Wilwood brake upgrade pros cons?

I get into this discussion with the MGB guys that stick a V6 or V8 into and then claim they NEED a big brake kit.

I ask them if they plan to be driving at illegal speeds all the time on the street. They say no.  I ask if they will be doing some sort of road racing competition where the higher terminal speeds might require better heat management.  Also no.  I ask if they plan on racing down a mountain road and might over heat their brakes by the bottom. Another no.

It boils down to them just wanting a butch big brake set up for bragging rights but not wanting to just say that. 

Be honest when assessing the capabilities of your existing system and take steps, if necessary, to address any true shortcomings, and if there aren't any, just man up and say that you want the big brakes because you think they will look cool and you want that.

Here is my point in pretty picture form.

All brakes provide more braking torque as a response to more pressure provided by your foot.  This is an extremely simplified chart based on a single coefficient of friction.  When the lines reach 10 on the chart, that is indicative of lockup.   Once the lines reach that top level, you're squealin' rubber.  Drums tend to reach a point of infinite effect (lockup) sooner... thereby removing that area above the curve of effective braking without lockup.  On the extreme side, I included the yellow line which simulates what it would be like if you added a cog instead of brakes.  They are either open or locked.  Not very effective braking.

As to my point... all of these hypothetical braking systems can lock up the tires.  Their peak torque is not in question.  Being able to modulate braking in the those areas between effective brake torque and lockup is where the disc brakes (and larger radii having an even greater modulation control) have the advantage.  I was simply trying to demonstrate that because a braking system's sole property is that it CAN lock up the tires doesn't mean that it has an optimal braking system.

This isn't really in question, it's math and physics.

In reply to Curtis73 (Forum Supporter) :

Source for graph?

I've been a brake systems engineer for 27 years now and have never seen data supporting this behavior from drum or disc brakes. 

In reply to AngryCorvair (Forum Supporter) :

I can't speak for the data but I can speak to practical experience of brakes performing this way on both my Datsun with stock brakes and one of my vintage motocross bikes.

AngryCorvair (Forum Supporter) said:

In reply to Curtis73 (Forum Supporter) :

Source for graph?

I've been a brake systems engineer for 27 years now and have never seen data supporting this behavior from drum or disc brakes. 

Source for graph is my computer and MSWord > insert > graphs and charts.  It's simply a demonstrative depiction of what I was saying..

My brain's source is Milliken's Race Car Vehicle Dynamics and 30+ years of driveline engineering for custom and hot rod shops.

Think of it this way.  Let's say you put a brake disc and hub on a lathe.  Now using channel locks, grip the hub with increasing pressure. (drum brakes) Modulating between grip and slip will be very difficult to control.  You might slow the lathe to 40% of its speed before the pliers lock up and stop everything.

Now use the pliers to grip half way out the radius of the disc.  The mechanical advantage is greater given the radius (although required pressure will be greater... within a braking system, as you know this is a simple function of master/slave diameters and pedal M.A.)   Given your greater radius, your ability to modulate brake hub torque is increased.  You might be able to slow the rotor to 20% before additional friction causes it to stop.

Now use the pliers to grip near the circumference of the disc.  Now you might be able to slow the disc to 15% before it locks up.

Obviously, the greater radius is able to exert greater braking torque as seen at the hub from simple physics, and we're assuming a fixed tire/surface friction - but as we've mentioned, it's not simply about how much peak torque you can offer.  If that were the case, any system which could overcome the tire's friction (lock em up) would be equally adequate.  It's what can be done prior to lockup that (in part) separates good braking from crappy braking.

This has been common knowledge to me since forever.  I'm willing to debate as I could be wrong, but it's so known to me that I don't know how else to describe it.

