PCCB out braked the steels last night on 5th gear.
Discussion
A heavier car has more inertia and momentum compared to a lighter one..Inertia is the force that wants the car to keep going at the same speed.A car's braking distance is proportional to its kinetic energy..This energy is dissipated as heat in the brakes,tyres and road surface,more energy requires more braking distance.This also explains why braking distance increases as the square of a car's speed.
Take an empty estate car and add a ton of weight in its luggage compartment and you will find it will take longer to stop as you've increased its inertia and momentum..Take a pick up truck and make it tow a 3.5T unbraked trailer and the braking distance will more than double.
Take an empty estate car and add a ton of weight in its luggage compartment and you will find it will take longer to stop as you've increased its inertia and momentum..Take a pick up truck and make it tow a 3.5T unbraked trailer and the braking distance will more than double.
Taffy66 said:
A heavier car has more inertia and momentum compared to a lighter one..Inertia is the force that wants the car to keep going at the same speed.A car's braking distance is proportional to its kinetic energy..This energy is dissipated as heat in the brakes,tyres and road surface,more energy requires more braking distance.This also explains why braking distance increases as the square of a car's speed.
Sigh. Go and check your maths textbook at age 10 then on whether constants can cancel out.
Now unless you have come up with a new formula for kinetic energy (0.5 mv^2) or power (force x distance in my limited understanding of these complicated things...), mass cancels on both sides of the energy equation given force is mass x acceleration. Or perhaps you have found that conservation of energy no longer applies or maybe that even in normal speeds these days one needs quantum mechanics rather than merely Newton's 2nd law.....
isaldiri said:
Sigh.
Go and check your maths textbook at age 10 then on whether constants can cancel out.
Now unless you have come up with a new formula for kinetic energy (0.5 mv^2) or power (force x distance in my limited understanding of these complicated things...), mass cancels on both sides of the energy equation given force is mass x acceleration. Or perhaps you have found that conservation of energy no longer applies or maybe that even in normal speeds these days one needs quantum mechanics rather than merely Newton's 2nd law.....
Forget complicated physics and formulas and replace them with a modicum of common sense..As my two real world examples clearly shows add significant weight to any vehicle and you will require a longer distance to brake..Go and check your maths textbook at age 10 then on whether constants can cancel out.
Now unless you have come up with a new formula for kinetic energy (0.5 mv^2) or power (force x distance in my limited understanding of these complicated things...), mass cancels on both sides of the energy equation given force is mass x acceleration. Or perhaps you have found that conservation of energy no longer applies or maybe that even in normal speeds these days one needs quantum mechanics rather than merely Newton's 2nd law.....
The trouble is you're over thinking it and trying to bamboozle what happens in the real world with some theoretical jumbled bull
t taken straight from some physics lecture you attended long ago..Your trying to bull
t your way out of a debate you've clearly lost but too proud and stubborn to admit it..What might theoretically happen in a text book doesn't always tally with real life situations.You'll be saying next that a 44T laden truck stops in the same distance as Lotus Elise travelling at the same speed.
Taffy66 said:
Forget complicated physics and formulas and replace them with a modicum of common sense..As my two real world examples clearly shows add significant weight to any vehicle and you will require a longer distance to brake..
The trouble is you're over thinking it and trying to bamboozle what happens in the real world with some theoretical jumbled bullt taken straight from some physics lecture you attended long ago..
Your trying to bullt your way out of a debate you've clearly lost but too proud and stubborn to admit it..What might theoretically happen in a text book doesn't always tally with real life situations.
You'll be saying next that a 44T laden truck stops in the same distance as Lotus Elise travelling at the same speed.
Ok, prove me wrong in anything I have said. Rewrite a bloody physics formula the right way and show me I am wrong then. Hell you'll probably win a nobel prize if you can. If I'm overthinking it and trying to bamboozle what happens in real life, you are even more so underthinking things and sprouting off pseudo science. In particular this.The trouble is you're over thinking it and trying to bamboozle what happens in the real world with some theoretical jumbled bull
t taken straight from some physics lecture you attended long ago..Your trying to bull
t your way out of a debate you've clearly lost but too proud and stubborn to admit it..What might theoretically happen in a text book doesn't always tally with real life situations.You'll be saying next that a 44T laden truck stops in the same distance as Lotus Elise travelling at the same speed.
