At what point are the 12" Cordoba front discs not enough?

[Kern Dog]

My 70 Charger was a 4 wheel manual drum car until I swapped in front discs from a 75 Dart in 2000. Later I switched to the 11.75 Cordoba discs. A couple of years back, I swapped in carbon metallic disc pads. In 2006 I added a rear disc kit from Doctor Diff.
The car stops great. It has a power booster and master cylinder from that 75 Dart and actually works quite well with 4 wheel discs.
So often, I see or hear about guys with 13" or larger front rotors and wonder if the bigger sizes ever get tested to actually see their value. In short, if the 12" rotors stop the car well without fading or warping the rotors, are these guys just installing huge rotors for their appearance? I'll admit that this was the motivation to switch to the rear disc brakes. Looking through the spokes of the wheels to see 10" drums just wasn't for me.

[HPP]

IMO, for a number of people, the bigger stuff is simply trendy and it fills up the bigger diameter wheels better so they go with it as part of a series of upgrades to better fit in with the current stuff theme. No different than using a 3000 stall converter or dual quad tunnel rams on a purely street driven car.  IMO, the vast majority of classic owners don't drive their vehicles hard enough or use them in a regular commute often enough to justify the 12" rotors, much less 13" or 14".

At what point do you need them? On open track days when you are cooking your 12" rotors and pads pulling down from 150 mph 5 times in 10 minutes. For autocross, they actually are not needed at all if you have a good pad on a 12" rotor as anything else is extra weight you are throwing around on a short duration,  low heat generating, transitional activity. At want point do you want them, whenever the budget allows.

[Mike DC]

I agree with the gist of what HPP just said. 

But at the same time, I think bigger brakes can offer more gains in real world conditions than they do in road tests.  Bigger brakes seem to yank the car down harder with less effort early in the stop.  In a real-world situation where the danger is mounting up rapidly you may not be fully pushing the brakes quite early enough.  IMO bigger brakes seem to help the driver err on the side of doing the stopping earlier.  In a controlled road test the driver always knows to STOMP HARD at a certain moment so this issue may be getting hidden by the testing methods.

[WHITE AND RED 69]

As someone who made the jump from 11.75" rotors to a 13" rotors with larger calipers I couldn't be happier with my choice. My old brakes were good but the current ones are better in every way. Stopping power is increased, slotted rotors get the heat out, they don't fade as quickly, quality of pad selection is way better, and I like the look. I also see myself upgrading them even further at some point. Do I need that much brake on my car, probably not but I'm glad it is there when I do need it.

I think brakes are one of the most neglected parts on old cars. Guys will install 500+ hp motors but run stock drums or single piston fronts and call it good? I'm all for fitting as much brake as possible into whatever wheels you are running and what your budget allows. I have more options with my 18" wheels but even if I swapped back to 15's I'd fit the biggest disc brakes front and rear as I could.  

And I didn't install them so I would look "cool" or to keep up with trends. I do like the look of them filling up the wheels but I installed them so my car would be safer for everyday driving. I live in a busy area with some of the worst drivers around so there is nothing scarier than having a panic stop at 60 mph and knowing that 99.9% of the cars in front of you can stop 25-50 (or more) feet before you can.

[Brass]

You can get drilled/slotted 11.75" rotors, and EBC Red/Yellow Stuff pads are available for them.  Also, from what I have gathered, it is the aggregate piston size that matters; not just how many.  White and Red, what made the bigger difference – the larger rotor or the hydroboost?  Also, I never completely understood why HP should dictate how much braking power you need.  Even a 6 cylinder car with tall gearing is capable of high speeds – it just takes longer to get there.  It would still have no problem exceeding any given speed limit.  Isn't the braking demand of a 6 cylinder car traveling at X mph the same as a 500+ HP car driving at the same speed; assuming the same weight, etc.?  I suppose if you're accelerating hard you may need to decelerate hard too – but that is just dangerous driving.  Of course better braking is always preferred/safer but I think the OP's question is a question of degree.  At what point do massive brakes become overkill for the application they are intended?