In reply to Curtis73 (Forum Supporter) :

Everything I've read on mountain biking forums agrees with your assessment, as does my own experience on bikes.  Bigger rotors modulate better.  I think it's partly because the linear speed of the rotor past the pads is higher.  If that's actually the case, then all other things kept equal, taller tires (less rpm at a given road speed) would make a given diameter rotor act effectively smaller. 

rslifkin said:

In reply to Curtis73 (Forum Supporter) :

Everything I've read on mountain biking forums agrees with your assessment, as does my own experience on bikes.  Bigger rotors modulate better.  I think it's partly because the linear speed of the rotor past the pads is higher.  If that's actually the case, then all other things kept equal, taller tires (less rpm at a given road speed) would make a given diameter rotor act effectively smaller.

Velocity has a big part in it.

Another way to think of it:  (just an example, don't try this at home).  Take a 5hp Briggs and send it to a 10:1 gearbox with a 20" flywheel on it.  It's really easy to affect engine RPM by gripping the outside of the flywheel and providing resistance.  Now replace the flywheel with a 10" piece.  It will be much harder to modulate your grip on the flywheel to achieve those same controllable RPMs before you just stop the engine entirely.

Tom1200 said:

In reply to AngryCorvair (Forum Supporter) :

I can't speak for the data but I can speak to practical experience of brakes performing this way on both my Datsun with stock brakes and one of my vintage motocross bikes.

And anyone who's driven an AMC Hornet from the 70s with drum brakes probably knows this all too well.  Coming to a stoplight is a scary thing.  You get linear brake torque up until a very unpredictable point and then the self-actuating nature of the drums locks them up without warning.  The effective range of brake torque in my 73 was hideously awful.  You would get enough braking for mildly aggressive stops but one pound more on the brake pedal just locked them up like a lock pin engaged on the axle.

I know that brakes are sometimes referred to as anchors, but I don't believe anyone has spoken about weight. Cast iron calipers vs aluminum?

Curtis73 (Forum Supporter) said:

AngryCorvair (Forum Supporter) said:

In reply to Curtis73 (Forum Supporter) :

Source for graph?

I've been a brake systems engineer for 27 years now and have never seen data supporting this behavior from drum or disc brakes. 

Source for graph is my computer and MSWord > insert > graphs and charts.  It's simply a demonstrative depiction of what I was saying..

My brain's source is Milliken's Race Car Vehicle Dynamics and 30+ years of driveline engineering for custom and hot rod shops.

Think of it this way.  Let's say you put a brake disc and hub on a lathe.  Now using channel locks, grip the hub with increasing pressure. (drum brakes) Modulating between grip and slip will be very difficult to control.  You might slow the lathe to 40% of its speed before the pliers lock up and stop everything.

Now use the pliers to grip half way out the radius of the disc.  The mechanical advantage is greater given the radius (although required pressure will be greater...

no, as you increase distance from center of rotation (ie effective radius), the required clamping force (= pressure x area) *decreases*. 

and that's why putting bigger calipers and rotors on the front of the OP's car without making any other changes is directionally incorrect. 

within a braking system, as you know this is a simple function of master/slave diameters and pedal M.A.)   Given your greater radius, your ability to modulate brake hub torque is increased.  You might be able to slow the rotor to 20% before additional friction causes it to stop.

Now use the pliers to grip near the circumference of the disc.  Now you might be able to slow the disc to 15% before it locks up.

Obviously, the greater radius is able to exert greater braking torque as seen at the hub from simple physics, and we're assuming a fixed tire/surface friction - but as we've mentioned, it's not simply about how much peak torque you can offer.  If that were the case, any system which could overcome the tire's friction (lock em up) would be equally adequate.  It's what can be done prior to lockup that (in part) separates good braking from crappy braking.

This has been common knowledge to me since forever.  I'm willing to debate as I could be wrong, but it's so known to me that I don't know how else to describe it.

I have designed and specified the brake systems that are on millions (literally, millions) of vehicles produced since 1996. If I was wrong, we'd know.

Bicycles and motorcycles are poor examples because front and rear brakes are modulated independently.

Curtis, you've got big rotor and small rotor juxtaposed on your graph.  I won't debate the shape of the traces because they're not traces of real data. They serve to illustrate a concept, and in that they do have some value.

the specific example posed by the OP isn't a clean sheet design. He's already got a system (pedal, booster (?), master, front calipers and rotors and pads and tires, rear rotors and calipers and pads and tires).

