The Effects of Adding Weight to a Car and Its Impact on Braking Performance

If we take the same car and add 2,000 pounds to it, making it a 4,000 pound car, we wouldn't be able to stop at necessarily 1g. This is because the coefficient of friction decreases as the weight of the car increases. The exact same tires, with the same weight distribution as before, are now carrying more weight. As a result, the car will stop a little bit slower.

This phenomenon occurs regardless of whether the brakes can handle it or not. The reason for this is because the coefficient of friction decreases with an increase in load on the contact patch. This means that four tires, even if they have even loading, such as a 50/50 weight distribution, will stop faster than one tire with uneven loading. When a car has a balanced weight distribution, each tire has relatively equal pressure and therefore experiences a more consistent coefficient of friction.

To understand why this is the case, it's essential to explore the property of rubber known as viscoelasticity. Rubber works in a unique way, which can be explained by its molecular structure. The molecules are long chains that are tangled and cross-linked with one another. When you apply stress or strain to the rubber, these polymer chains stretch out and then return to their original state.

The arrangement of these polymer chains changes depending on the level of stress and strain applied. Initially, when you apply a small amount of force to the rubber band, it will only undergo elastic deformation. The polymer chains are stretching out and returning to their original shape without breaking or tearing. However, if you continue to apply pressure, the polymer chains will become stretched out and thinned out, reducing the resistance to strain.

As the polymer chains thin out, they start to break away from each other, which results in a decrease in the rubber's ability to resist frictional shearing. This is what happens with tires when they are loaded with weight. The pressure on the contact patch increases as the load increases, but the area of the contact patch remains relatively constant. As a result, the pressure increases, and the rubber's resistance to frictional shearing decreases.

This decrease in resistance to frictional shearing means that the coefficient of friction between the tire and the road surface will also decrease. When this happens, the tire's ability to resist lateral forces is reduced, making it more susceptible to sliding or losing traction. This is why adding weight to a car can make it stop slower and lose its handling capabilities.

The same principle applies when comparing tires with even loading versus those with uneven loading. If you have four tires that are evenly loaded, each tire will experience relatively equal pressure and therefore maintain a consistent coefficient of friction. However, if the tires are unevenly loaded, one tire will be subjected to more pressure than the others, which can lead to a decrease in its coefficient of friction.

As a result, the car with uneven loading will be less stable and more prone to sliding or losing traction when cornering. This is why it's essential to maintain even weight distribution on your tires to ensure optimal handling and braking performance.