[myk]

You can get drilled/slotted 11.75" rotors, and EBC Red/Yellow Stuff pads are available for them.  Also, from what I have gathered, it is the aggregate piston size that matters; not just how many.  White and Red, what made the bigger difference – the larger rotor or the hydroboost?  Also, I never completely understood why HP should dictate how much braking power you need.  Even a 6 cylinder car with tall gearing is capable of high speeds – it just takes longer to get there.  It would still have no problem exceeding any given speed limit.  Isn't the braking demand of a 6 cylinder car traveling at X mph the same as a 500+ HP car driving at the same speed; assuming the same weight, etc.?  I suppose if you're accelerating hard you may need to decelerate hard too – but that is just dangerous driving.  Of course better braking is always preferred/safer but I think the OP's question is a question of degree.  At what point do massive brakes become overkill for the application they are intended?

You're assuming that both faster and slower cars are being driven equally.   The faster car, cars like White and Red's, are being pushed to their acceleration and handling limits and will need as much braking and suspension power they can get.  When was the last time someone took a slant 6 Mopar to an autocross, road race, or did anything with it other than drive to the grocery store or the local show and shine?  Cars that drive faster, also need to stop faster.  White and Red tracks his car, so he will need as much brake as he can get, especially when he's driving a two ton pig against much more svelte cars.  Not all cars are driven equally...

[Dino]

Oh man...you called his car a pig...now you're gonna get it.   

I don't think there's anything wrong with 12" rotors, but since I need to go from stock drums to discs and the option is there to install 13" rotors on a budget I think it's the way to go. I'll also be running hydroboost so I think the beast wil be able to stop quite nicely!

If I was running 12" rotors now, I'm not sure I'd do an upgrade, but I do tend to drive my car like it was a compact race car so it would all depend on how well the 12 inchers did the job.

[WHITE AND RED 69]

My brakes were done in many stages so each time I upgraded them I could feel major improvements. The 11.75" rotors with 4 piston calipers and drums I had on originally that ran off the stock booster were not bad. Better than stock but still not where I wanted them to be. Then the hydroboost made a huge improvement over the stock booster. Then came in the 13" Baer fronts and the improvement was even greater.

Piston size and quantity are just as important as rotor size as well. Multiple pistons at equal pressure are going to add to a more balanced clamping force over the entire area of the pad.

Like Myk said, a high horsepower car and a slant 6 are not driven equally. They may get up to the same speed but one's going to get there a lot quicker so in my mind it needs better brakes. Even though my car is driven on the street 99% of the time the extra brakes are a comforting feeling knowing they are there when I need them for that last 1% for other uses. I'm not saying that everyone needs to have 13" rotors but go with the best that fits your build and the goals with the car.  

At what point do massive brakes become overkill for the application they are intended?

That was my point mentioning high horsepower. 400+ horsepower is overkill on a street car but when you get to use all that power, you are glad you have it. Same theory for brakes. And you never hear anyone say "I wish my car had smaller brakes".

Oh man...you called his car a pig...now you're gonna get it.  

I don't think there's anything wrong with 12" rotors, but since I need to go from stock drums to discs and the option is there to install 13" rotors on a budget I think it's the way to go. I'll also be running hydroboost so I think the beast wil be able to stop quite nicely!

If I was running 12" rotors now, I'm not sure I'd do an upgrade, but I do tend to drive my car like it was a compact race car so it would all depend on how well the 12 inchers did the job.

 But it is a pig! 2 tons of fun!  

12" rotors will do the job just fine. There is nothing wrong with them, but if you are looking for an upgrade and have the wheels to fit them why not go with the biggest rotors that will fit?

[cdr]

AAHHH  I still got my manual 10in drums on 4 corners, the wife says she wont drive it until it has power disc on the front,  guess I am keepin my drum brakes.     

[Brass]

I don't think my point got across but that's okay.  For now, I still have 10" manual drums on all four corners too, and it stops adequately and true, even for gnarley Seattle traffic.  You just have to get used to them.   So l guess I never had a big-brake fetish. As long as the car stops and turns well for its intended use, acceleration is way more sexy to me.  All that being said, I am upgrading soon to the stage 2 kit from Dr Diff, and a hydroboost unit. The car is unlikely to see track time but it should give a better piece of mind.  And my girlfriend will be able to drive it now if necessary. ; )

[tan top]

My 70 Charger was a 4 wheel manual drum car until I swapped in front discs from a 75 Dart in 2000. Later I switched to the 11.75 Cordoba discs. A couple of years back, I swapped in carbon metallic disc pads. In 2006 I added a rear disc kit from Doctor Diff.
The car stops great. It has a power booster and master cylinder from that 75 Dart and actually works quite well with 4 wheel discs.
So often, I see or hear about guys with 13" or larger front rotors and wonder if the bigger sizes ever get tested to actually see their value. In short, if the 12" rotors stop the car well without fading or warping the rotors, are these guys just installing huge rotors for their appearance? I'll admit that this was the motivation to switch to the rear disc brakes. Looking through the spokes of the wheels to see 10" drums just wasn't for me.

