Daftest stuff said on PH which isn't really true
Discussion
Caddyshack said:
A real world test by a science teacher:
Funny that you bring this up just last week I did a demonstration for my students on this subject.
The weight of a vehicle affects the braking distance dramatically, to the point where an overloaded vehicle is very unsafe. It’s not so noticeable in a car with extra weight in it or even going up to the weight of a SUV or even a mini Van, these are all considered light vehicles.
So to answer this question correctly I need to use some terminology that are mostly only used in the heavy vehicle industry, however is it the best way to describe what happens and why it’s so dangerous. And sorry the answer will be long, I will include some picture to show the different vehicles, hopefully you will be able to identify .
So first the terminology mostly so I can type the abbreviation rather than the full description.
GVM / GVWR = Gross Vehicle Mass / Gross Vehicle Weight Rating = maximum weight allowable of the vehicle and it’s load also the weight that the brakes are able to stop safely.
GCM = and Gross Combination Mass = maximum weight of the vehicle and trailer and the loads.
Tare = Tare Weight = the weight of the vehicle without load, often called the kerb weight especially in light vehicles.
Load = the weight that the vehicle is carrying, the weight of the people are included in the load figures , also this is the difference between the tare and GVM.
In light vehicles the maximum load is a percentage of the tare therefore the load is a small part of the total weight so doesn’t effect the braking distance too much.
I have just bought a car like this car below
It’s a 2006 Holden Crewman Cross 8 so it has a 6.1L V8 and 5 Speed Automatic
Crewman Cross 8 kerb mass (Tare) (kg): 1942
Crewman Cross 8 Gross Vehicle Mass (GVM) (kg): 2685
Crewman Cross 8 Braked Towing Mass (kg): 2100
Crewman Cross 8 Gross Combination Mass (GCM) (kg): 4785
These Figures come from the Holden Website
From these figures we can calculate that the maximum load is 2685–1942 = 743kg
So after putting 4 Big guys inside 743 - 400 = 343kg for stuff and luggage.
I’m going to be using this with a trailer like this all the time
This trailer
Trailer kerb mass (Tare) (kg): 1234
Trailer Gross Vehicle Mass (GVM) (kg): 2500
The trailer has cab operated brakes and will be used to the maximum weight of the towing vehicle all the time.
To demonstrate the difference in braking I did a test with this combination to show my students what happens. On a blocked off straight road near my base at 80 kilometres per Hour emergency stopping to stationary, after every run we topped up the fuel tank.
Vehicle and Driver only = 32 Metres
Vehicle, Driver only and 300 kg load = 38 Metres
Vehicle, Driver and 3 Passengers = 39 Metres
Vehicle, Driver, 3 Passengers and 300kg load = 45 Metres
Vehicle, Driver and empty Trailer = 38 Meters
Vehicle, Driver, 300kg load and empty Trailer = 41 Meters
Vehicle, Driver, empty Trailer and 3 Passengers = 41 Metres
Vehicle, Driver, 300 kg load, empty Trailer and 3 Passengers = 43 Metres
Vehicle, Driver and 800 kg loaded Trailer = 48 Meters
Vehicle, Driver, 300 kg load and 800 kg loaded Trailer = 52 Meters
Vehicle, Driver, 800 kg loaded Trailer and 3 Passengers = 52 Metres
Vehicle, Driver, 300 kg load, 800 kg loaded Trailer and 3 Passengers = 58 M
This is real world testing with a car that had been fully serviced with new tyres, new brake pads and discs. everything was working to specification on the car. These results are the average of 5 different drivers. we had warmed the tyres before we started, the road was dry and nice warm sunny weather.
Now this vehicle below is very different but physics are the same
Tare = 19,440 kg
Load = 23,000 kg
GVM = 42,440 kg
Top speed = 60 kmh
stopping distance at top speed when empty = 67 metres
stopping distance fully loaded = 93 metres
I would say that if that pickup is incapable of matching its unladen braking performance with people and load onboard, the brakes could be better. It's not the grip of the tyres limiting that. Braking performance of 7.7 metres per second squared (0.8g) on warm dry tarmac is not terribly impressive. 32m for a 1942kg vehicle from 80km/h is pretty dire.Funny that you bring this up just last week I did a demonstration for my students on this subject.
The weight of a vehicle affects the braking distance dramatically, to the point where an overloaded vehicle is very unsafe. It’s not so noticeable in a car with extra weight in it or even going up to the weight of a SUV or even a mini Van, these are all considered light vehicles.
So to answer this question correctly I need to use some terminology that are mostly only used in the heavy vehicle industry, however is it the best way to describe what happens and why it’s so dangerous. And sorry the answer will be long, I will include some picture to show the different vehicles, hopefully you will be able to identify .
So first the terminology mostly so I can type the abbreviation rather than the full description.