"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video i'm going to be discussing tire load sensitivity and it's really cool subject because it's one of the reasons why engineers like to use a 50 50 weight distribution in cars or something close to it and also why you like to use wider tires for better handling and it's certainly not the only reason why 50 50 weight distribution or wider tires provide better handling but it is one of them and it's often misunderstood so i thought i'd take the time kind of go through it and explain how it works so first off we're gonna be starting with the great equation f equals mu n which is basically saying uh if you have a box sitting on a surface uh there's a certain coefficient coefficient of friction between that box and the surface and that box has a certain weight and therefore a normal force pushing back up on it which is equivalent to that box's weight and in order to move that box you're going to have to overcome that friction and that friction force is equivalent to the coefficient of friction multiplied by the normal force so i've used that in plenty of my videos so many of you have probably already seen that heard of it before but this phenomenon that i'm going to be talking about called tire load sensitivity what it says is that as your normal force increases your coefficient of friction decreases and looking at this equation you would never say that you would say okay that means if i have a car that weighs two thousand pounds or four thousand pounds it'll be able to handle the same corner because the normal force will increase and therefore the force will increase that it can hold well that's not necessarily true because the coefficient of friction decreases as your normal force increases so here's just a basic outline of where you can see the coefficient of friction is going to remain relatively stable until you get to a certain point and it's just going to start to taper off and decrease as the normal force increases so my example here is if i have a car that weighs 2000 pounds and a coefficient of friction equal to one and i assume that brakes aren't the limiting factor so if i slam on the brakes uh this car will be able to stop at one g uh two thousand pound force divided by two thousand pound car that's one g uh now if i were to take the same car and add 2 000 pounds to it so it's now a 4 000 pound car i wouldn't be able to stop at necessarily 1g so this is on the exact same tires exact same weight distribution as before but we've simply added 2 000 pounds the car is going to stop a little bit slower and once again we're assuming the brakes can handle it regardless but the reason why is because that coefficient of friction is going to decrease so what does that tell us if we know that to be fact well it tells us that four tires with even loading say your car has four tires then it's going to stop faster it's going to accelerate faster and it's going to be able to hold higher lateral g's basically it's going to handle better in every way versus a car that has uneven loaded tires so like i was saying earlier 50 50 weight distribution you've got 50 percent of weight on the front and on the rear as you're going around the corner you're gonna have more even loading so you're going to be able to go around that corner faster and that's because the weight distribution is fairly even across all the tires you don't have one getting overloaded and thus it's coefficient of friction decreasing so of course you're going to ask why why would this be and it's a very challenging question and it's somewhat difficult to explain and there's not a lot of good information out there but i kind of dug through it and i'm going to try and explain it best i can basically it comes down to a property of rubber called viscoelasticity and it's kind of just how rubber works and so let's just work through some of the logic here what we've got going on so we have a contact patch on the ground from the weight of our car and as we increase the weight of the car and we've got these same tires that contact patch isn't really going to change that much in size yes it will deform with the road a little bit and you're going to start to have a little bit more surface area but overall the relative size of that contact patch isn't going to increase dramatically so what this tells us is as the load on this contact patch increases the pressure increases because pressure is load over area so if your load goes up your area stays the same pressure goes up now as our pressure increases the rubber of this tires its resistance to frictional shearing decreases and basically what that means is its coefficient of friction is going to be decreasing because it's less resistant to frictional shearing so it's basically just going to kind of break away rather than deform with the road and the example i like to use is a rubber band and now so think of rubber as it's it's made up of long chains of molecules and these molecules are all tangled and cross linked with one another so that as i pull it out you know they stretch and then they pull themselves back together so the arrangement of these polymer chains alters depending on the stress and strain that you place on it so as i pull on it you know these polymer chains are stretching out and as i let go they go back to their steady state now initially while i pull on this rubber band it's only you know elastic deformation where nothing's really tearing no no bad things are occurring the rubber band can go to exactly where it was before however if you continue to pull on it you can see these polymer chains are now extremely stretched out and they're getting very thinned out so there's less of it to resist you stretching it and because there's less chains overall that means there's less resistance to strain and that's what i'm talking about here when i'm saying the rubber's resistance to frictional shearing decreases there's less resistance to the shearing it's the same thing there's less rubber here so there's less resistant to pulling on it and it starts to plastically deform eventually so if you think about a tire and that's more like compressing it so if i squeeze this rubber band really hard you know i'm starting to stretch out those polymer chains and it gets to the point where they're so thinned out they don't have that many there to resist that deformation and so they start to break away so with your tire as you start to smash that rubber down and it starts to kind of press itself out and thin out these polymer chains it'll start to break away rather than deform with the road and you don't want that to occur you want just an elastic deformation with the road and that gives you your maximum frictional coefficient and thus giving you the greatest force you can go around a corner that you can resist so that's tire load sensitivity how it works if you have any questions or comments feel free to leave them below thanks for