these are some interesting videos  , ( bit long may not be for everyone ) , from the Ram Man , well worth watching  , makes a lot of sense , IMO



https://www.youtube.com/watch?v=ShEPrPs-U0s
https://www.youtube.com/watch?v=EnXfYSeEIEw
https://www.youtube.com/watch?v=2xjMEKBE5CA
https://www.youtube.com/user/THERAMMAN01/videos?shelf_id=1&sort=dd&view=0

[cdr]

My 70 Charger was a 4 wheel manual drum car until I swapped in front discs from a 75 Dart in 2000. Later I switched to the 11.75 Cordoba discs. A couple of years back, I swapped in carbon metallic disc pads. In 2006 I added a rear disc kit from Doctor Diff.
The car stops great. It has a power booster and master cylinder from that 75 Dart and actually works quite well with 4 wheel discs.
So often, I see or hear about guys with 13" or larger front rotors and wonder if the bigger sizes ever get tested to actually see their value. In short, if the 12" rotors stop the car well without fading or warping the rotors, are these guys just installing huge rotors for their appearance? I'll admit that this was the motivation to switch to the rear disc brakes. Looking through the spokes of the wheels to see 10" drums just wasn't for me.

these are some interesting videos  , ( bit long may not be for everyone ) , from the Ram Man , well worth watching  , makes a lot of sense , IMO



https://www.youtube.com/watch?v=ShEPrPs-U0s
https://www.youtube.com/watch?v=EnXfYSeEIEw
https://www.youtube.com/watch?v=2xjMEKBE5CA
https://www.youtube.com/user/THERAMMAN01/videos?shelf_id=1&sort=dd&view=0

Thanks Tan Top !!!!

[JR]

Well, I've certainly never thought to myself "Gee, these brakes work too well."

I say give me all the braking power possible. My car still has the original discs/drumb combo, and I can't wait to upgrade to bigger discs with hydroboost. As soon as I get other basics sorted out, they're on the list.

My factory brakes suck at the autocross. No braking power at all. (No booster has alot to do with it of course.) I imagine they'd be terrifying in a real panic stop.

[WHITE AND RED 69]

My 70 Charger was a 4 wheel manual drum car until I swapped in front discs from a 75 Dart in 2000. Later I switched to the 11.75 Cordoba discs. A couple of years back, I swapped in carbon metallic disc pads. In 2006 I added a rear disc kit from Doctor Diff.
The car stops great. It has a power booster and master cylinder from that 75 Dart and actually works quite well with 4 wheel discs.
So often, I see or hear about guys with 13" or larger front rotors and wonder if the bigger sizes ever get tested to actually see their value. In short, if the 12" rotors stop the car well without fading or warping the rotors, are these guys just installing huge rotors for their appearance? I'll admit that this was the motivation to switch to the rear disc brakes. Looking through the spokes of the wheels to see 10" drums just wasn't for me.

these are some interesting videos  , ( bit long may not be for everyone ) , from the Ram Man , well worth watching  , makes a lot of sense , IMO



https://www.youtube.com/watch?v=ShEPrPs-U0s
https://www.youtube.com/watch?v=EnXfYSeEIEw
https://www.youtube.com/watch?v=2xjMEKBE5CA
https://www.youtube.com/user/THERAMMAN01/videos?shelf_id=1&sort=dd&view=0

So according to him there is no other caliper/rotor combo that can out perform his setup...Yeah right! Better call up the Viper guys and tell them to throw their brakes in the garbage and swap to single piston calipers from the 70's.    I'm not here to bash the product, I'm sure it works great for an upgrade but to say that his setup will out perform a modern 14" rotor and caliper off an srt8...That's complete bullshit!

If he just said that his setup is an improvement over stock that would be fine. But to say nothing besides $5,000 setups can out perform his setup. Really??? Better call up every brake manufacturer on the planet and tell them to put a hold on those multi piston calipers.  

