was driving past a bus (parked
up at the bus stop) and three girls ran across the road, he
was only going 15MPH at the most, but my sister still got
flung from the back seat through the front two seats and
ended up with her head almost bashing into the dashbaord,
almost. 20MPH and it would have been different.

Stopping a car dead is incredibly dangerous even at 10MPH.

Please enlighten me some more on how stopping faster
is safer! You can only make improvements to ABS and
make the discs bigger. You can only increase braking power
so much until it becomes as dangerous as crashing itself.

I'm unsure of the answer here: should it have been it the grandad's responsibility to ensure everyone is strapped in with seatbelts?

There's oodles of room between modern brakes and crashing.

Modern brakes manage about 1g. Crashing might give rise to up to 200g on occasion.

I'll take 4g - maybe 5g - brakes if anyone can make 'em.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Sorry - forgot I left you guys clinging on a line

I now realise that most of the hypothesis I was putting forward has already been patented, leaving not enough for me to get teeth in to commercially. Therefore, herewith the complete thought train.

Emergency stopping in response to a hitherto unforeseen hazard is widely believed to consist of two parts, viz, reaction time and braking time. In fact there is an interim component between the realisation (reaction time) and the braking time (ie the time that friction material starts biting). This is the time it takes to lift off, move the foot across, contact the pedal, press it hard to overcome any viscosity/friction/play in the braking system to plant the pedal etc, when the friction material finally starts to press in to the discs. Of course, the advanced driver in a dense hazard area may well be covering the brake and, depending on the car, might even be feathering the brake, thereby turning this middle component effectively into zero.

I am fairly sure that certain traits in drivers will be common in this "oh shit I have to plant the brake" window, and that these traits will not exist as a set in other situations. If we could get a set of sensors to detect this scenario and take up all the slack in the braking sysatem - feathering (but NOT planting) the brake, whilst acknowledging the driver still has to move his foot across to the brake, the first contact with the middle pedal actually retards the car - no play. Why not have the system plant the brake for you if it's fool proof? Easy. No matter what you telegraph by sensors, you might still change your mind at the last moment. The last thing you want is a planted brake if you are deciding now to gun it, but a feathered pedal will make no appreciable difference (and indeed will release immediately the loud pedal is touched)!

I was talking with my father about this and he said
"a parachute" but on congested roads where 5
cars are piling into each other I can't see that
being of any use, but it would add more braking
on an open road, certainly.

I had a near miss on the motorway recently, at the
usual blackspot on the M60. I managed to stop but
I don't even know how, I must have stopped 3 feet
from the car in front. I pulled my handbrake on,
would that have helped any, or made it worse?

Sounds like a case of bad
planning to me, especially
as you already know it’s
a blackspot.


Worse, there's no ABS
function for the handbrake
and it’ll affect the brake
balance of the car. Lockup
of a wheel will usually
result with less traction
and deceleration (stationary
friction > slipping friction).
Lockup of just the rear wheels
(handbrakes usually act upon
the rear wheels) will result with
high risk of ‘pendulum effect’
and subsequent loss of control.

Also, it would mean removing a
hand from the steering wheel
during the time when you really
need both firmly on it.

EDIT: re-formatted for a laugh

Yup, made me laugh too.

'L' really needs to learn to basic points of normal driving & car control - a hand brake is NOT for braking. Muppet. All it will do (at best) is lock the rear wheels resulting in an uncontrolled slide, at worst (if poorly adjusted) is lock one wheel and spin you off at high speed.

Handbrake uses = hill starts for beginners, and not dazzling other drivers at sloping juctions, other than that chavs in car parks & rally drivers flicking their cars round.

Honestly, I dispair....

Really, stop going on about tyre adhesion - it doesn't come into play unless you are skidding.

The braking system on a car is for transfer of energy into heat, and this is mainly done by the friction of the dics/pads, not the tryes/road surface.
If it was solely tyre adhesion then all F1 cars would have the same discs as my mum's metro and the same stopping distances.

Huge, drilled and ventilated top quality discs will provide you with a better stopping distance than small cheap ones because they are vastly superior at transferring all that kinetic into heat and more importantly, at dispersing that heat away from themselves.
Anyway, in a modern car it would be very rare to reach the tyre adhesion limits (around 1.2-1.7g) as the ABS will kick in to keep the wheel rolling (and the energy transfer at its maximum).

MHO on the current ideas:

The retro rocket idea would help with energy transfer, but I would doubt that you could get anything solid fuelled to fire in the time required (or stop when you needed it to) and would probably be a bit on the dangerous side.

Traits of drivers thing has already been done - think Volvo had a thing that flashed the hazard lights if you took your foot off the accelerator very rapidly. Didn't apply the brakes but I would be surprised if they didn't patent the idea.

Aerodynamic braking has promise, but only at higher speeds (the surface area needed for any reasonable effect at low speed would be huge) The old inverse square law could be a bit of a sod too - the correct area to provide super stopping at 60mph would punch the occupants (seats included) through the windscreen at 100mph!

Flywheel thing would take so much energy to get it spinning that the MPG would be through the roof. It might also have a wierd gyroscopic effect that would decrease cornering forces if big enough.

Extra rubber might help if it all goes wrong and you end up skidding - top fuel dragsters can manage 3.0g tyre adhesion under acceleration, so bung some dragster tyres on and maybe your sorted.

We’re trying to prevent skidding, which is where the tyre adhesion comes into play.
The available force (parallel to the road surface) will be in proportion to the downforce; the braking system is a separate problem, heat dissipation is not a problem at lower speeds (my basic maths suggest at < 50mph the thermal mass of the disks will be great enough to not require dissipation).
Tyre adhesion is currently the weakest link on almost all cars.

Fit dragster types on a car and it won’t make much difference (even with super brakes); instead fit a vertical exhaust with a net thrust of 3 tons and the car will stop like a dragster accelerates (assuming uprated brake servos). That’s why F1 cars use spoilers (as well as better tyres).

F1 cars have incredible braking power Why?
large tyres = large surface area in contact with the road slicks have more surface area in contact with the road than treaded tyres.

and

low wieght = less kinetic energy, yes wieght does make a difference and it makes a huge difference if you actually hit something. Wieght is the destructive force that does the damage if cars weighed the same as balsa wood what damage would they cause. If the were made of lead a car doing 50 could go striaght through a house (or two) Bullets are made from lead for this reason.

so wieght down and tyre area up would do the trick but you would have to lower the center of gravity because a 4X4 would just roll over forwards if was really light. What fun...

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Signal Thumbs Down http://www.donate-a-mate.com/std

You missed the extra down-force due to the spoilers; this is a critical component of the traction system.

It is said that these cars can drive upside-down on a ceiling at 100mph - literally defying gravity. It is this extra down-force which multiplies the available traction from the tyres. This extra downforce being massless allows the car to accelerate/brake/corner faster.