Taffy66 said:
more energy requires more braking distance.
Which conservation of energy plainly shows to be incorrect. Unless you have found a way to refute that. I'll repeat myself from earlier which doesn't seem to register with you.
isaldiri said:
If your brakes can cope with that heat dump converted from the kinetic energy, yes braking distance is not affected by mass.
That was in reference to the earlier claim the 991 being heavier will need more distance to stop than a 997 'due to physics' or some claptrap which I disagreed with because that is simply not the case. If you want to haul out all manner of idiotic examples about 44 tonne trucks taking longer to stop than an elise and ignore the different variables involved to 'prove' you are correct well suit yourself but that in no way refutes basic physics. Unless as I said you can actually come up with a new formula... I await with bated breath.
It is always quite amusing when people start saying stuff like 'forget complicated physics and formulas' or 'no need to look at maths'/'maths is moot' per another regular poster here though I have to say.
Edited by isaldiri on Tuesday 19th November 22:57
Isaldiri,you are right, theoretically, braking distance does not depend on mass.But in practice it does.The explanation is that tyre effective friction coefficient cannot be assumed constant: it slightly decreases with increasing force.So braking distance are longer when mass is added which is what happens in reality compared to theoretically.
As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
Taffy66 said:
You are right, theoretically, braking distance does not depend on mass.But in practice it does.The explanation is that tyre effective friction coefficient cannot be assumed constant: it slightly decreases with increasing force.So braking distance are longer when mass is added which is what happens in reality compared to theoretically.
As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
You are mixing up what the tires will do before locking up and what the disks/pads can deliver. You are quite right that doubling the mass of a car doubles (almost) the friction between the tires and the road (due to gravity). However braking distance is deterimned by both a) the limit of friction between tire and road and b) the braking force the disk/pads can deliver.As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
The braking force for the disks/pads is determined by pad size, pad friction and piston force. If you double the mass of a car you have to double the braking force the disks/pads deliver to stop in the same distance. Either apply twice as much piston force, double pad size or double pad friction. If you don't increase the braking force the brakes are delivering the heavier car will take twice as long to stop.
Edited by C4ME on Wednesday 20th November 00:19
The only way Isaldiri's theory is correct in actual real life situations is if you artificially increase the tyre frictional coefficient with increase in mass..This can be done in two ways: the first is to increase the tyre contact patch as you add mass.The second way is to increase downforce by adding a big wing.
Example is if you have two GT3 RSs doing 180 mph on a runway, both weigh the same however one has the wing removed..The winged one produces 300Kg DF which increases tyre frictional coefficient compared to the non winged car.
The winged car will stop in a shorter distance even if you discount increased aero drag..TFC is not constant at 1 in real life only in text books.
Example is if you have two GT3 RSs doing 180 mph on a runway, both weigh the same however one has the wing removed..The winged one produces 300Kg DF which increases tyre frictional coefficient compared to the non winged car.
The winged car will stop in a shorter distance even if you discount increased aero drag..TFC is not constant at 1 in real life only in text books.
Taffy66 said:
Isaldiri,you are right, theoretically, braking distance does not depend on mass.But in practice it does.The explanation is that tyre effective friction coefficient cannot be assumed constant: it slightly decreases with increasing force.So braking distance are longer when mass is added which is what happens in reality compared to theoretically.
As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
Ok since you are so keen on 'real life examples' - Why do sport bikes almost always require much further stopping distances than vaguely comparable sports cars despite being able to easily out-accelerate them? hint - perhaps mass is a factor in acceleration but not braking even leaving aside the bike not tipping over.As an extreme example on heavy lorries the tyre coefficient is usually smaller than 0.65 even on dry roads, compared to 1 which is the theoretical figure you refer to.
So to recap you are correct in theory if the tyre effective friction coefficient is a constant 1 however in reality its not.
A heavy lorry tyre is let's just say a bit unlikely to be as sticky as any sports car tyre and it's not just the weight of the lorry that is making it so....
if you are wanting to get into stuff like tyre load sensitivity, you are talking about very considerable increases in tyre load before you have significant differences in tyre coefficient of friction. A 50-80 ish kg difference in weight between a 991/997 will have practically no relevance in terms of affecting the tire coefficient...