[tan top]

My 70 Charger was a 4 wheel manual drum car until I swapped in front discs from a 75 Dart in 2000. Later I switched to the 11.75 Cordoba discs. A couple of years back, I swapped in carbon metallic disc pads. In 2006 I added a rear disc kit from Doctor Diff.
The car stops great. It has a power booster and master cylinder from that 75 Dart and actually works quite well with 4 wheel discs.
So often, I see or hear about guys with 13" or larger front rotors and wonder if the bigger sizes ever get tested to actually see their value. In short, if the 12" rotors stop the car well without fading or warping the rotors, are these guys just installing huge rotors for their appearance? I'll admit that this was the motivation to switch to the rear disc brakes. Looking through the spokes of the wheels to see 10" drums just wasn't for me.

these are some interesting videos  , ( bit long may not be for everyone ) , from the Ram Man , well worth watching  , makes a lot of sense , IMO



https://www.youtube.com/watch?v=ShEPrPs-U0s
https://www.youtube.com/watch?v=EnXfYSeEIEw
https://www.youtube.com/watch?v=2xjMEKBE5CA
https://www.youtube.com/user/THERAMMAN01/videos?shelf_id=1&sort=dd&view=0

So according to him there is no other caliper/rotor combo that can out perform his setup...Yeah right! Better call up the Viper guys and tell them to throw their brakes in the garbage and swap to single piston calipers from the 70's.    I'm not here to bash the product, I'm sure it works great for an upgrade but to say that his setup will out perform a modern 14" rotor and caliper off an srt8...That's complete bullshit!

If he just said that his setup is an improvement over stock that would be fine. But to say nothing besides $5,000 setups can out perform his setup. Really??? Better call up every brake manufacturer on the planet and tell them to put a hold on those multi piston calipers.  

    yeah makes you think ,   recon if you have some big rotors  4 or  6 piston calipers & hydroboost , there wont be much , if anything beating that .... maybe .....

for me personally I would rather stick with an assortment of factory hardware  for a disc set up ,  least I know , there will always be OEM type service parts available , pistons seals  calipers  rotors etc  ,  do the aftermarket brake companies sell these parts separate ? & or will they even  be around in 20 years time    yeah I know i'm going a little off track ,    I over think stuff ,      ,

[Kern Dog]

Way back, Rick Ehrenberg did a Viper caliper swap in the 69 Valiant "Green Brick". Just for laughs, he installed just ONE Viper caliper and left the other side intact with a 2,75 single piston iron caliper. The car stopped straight, time after time. While not exactly scientific, it may suggest that a well sorted stock setup is hard to beat without spending a bunch of cash!
I am starting to think that unless I run the car hard at the road course, the current setup should be fine. Those guys with 13" and larger rotors, multi-piston calipers and such remind me a bit of the guys with aftermarket front suspension kits. They brag about how much better the car performs but my question is this: How was the car equipped before swapping in that $4500 front end kit? Was the stock setup you removed ever rebuilt and upgraded with HD parts or just 48 year old worn out stuff? That isn't a fair comparison.

[tan top]

Way back, Rick Ehrenberg did a Viper caliper swap in the 69 Valiant "Green Brick". Just for laughs, he installed just ONE Viper caliper and left the other side intact with a 2,75 single piston iron caliper. The car stopped straight, time after time. While not exactly scientific, it may suggest that a well sorted stock setup is hard to beat without spending a bunch of cash!
I am starting to think that unless I run the car hard at the road course, the current setup should be fine. Those guys with 13" and larger rotors, multi-piston calipers and such remind me a bit of the guys with aftermarket front suspension kits. They brag about how much better the car performs but my question is this: How was the car equipped before swapping in that $4500 front end kit? Was the stock setup you removed ever rebuilt and upgraded with HD parts or just 48 year old worn out stuff? That isn't a fair comparison.

yes I remember that article !  ,   yeah  I've thought that too !  makes you wonder !!
would be good/ interesting a real world  un biased  testing  on one mopar  ,   all  the aftermarket brake set ups , with  the best combination of OEM charysler disc stuff from the Ramman    doubt it will ever happen  , all these hi dollar brake companies might not like the out come .  braking performance per cost  
sticking with OEM Disc type combinations makes sense , for a street car , only big gain I see is fitting a hydroboot .  but what do I know  , I still have manual , HD 11 inch drums at all four corners   , so any disc brake swap is going to be better   maybe ...........





** side note **  no way am I associated with the Ramman in any shape or form ,. just  making  the best Disc combination of the factory hardware makes a lot of sense imo

[Derwud]

Well time to dive in..

Our cars will stop with a 10 inch Rotor and a single piston caliper, real hard a few times. Our cars will stop with 13 inch rotors and 6 piston calipers, real hard a lot of times.

