A local mechanical engineer told me increasing brake pad area has no effect on braking torque.He said it only changes heat dissipation. How the fuck does that work?
You can only brake as quickly as the tire can maintain traction. The pad just dissipates heat through friction. larger pad means more surface area and mass so it doesn't heat up as much
>>28671174Friction force = normal force x coefficient of friction Brake torque = friction force x distance from center of rotationNo area in either formula. Friction coefficient is dependent on the pad and rotor material only.
>>28671182They why do wider tires increase friction and grip then?If the surface area isn't part of the equation that is
>>28671187>why do wider tires increase friction and grip then?They don't. But narrow tires have trouble following surface imperfections and are quickly destroyed by heat.
>>28671182Youre a fucking failure in life and especially the automotive world.
>>28671207Ackshually wider tires do increase grip in cornering and in the dry
>>28671187It's a little different and brakes are quite a bit simpler because there's no deformation it's just pad on rotor with a fairly uniform normal force distribution. Also it's inherently a dynamic friction problem i.e. the two parts are slipping.The question of contact patch is how do I distribute the load across the ground to prevent the tires from tires from slipping. It's a static friction problem with nonuniform load distribution. The tire deforms quite a bit too even at the tread block level. Also unless you're on a prepped surface the ground is a less uniform surface than a brake pad and rotor, both geometrically and materially.
>>28671208Thanks for posting the formula for clamping force for injection molding. Can you tell me what the cavity pressure is for a brake/rotor combo?
>>28671208Also before you say cavity pressure is the hydraulic pressure in the caliper ram. That's great you calculated the clamping force which in this case is the normal force from the first equation
>>28671182So, assuming they're the same material, there's no difference in brake torque using a normal brake pad or a brake pad the size of a pin head?
>>28671231Technically no they would be identical.Practically the pinhead would shear off, the brake pad would buckle, and the friction from heat would vaporize it instantly.So from a practical standpoint it still makes sense to get bigger brakes because you can get better heat distribution, less brake wear, and brake fluid heating.
>>28671247Huh, that's really unintuitive. I knew that disc size was a consideration for heat dissipation and that a bigger disc didn't mean more stopping power, but for some reason I didn't consider that the same thing applied for the pads as well. My monkey brain assumes that more surface area grabbing means more stop.
>>28671223Yep.Youre fucking retarded.>clamping force doesnt exist for automotive brakes because that specific example is from another device which functions under different physics principles.Just gtfo of /o/ and dont come back.
>>28671182We have a mech physicist here !
>>28671231Keep in mind, Couloumbs friction formula doesn't have surface area becuase any increase in surface area decreases pressure. But that's only for perfectly rigid materials that do not deform in any way. Once you get deformation and shit like elasticity, I saw the formulas in a Dynamics textbook and I closed that shit and walked away.
>>28671269Because that dipshit is wrong.Hes only quoting half of the physics.Hes leaving out clamping force which DOES rely on surface area.Hes a high school dropout.
>>28671287This, theoretical models are all well and good but reality isn't perfect and there's always more at play.
>>28671288I was hoping this guy would come back, I love smacking people down with science. Too bad he's illiterate because it's all spelled out above.
>>28671288Retard, if the surface area gets bigger then the force per unit area gets smaller. The force is the force regardless of how big or small your clamp is and is determined by the size of the pistons.The real answer is that in a non ideal world materials have limits and applying a massive force over a tiny area will destroy the surfaces.
>>28671174>>28671178 is accurate, any modern braking system that can lock up the wheels (or engage abs) is grip limited.
>>28671363>applying a massive force over a tiny area will destroy the surfaces.so surface area does matter for braking torque. I imagine a disintegrated pad would have much less torque than a larger intact pad
>>28671383Well yes, but If we compare a smaller brake pad to a pad 30% larger, the torque will still be the same.Now if the smaller pad can't manage the heat, then that's different.>>28671373We went talking about tire grip Completely irrelevant to this topic.
