Let's discuss the "if you can lock the wheels the brakes have enough power myth"

So here is what is brought this topic to mind:

I'm not entirely happy with the brakes on my Datsun 1200, I can brake as late as any of my vintage racing competitors (mostly Datsun 510s BMW 2002s) but I'm left with the feeling that there is an improvement to be had. The brakes are 280ZX front discs and calipers with 510/ 240Z alloy rear drums, the 1200 is over 1000lbs lighter. Because of this I use cheap pads and shoes (Beck Arnley) 

So back to the myth, once upon a time I commented to a friend about the lousy brakes on my vintage motocross bike, he said that well if you can lock the wheels up then you have enough brake. The best analogy of the issue I can give is one of 40lbs of pressure barely stoping, 80lbs of pressure barely doing more and then finally 100lbs of pressure locking the wheels. A proper set of brake shoes (I did say vintage bike) made a huge difference both as far as progression and actual stopping power.

Now back to my Datsun, while the brakes are progressive it's a case similar to the example above. Maximum braking occurs at say 90lbs of pressure but it won't start locking a wheel until 100lbs of pressure. That last 10% is where the brakes don't seem to be as progressive as they should be. Porterfield makes pads and shoes for my application, my thought is there is a small to moderate gain to be had with pads that have a little more bite.

Note the car is 1780lbs with me in it and I never have any sort of brake cooling issues, so street /track day compounds work fine. Additionally because it's a momentum car there really are only to places on the track where I really get into threshold braking. Every where else I'm trailing the brakes to rotate the car. It's probably only a few tenths so to be gained.

That comes down to tires I believe. If you can lock tires up, and you want to improve your limit before lock up, then better adhesion of the front (and possibly rear) tires may be needed. Whether that’s compound or pressure, I don’t know. 

Also, you could play with bias to gain better braking potential. And even spring rates in the front can assist. 

I would say you should try a track day with a very similar 1200. See if he out brakes you, swap cars, and find out why. 

The closer you can get to that lockup threshold, the better off you are.

Larger rotors allow more leverage and stiffer calipers allow better modulation to get closer to that threshold.

That myth really applies to street driven cars where you are rarely using the brakes to their limits for more than one or two panic stops in a row and often you’ll lock the tires much longer before you’ll reach the thermal threshold of the braking system.  In some cases, too much brake capability can even lead to premature lock up and/or very sensitive brakes.

Racing is a different situation where in an ideal world, the braking system would be used in full throughout the entire session.  This is where brake improvements can net gains in expanding the working temperature range, coefficient of friction, etc.

Food for thought.

If all you are concerned with is locking up the brakes, go with self-energizing drum brakes.

Disk brakes actually have less braking power per volume or mass.  Their advantage is that they are less likely to lock up because they are more linear.

I am a fan of drum brakes for their reliability but I wonder if it's holding you back right now.  If you don't need much braking, then I assume this means your rear brakes can do more of the braking for you.  Less weight transfer under braking(*)  If they were disks, you could get more braking force out of the rears before incipient lockup, especially in a rear drive car where all of that rotating mass is attached to the rear wheels.

(*) The reason why rear brakes are pretty much worthless on bicycles.  The center of gravity is so high relative to the wheelbase that any significant braking will have the rear wheel off the ground.  Of course, with a bike you can shift the CG around, like stretching your arms out and sitting your sternum on the saddle to get your weight real far back so you can brake REALLY hard, while keeping the back tire hovering just off the road/trail...

I like good brakes

There's a whole bunch of stuff going on when braking mostly involving heat. The disks/calipers/hubs/pads get hot. Which makes sense because the whole point is to turn forward motion into heat. The heat goes into the components and eventually into the air. Rotor/drum mass is a good place to put heat. If you don't have enough of that then things get really hot and the heat bleeds into everything connected to the system, calipers, hubs, wheel bearings, the whole lot. Whether this is a problem or a feature depends on how hot it all gets. You don't want to boil fluid or melt the grease out hubs for instsnce. The other part of heat is that it affects the brake pads/shoes. Those little guys are designed to work within a given heat range and their coefficient of friction will change with heat. One end of this is track pads that don't work well until they have heat in them, and the other end is pads that start to turn to goo and dramatically reduce braking. You're always melting pads ro some extent (if I understand the reactions correcly) which is why you get paid deposits when you bed the brakes. And as anyone here knows the act of depositing pad material on the rotor during bedding makes the brakes work better and the pads last longer. 