Taffy66 said:
The only way Isaldiri's theory is correct in actual real life situations is if you artificially increase the tyre frictional coefficient with increase in mass..This can be done in two ways: the first is to increase the tyre contact patch as you add mass.The second way is to increase downforce by adding a big wing.
Example is if you have two GT3 RSs doing 180 mph on a runway, both weigh the same however one has the wing removed..The winged one produces 300Kg DF which increases tyre frictional coefficient compared to the non winged car.
The winged car will stop in a shorter distance even if you discount increased aero drag..TFC is not constant at 1 in real life only in text books.
Example is if you have two GT3 RSs doing 180 mph on a runway, both weigh the same however one has the wing removed..The winged one produces 300Kg DF which increases tyre frictional coefficient compared to the non winged car.
The winged car will stop in a shorter distance even if you discount increased aero drag..TFC is not constant at 1 in real life only in text books.
No you are absolutely not increasing tyre coefficient of friction with downforce. You are increasing the force acting on the tyre over and above the weight of the car. Very simplified - F = coefficient of friction x N (in this case N = weight of car PLUS downforce produced in newtons). That is bloody well not the same as 'increasing tyre frictional coefficient' as you claim. Downforce acts as a multiplier to performance (acceleration whether lateral or longitudinal) over what the car would otherwise be capable of but it does not increase tyre frictional coefficient.
Coefficient of friction will decrease as vertical load increases but that typically requires a very large increase in load (typically in this case relevant for racing cars producing multiple times their weight in downforce).
I have an old experience here with wings and braking ...... It was an F3 race in a Dallara at Thruxton , where we decided to go really low downforce as the long section around the back is flat up to the chicane . So we put on an old team Beneton , rear wing ( used at old Hockenhiem ) , flattened the front wing and of I went .
All went well until the braking point for the the chicane ...... it just would not stop at all so had to go down the escape road , scary time ..... Old wing went back on .....
But yes it is different in a heavy road car
All went well until the braking point for the the chicane ...... it just would not stop at all so had to go down the escape road , scary time ..... Old wing went back on .....
But yes it is different in a heavy road car
This has become so dull.
Let's go to this 10 year old physics lesson then shall we and put this to bed.The formulas below show, that if you have the same braking force increasing the weight of a car will increase its braking distance.
From a GCSE tutorial website
https://www.gcsescience.com/pfm30.htm
How does Mass affect the Braking Distance of a Car?
The braking distance of a car increases as the mass increases.
The two calculations below show how
doubling the mass changes the braking distance of a car.
Q1. The brakes of a car apply a force of 1500N.
If the car has a mass of 750 kg, what is its acceleration?
(How quickly does it slow down?)
A1. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 750
= 2 m/s2.
Q2. The brakes of the car apply the same force of 1500N.
If the car has double the mass at 1500 kg, what is its acceleration?
(How quickly does it slow down?)
A2. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 1500
= 1 m/s2.
After we have doubled the mass of the car and
applied the same force from the brakes,
the car is now slowing down at only half the rate.
The car with twice the mass will take twice as long to stop
(requiring twice the braking distance - see kinetic energy).
Let's go to this 10 year old physics lesson then shall we and put this to bed.The formulas below show, that if you have the same braking force increasing the weight of a car will increase its braking distance.
From a GCSE tutorial website
https://www.gcsescience.com/pfm30.htm
How does Mass affect the Braking Distance of a Car?
The braking distance of a car increases as the mass increases.
The two calculations below show how
doubling the mass changes the braking distance of a car.
Q1. The brakes of a car apply a force of 1500N.
If the car has a mass of 750 kg, what is its acceleration?
(How quickly does it slow down?)
A1. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 750
= 2 m/s2.
Q2. The brakes of the car apply the same force of 1500N.
If the car has double the mass at 1500 kg, what is its acceleration?
(How quickly does it slow down?)
A2. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 1500
= 1 m/s2.
After we have doubled the mass of the car and
applied the same force from the brakes,
the car is now slowing down at only half the rate.