>>28671494braking torque is the topic of the thread. braking torque is limited by tire grip. its 100% relevant to the topic because its the exact answer to OP's question
>>28671303Literally "Normal Force" is clamping pressure.You dont understand the most basic principles of braking and are comparing 5th grade formulas of understanding fricrion of static objects.Just gtfo and dont come back.
>>28671174at some point you put tires wider than the small pads can handlethen you put big brakes with big pads that the small tires can't handle.the ideal is to have the most tire you can safely fit on the car without scrubbing or bottoming out and putting big brakes on that can stop it affectively.course you don't need any of that for bench racing.
>>28671187Because what these retards aren't considering is the velcro effect which isn't mentioned in highschool physics.Why does a bigger piece of velcro hold better if it gets wider. Same reason for tires. The rubber forms around the imperfections in the asphalt and "locks" it in at that moment in time. Wider tire = more area to lock into the pavement. At a certain point the pressure per unit area works against you and theres not enough point contact to push the rubber into the imperfections in the asphalt. So putting 300 width tires on a stock-aero gt86 wouldn't work because it will just glide on top of the asphalt. But putting bicycle tires on it will not give you the same grip as 250mm tires all things being the equal. Heat and wear also works against you with skinny tires but that's for people who actually track their cars instead of larping on 4chan.
>>28672261Its crazy how after more than a decade on this board you still talk like a catty hr manager with a yeast infection
>>28671494So the statement "increasing brake pad area has no effect on braking torque" isn't true though. It does have effect, just only to a certain size
Think of it this way. No matter how large or small the pad/rotors are the amount of friction required for a certain amount of stopping force is going to be the same, and the limit of effective braking is the tire grip.I won't bother Paul Harrell'ing my further comments with caveats and explanations of how infinitely large or small units are a stupid thought nor the intricacies of rotational inertia contributions to required braking effect.If you want to be that pedantically autism retarded just go kill yourself.
>>28672279>amount of stopping force is going to be the same, and the limit of effective braking is the tire grip.that's only true of the tire grip is the limiting factor, which is not necessarily the case
>>28672394Are you doing track/autocross or pushing the car on a windy road?Are you driving down a mountain or other perpetual decline?Are your stock brakes too weak to lock up the tires when ABS is disabled, even when cold? (EXTREMELY RARE)If you can't answer "Yes" to any of the above questions then there's no reason for you to upgrade your brakes.
>>28671174he's technically wrong, but morally right.best brake upgrade you can do is add another caliper piston
>>28672508What about brake cooling systems?Ducts/scoops and better fluid are amazing for preventing brake fade as well
>>28672505OK?
>>28672633Okay then.
>>28672657That's not really relevant to the question in OP or anything I said...
>>28671174More thermal mass to absorb more heat and more surface area to dissipate heat faster.
Just thought I’d throw this in amongst the stew of correct and incorrect posts ITT.OP specifically talks about braking torque. Accepting that if there is sufficient torque to break the dynamic friction of the tyres, the system is grip limited, in answer to OP’s actual question is it depends on how the pad area is increased. If the additional area is bigger pads radially, then the effective radius that the pads operate at will be increased, which will increase the torque exerted for any particular braking force.
>>28672787(cont)In fact, as one of my college lecturers pointed out, up to lock up you get the best braking performance from the largest diameter rotors inside the smallest possible diameter tyres. Just make a free body force diagram and use the formula for torque T = Fr
>>28672819>torqueyou're thinking of braking torque, and your equation is wrong, and you're missing many parts, such as friction coefficient of your tyres and also braking force.Your lecturer was a midwit.
>>28672833>friction coefficient of your tyres1. imagine being a eurofag2. we're assuming that tires are not the limiting factor here. did you even read the post>braking forcenot at all what we're talking about here. braking force is the rate of deceleration times the mass of the vehicle. braking torque is the friction between the pads and rotors, multiplied by the distance between those points of friction and the axle.You are a midwit.
>>28672854>we're assuming that tires are not the limiting factor here>talking about brakingfawk me, you need to drive a car to post here cunt
>>28672869>aussie midwit>falls back to shitposting when he's been proven wrongget better material mate
>>28672261If I put 295mm tires on a Miata, it would be faster than a set of 225s on the same car.The DP class of Miatas run 295s.I believe you are missing something here.