Now, do we agree that the lockup deceleration due to the front brakes is governed by the front tires? (ie the brakes generate enough force to lock the tires)

and do we agree that the front tires have not changed?

ok, yes and yes, good.

Increasing front caliper piston area by 20% means that the front brake locking pressure will be decreased by 20%. If the goal is to brake up to just an RCH before front lockup, and there are no other changes made to the system, then the rears will be doing 20% less work because they're getting 20% less pressure.

So the total vehicle deceleration after the change will be:

[100% of what the fronts were doing before the change (because tire-limited)]

plus

[80% of what the rears were doing before the change (because 20% less pressure)]

So, less overall deceleration capability. Is that good for a race car? Probably not.

and because the total vehicle deceleration is lower, the total weight transfer in braking is lower, and now the front tires have less normal force available to use at turn-in. Is that good for a race car? Probably not.

now, 20% less hydraulic pressure means 20% less pedal force.

and 20% larger caliper piston area means 20% more fluid volume, which means 20% longer pedal travel.

so now we have to define what we mean by "easier to modulate".  Do we modulate by force, or by travel? Hint: it's a little of both, and what is rated perfect by one driver might be rated dogE36 M3 by another. Pedal feel is the only part of brake system design that is subjective rather than objective.

still, the OP stated:

Compared to stock the wilwood piston area is about 20% larger.  What will this mean in terms of pedal feel?  Stopping ability?  Will the stock proportioning be messed up?

and I've pretty clearly framed my responses to address those questions.

Maybe not the OPs intention, but this is a good read. I'm trying to figure out the brake system on my Exocet, it's fairly lock up happy, so this is interesting....

Excuse the ignorance, but what is "RCH"? 

Drum brakes offer the highest brake torque per size.  They are also highly nonlinear and have cooling issues.

Linearity and cooling are why there was a push to disk brakes in the 50s and 60s.

As a driver I am not interested in locking the brakes up, I'm interested in slowing down effectively and controllably over a range of temperatures.

Pete. (l33t FS) said:

Drum brakes offer the highest brake torque per size.  They are also highly nonlinear and have cooling issues.

 

Linearity and cooling are why there was a push to disk brakes in the 50s and 60s.

 

As a driver I am not interested in locking the brakes up, I'm interested in slowing down effectively and controllably over a range of temperatures.

This is exactly what I was saying.

My point was not to argue all of the super fine points, it was to refute Corvair's assertion that simply having enough braking to lock the wheels was incorrect.  If you can only get to about 50% of linear braking before you get to lockup, it's not as good as braking that can modulate that area between 50-100%

And I stand by my assertion.  If you have tiny rotors, yes, they require more energy to exert the same torque at the hub than larger rotors, but they also reduce the effective range of brake torque that they can apply prior to "spiking" and providing lockup.

To the OP's original question, the way I understood it was not "I want to mix and match master/slave sizes," it was "I want to install a Wilwood piece that others have already tried on my vehicle and already takes that engineering into consideration."  I may have misread the post.  I wasn't even really replying to his post, I was just clearing up what could have been a misunderstanding when you asserted that if you can lock them up, your braking is already the best it can be.

Let me rephrase it this way.  Let's say (just using round, simplified numbers that aren't real) that for a given max pedal pressure (and therefore brake pressure), a fixed coefficient of friction between the tires and the ground, let's assume that your tires will lock up at 90% of peak braking force.  Drums might provide a linear braking torque up to 50% of peak before their self-actuating nature creates a spike in brake torque that is no longer linear with braking pressure and the tires stop.  Small rotors may reach 70% before this non-linearity occurs and the tires stop.  Large rotors might reach 85% before this non-linearity occurs and the tires stop.

As you increase the rotor diameter, (and therefore radius of where the friction occurs) you are increasing the mechanical advantage that your brake friction has on the hub, therefore increasing the control you have on the difference between braking and lockup.  

