Caught doing 120mph on the motorway

[Pete317]

Devil2575 said:

Pete317 said:

Devil2575 said:

Pete317 said:

LoonR1 said:

The decibel scale is logarithmic not linear. A 10dB increase is 10 times louder than before. Work out what 5dB is from that.

You've got that exactly backwards

Please elaborate on this point. How is that backwards?

There's a wealth of material on the web which explains it. Try this for starters: "Experimentally it was found that a 10 dB increase in sound level corresponds approximately to a perceived doubling of loudness"

Edited by Pete317 on Wednesday 8th July 20:02

So it's not backwards at all then. Perceived loudness still increases at a faster rate than it would if it was a linear relationship.

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

[WinstonWolf]

Interesting nugget about braking distances, if one vehicle is doing 100 and another is doing 70 the one doing 100 will still be going at 70 when the slower one has stopped

[jmorgan]

I assume this is all this super duper braking is on a track where people are with the right cars, tyres and switched on to what is happening. When I have to brake on the m way looking out for cars in front and more importantly cars behind and my escape routes for the sleepers because the drivers are on another planet, don't care if it can stop on a six pence.

[LoonR1]

Pete317 said:

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

Is perceived to be, which is a subjective measure based on what the web said. Sound pressure level says it's 10 x louder

[0000]

LoonR1 said:

Is perceived to be, which is a subjective measure based on what the web said. Sound pressure level says it's 10 x louder

Best. Line. Ever.

[Pete317]

LoonR1 said:

Pete317 said:

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

Is perceived to be, which is a subjective measure based on what the web said. Sound pressure level says it's 10 x louder

It's loudness that a person perceives, not SPL, so that's what counts here - or anywhere else for that matter.

[V8LM]

LoonR1 said:

Pete317 said:

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

Is perceived to be, which is a subjective measure based on what the web said. Sound pressure level says it's 10 x louder

10db (SPL) is 3.16 times, not 10x.

[Devil2575]

Pete317 said:

Devil2575 said:

Pete317 said:

Devil2575 said:

Pete317 said:

LoonR1 said:

The decibel scale is logarithmic not linear. A 10dB increase is 10 times louder than before. Work out what 5dB is from that.

You've got that exactly backwards

Please elaborate on this point. How is that backwards?

There's a wealth of material on the web which explains it. Try this for starters: "Experimentally it was found that a 10 dB increase in sound level corresponds approximately to a perceived doubling of loudness"

Edited by Pete317 on Wednesday 8th July 20:02

So it's not backwards at all then. Perceived loudness still increases at a faster rate than it would if it was a linear relationship.

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

But still not backwards though

If the dB levels in an A8 rise by 5 from 62 to 80 mph how much do you think they rise from 70 to 120 mph? I'd suggest that they'd rise by at least 10.

Do you really think that you wouldn't notice a doubling in the perceived sound level over a period where you have stamped on the loud pedal to get there "in the blink of an eye"?

[Pete317]

Devil2575 said:

Pete317 said:

Devil2575 said:

Pete317 said:

Devil2575 said:

Pete317 said:

LoonR1 said:

The decibel scale is logarithmic not linear. A 10dB increase is 10 times louder than before. Work out what 5dB is from that.

You've got that exactly backwards

Please elaborate on this point. How is that backwards?

There's a wealth of material on the web which explains it. Try this for starters: "Experimentally it was found that a 10 dB increase in sound level corresponds approximately to a perceived doubling of loudness"

Edited by Pete317 on Wednesday 8th July 20:02

So it's not backwards at all then. Perceived loudness still increases at a faster rate than it would if it was a linear relationship.

+10dB is twice as loud, not ten times as loud as LoonR1 asserted

But still not backwards though

If the dB levels in an A8 rise by 5 from 62 to 80 mph how much do you think they rise from 70 to 120 mph? I'd suggest that they'd rise by at least 10.

Do you really think that you wouldn't notice a doubling in the perceived sound level over a period where you have stamped on the loud pedal to get there "in the blink of an eye"?