>>28672787>effective radius that the pads operate at will be increased, which will increase the torque exerted for any particular braking force.That's incorrect though.Larger brake Pads DO NOT increase braking torque.They only increase the area for heat to transfer.Your teacher is a Midwit.
>>28673001Ive drawn a highly scientific and cited diagram to explain. Tldr diminishing returns.It's not a linear curve. I dont know the exact numbers obviously but at a certain point you stop gaining grip for adding a wider tire. You'll see the biggest gains going from say a 225 to 255, and then after that you won't see those same gains to say a 300mm tire. Not only that but you lose out on power to weight and adding unsprung weight.
>>28673017Bless him and pardon him, he's talking about braking optimizations that mean so little to the average /o/ user they simply do not apply.Also, when I said>no matter how large or small the pad/rotors are the amount of friction required...is the sameObviously that means the total real friction force, not the friction per unit of surface area.>>28673055A couple years ago I spent some time reading on the subject and found about 3 examples of people discussing it to a sufficient detail.There is an optimum width for the corner weight, basically, and going above it loses speed because the tire just cannot adhere correctly due to a lack of pressure, the contact patch cannot form evenly, the sidewall cannot flex enough to allow enough slip, etc.anyone who says or thinks the most massivest tires on any car simply make it faster with no end is uninformed.
>>28673055Sure there's likely a limit to some point, but I doubt street cars can even come close to that.Even F1 cars with 400mm+ wide tires from the older sub 380mm tires still picked up grip.>>28673061Wider tires means I get more traction.That means my speeds will be higher.Higher speeds= more load transfer.More load transfer means my tires are working harder.Regardless of what race car I've worked on, wider tires almost always increases grip.Only caveat would be trying to squeeze wider tires on smaller wheels. 345s on 18x12 wheel is slower than a 335 on a 18x12 for example.
>>28671174Point your hands together like a prayer. if you touch your fingers together as hard as you can, then switch to your palms, you have had no affect on the torque you're applying, you just increased the surface area from your fingertips to your hands.
>>28673055Optimal width depends on the vehicles ability to use that grip. There is no point giving a car more traction than it can use, that just becomes wasted energy in pointless friction and added rotation mass. The guys in pic related understand this. Steering tires are tiny because they just need enough grip to go straight, back tires a huge because they need that contact area for the amount of torque they are producing. I non-straight line examples the balance is between grip in corners and straight line speed. Wider tires will allow higher cornering speeds at a cost of top speed and acceleration.
I'm an electrical engineer and I don't trust mechanical engineers to know their shit.
>>28673107>Even F1 cars with 400mm+ wide tires from the older sub 380mm tires still picked up grip.F1s can make over 4000lbs of downforce which forces the wide tires in to the road. Same reason why heavier cars in general benifit from wider tires more.That and the compound they race with is extremely soft compared to say a 200tw comp tire. The softer compound wraps around the imperfections in the asphalt and lot easier so you still get that benifit from a wider tire. Tldr: soft tire sinks in easier, downforce sinks it in more, you can still see more gains from a wider tire. I'm willing to bet an f1 with no downforce and a 200tw road tire wouldn't see any gains going from a 290 to a 325 tire.
>>28673140Well that's not gonna be true.My SCCA car used to run 275sThe jump to 315s saw a fucking 2 second drop in lap times (same RE71RS compound)The tire width limit is probably far beyond any tire being offered today
>>28671174increasing brake pad area allows for a better bite on the rotor. thus he's wrong because it'll take less effort to stop the car, if you have a smaller pad, it'll heat up quicker. just saying, heat degrades brake pads.
>>28671182Great, another armchair engineer with 0 experience.
>>28672231but according to retard science bro, wider tires will just distribute the pressure more and you’ll end up with the same grip no matter what the area of the contact patch is. So clearly in the real world tire width doesn’t matter because my highschool physics book oversimplified things for brainlets.