GVM / GVWR = Gross Vehicle Mass / Gross Vehicle Weight Rating = maximum weight allowable of the vehicle and it’s load also the weight that the brakes are able to stop safely.
GCM = and Gross Combination Mass = maximum weight of the vehicle and trailer and the loads.
Tare = Tare Weight = the weight of the vehicle without load, often called the kerb weight especially in light vehicles.
Load = the weight that the vehicle is carrying, the weight of the people are included in the load figures , also this is the difference between the tare and GVM.
In light vehicles the maximum load is a percentage of the tare therefore the load is a small part of the total weight so doesn’t effect the braking distance too much.
I have just bought a car like this car below
It’s a 2006 Holden Crewman Cross 8 so it has a 6.1L V8 and 5 Speed Automatic
Crewman Cross 8 kerb mass (Tare) (kg): 1942
Crewman Cross 8 Gross Vehicle Mass (GVM) (kg): 2685
Crewman Cross 8 Braked Towing Mass (kg): 2100
Crewman Cross 8 Gross Combination Mass (GCM) (kg): 4785
These Figures come from the Holden Website
From these figures we can calculate that the maximum load is 2685–1942 = 743kg
So after putting 4 Big guys inside 743 - 400 = 343kg for stuff and luggage.
I’m going to be using this with a trailer like this all the time
This trailer
Trailer kerb mass (Tare) (kg): 1234
Trailer Gross Vehicle Mass (GVM) (kg): 2500
The trailer has cab operated brakes and will be used to the maximum weight of the towing vehicle all the time.
To demonstrate the difference in braking I did a test with this combination to show my students what happens. On a blocked off straight road near my base at 80 kilometres per Hour emergency stopping to stationary, after every run we topped up the fuel tank.
Vehicle and Driver only = 32 Metres
Vehicle, Driver only and 300 kg load = 38 Metres
Vehicle, Driver and 3 Passengers = 39 Metres
Vehicle, Driver, 3 Passengers and 300kg load = 45 Metres
Vehicle, Driver and empty Trailer = 38 Meters
Vehicle, Driver, 300kg load and empty Trailer = 41 Meters
Vehicle, Driver, empty Trailer and 3 Passengers = 41 Metres
Vehicle, Driver, 300 kg load, empty Trailer and 3 Passengers = 43 Metres
Vehicle, Driver and 800 kg loaded Trailer = 48 Meters
Vehicle, Driver, 300 kg load and 800 kg loaded Trailer = 52 Meters
Vehicle, Driver, 800 kg loaded Trailer and 3 Passengers = 52 Metres
Vehicle, Driver, 300 kg load, 800 kg loaded Trailer and 3 Passengers = 58 M
This is real world testing with a car that had been fully serviced with new tyres, new brake pads and discs. everything was working to specification on the car. These results are the average of 5 different drivers. we had warmed the tyres before we started, the road was dry and nice warm sunny weather.
Now this vehicle below is very different but physics are the same
Tare = 19,440 kg
Load = 23,000 kg
GVM = 42,440 kg
Top speed = 60 kmh
stopping distance at top speed when empty = 67 metres
stopping distance fully loaded = 93 metres
The situation with a trailer is always going to be a wildcard. If the trailer is unbraked, that's mass the car has to stop without any extra weight over its own tyres. In this case the trailer is braked, but how efficiently? Braking performance of 5.1 metres per second squared (0.52g) suggests "not very".
The relevance is that it’s the exact same vehicle and the only variable being mass change.
What you have said there totally supports what I have been saying, the mass extends the braking distance.
100% it isn’t friction (grip of the tyres limiting the braking as you say) but As I have said lots before - friction isn’t being overcome by the brakes until the very last points of the deceleration runs, most of the cars, including the gtr and GT3 won’t be locking their tyres at anything much above all but the lower speeds. I think some of the posters have assumed that the brakes are locking the wheels and therefore adding mass might aid the friction, mass does add to the friction as we have all agreed but the brakes on the unladen car are already doing their best to stop from 100mph in the 32 seconds as posted by the op, if you then add mass the braking distances just increase.
Would any car match the unladen braking performance when fully laden? I highly doubt it would, the unladen braking would always be better than laden. Doesn’t it stand to reason that if you have just performed the best possible stop you can in the car and then start adding mass the distances will just increase, if not what happened to stop the car stopping faster in the previous stop…you are not leaving any performance behind or you would have stopped sooner. I know the answer is going to be the added weight adds friction and around we go again…but the mass increases the momentum and the friction trade off does not cancel it out.
0.8g isn’t bad Imo when most cars don’t exceed 1g by much.
The trailer in the test was braked.
What you have said there totally supports what I have been saying, the mass extends the braking distance.