watchinghello everyone and welcome in this video i'm going to be discussing tire load sensitivity and it's really cool subject because it's one of the reasons why engineers like to use a 50 50 weight distribution in cars or something close to it and also why you like to use wider tires for better handling and it's certainly not the only reason why 50 50 weight distribution or wider tires provide better handling but it is one of them and it's often misunderstood so i thought i'd take the time kind of go through it and explain how it works so first off we're gonna be starting with the great equation f equals mu n which is basically saying uh if you have a box sitting on a surface uh there's a certain coefficient coefficient of friction between that box and the surface and that box has a certain weight and therefore a normal force pushing back up on it which is equivalent to that box's weight and in order to move that box you're going to have to overcome that friction and that friction force is equivalent to the coefficient of friction multiplied by the normal force so i've used that in plenty of my videos so many of you have probably already seen that heard of it before but this phenomenon that i'm going to be talking about called tire load sensitivity what it says is that as your normal force increases your coefficient of friction decreases and looking at this equation you would never say that you would say okay that means if i have a car that weighs two thousand pounds or four thousand pounds it'll be able to handle the same corner because the normal force will increase and therefore the force will increase that it can hold well that's not necessarily true because the coefficient of friction decreases as your normal force increases so here's just a basic outline of where you can see the coefficient of friction is going to remain relatively stable until you get to a certain point and it's just going to start to taper off and decrease as the normal force increases so my example here is if i have a car that weighs 2000 pounds and a coefficient of friction equal to one and i assume that brakes aren't the limiting factor so if i slam on the brakes uh this car will be able to stop at one g uh two thousand pound force divided by two thousand pound car that's one g uh now if i were to take the same car and add 2 000 pounds to it so it's now a 4 000 pound car i wouldn't be able to stop at necessarily 1g so this is on the exact same tires exact same weight distribution as before but we've simply added 2 000 pounds the car is going to stop a little bit slower and once again we're assuming the brakes can handle it regardless but the reason why is because that coefficient of friction is going to decrease so what does that tell us if we know that to be fact well it tells us that four tires with even loading say your car has four tires then it's going to stop faster it's going to accelerate faster and it's going to be able to hold higher lateral g's basically it's going to handle better in every way versus a car that has uneven loaded tires so like i was saying earlier 50 50 weight distribution you've got 50 percent of weight on the front and on the rear as you're going around the corner you're gonna have more even loading so you're going to be able to go around that corner faster and that's because the weight distribution is fairly even across all the tires you don't have one getting overloaded and thus it's coefficient of friction decreasing so of course you're going to ask why why would this be and it's a very challenging question and it's somewhat difficult to explain and there's not a lot of good information out there but i kind of dug through it and i'm going to try and explain it best i can basically it comes down to a property of rubber called viscoelasticity and it's kind of just how rubber works and so let's just work through some of the logic here what we've got going on so we have a contact patch on the ground from the weight of our car and as we increase the weight of the car and we've got these same tires that contact patch isn't really going to change that much in size yes it will deform with the road a little bit and you're going to start to have a little bit more surface area but overall the relative size of that contact patch isn't going to increase dramatically so what this tells us is as the load on this contact patch increases the pressure increases because pressure is load over area so if your load goes up your area stays the same pressure goes up now as our pressure increases the rubber of this tires its resistance to frictional shearing decreases and basically what that means is its coefficient of friction is going to be decreasing because it's less resistant to frictional shearing so it's basically just going to kind of break away rather than deform with the road and the example i like to use is a rubber band and now so think of rubber as it's it's made up of long chains of molecules and these molecules are all tangled and cross linked with one another so that as i pull it out you know they stretch and then they pull themselves back together so the arrangement of these polymer chains alters depending on the stress and strain that you place on it so as i pull on it you know these polymer chains are stretching out and as i let go they go back to their steady state now initially while i pull on this rubber band it's only you know elastic deformation where nothing's really tearing no no bad things are occurring the rubber band can go to exactly where it was before however if you continue to pull on it you can see these polymer chains are now extremely stretched out and they're getting very thinned out so there's less of it to resist you stretching it and because there's less chains overall that means there's less resistance to strain and that's what i'm talking about here when i'm saying the rubber's resistance to frictional shearing decreases there's less resistance to the shearing it's the same thing there's less rubber here so there's less resistant to pulling on it and it starts to plastically deform eventually so if you think about a tire and that's more like compressing it so if i squeeze this rubber band really hard you know i'm starting to stretch out those polymer chains and it gets to the point where they're so thinned out they don't have that many there to resist that deformation and so they start to break away so with your tire as you start to smash that rubber down and it starts to kind of press itself out and thin out these polymer chains it'll start to break away rather than deform with the road and you don't want that to occur you want just an elastic deformation with the road and that gives you your maximum frictional coefficient and thus giving you the greatest force you can go around a corner that you can resist so that's tire load sensitivity how it works if you have any questions or comments feel free to leave them below thanks for watching\n"