>>28672529brake fade is a totally separate issue
>>28673132I'm a mech eng and EEs only know how to make wires get hot.
Man there sure are a fucking lot of dipshits who think their ChatGPT diploma means they know wtf they're talking about.
i am just a crackhead shitbox enthusiast but i don't like the wordingthe concept of torque being available during a reductive system operation has me a bit confused since torque seems only available if the system it is applied to is static or additive in pressure from a pivot
>>28671174Kek at two retards who flunked out of physics arguing itt
>>28675187i'd go so far as to say engine braking may not even be an available use of torque, since the reductive pressure is created from the resistance of the components retarding
>>28671174I can't be arsed to read the thread but it's because if you don't change any other parts of the braking system, you're not increasing the clamping force by adding more area, you're just spreading the force you have over a larger area so the clamping pressure - not force - gets reducedI'm gonna use some retarded values here but the math is the same. If you have 200N of clamp force and a brake pad that's 0.1 sqm, you have 200/0.1 Pa of pressure (2000Pa). If you don't change the clamping force but double the size of the pad you have 200/0.2=1000Pa of pressure but it's still the same force on the brake it's just spread out wider.
>>28673017>Larger brake Pads DO NOT increase braking torque.Depends on the average radius that they are effective at. The further from the disc cebtre the effective radius is, the larger the torque for any given clamping force. T=Fr (as said above)You're either dim or a troll
>>28671174In an ideal system yes, see>>28671182However, brake pads shear off material as they are used. If the brake pad is tiny and thus the shearing rate is higher, the apparent effect will be a lower coefficient of friction. This is why wide tires help you accelerate and corner even though the friction math says otherwise.
If your stock brakes have enough force to lock up the wheels with ABS off, then adding more force does literally nothing for you.
>>28675734OP is asking about pad size vs braking torque - nothing about lock-up or retardation deceleration.
>>28675834I'm aware, and plenty have responded to them. Just felt like adding that knowledge nugget to the convo.
>>28675844That has also already been mentioned in the thread. Several times. But I suppose answering a question that wasn't asked in order to demonstrate knowlede that doesn't apply this this case is a win. Sort of.
>>28675210The average radius is going to be the same because the rotor is a circle.You can have a brake pad that's the entire circumference of the disc. The average radius is going to be the same because it's a fucking circle. Increasing rotor diameter does increase torque sure. but all things being equal; the size of the pad is not going to change torque
>>28671208>ai slop as a source
>>28675923I was hoping you were smart enough not to need a diagram. I was wrong. So here you go - see picHub B is the same as A, except B has a larger diameter disc and larger pads. The effective radius that the pads operate at for Hub B is greater than that for Hub AThe "average radius" of the pad is the difference bewtween the inner radius of the pad and the outer radius of the pad. If you were working out the torque the brakes would apply for a given clamp force then this simplification of average radius is what you'd use, rather than using calculus
>>28675999(cont)similarly, the "average radius" of the rotor, (or its effective radius), is between the inner radius and the outer radius of the swept pad area
>>28675999>>28676008That guy was clearly talking about increasing the arc length, not the radius. Note:>You can have a brake pad that's the entire circumference of the disc.
>>28676012Now go and look at OP's pic. it's pretty obvious that he's talking about bigger pads overall. Who the fuck fits pads with a longer arc radius but the same effective diameter? It makes no sense as the rotor would be the same size.
>>28676021Maybe that's why the mechanic pooh-poohed OP's idea - he didn't plan on changing out the rotors
>>28671174Your engineer can't just make a blanket statement like that. There are too many other factors. Also he's probably wrong.
>>28675999>Larger rotors increase braking torque.Ya I know anon. We all know.I said increasing the pad area by lengthening the pad does nothing for braking torque.>>28676021Anon, that's what the OP is saying.Larger pads DO NOT increase braking torque.
Boy there sure are lots of truck users who carry absolutely fucking nothing in their trucks, also a lot of "engineers" not accounting for the weight that should be in your useless little Ridgeline shitters. Otherwise they would have accounted for the amount weight on the tire in question and how the brake pad is designed with that in mind.>but muh sedanNo one cares about you.