100% it isn’t friction (grip of the tyres limiting the braking as you say) but As I have said lots before - friction isn’t being overcome by the brakes until the very last points of the deceleration runs, most of the cars, including the gtr and GT3 won’t be locking their tyres at anything much above all but the lower speeds. I think some of the posters have assumed that the brakes are locking the wheels and therefore adding mass might aid the friction, mass does add to the friction as we have all agreed but the brakes on the unladen car are already doing their best to stop from 100mph in the 32 seconds as posted by the op, if you then add mass the braking distances just increase.
Would any car match the unladen braking performance when fully laden? I highly doubt it would, the unladen braking would always be better than laden. Doesn’t it stand to reason that if you have just performed the best possible stop you can in the car and then start adding mass the distances will just increase, if not what happened to stop the car stopping faster in the previous stop…you are not leaving any performance behind or you would have stopped sooner. I know the answer is going to be the added weight adds friction and around we go again…but the mass increases the momentum and the friction trade off does not cancel it out.
0.8g isn’t bad Imo when most cars don’t exceed 1g by much.
The trailer in the test was braked.
Edited by Caddyshack on Friday 8th December 21:14
Edited by Caddyshack on Friday 8th December 21:16
Edited by Caddyshack on Friday 8th December 21:21
Edited by Caddyshack on Friday 8th December 21:23
I'm asking politely, do you think you could move your discussion to a new thread please? You're in danger of killing this one stone dead by your hijack.
I don't mean to be rude, but I don't care about mass and braking distance and s
t. I know the heavier it is, the faster it's going, it's going to be harder to stop.
Now, can we please move on?
I don't mean to be rude, but I don't care about mass and braking distance and s
t. I know the heavier it is, the faster it's going, it's going to be harder to stop.Now, can we please move on?
Bsc in automotive engineering Rotterdam says:
2x as much mass means 2x as much braking distance
2x as much speed means 4x as much braking distance
per 𝐸𝑘=𝑚∗𝑣2
E
k
=
m
∗
v
2
This is how they relate to each other. Speed is squared, as in many situations, mass is proportional.
In theory, at a certain pressure from your foot on the braking pedal, a proportionally bigger force is applied to the brake pads on the disc, resulting on the tyres exerting that force on the road, and thus the car(and you) experiences a proportionally big drag force, slowing it down.
In other words, a certain pressure on the brake pedal induces a certain deceleration. At any speed, this is the same. This means that your speed is reduced at a fixed rate. But you cover more distance per time at a higher speed.
NB: this is in theory, reality is much more complex to explain. The brakes heat up improving their efficiency to some point, only to plummet after that point. Tyres have a similar effect.
I keep posting things from videos proving the real life, scientists, Newton’s first law of motion, science teachers doing experiments but it is almost as if people are not willing to change their perspective despite however much evidence they are presented with….
Nobody has posted anything to show the same vehicle able to stop in the same distance once more mass has been added and much less a shorter distance. The original post was "mass has no affect on braking" then we had that mass was cancelled out by increased friction so the car will stop the same or better with more weight which was later accepted to ‘it won’t be longer by as much as you might think’
2x as much mass means 2x as much braking distance
2x as much speed means 4x as much braking distance
per 𝐸𝑘=𝑚∗𝑣2
E
k
=
m
∗
v
2
This is how they relate to each other. Speed is squared, as in many situations, mass is proportional.
In theory, at a certain pressure from your foot on the braking pedal, a proportionally bigger force is applied to the brake pads on the disc, resulting on the tyres exerting that force on the road, and thus the car(and you) experiences a proportionally big drag force, slowing it down.
In other words, a certain pressure on the brake pedal induces a certain deceleration. At any speed, this is the same. This means that your speed is reduced at a fixed rate. But you cover more distance per time at a higher speed.
NB: this is in theory, reality is much more complex to explain. The brakes heat up improving their efficiency to some point, only to plummet after that point. Tyres have a similar effect.
I keep posting things from videos proving the real life, scientists, Newton’s first law of motion, science teachers doing experiments but it is almost as if people are not willing to change their perspective despite however much evidence they are presented with….
Nobody has posted anything to show the same vehicle able to stop in the same distance once more mass has been added and much less a shorter distance. The original post was "mass has no affect on braking" then we had that mass was cancelled out by increased friction so the car will stop the same or better with more weight which was later accepted to ‘it won’t be longer by as much as you might think’
Arthur fouce dellara race driver and GT3 race engineer:
Actually… Technically… No! (Yes it does, more on that at the end)
Are you familiar with Newton 2nd Law?
F = m.a
the sum of external forces is equal to mass times acceleration.