The car with twice the mass will take twice as long to stop
(requiring twice the braking distance - see kinetic energy).
hunter 66 said:
I have an old experience here with wings and braking ...... It was an F3 race in a Dallara at Thruxton , where we decided to go really low downforce as the long section around the back is flat up to the chicane . So we put on an old team Beneton , rear wing ( used at old Hockenhiem ) , flattened the front wing and of I went .
All went well until the braking point for the the chicane ...... it just would not stop at all so had to go down the escape road , scary time ..... Old wing went back on .....
But yes it is different in a heavy road car
Hey prof,best stick to teeth and leave the scientists to itAll went well until the braking point for the the chicane ...... it just would not stop at all so had to go down the escape road , scary time ..... Old wing went back on .....
But yes it is different in a heavy road car
i have seen you helping me with brake disc change;)Thats a scary place if it goes wrong,probably going a lot faster with the less wing,do you remember the pic of the cup car leaving the circuit over the fence there,forgotten his name in the pilot seat
Mousem40 said:
This has become so dull.
Let's go to this 10 year old physics lesson then shall we and put this to bed.The formulas below show, that if you have the same braking force increasing the weight of a car will increase its braking distance.
From a GCSE tutorial website
https://www.gcsescience.com/pfm30.htm
How does Mass affect the Braking Distance of a Car?
The braking distance of a car increases as the mass increases.
The two calculations below show how
doubling the mass changes the braking distance of a car.
Q1. The brakes of a car apply a force of 1500N.
If the car has a mass of 750 kg, what is its acceleration?
(How quickly does it slow down?)
A1. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 750
= 2 m/s2.
Q2. The brakes of the car apply the same force of 1500N.
If the car has double the mass at 1500 kg, what is its acceleration?
(How quickly does it slow down?)
A2. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 1500
= 1 m/s2.
After we have doubled the mass of the car and
applied the same force from the brakes,
the car is now slowing down at only half the rate.
The car with twice the mass will take twice as long to stop
(requiring twice the braking distance - see kinetic energy).
accurate if your braking force remains the same for a heavier car. It does not for the purposes of earlier example as the car slows at the force of friction from tyre to road....Let's go to this 10 year old physics lesson then shall we and put this to bed.The formulas below show, that if you have the same braking force increasing the weight of a car will increase its braking distance.
From a GCSE tutorial website
https://www.gcsescience.com/pfm30.htm
How does Mass affect the Braking Distance of a Car?
The braking distance of a car increases as the mass increases.
The two calculations below show how
doubling the mass changes the braking distance of a car.
Q1. The brakes of a car apply a force of 1500N.
If the car has a mass of 750 kg, what is its acceleration?
(How quickly does it slow down?)
A1. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 750
= 2 m/s2.
Q2. The brakes of the car apply the same force of 1500N.
If the car has double the mass at 1500 kg, what is its acceleration?
(How quickly does it slow down?)
A2. Use F = m x a
or a = F ÷ m
a = 1500 ÷ 1500
= 1 m/s2.
After we have doubled the mass of the car and
applied the same force from the brakes,
the car is now slowing down at only half the rate.
The car with twice the mass will take twice as long to stop
(requiring twice the braking distance - see kinetic energy).
KE = 0.5 mv^2 = force x distance = work done to stop the car.
Force being coefficient of friction x mass x gravitational acceleration.
Mass cancels on both sides of the equation.
I'm all ears if someone can disprove the above btw as well.
isaldiri said:
accurate if your braking force remains the same for a heavier car. It does not for the purposes of earlier example as the car slows at the force of friction from tyre to road....
KE = 0.5 mv^2 = force x distance = work done to stop the car.
Force being coefficient of friction x mass x gravitational acceleration.
Mass cancels on both sides of the equation.
I'm all ears if someone can disprove the above btw as well.
it is basics as far as I can see, but did leave school at 15, you again are going to deep and think your bakes can over come the grip of a tyre which they cannot at speed.KE = 0.5 mv^2 = force x distance = work done to stop the car.
Force being coefficient of friction x mass x gravitational acceleration.
Mass cancels on both sides of the equation.
I'm all ears if someone can disprove the above btw as well.