>>28676406>Larger pads DO NOT increase braking torque.Of course they do. Are you fucking retarded?Using your retard logic they could make the pad half the size or fuck it one quarter of the size and get the same braking torque.
>Le brakes pads don't matter guys, le tire, le friction, le uh oh I put 2000 extra pounds in the back and my fat frenchman crew is in le baguette van and my le calculations got me le t-boned. Mon dieu!
>>28676427 brake pad area DOES NOT increase braking torque.I repeat: larger brake pads do NOT increase braking torque. T = F x R notice how the equation doesn't have anything to do with pad area?
>>28676550T = F x R only applies when the entirety of the clamping force is applied to a single point on the rotor.In reality, the force is equally applied across all points inside the contact patch between the rotor and pads. Each point has its own radius. As a result, to answer this question you'd have to integrate all of the individual braking torques, each with infinitesimally small individual braking force, to determine the overall braking torque.Of course, if the brake pad is just the same annular sector with a larger central angle then there's no change in braking torque but it depends on the two pads' geometries.
>>28671182"Because the math says so" is never a satisfying explanation
>>28676012>>28676406>>28676550OK, I'll have a second attempt. Let's assume that there is a way to fit pads with a longer arc but the same inner and outer pad radius (so a trip into Narnia, to deal with the Unobtanium Brakes Company)We all (?) know that the formula for the length (L) of an arc of a circle of radius R is L = pi x R x (A/180), (where A is the angle of the arc)If we take some simplified numbers, lets assume that the inner radius of our pad is 150 mm, the outer radius is 250 mm, and the arc length of the pad is a skinny 30 deg The inner arc length of these pads will be 79 mm. Similarly the outer arc length is 131 mm, so these pads have 52 mm more fibers at the outer radius than the inner.Now Anon consults with UBC about their "superlong" calliper, whose pads have the same inner and outer radii as his current pads but with an arc of 120 degThese pads will have an inner arc length of 314 mm and an outer arc length of 524 mm, with a delta of 209 mm more fibers at the outer arc.We have accepted (I hope) that T = F x R applies at a point. Therefore each individual brake pad fibre will, when clamped onto the rotor (with the same load as all its neighbors), exert a torque depending on its radius from the centre.This means that if a brake fiber is 1mm the Superlong 120 deg pads will have 209 more fibres exerting torque at the max radius compared to his standard pads with 52 more fibres, so the Superlong will exert a greater torqueThis would be mpore elegantly proved with calculus, but it's been so long I've used it I wouldn't trust myself to compose and execute the formulae correctly. This also analysis assumes the pad shape is a perfect sector of a circle
>>28676957(cont)And here's the numbers in Excel for those who didn't follow
>>28676651>"Because the math says so" is never a satisfying explanationBut it's usually the right one, rather than hope and intuition.
>>28676957>>28676962The average radial distance of an annular sector is equal to the radial position of its centroid relative to the axle.Let r_1 and r_2 be the inner and outer radii, respectively, and θ be the central angle.The area of the annular sector, A, is thus θ(r_2^2 - r_1^2)/2.The average distance between every point in the annular sector and the center of the circle, denoted as r_a, is 1/A * ∫∫_R r * dA, where R is the region of the annular sector. After substituting this into radial terms and evaluating the integral, we get that r_a = (r_2^3 - r_1^3)/3.We can then plug this into the overall equation to get T = F * (r_2^3 - r_1^3)/3.Note that the final formula for r_a (and T, for that matter) doesn't depend on θ, and only on the inner and outer radius. This means that the arc length of the annular sector (and thus, the hypothetical brake pad) has zero effect on the peak braking force.TLDR your are wrong idiot, get btfo
>>28677320Please disregard picrel, that's just the formula for the center of mass in Cartesian coordinates, not radial coordinates
>>28677320Yep, looks like you were right. Wish I could have remembered my calculus - just too many years have passed and I wasn't that good anyway.And for the icing on the cake you just had to be a snide little shit with your last line. I won't even try to claim your poor English (or typo) invalidates your enshittiness, either. Just so eager to score a point you fumbled the keyboard, I guess.
