maseratiguy
maseratiguy Reader
7/5/16 10:40 p.m.

Hi, This is more of a theoretical question right now, as I am not working on anything right now, But.... I always assumed that bigger rotors and larger calipers added more stopping power not just better heat dissipation. My thought process was that a larger rotor with more surface area and more pad area would give you more friction to slow the car down. I am asking in reference to say coming around a corner and seeing an accident and having to stop quickly, or say a deer running out into the road. So all things being equal, tires, pads, wheel size, etc. Also without locking up the tires.

However I have been told I am wrong, that all things being equal as long as you can lock up the tires with a stock system larger brakes don't stop you faster. That it is all about tire to road and more pad friction doesn't help. This seems counter intuitive to me. Am I wrong?

(again, all things being equal and not locking up the brakes but modulating the pedal so you don't, but still stopping in as short a distance as possible in a cold one time stop). Thanks.

Dashpot
Dashpot Reader
7/6/16 9:45 a.m.

Your advisor is correct, but you're not wrong either.

Bigger brakes will provide more thermal mass to dissipate heat on repeated stops. Factory brakes in good shape should provide roughly equal stopping power for the 1st several applications, then fade.

What a well engineered set of aftermarket calipers/rotors/pads will give you is better feel. Pedal pressure is much more linear with multi piston fixed calipers vs OEM single pot sliding calipers. The challenges are matching piston size to OEM master and F/R balance in the new system.

Make sense?

Rupert
Rupert Dork
7/6/16 2:12 p.m.

I agree with Dashpot. But I have a suggestion which will help many people at much lower expense. Stainless Steel Brake Hosesmake a huge difference in pedal feel and braking control at very low cost. IMHO: Anyone who's not running with Stainless Steel Hoses should!

maseratiguy
maseratiguy Reader
7/6/16 3:37 p.m.

@Rupert, Yes with SS lines and as said all things being equal. So if it is all about tire to road friction and not pad size/rotor size, Why does pad material matter? Why fit bigger brakes, just for heat dissipation? I know my stock brakes can lock up my tires but wouldn't more stopping power, (larger pads and rotors) equate to being able to lock them up faster? ...and I don't like the "locking up" argument people and I am using as the object is to NOT lock them up, just to slow down the rotation of the wheel/tire faster and in less distance. If it is all about the tire then sports cars should have huge tires and tiny, tiny brakes to save unsprung weight, no? (AGAIN , I am talking about road use not race/ track day cars, where the object is to not slow down.)

Is it just me who values stopping power more than outright speed ability on a road car? I am not looking for an argument, just an answer to my question which makes sense to me. I mean if it is just about tire to road, then for one stop a set of pads made out of wood will work like a good brake pad...but I doubt that is true.

VClassics
VClassics Reader
7/6/16 7:17 p.m.

Ditto on the stainless hoses. Pad material does matter a lot -- I've had excellent luck with EBC "Yellowstuff" pads when I can find them, and their "Greenstuff" is also very good. They are fairly low-dust, not hard on rotors, long-wearing, and you'll definitely notice the difference compared to so-called organic pads.

Gary
Gary Dork
7/6/16 9:23 p.m.

In reply to VClassics:

Good to hear from you Phil after an extended hiatus! Don't hear much from the old-timers on this forum anymore.

NOHOME
NOHOME PowerDork
7/7/16 9:07 a.m.

"Weakest link" in the friction chain situation.

The OP wants on-time accident avoidance stopping improvement.

I would add tire friction until the brakes no longer lock up. Probably where I would stop.

If more negative acceleration is wanted,then add more lever (bigger disc) and force (hydraulics, pad size and material and brake pedal) to the brakes.

If you want to stop repeatedly at max rate, add cooling and ma$$ that shed$ heat.