I'm really not interested in repeating myself yet again in the space of a few posts, so if you can't be bothered to try to grasp what I wrote before, and if you continue to put words into my mouth, then I'm afraid you're going to get the quality of discussion which you deserve.

Edited by Pete317 on Thursday 9th July 12:54

[gruffalo]

Pete317 said:

You said:"Between 60 and 80 mph the noise level in an A8 more than doubles", when the actual increase is 5dBA

And show me where I mentioned anything more than 20mph as a speed increase one might not readily notice under certain circumstances.

Edited by Pete317 on Wednesday 8th July 18:54

You are correct sorry, I should have said SPL more than doubles.

I would still say that at the speeds mentioned by the OP that the percieved noise level in the car more than doubles but without any accurate data to see what the measured noise levels are I cannot say for sure.

[AW111]

LoonR1 said:

Do some better maths than me and prove your point

My rough guide is that 100mph is 161kmh. Which is 161,000 m per hour, so 2683 m per minute, 44.72 m per second.

If it takes 5 seconds to stop from 100mph as most of the cars on your list do, then at a rough guess it'll take (5 x 44.72) / 2. I've divided by two to account for the slowing down to zero. I'm sure someone with a better grasp of maths will explain why that's wrong, but it's late and seems like a reasonable base assumption to me.

So that means 112 metres, so about one and a quarter football pitches

At 120mph following the above means 134 metres which is more or less bang on 1.5 football pitches.

120 mph = 53.3 m/s. At constant 1g braking, time to stop = 5.44 s.
Distance = V * t + 1/2 A * t ^2
= 53.3 * 5.44 - 9.8 * 5.44^2 / 2
= 144.8 m to stop from 120 mph, as someone posted above.

Edit to fix mistyped formula : result unchanged

Edited by AW111 on Friday 10th July 09:34

[Devil2575]

Pete317 said:

I'm really not interested in repeating myself yet again in the space of a few posts, so if you can't be bothered to try to grasp what I wrote before, and if you continue to put words into my mouth, then I'm afraid you're going to get the quality of discussion which you deserve.

Edited by Pete317 on Thursday 9th July 12:54

I'd recommend that you you just stop posting because at the moment you're just comming across as someone who is sticking to a position despite the fact that it's been shown to be fairly silly

I did grasp what you wrote, it just happens to be wrong.

[youngsyr]

AW111 said:

120 mph = 53.3 m/s. At constant 1g braking, time to stop = 5.44 s.
Distance = V * t + 1/2 A * t ^2
= 53.3 * 5.44 - 9.8 * 5.44^2
= 144.8 m to stop from 120 mph, as someone posted above.

Plus whatever time to react to event that makes you need to stop and actually apply the brakes, most authorities assume one second for the average driver.

At 120 mph, that's 53 metres.

So, two football pitches to stop from 120 mph at 1g braking force.

[Pete317]

Devil2575 said:

Pete317 said:

I'm really not interested in repeating myself yet again in the space of a few posts, so if you can't be bothered to try to grasp what I wrote before, and if you continue to put words into my mouth, then I'm afraid you're going to get the quality of discussion which you deserve.

Edited by Pete317 on Thursday 9th July 12:54

I'd recommend that you you just stop posting because at the moment you're just comming across as someone who is sticking to a position despite the fact that it's been shown to be fairly silly

I did grasp what you wrote, it just happens to be wrong.

No, you seem to think I'm sticking to some position which wasn't mine in the first place.

Edited by Pete317 on Thursday 9th July 17:20

[ZX10R NIN]

youngsyr said:

Plus whatever time to react to event that makes you need to stop and actually apply the brakes, most authorities assume one second for the average driver.

At 120 mph, that's 53 metres.

So, two football pitches to stop from 120 mph at 1g braking force.

GT3 & M3 took 4.26/4.81 seconds to stop from 100mph this includes the reaction times, a football pitch is between 90m-120m in length, the above figure of 53 metres is well short of a pitch.

Unless I've mis understood the maths.