What this means is that the total mass of the system and it's ability to shed heatmatters, and it sounds like you have that covered, but having a compound that works within the operating temperature of your brakes matters too. You want brakes where the coefficient of friction stays consistent and predictable in the temperature range that your brakes operate in. If your pads are changing their feel dramatically as they heat up then it gets very hard to brake consistently. People who give you the line about having enough to lock them are missing the whole feel part. If you can't tell the difference between 80% braking or 100% braking because sometimes you push this hard and it locks and sometimes you push that hard and it doesn't, then you'll develop the habit of using about 80% of the brake under a lot of circumstances. 

And let's not forget that people like different brake feel. Perfect brakes to one person are too grabby to another. Some guy wants 100lbs of pressure while another wants 70lbs. 

It sounds like your brakes are adequate for the job at hand but the feel sucks, or it isn't good enough for you to do what you need to do anyway. 

S.S lines, new master, good pads/fluid should give you the communication and accuracy for that extra modulation.

In reply to ztnedman1 :

That's the part that I didn't write about above. After a certain amount of pedal/line pressure, more pressure squeezes harder, but it also swells lines, flexes the firewall, and flexes calipers and their mounts. All of this messes with linearity. 

The power vs lockup thing isn't wrong, it just doesn't tell the whole story.  You can have enough braking power in an absolute sense and still not have good brakes.  Just looking at power doesn't tell you how linear and easy to modulate the brakes are, how reasonable the pedal forces are, how well they take heat, etc. 

Knurled. said:

If all you are concerned with is locking up the brakes, go with self-energizing drum brakes.

 

Disk brakes actually have less braking power per volume or mass.  Their advantage is that they are less likely to lock up because they are more linear.

I tend to agree with this but only for the street. Modern pad companies just don't make pads with good enough material for drum brakes. IE my 6500lb cadillac with drum brakes stops really well. But can only do it twice maybe three times before then over heat

Bigger brakes won’t really help with what you are talking about.  In fact, a bigger diameter rotor would probably give you quicker lock-up.  You need much better pads.  Higher quality pads and rotors will make a world of difference, along with the SS lines and a firewall brace (if legal).

My dad and I ran a ‘73 Corolla SR-5 in SCCA ITC.  2200lbs with driver.  We never had brake problems, and were consistently outbraking our competition (1200’s, 510’s, Rabbits, 124C’s).

Many good points so far. More that I also like to think about but have little experience in actually changing:

Repeatability: brakes may be good enough to lock the tires once, but quickly heat up enough to lose this ability

Smoothness: if you smoothly roll into the brakes, you transfer weight to the front meaning that the front wheels have more traction and may take more braking force to lock. You could conceivably have brakes that could lock tires if you jabbed them, but don't have the power if you squeeze.

Weight: brakes are almost all rotating unsprung mass, some of the worst kind of weight.

Balance: sometimes, you could end up doing something like braking while turning. Similarly to the smoothness argument, you could conceivably have brakes strong enough to lock wheels in a straight line, but when you turn and the outside wheels get more traction and take more force to lock, you may not be able to lock them anymore. (Also as a driver this is a difficult situation because you are inevitably locking the inside wheels - you feel that wheels are locked but you may not be braking very hard. The inclination would be to release brake pressure because wheels are locked, but you could still have plenty of braking grip available on the outside wheels that isn't being used.)