Dashpot
Dashpot Reader
7/7/16 9:49 a.m.
maseratiguy wrote: @Rupert, Yes with SS lines and as said all things being equal. So if it is all about tire to road friction and not pad size/rotor size, Why does pad material matter? Why fit bigger brakes, just for heat dissipation? I know my stock brakes can lock up my tires but wouldn't more stopping power, (larger pads and rotors) equate to being able to lock them up faster? ...and I don't like the "locking up" argument people and I am using as the object is to NOT lock them up, just to slow down the rotation of the wheel/tire faster and in less distance. If it is all about the tire then sports cars should have huge tires and tiny, tiny brakes to save unsprung weight, no? (AGAIN , I am talking about road use not race/ track day cars, where the object is to not slow down.) Is it just me who values stopping power more than outright speed ability on a road car? I am not looking for an argument, just an answer to my question which makes sense to me. I mean if it is just about tire to road, then for one stop a set of pads made out of wood will work like a good brake pad...but I doubt that is true.

Are you asking "How can I better achieve threshold braking in an emergency situation?" or are you asking "Will I get better performance out of a big brake kit?"

If the former is it, optimize the condition of your current system. Fluid, caliper sliders, pistons/seals, flex hoses, etc should all be up to snuff. Do a little research on aftermarket pads (the actual specs - friction coefficients & heat ranges). You can change the feel a lot with just new pads & rotors.

If it's the latter - sure, it can be better. You'll want to make sure there are no surprises with wheel fitment, parking brake issues or stuff like that with any aftermarket kit. You may or may not get shorter braking distances, but you will get less fade/better repeatability.

What car?

Tom1200
Tom1200 Reader
7/7/16 9:17 p.m.

I have to say for me the worst theory ever is the "if you can lock the tires bigger brakes won't make you stop faster" if I jam a steel rod in my bicycle spokes the tire will lock up.

My fathers Plymouth Scamp had drum brakes and panic stops were a case of you'd get about 40% of the tires grip then pushing pushing pushing then wham lock up.

This is more than a case of modulation; 40% takes 50lbs of pedal pressure and then you get no extra stopping power until 120lbs of pedal pressure until the wheels lock. This is akin to driving a car with cold race pads.

The problem is mostly on lower end cars that are under braked to begin with.

@maseratiguy I also value really powerful brakes, especially on a road car, as it gives you another option when trying to avoid an accident. Coming from motorcycles (both daily driving and racing) the one thing I noticed about automobiles is they had no where near the stopping power of sport bikes. Obviously bikes don't turn as quickly as a bike so the brakes are important in traffic. If you look at modern SUVs many of them have very short stopping distances, wide tires and brakes intended to handle towing.

Tom

maseratiguy
maseratiguy Reader
7/7/16 10:28 p.m.

Hi, Dashpot, Tom1200 & others, didn't want to quote everyone. But my question is just a general question, I drive a 1983 Alfa Spider and am quite happy with the brakes. I was just reading another post on another chat board where the question came up. It doesn't sound quite right to me that larger brakes do not equal better stopping as long as your current brakes can lock up the tires.

Well eventually all brakes can lock up your tires and locking up your tires shouldn't be the goal. Shouldn't it be "drawing down your speed in the shortest distance without locking up your tires"? ..and wouldn't larger brakes, (rotors and pads) be able to slow down the rotational mass of a wheel tire faster? Especially considering as ion my case and many with classics we have up sized the tires somewhat? (mine is only 185/70/14 but that is still slightly bigger than what was original to the car I believe). So, yes, I am just interested theoretically if bigger brakes do slow the car down faster...and if not as some argue why not? (I haven't accepted the,"if you can lock the tires bigger brakes won't make you stop faster" argument.

Tom1200
Tom1200 Reader
7/8/16 11:33 p.m.

If I remember correctly the stock tire is 165/70 so I would think that installing calipers and or a larger rotor would offer an improvement.

What a lot of the Datsun 1200 guys do on street cars is install rotors an calipers from the heavier 310 (they weigh about 400lbs more) they have larger pads and slightly larger rotors. They also go to a more aggressive brake shoe for the rear.

1200s had 155-12s originally and most cars are running 185/60-13s or bigger. I did my first season racing with the stock brakes and upgraded pads. Even with the stock 68hp motor I found the brakes woefully inadequate even though the car would do all of 85mph. I could only imagine if you were on the expressway and someone punted a wall and bounced back in front of you in heavy traffic.