>>28677320You didn't need all of that. Any brake formula refers to effective pad radius and makes no mention of pad arc.All irrelevant anyway, as pad area will not affect torque, but in reality: larger pads = larger rotors = larger effective radius = larger torque
>>28677513Forgot image
>>28676968It does nothing to help someone understand something on a conceptual levelIt only just says that area doesn't factor in, it doesn't explain why that is the case, only that it is
>>28677513>>28677532How do you think they got to that brake formula? It helps to prove that, even when "factored in", the central angle doesn't matter
>>28677604You're one of these guys who are so clever you're actually slightly stupid.If the arc angle mattered, they'd mention it. Not everytthing needs to go back to first principles every time
>>28677320>r_a = (r_2^3 - r_1^3)/3.Are you sure about that? I'm not going to challange your calculus as I don't have the skills, but I do like plugging numbers into formulae to se if they make sense.So if we let your r_2 be Rand your r_1 be r (because it makes it easier to follow)Let R = 200 mm and r = 150 mmSo r_a = (200^3 - 150^3)/3r_a = (8,000,000 - 3,375,000)/3r_a = (4,625,000)/3r_a = 1,541,667Which is, of course, nonsense. So perhaps I misunderstood your notation, and you meant a cube root?So in this case, missing out the first few steps, I'd getr_a = "cube root"(4,625,000) which, accroding to the internet, meansr_a = 166.6 So assuming you meant cube root, your then formula seems to imply that the average radius is 167 mm, which is 17 mm outboard of the inner radius and 33 mm inboard of the outer radius.To which I'd say "Really?" The "rule of thumb" calculation in this case would giver_a = r + (R - r)/2 >[or r_a = R - (R - r)/2; same difference]r_a = 150 + (200 - 150)/2 = 175So your formula seems to imply that the average radius on a segment that gets wider as r increases towards R, is inside an arc that is mathematically half way out?I must have made a mistake with your formula somewhere - can you point out where I went wrong? Because this doesn't seem to make sense now
>>28678933Ah, you're right. The right formula for r_a would ber_a = (2/3)(r_1^2 + r_1 * r_2 + r_2^2)/(r_1+r_2)
>>28679189That makes more sense now (at least numerically). Using my numbers of 150 and 200 I now get r_a = 176.2, the right side of the mathematical average arcSo the "rule of thumb" in this case is within 1%.And I think you may owe an apology earlier in the thread - that anon may have been wrong, but so were you. I'll leave that to your conscience.Always worth plugging some simple "real world" numbers in to see if a formula makes sense before you flaunt it.
>>28679203me rn
>>28679207A little unfair on yourself. You had the smarts to attempt the calculus from first principles, and to apparantly work out where you went wrong and now correct it when I pointed out an issue.Maybe a little more humility and a little more checking. And now you understand why, even with two degress in technology and an HND Mech Eng (with distinction, I'll have you know!) I work as a project manager and leave this stuff to the smart guys. I just like to check their output, because I'm a suspicious bastard
This isn't calculus.
>>28679217(cont)Oh, and one more interesting and non-intuitive thing struck me as I was playing with your formulae. Reducing pad size can give increased braking torque.We know that pad area doesn't factor, nor does the pad arc. But if we make the pad slimmer (and therefore smaller) by increasing r (or r_1 in your nomenclature), you'll shift the r_a out towards the outside edge of the disc and thus increase the brake torque.
>>28679239This is not a pipeI didn't realise we were now in the realm of the surrealists
>>28679239RTFT
>>28679257I did. There's no calculus in it. You could use calculus to find other interesting data about pad area, but none of that is happening in braking torque. This is just algebra, lol. Which is 90% of calculus, and classical mechanics is interesting, but it ain't calculus without the fundamental leap ya smell me?
>>28679247Drum brake superiority confirmed yet again
>>28679265see>>28677320Last time I checked, integration was calculus.>and no, I'm not the author of that post