[McTory]

I am sure my daily driver would stop in well under a second if it was doing 120mph plus

[youngsyr]

ZX10R NIN said:

youngsyr said:

Plus whatever time to react to event that makes you need to stop and actually apply the brakes, most authorities assume one second for the average driver.

At 120 mph, that's 53 metres.

So, two football pitches to stop from 120 mph at 1g braking force.

GT3 & M3 took 4.26/4.81 seconds to stop from 100mph this includes the reaction times, a football pitch is between 90m-120m in length, the above figure of 53 metres is well short of a pitch.

Unless I've mis understood the maths.

You've misunderstood the scenario and the maths - police and other authorities typically assume an average driver will take 1 second to react to an event and apply the brakes.

A racing/experienced driver, anticipating the need to apply the brakes in advance (say in a 0-100-0 test) could take considerably less. From memory, an F1 driver does it in under 0.3 of a second.

As we're talking about PHers driving on public roads, I suggest the former is the most relevant time to use, so at 120 mph, that's 53 metres covered before you've even started to slow the vehicle.

[jmorgan]

Casual observations seem to indicate that drivers react in times that sometimes are measures in weeks. I would be surprised if a quick (not emergency) stop is needed, the average driver is on the brake in a second. Emergency stop, well, how long is a bit of string. Same thing, the situation has to register in the nogging of the nodding what stuff needs to happen.

[ZX10R NIN]

youngsyr said:

You've misunderstood the scenario and the maths - police and other authorities typically assume an average driver will take 1 second to react to an event and apply the brakes.

A racing/experienced driver, anticipating the need to apply the brakes in advance (say in a 0-100-0 test) could take considerably less. From memory, an F1 driver does it in under 0.3 of a second.

As we're talking about PHers driving on public roads, I suggest the former is the most relevant time to use, so at 120 mph, that's 53 metres covered before you've even started to slow the vehicle.

So what you're saying is a decent driver might react in say 0.6 seconds & depending on what he's driving they'll stop from 120mph in less than the length of a football pitch, but jo public driver with budget tire & brake pads will take almost two football pitches.

The authorities will be quoting highway code stopping distances which are totally off, just to make it seem more dramtic.

I think it was Top Gear showed a Focus could do 0-70mph-0 in the quoted distance for a car stopping distance from 70mph

Cars stop so well these days (dependent on the car & driver) it's very subjective, Carbon Ceramics & ESP Systems means cars stop very quickly.

Either way the OP is in a whole heap of trouble

Edited by ZX10R NIN on Thursday 9th July 21:27

[youngsyr]

ZX10R NIN said:

youngsyr said:

You've misunderstood the scenario and the maths - police and other authorities typically assume an average driver will take 1 second to react to an event and apply the brakes.

A racing/experienced driver, anticipating the need to apply the brakes in advance (say in a 0-100-0 test) could take considerably less. From memory, an F1 driver does it in under 0.3 of a second.

As we're talking about PHers driving on public roads, I suggest the former is the most relevant time to use, so at 120 mph, that's 53 metres covered before you've even started to slow the vehicle.

So what you're saying is a decent driver might react in say 0.6 seconds & depending on what he's driving they'll stop from 120mph in less than the length of a football pitch, but jo public driver with budget tire & brake pads will take almost two football pitches.

The authorities will be quoting highway code stopping distances which are totally off, just to make it seem more dramtic.

I think it was Top Gear showed a Focus could do 0-70mph-0 in the quoted distance for a car stopping distance from 70mph

Cars stop so well these days (dependent on the car & driver) it's very subjective, Carbon Ceramics & ESP Systems means cars stop very quickly.

Either way the OP is in a whole heap of trouble

Edited by ZX10R NIN on Thursday 9th July 21:27

No, what I'm saying is that you're talking out of your backside when you say a road legal car can stop from 140 mph in 100 yards.

And, for what it's worth, some "braking" aids actually increase the stopping distance, e.g. ABS.

Others are marketed as improving braking, but have almost no impact at all on stopping distance, unless you're doing repeated extremely heavy braking, e.g. Ceramic brake discs.