If you feel like the brakes aren't linear up to a certain point then you're probably just storing energy in all the things that flex and swell like the firewall, hoses, calipers and brackets, etc. But you sound like you're having the opposite problem which is that you don't have enough 'resolution' in the threshhold braking zone. I guess at that point i would see if you can try a smaller master cylinder bore. It'll have longer travel and less pedal pressure which should increase your 'resolution' in that area. 

Assuming that you don't have any brake equipment issues (e.g. overheating them) it is all in the tires.  Put stickier tires on it and the lock up limit is raised.

Tire adhesion is paramount - you could put giant brakes on your car, but with crappy ties it isn't going to stop efficiently.  Ever wondered why classic high output cars like Hemi Cudas posted times slower than many modest modern cars (a Hemi Cuda back in the day posts a 1/4 mile time a bit slower than my current 2.0 liter street car)?

Tires.

It's not a myth, the rule is generally true...you say it takes too much pedal pressure for your taste to get close to lockup. More powerful brakes could indeed fix that, or a change to the hydraulic system could - like adding brake boost if you don't have it, or switching to a smaller bore MC with more travel, but that's not practical in a production car.  Technically you may have a brake control system problem rather than a lack of braking power, although you can work around it with more powerful brakes. Which in this case might just mean higher-friction pads - maybe step up to an aggressive street/autocross pad, like Axxis ULT or EBC Redstuff?

wearymicrobe said:

Knurled. said:

If all you are concerned with is locking up the brakes, go with self-energizing drum brakes.

 

Disk brakes actually have less braking power per volume or mass.  Their advantage is that they are less likely to lock up because they are more linear.

I tend to agree with this but only for the street. Modern pad companies just don't make pads with good enough material for drum brakes. IE my 6500lb cadillac with drum brakes stops really well. But can only do it twice maybe three times before then over heat

That's the other downfall of drums, they are hard to cool.

Big Trucks have drum brakes because they pack a lot of braking power inside a 22.5 wheel, but they aren't expected to be used frequently and heavily.

OK first I should clarify things a bit.

The 280ZX front discs are massive in relation to the standard 1200 front discs. The rear axle is from a 510 wagon, which have 1.5" larger drums and the drums are finned alloy 240/280Z. The master cylinder and rear wheel cylinders are 240Z units. All of the brake soft lines are braided steel. The pads and shoes are wearing evenly, although I am going to install slightl larger wheels cylinders as I want a little more rear bias (I'm odd in that I like the rears to lock a fraction before the front).

The only occasions were I really lock the brakes are on corner entry just as the inside front unloads. I seldom do this as the modulation is as good as most cars, I've raced the car for the 29 years so I am intimately familiar where the exact lock up point is.

Now back to why a say myth; if you could take a steel rod and jam it in the wheel spokes it would lock the tire............therefore all you need is a steel rod for brakes. When you have to start using non linear pedal pressure you lose the ability to modulate the brakes well.

It is hard for me to explain so I will use the following numbers strictly for example:

10lbs of pedal pressure gets 10% of the front tire traction 50 gets 50 etc. and then when you get to the 90-95lb range the progression changes and it now requires say 110lbs to get 98% and then at 115lbs the wheel will lock. So it's not huge but the very last bit is not what it should be in my mind.

If I have to use a parallel car I'd say it's 98% of what a properly set up Spec Miata is.

Again my thought is pads and shoes with a more aggressive bite would offer that extra bit. 

As I see it (just an opinion, not experience)- you are trying to balance the static vs dynamic friction on opposite things.  Before lock up, you are using the dynamic friction between the pads and the rotors to make static friction between the tires and the road.  And once you get to the static friction with the rotor/pad, you get dynamic friction (sliding) with the tires.

And I *think* that it's more pad related- giving you more control to approach but not exceed that point.  And you complain of the feel for the best braking.

Fully agree that the fluids, lines, etc- all need to be looked at; as well as heat rejection (and it's relationship with the fluid, too).  

But the action is in the pads to the rotors and how you can control them with your foot.

You may also need to look at the pivot point of your peddle and peddle length. With all the parts and pieces that you have making up your system I could see this as a possible issue that needs sorting.  

