Why Big Brakes Won't Stop You Faster but Wider Tires Will - Friction and Surface Area Explained
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2022-10-23に共有
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If you have ever considered upgrading your brakes to larger ones and did a bit of research online you have probably found out that, contrary to intuition, bigger brakes won't reduce your braking distance. On the other hand we all know that upgrading to wider tires can improve both your cornering and braking. So the underlying question we're answering today is why does surface area matter with tires but not with brakes.
If this is your first time hearing it than you might be surprised to learn that upgrading from stock brakes and calipers to larger brakes and calipers will not reduce your braking distance. This is surprising because intuition tells us that if we increase the surface area of both the brake and caliper than we increase the amount of friction which should improve braking and stop the car faster.
But, physics disagrees with intuition and physics says this: F = μN
Yes, it's a formula but don't get scared it's the simplest formula there is. And it tells us that F, which is frictional force equals the coefficient of friction which mu or mew different people pronounce it differently, it's a Greek letter times the normal force.
So let's explain this a bit. Frictional force is obviously the amount of friction. The higher the frictional force the more friction we need to overcome and the harder it will be to move a certain object. The coefficient of friction is a constant and it depends on the nature of the material and surface roughness. For example sandpaper has a much higher coefficient of friction than glass. Basically the coefficient of friction tells us how friction-y a particular material is. Our normal force is the force acting on the object and pressing it down. In case of a stationary object that force will be the weight of the object pressing it against the surface.
As you can see there's no surface area in the formula. Physics doesn't care if the object is on it's side or on it's face. Even if the difference in surface area is extreme the frictional force is the same because the weight of the object is the same and the material is the same no matter how we place the object.
Although we increase the number of hills facing each other when we increase the surface area we are also distributing the same force over a larger surface area which means that the hills interlock less, they touch each other less. This is why stabbing yourself with a needle is far more painful than doing the same thing with let's say a bottle. You may apply the exact same force in both scenarios but in the case of the needle all the force is concentrated on an extremely small surface area leading to a much higher pressure. In case of the bottle the force gets distributed over a larger area leading to reduced pressure. The same thing happens with our plank. Friction stays the same because we're offsetting the increased number of peaks with reduced pressure on the peaks since we're distributing the same force over a greater surface area.
Ok but then but why do all the fancy sports cars have giant brakes which are obviously so much larger than the brakes on most other cars? The answer is heat or more accurately the prevention of brake overheating.
If you observe brakes more closely you will see that almost everything has to do with heat management. For example brakes on cars are tucked in inside the wheels and the body of the car which means that they receive far less airflow than brakes on motorcycles which are sitting directly in the air stream. This is why car brakes are ventilated and motorcycle brakes are not. Ventilation works to try and flush out as much heat out of the brake system as possible. Why is heat such a problem with brakes? Because it leads to brake fade. When brakes overheat a thin layer of gas forms on the surface and this leads to reduced friction and braking performance otherwise known as brake fade.
So this formula applies to brakes but it does not apply to tires. Many tests have been done over the years and have proven that wider and larger tires improve braking and cornering performance. The answer is surprisingly obvious. Brakes are solid and rigid.....tires are elastic. They're made from rubber after all. Brakes are not designed to deform or change shape under normal operation. Tires deform and change shape all the time. The loads applied on brake pads and rotors are simple – the brake pad only moves in one direction. The loads applied on tires are very complex and ever-changing
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#d4a #bigbrakes #tires
コメント (21)
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It was over 30 years ago that my physics professor used the formula for friction to tell me I was wrong in believing that wider tires provide more grip. I knew I was right but I couldn’t prove it to him. I very much appreciate the answer, even if it’s 30 years late. Ha. Thank you!
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I'm a tire design engineer who worked on some of the slicks you showed, wanted to say, great explanation!
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Bigger brakes will usually have larger pistons and possibly a higher number of pistons, so the same hydraulic pressure applied to the brakes will actually result in a higher force pressing the pads to the rotors. But this of course means very little, when the tires themselves are unable to withstand the increased braking power. Upgrading both is the way to go. :)
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Good explanation, but one point missed. If you are upgrading to larger diameter rotor with appropriate caliper and pad. In this case even the braking force on pad might be the same as before, the brake torque is still higher measured on the hub, because of the larger radius.