Kinetic Energy = 0·5 x mass x velocity2 when you have that figure you can then do the Use F = m x a
so MASS is the KEY figure in both which doubles the braking distance if you double the mass for the same force.
you seem to think your brakes are 700mm and have the force to lock a wheel, they don't so the force is the same is it not ?
and the skill in braking once you have over come friction of a tyre is threshold braking. ie you can out brake a ABS car using advanced threshold techniques.
so at 120 mph say, you only have the force of the brakes which cannot over come friction of the tyres until about 60 /70 mph then it's the skill of the driver to modulate the pedal reducing the force needed which could then over come the grip of said tyre.
the Only way to match the stopping distance is reducing mass of the car, or increase the force of the brakes, NOTHING to do with tyres in like for like cars.
the issue here is as far as I can tell is 10 or 20 people in the last 20 years since I have been on here think they can lock a wheel at 150 mph !!! YOU CANNOT !!!
the gravity thing I don't understand. I guess that plays a part at which point you over come friction and then tyres some into play.
All I can tell you in real life is if you add a passenger you need to brake earlier, not only that you are also going slower at the braking point. so a loose loose for a track time.
I still think it comes down to people thinking they have the force to lock a wheel at any speed !!!!
Edited by Porsche911R on Wednesday 20th November 10:03
Porsche911R said:
it is basics as far as I can see, but did leave school at 15, you again are going to deep and think your bakes can over come the grip of a tyre which they cannot at speed.
Kinetic Energy = 0·5 x mass x velocity2 when you have that figure you can then do the Use F = m x a
so MASS is the KEY figure in both which doubles the braking distance if you double the mass for the same force.
you seem to think your brakes are 700mm and have the force to lock a wheel, they don't so the force is the same is it not ?
and the skill in braking once you have over come friction of a tyre is threshold braking. ie you can out brake a ABS car using advanced threshold techniques.
so at 120 mph say, you only have the force of the brakes which cannot over come friction of the tyres until about 60 /70 mph then it's the skill of the driver to modulate the pedal reducing the force needed which could then over come the grip of said tyre.
the Only way to match the stopping distance is reducing mass of the car, or increase the force of the brakes, NOTHING to do with tyres in like for like cars.
the issue here is as far as I can tell is 10 or 20 people in the last 20 years since I have been on here think they can lock a wheel at 150 mph !!! YOU CANNOT !!!
the gravity thing I don't understand. I guess that plays a part at which point you over come friction and then tyres some into play.
All I can tell you in real life is if you add a passenger you need to brake earlier, not only that you are also going slower at the braking point. so a loose loose for a track time.
I still think it comes down to people thinking they have the force to lock a wheel at any speed !!!!
The whole point is that you are not necessarily braking at the same force for a heavier car.Kinetic Energy = 0·5 x mass x velocity2 when you have that figure you can then do the Use F = m x a
so MASS is the KEY figure in both which doubles the braking distance if you double the mass for the same force.
you seem to think your brakes are 700mm and have the force to lock a wheel, they don't so the force is the same is it not ?
and the skill in braking once you have over come friction of a tyre is threshold braking. ie you can out brake a ABS car using advanced threshold techniques.
so at 120 mph say, you only have the force of the brakes which cannot over come friction of the tyres until about 60 /70 mph then it's the skill of the driver to modulate the pedal reducing the force needed which could then over come the grip of said tyre.
the Only way to match the stopping distance is reducing mass of the car, or increase the force of the brakes, NOTHING to do with tyres in like for like cars.
the issue here is as far as I can tell is 10 or 20 people in the last 20 years since I have been on here think they can lock a wheel at 150 mph !!! YOU CANNOT !!!
the gravity thing I don't understand. I guess that plays a part at which point you over come friction and then tyres some into play.
All I can tell you in real life is if you add a passenger you need to brake earlier, not only that you are also going slower at the braking point. so a loose loose for a track time.
I still think it comes down to people thinking they have the force to lock a wheel at any speed !!!!
And you bloody well can lock a tyre easily above 70mph. Braking for stowe down hangar straight at 140+ on a rs or even at 150+ on a Mclaren, with enough shove ABS will trigger very quickly and in no way only at 60/70mph as you are claiming which is below the minimum apex speed of stowe in one of those cars anyway..
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