So my answer is yes with the wider tires I think there would be an advantage. Do brakes from something like a 164 or other larger Alfa bolt on. Wheels are essentially 4 giant flywheels (an object in motion) and to my mind having more leverage to wind the tire down instantaneously is going to equate to shorter stopping distances.

Locking the tires results in dramatically longer stopping distances, I want to be able to get the car squirming around on the tires instantly in an emergency stop situation. Sure the bigger brakes won't stop the car any sooner once you get the tires on the verge of lock up but they will get to the threshold quicker. At 60 mph every tenth of a second shaved is going to be 9 feet, it's not hard to imagine gaining 18ft............how fast is the car going 18 feet from impact? 20mph? It may not be life or death but I bet the car wouldn't like very good.

My .02 naturally.

Vigo
Vigo PowerDork
7/12/16 7:00 p.m.
all things being equal as long as you can lock up the tires with a stock system larger brakes don't stop you faster.

That's correct. However, IMO actually being able to quickly and consistently get into that 'max braking' pedal pressure would probably require actual practice for the majority of drivers. Some of that is being alleviated by a lot of new cars having 'emergency braking assist' where the abs module tries to determine whether you are attempting a panic stop and then goes into full assist/abs instantly. This is good for people who can't muster the force to get full potential from the brakes, or people who don't realize that just because the fronts are in ABS doesn't mean the backs are grabbing as hard as they could be. Some combination of those two things probably applies to a huge number of drivers on the road.

If you're talking a car with no electronic assists and intended to be used mainly in competition, then modifying the brakes to make the car most easily and quickly stopped by YOU is totally valid as far as modifying pedal effort and brake balance (and heat management). Having said that, any 'dumb' non-abs/tcs/esp/etc car set up to get optimized braking done in a straight line will probably be unsafe to stab the brakes on after jerking the wheel, whereas a brand new car basically isn't. So try to be aware of all your compromises if you still plan to use the car on the street.

NOHOME
NOHOME PowerDork
7/13/16 3:11 p.m.
Tom1200 wrote: I have to say for me the worst theory ever is the "if you can lock the tires bigger brakes won't make you stop faster" if I jam a steel rod in my bicycle spokes the tire will lock up. My fathers Plymouth Scamp had drum brakes and panic stops were a case of you'd get about 40% of the tires grip then pushing pushing pushing then wham lock up. This is more than a case of modulation; 40% takes 50lbs of pedal pressure and then you get no extra stopping power until 120lbs of pedal pressure until the wheels lock. This is akin to driving a car with cold race pads. The problem is mostly on lower end cars that are under braked to begin with. @maseratiguy I also value really powerful brakes, especially on a road car, as it gives you another option when trying to avoid an accident. Coming from motorcycles (both daily driving and racing) the one thing I noticed about automobiles is they had no where near the stopping power of sport bikes. Obviously bikes don't turn as quickly as a bike so the brakes are important in traffic. If you look at modern SUVs many of them have very short stopping distances, wide tires and brakes intended to handle towing. Tom

I get your point, but if you had enough traction, the steel rod would just be snapped in half.

Tom1200
Tom1200 Reader
7/13/16 11:33 p.m.

I take you point as well but on older cars you get X level of bite and then after applying triple the pedal pressure the wheel lock in an instant. You get 40% and nothing between there and lock. My vintage MX bike did the same with stock brake shoes, modern brake shoes helped some but with modern tires the brakes are still marginal, especially in comparison to first generation of disc braked bikes and they are only 5 years newer. Remember when Vredesteins (sp) where the autocross tires. Brakes 70s cars suck in comparison to now and the tires are like comparing pneumatic tires to wooden wagon wheels. I'm not suggesting putting 6 piston Wilwoods or Brembos on the Alfa will make it stop like an F1 car but I'd bet that a moderate upgrade would shorten the stopping distances 10-20ft.

Again my .02

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