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I always considered it this way: If your brakes can lock up, you already have more stopping power than you need. If you really want to stop, you need more rubber on the road. This is why ABS is a thing. Practically all modern car brakes are too strong for their purpose. As such, the means to improve them is to artificially weaken them so they don't defeat the tires capability.
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As an Engineer, I love how you explain things with formula and science but simplifies the theories so people without the technical knowledge can understand. Also as I car guy, I love how things I learned in University have application to my hobby. Win, win in my books.
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Once again, you've thoroughly explained the subject with magnificent clarity. I'm constantly blown away by the quality of your videos.
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Totally agree with what you say. Where the bigger breaks bring benefits is that they have a higher thermal mass to absorb and then dissipate the large and repetitive energy of breaking. I fit upgraded two piece breaks, pads, and very high temp fluid in the STI. The result was less fade and shorter stopping distances. A side benefit was lighter disk assemblies as well as forged rims for a loss of near 9Kg per corner. Larger and better gripping tires tend to bring with them the requirement of up graded breaking components.
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as someone working in a dealership, i see this quite often. people want good brakes, such as ate, brembo, but if you ask them about tires they often pick the cheap options because the actually goods ones are too "expensive". so you want good brakes while also dont?
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i thought bigger brakes were more to aid in cooling by having more surface area and longer times to heat up through greater mass...
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I have a small car workshop in Thailand. I explained a lot to my customers, as you said. If they use the car in normal conditions, e.g., in everyday life. It's optional to upgrade the brake if they want, but just OEM. It's entirely enough. Investing more money in new tires is a better option. It's the fence between the car and the street. For example, most cars didn't upgrade their brakes and could drive on the German autobahn safely without a speed limit. That means the OEM specification it's enough. You're very professional from the practical to the theoretical view. With suitable examples, good explanations, and easy listening. That's super cool!
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Bigger brakes can hold more heat before overheating and they dissipate heat faster. Putting tiny brakes on a race car may lock up the tires, but they will overheat instantly. Also a larger rotor will give the calliper more leverage to stop the wheel. Anyway I think that unless your brakes are tiny, or you do hard tracking with a powerful car, a simple pad upgrade is all you need.
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I think that the reason is much simpler. Most brakes are already able to lock up the wheels while braking so pressure increase won't help, because the wheel can be already locked up with smaller brakes (that is also why every new car has ABS). This means that breaking performance for most cars isn't brake pressure limited, bud tire grip limited. Larger tires will have more grip and more grip means more friction, which improves braking performance.
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I feel like you could do a more advanced video on brakes too. Such as larger brakes having a centre of braking pressure further from the wheel hub so you can brake harder with less force. Or even talking about how pads warp and why multi piston brakes have an advantage etc etc. love the vids ❤
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Your videos are excellent! I basically knew what you discussed about brakes already, but your explanation of how brakes and tires differ was fantastic.
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I always wondered why tire width matters but the formula says otherwise. After watching your "Why are Front Brakes Larger than Rear Ones? Brake Bias Explained" I was really wondering. Thank you for explaining all the complexities and how it applies in reality reguarding tire width. It is hard to find good information like this. Your explanations are excellent! Thank you.
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Wow!!! The way that you differentiate between friction of various materials--and wet vs dry--was fantastic! And your illustrations were excellently suited to the topic at hand while keeping things interesting and fun to watch! Well done, Sir! I'm looking forward to learning more about tires in the future--high vs low profile, soft vs hard compound, wide vs narrow, summer vs winter, etc. Keep up the great work!
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Thank you sooo much for making a video in response to my comment.This question has been in my mind for years and now I got an answer from one of my favourite YouTubers.Your channel is brilliant and deserves more views,keep going, great work!
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Great video. I actually asked a friend of mine when I learned about this formula almost 10 years ago. He's an automotive engineer, but he couldn't really explain it and shrugged saying it's experimental evidence that did not align with the mathematical formula. I of course already figured it out by now, but I would have loved your explanation back then!
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I don't know how you can continually spit out useful information sentence after sentence non stop. Impressive.