What you want to do with your car and how much cash in your wallet will dictate how much rotor and caliper you have.

Had a client that took his Maserati to two track days... 5 thousand dollars (New Rotors and Pads) later, I had to ask, "did you have fun?" He said yes, until today!!

[HPP]

Something just touched on but not in great detail is pad compounds, cooling, and disc thickness and their impacts on the systems compatibility with  specific activities.  One of the advantages to going with an aftermarket system with  significant  support is the variety of  pad compounds out there and available for  differing applications that will change the  bite and duration of bite.  Also, duct work routing fresh air to the  rotor and the thickness of the rotor and its ability to act as a heat sink can also be factors in how well the combination will work during repeated applications and heavy use or if it is  simly adding rotational mass for minimal benefit.

Depending on the application, a 12"x1.25" rotor may produce better braking than a 13"x.875" rotor over multiple stops, or it may be an anchor on acceleration.

[Mike DC]

  
I disagree that small drums stop just as well as bigger discs.  Even on the first stop the drums will typically take more distance IMO.  

I know I've read at least one road test over the years that bore this out.  

[ws23rt]

 
I disagree that small drums stop just as well as bigger discs.  Even on the first stop the drums will typically take more distance IMO.  

I know I've read at least one road test over the years that bore this out.  

I agree.   Drums have surface area in their favor but that is not the big picture.

In 1970 I was driving my new superbee. I was going too fast. (130+).  A driver in the right lane pulled left as I got near to pass someone in the right lane. He was doing about 60mph.
I hit the brakes and lost maybe 30mph but that was all. I put both feet on the brake pedal and pushed all I had.  It was like I had no brakes at that point.
I passed that guy on the left shoulder with both feet braking at maybe 90mph and it felt like I was coasting down in speed.
When my drums cooled all seemed fine with my brakes again.

Their is a reason that few cars come with drum brakes these days.

[Highbanked Hauler]

 
I disagree that small drums stop just as well as bigger discs.  Even on the first stop the drums will typically take more distance IMO.  

I know I've read at least one road test over the years that bore this out.  

I agree.   Drums have surface area in their favor but that is not the big picture.

In 1970 I was driving my new superbee. I was going too fast. (130+).  A driver in the right lane pulled left as I got near to pass someone in the right lane. He was doing about 60mph.
I hit the brakes and lost maybe 30mph but that was all. I put both feet on the brake pedal and pushed all I had.  It was like I had no brakes at that point.
I passed that guy on the left shoulder with both feet braking at maybe 90mph and it felt like I was coasting down in speed.
When my drums cooled all seemed fine with my brakes again.

Their is a reason that few cars come with drum brakes these days.

  Having driven a similar  car in that era I do feel the the quality of  the brake shoe material has greatly improved over what it was then. It was 4 wheel drum and  At present I have manual 12 in Cordoba fronts and master cyl. and original 11 in drums in the rear and I am seriously thinking of adding a power booster to it as my Cummins stops easier than the Charger..

[ht4spd307]

isn't it funny that a semi trailer of modern day still uses drum brakes all round

[myk]

isn't it funny that a semi trailer of modern day still uses drum brakes all round

Ive been told that customers that order semis and their trailers do so with drums because of cost, as in they're much cheaper than disc brake systems.  This includes parts, labor, downtime, etc.  Also, the cost of retrofitting older trucks and trailers to disc systems is cost prohibitive.  It would seem that the decision to buy drums over discs isn't for performance, rather cost...

[Mike DC]

 
I remember hearing that the raw surface (clamping) area of drums makes them better for semis.  Semis are heavy as hell.  They don't do enough rapid & hard stops to worry as much about fade. They also use their gears to hold down speeds a lot.  But they need a ton of clamping power when they do use the brakes.  


Aircraft weigh less for their size than road vehicles.  So they don't need the huge clamping forces quite as much in proportion.  But slowing down from very high speeds is the norm so the fading issue is still a big one.  On a car you can feel drums fading during the course of a single long stop if you're slowing down from 100+ mph.    


As for sporty/powerful cars?  They need discs.  People are keeping drums because of either originality, cost cutting, or maybe weight cutting.  The reason is not brake performance.  

[flyinlow]

I have 11.75F/11.25R which was the biggest that would fit with 15 wheels. Hawk pads on good slotted rotors helped. Now that I have 18 wheels and modern tires I start to think about bigger front brakes. I can already lock up the wheels so bigger brakes would not necessarily make shorter stops, but I think they would give me better brake control.