On a personal note as pads got much better in the late 80s and early 90s I found that stock smaller brakes with better pads was almost always the best way to get great brakes. Then add cooling as needed.  I experimented with many brake upgrades in my 924s and in the end stock calipers and rotors with properly selected pads was best. 

Well, your second post definitely helped clarify things. It sounds like your brakes work 'fine' but you want to fine tune them to the Nth degree where N is very difficult to quantify to anyone outside your own head. Pretty normal way for a car enthusiast to think, so I can relate more than i can actually help.. I think you are just going to have to try different pad compounds. Although, since you changed to a 240z mc, you could probably switch back to stock (smaller, i'm assuming) and see if you liked it. At least you wouldn't have to dig up some odd cross-referenced part or customize anything to try it. It's a little more labor intensive than a pad swap, but the MC swap is probably actually cheaper to try by the time you're on the 2nd, definitely 3rd set of pads seeking the ultimate combo. 

One thing you might try just to verify that changing the pads might address the actual 'issue' is to chamfer/bevel/grind off some of the current pad material and see if that moves the needle.  

Best of luck with this one! If it was math we could solve it, but this is a human brain we're dealing with! 

The tough part is being raised by New Yorkers (Queens) I talk with my hands.......which is hard to do with the Internet. 

Vigo you are correct I am indeed trying to get the enth degree out of it.  I'm looking to get the brakes fine tuned to the point being able to get the thing snaking around on all four tires. It just not quite there.

Thanks guys I'll be trying pads and shoes.  

The big difference is how discs and drums differ in how they apply brake torque.  The threshold between braking and locking is much different.  Disc brakes provide a pretty linear application of brake torque up to the point where they overcome tire friction and lock up.  Drum brakes do not do as good a job at that.  Their threshold of lockup means that you miss a whole range of brake torque that is usually otherwise available with discs.

So simply saying that "if you can lock them up you have enough brakes" is a myth in my opinion.

Example:  Take the adjustment bar out of those drum brakes.  What will happen is that as soon as the trailing edge of the rear shoe engages, the bottom will slap out against the drum and lock up the wheel.  You only effectively get about 10% of the brake torque before lockup.  Its not about peak brake torque, its how much of the curve you can use.  Discs do a better job.

To put some representative numbers to it, if 0% is no braking and 100% is lockup, Drums tend to utilize (let's say) 0-70% of their available brake torque, then suddenly jump to 100%.  Discs tend to use 0-95% before jumping to lockup.  Its that progressive use of more of the brake torque range that makes discs generally superior to drums.

Most any brake system can lock up the wheels.  Its how much of the torque you can apply before lockup that makes discs a generally better choice.

The classic quote is that the brakes have enough *power*, and that part is true.  They have enough power to stop the car, and adding more power to them isn't going to stop the car any faster on a single 70-0 brake distance test.  It's been a long time since any manufacturer sold a car in the US that had inadequate brakes for street use.

That said, there are lots of reasons to upgrade brakes that have nothing to do with the power they deliver.  Improved brake feel, improved heat resistance for multiple stops, lightweight components for decreased unsprung weight, improved wet weather capability, better front/rear balance, adding ABS, all of them are worthwhile, but they don't add power.

AnthonyGS said:

In reply to Knurled. :

Disc brakes ate the greatest thing in cycling since the derailleur.  

I recently got my first bike with disks. Wonderful things they are.

I don't have any info to add. I'd just like to say how much I like this place. Most forums I've been on are troll infested pits, echoing "Power is everything, bow down to the 1/4 mile and yes, that intake gave my car 28hp to the wheels." This place is special. Actual knowledge, sharing, helping, and everyone seems pretty good at shutting down disagreements before things get nasty. Just nice to know that when someone like me who is actually trying to learn and improve there are still folks out there eager to really help.

I'm going back a reading a thread... figured this page had some topical information...

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/the-traccord-2003-honda-accord-coupe/136498/page9/