It's the same physics that causes you to get whacked in the face when you step on the business end of a rake, but not when you step on the spade of a shovel.  The fulcrums are in different places.  Try modulating foot pressure while stepping on a rake and controlling the height of the handle.  Not easily done.  Easier to do with a shovel.

captdownshift (Forum Supporter) said:

Switch to R4E pads unless the car sees primarily street use. The R4S is a good street pad and autocross pad, but it's not stellar for HPDE even on something that's feather light. 

They make a R4 pad that's for racing. That's what they recommended to me for HDPE. 
 

Here's the description of their pad compounds:

https://www.porterfield-brakes.com/manufacturers/shop/Porterfield%20Brakes.html

Awesome discussion, and truthfully (OP here...) I'm not sure that I was asking the questions that I actually needed to be answered.

I'm having an issue with heat at HPDE.  I'm not racing.  I'm certainly not a good enough driver to achieve maximum braking without lockup.  I'm just trying to gain some confidence in the brakes, and thereby maybe push a little harder - but ultimately, learn.  I was looking at the Wilwood's as a way to achieve "better braking" since that's what I've seen other Datsun people (510 folks, multiple vendors, etc).  Its a larger and thicker rotor, and the calipers are aluminum - so its got to be able to deal with heat "better" - was my thought process.  Then I was asking, well, what's the pro's and con's here?  

Not sure if its relevant, but other facts about my situation:  yes, the brakes are boosted.  I actually don't know if I can lock the tires up.  I simply haven't tried.  Is that stupid?  I can brake, hard, for sure.  On the street I have some balloon tires, 205/70/14's I think, and for HPDE I switch to some spec miata sized Nitto NT05's on 15 inch wheels.  For the heat issue, so far, I've replaced both front calipers and switched to ATE fluid.  I also opened up a small hole in the air dam.  

Next steps: open a bigger hole, rig some kind of ducting, and remove the dust shields from the front brakes.  Then see.

mikeatrpi said:

I actually don't know if I can lock the tires up.  I simply haven't tried.  Is that stupid?  I can brake, hard, for sure.

it's not stupid, it just means you don't know the limits of your system yet. With experience and confidence you'll get there.

 On the street I have some balloon tires, 205/70/14's I think, and for HPDE I switch to some spec miata sized Nitto NT05's on 15 inch wheels.

important question: will the wilwoods fit inside the 14" rims? Or are you going to 15" on the street?

  Next steps: open a bigger hole, rig some kind of ducting, and remove the dust shields from the front brakes.  Then see.

You're on the right track. keep the shields. They provide a convenient place to attach ducting. Remember the vanes in the rotor act like a pump, moving air from center to circumference, so you want the ducted air to hit the back of the hub area.

Heat management will mostly come down to two things:  thermal capacity and cooling.

You can gain thermal capacity with mass (bigger rotors), and better materials (pads, brake fluid).  Cooling will improve from proper ducting, and aluminum calipers will not retain heat like a cast iron caliper.

I would start with better fluid and pads.  Castrol SRF or Motul RBF are both superior to ATE in wet and dry boiling points.

Pads are a lot like tires... people like what they like.  The trick is finding a pad that works for you.  Usually a street or 'dual purpose' pad isn't going to cut it for faster HPDE use... ie., once you're past 'touring speeds'.  I would suggest looking at the lower end of the race pad spectrum.  I have been very happy with G-Loc pads on our Miata, though I do swap pads for the rare occasions when it's street driven, 'cause the race pads are awful on the street.

Some home made ducting should be your next step.

Also, remember that while you can usually make stock brakes work on the track, the more you ask of them, the more they will consume parts... upgrading may not only offer more performance, but also less maintenance and cheaper, longer lasting consumeables.

In reply to mikeatrpi :

How big are the existing holes? The ones on my Datsun air dam were 3" diameter.

AngryCorvair (Forum Supporter) said:

Bicycles and motorcycles are poor examples because front and rear brakes are modulated independently.