In this case: F = (power* of the car ) - (mechanical friction + aerodynamic friction)
substraction because both terms are in opposite direction.
a = 0 -> m.a = 0
which means that F = 0
-> power of the car = (mechanical friction + aerodynamic drag)
= h.V + 1/2.rho.Cx.V²
mechanical friction depends slightly on the weight. However:
friction is proportionnal to speed, whereas aero drag is proportionnal to speed squared. At high speeds, you can neglect friction (experimentally, you can over 120–130 kph) And aero drag doesn’t depend on weight at all.
-> top speed isn’t influed on by weight.
However, as soon as accleration comes in equation, (braking, turning, actually accelerating) you are going to lose proportionnaly. which means that, overall, your car will be slower.
That’s why I am faster in a Caterham than most supercars on twisty tracks (that’s my daily flex box checked). As st Colin said “add horsepower, you will be faster in the straight lines. Remove weight, you will be faster everywhere”
Actually… Technically… No! (Yes it does, more on that at the end)
Are you familiar with Newton 2nd Law?
F = m.a
the sum of external forces is equal to mass times acceleration.
In this case: F = (power* of the car ) - (mechanical friction + aerodynamic friction)
substraction because both terms are in opposite direction.
- power and not torque as inertia must be taken into account.
a = 0 -> m.a = 0
which means that F = 0
-> power of the car = (mechanical friction + aerodynamic drag)
= h.V + 1/2.rho.Cx.V²
mechanical friction depends slightly on the weight. However:
friction is proportionnal to speed, whereas aero drag is proportionnal to speed squared. At high speeds, you can neglect friction (experimentally, you can over 120–130 kph) And aero drag doesn’t depend on weight at all.
-> top speed isn’t influed on by weight.
However, as soon as accleration comes in equation, (braking, turning, actually accelerating) you are going to lose proportionnaly. which means that, overall, your car will be slower.
That’s why I am faster in a Caterham than most supercars on twisty tracks (that’s my daily flex box checked). As st Colin said “add horsepower, you will be faster in the straight lines. Remove weight, you will be faster everywhere”
Jordie Barretts sock said:
I'm asking politely, do you think you could move your discussion to a new thread please? You're in danger of killing this one stone dead by your hijack.
I don't mean to be rude, but I don't care about mass and braking distance and st. I know the heavier it is, the faster it's going, it's going to be harder to stop.
Now, can we please move on?
Yes, totally understand. You will not hear any more from me on this thread about this matter.I don't mean to be rude, but I don't care about mass and braking distance and s
t. I know the heavier it is, the faster it's going, it's going to be harder to stop.Now, can we please move on?
Here's one that could also serve in the "phrases that annoy you the most" thread, but is said a lot on PH that I'm sure isn't really true:
"Just spat my coffee out!", "New keyboard needed!" and variants thereof.
I just really doubt that so many users browse PH, beverage not only in hand but in mouth, spraying it all over their desks. Especially because it's so often (apparently) after some weak pun or piece of awkward sarky banter. I've never seen anyone do a caffeine-related spittake due to an on-screen joke, but apparently PH is keeping the keyboard repair industry alive.
The forum equivalent of the 'crying with laughter' emoji.
"Just spat my coffee out!", "New keyboard needed!" and variants thereof.
I just really doubt that so many users browse PH, beverage not only in hand but in mouth, spraying it all over their desks. Especially because it's so often (apparently) after some weak pun or piece of awkward sarky banter. I've never seen anyone do a caffeine-related spittake due to an on-screen joke, but apparently PH is keeping the keyboard repair industry alive.
The forum equivalent of the 'crying with laughter' emoji.
2xChevrons said:
Here's one that could also serve in the "phrases that annoy you the most" thread, but is said a lot on PH that I'm sure isn't really true:
"Just spat my coffee out!", "New keyboard needed!" and variants thereof.
I just really doubt that so many users browse PH, beverage not only in hand but in mouth, spraying it all over their desks. Especially because it's so often (apparently) after some weak pun or piece of awkward sarky banter. I've never seen anyone do a caffeine-related spittake due to an on-screen joke, but apparently PH is keeping the keyboard repair industry alive.
The forum equivalent of the 'crying with laughter' emoji.
I think modern folk use words without using them in their perfect sense….I saw a recent meme that was “legend’ used to be a knight pulling a sword from and ancient magical stone but now someone is a legend if they bring back an unexpected packet of crisps from the bar."Just spat my coffee out!", "New keyboard needed!" and variants thereof.
I just really doubt that so many users browse PH, beverage not only in hand but in mouth, spraying it all over their desks. Especially because it's so often (apparently) after some weak pun or piece of awkward sarky banter. I've never seen anyone do a caffeine-related spittake due to an on-screen joke, but apparently PH is keeping the keyboard repair industry alive.
The forum equivalent of the 'crying with laughter' emoji.
I was told to be impeccable with your words.
I have also very recently noticed people say, "a big massive’ -either say big or massive, not both.
Gassing Station | The Lounge | Top of Page | What's New | My Stuff