Curtis, you've got big rotor and small rotor juxtaposed on your graph.  I won't debate the shape of the traces because they're not traces of real data. They serve to illustrate a concept, and in that they do have some value.

the specific example posed by the OP isn't a clean sheet design. He's already got a system (pedal, booster (?), master, front calipers and rotors and pads and tires, rear rotors and calipers and pads and tires).

Now, do we agree that the lockup deceleration due to the front brakes is governed by the front tires? (ie the brakes generate enough force to lock the tires)

and do we agree that the front tires have not changed?

ok, yes and yes, good.

Increasing front caliper piston area by 20% means that the front brake locking pressure will be decreased by 20%. If the goal is to brake up to just an RCH before front lockup, and there are no other changes made to the system, then the rears will be doing 20% less work because they're getting 20% less pressure.

So the total vehicle deceleration after the change will be:

[100% of what the fronts were doing before the change (because tire-limited)]

plus

[80% of what the rears were doing before the change (because 20% less pressure)]

So, less overall deceleration capability. Is that good for a race car? Probably not.

and because the total vehicle deceleration is lower, the total weight transfer in braking is lower, and now the front tires have less normal force available to use at turn-in. Is that good for a race car? Probably not.

now, 20% less hydraulic pressure means 20% less pedal force.

and 20% larger caliper piston area means 20% more fluid volume, which means 20% longer pedal travel.

so now we have to define what we mean by "easier to modulate".  Do we modulate by force, or by travel? Hint: it's a little of both, and what is rated perfect by one driver might be rated dogE36 M3 by another. Pedal feel is the only part of brake system design that is subjective rather than objective.

still, the OP stated:

Compared to stock the wilwood piston area is about 20% larger.  What will this mean in terms of pedal feel?  Stopping ability?  Will the stock proportioning be messed up?

and I've pretty clearly framed my responses to address those questions.

Ok, so increasing the front caliper piston area by itself doesn't help, but if we also changed the pressure balance (more pressure to the rear brakes) and added stickier tires, we'd get more decel per psi.  Is that right? 

accordionfolder said:

 

 

Excuse the ignorance, but what is "RCH"? 

.0015" - .002", roughly

Uncle David (Forum Supporter) said:

accordionfolder said:

 

 

Excuse the ignorance, but what is "RCH"? 

.0015" - .002", roughly

Still slightly confused I googled it. Lol, wtf. I wasn't ready - but now I know!

It's a standard unit of precise measurement in the automotive industry.

In reply to wawazat :

Do you know that the abbreviation stands for??? Because it's quite off color if what I've read was correct! 

Rodan said:

Heat management will mostly come down to two things:  thermal capacity and cooling.

You can gain thermal capacity with mass (bigger rotors), and better materials (pads, brake fluid).  Cooling will improve from proper ducting, and aluminum calipers will not retain heat like a cast iron caliper.

I would start with better fluid and pads.  Castrol SRF or Motul RBF are both superior to ATE in wet and dry boiling points.

Pads are a lot like tires... people like what they like.  The trick is finding a pad that works for you.  Usually a street or 'dual purpose' pad isn't going to cut it for faster HPDE use... ie., once you're past 'touring speeds'.  I would suggest looking at the lower end of the race pad spectrum.  I have been very happy with G-Loc pads on our Miata, though I do swap pads for the rare occasions when it's street driven, 'cause the race pads are awful on the street.

Some home made ducting should be your next step.

Also, remember that while you can usually make stock brakes work on the track, the more you ask of them, the more they will consume parts... upgrading may not only offer more performance, but also less maintenance and cheaper, longer lasting consumeables.

Not to correct, merely to add.  Heat cooling can be improved not merely by ducting cool air but also by the wheels .  Heat is lost not merely by airflow but also by radiation. An open wheel will allow a lot more radiation than Steelies.  
   It's hard to buy a set of pads and not "like" them. We tend to work around shortcomings of our decisions. Leaving them in place because there is plenty of pad left. Be willing to buy several different sets and swap them after each track session to see not only what feels good but what yields faster laps.  
Then swap them back in place to ensure it's actually the pads and not just better track position/ conditions/ tires going off etc.