This may be a little long winded but im a mechanical engineer and this has always bothered me. can anyone explain this to me? Every magazine article that i read talks about upgrading brakes (BIG Reds, blah blah etc..) i have always been told that maximum breaking is with the tires on the threshold of lock-up (locked-up tires increase stopping distance) if this is the case then, and stock brakes are capable of locking up tires bigger brakes can not stop the car any quicker, they can only decrease the effort required to stop the car. stopping distance is only effected by weight, and grip, and larger breaks will add more weight (unsprung) and increase stopping distance! Brake Fade is a seperate issue and i will concede this, its just every article i read always talks about the increadable new stopping power. AM I WRONG?

For a street car you are so right, for a track car the brake fading issue is important. As long as your brakes are in top condition leave em alone. If you want to change something try changing the pads compound.

Geoff

I upgraded my brakes with my 5 lug conversion, but what I mainly did was have vented rotors, which will help for track. My main reason for wanting to upgrade brakes is because my stock calipers just where not cutting it, I rebuilt them and they would not stop worth beans.. Now I put a new 19mm m/c and a "t" fitting for the proportioning valve.

If your car is a street car, Just get some good expensive pads (unfortunately you get what you pay for..) a good bleeding job, make sure everything is in tip top condition (this is your safety and the safety of everyone else on the road where talking about..) and you should be fine.


PS. Andyrew's post.. too lazy to swich comps

You're right
Bigger brakes are only needed when you have encounter fading problems
Bigger rotors/calipers can handle the repeated hight temps better
And they'll give you more bragging rights

cheers,

Jeroen

Bigger brakes help recover from fade quicker, but you're right, they don't stop you any sooner. Thats why I still run stock calipers but with Cool Carbon pads.

Like everything else with these cars-it depends on what you what to do with it.

Paul

Consider these factors

1. Excessive braking, brake fade, and heat buildup. (bigger rotors and calipers, will help shed more heat).

2. Increased weight due to
a. Bigger engine (ala flat-6)

b. heavier chassis (steel flares)

c. Bigger wheels and tires

3. Braking from higher speed then normal street speeds (i.e. racing)

Thanks for the input guys (i have 911 suspension with vented rotors) but im tired of reading articles about someone installed xyz brakes and now their car stops in half the distance????

Also...many of us are running seriously upgraded tires. (For instance modern 205/50 DOT-R compound stuff vs. the original 165/82 fossils our cars were designed for). So, we can "use" the extra braking power.

It totally cracks me up to see all the the ricers and even the German "tuner" crowd who put the $3000 mondo brakes on their street cars that rarely see more than 50-70mph with our LA traffic. Maybe they need bigger brakes cuz of the 500lbs of stereo gear in the trunk???

Yep. Whut they said.

P.S. Welcome to the board!

-Rusty

A lot of people just repeat what the next guy says without even thinking for one second. And be honest, what would you say to your friends after a muchos-dollares brake upgrade?

IMHO a lot of performance claims are sent into the world just for one reason and that is someone making $$$.

My personal experience: new brake lines (OEM), 19mm MC upgrade, rear brake caliper revision, Ferodo braking pads, and the car stops better than ever before!!! I can even lock the wheels (with 195/65 HR 15 Pirelli P6000). Disadvantage: brake pedal force increase compared to the original MC.

Drive that 914 YOURSELF after a brake upgrade; only then you can judge .

Yeah, I keep thinking about the same kinda thing. On my car which doesn't beat you on the street and is a plenty competent AXer running 205 sticky street tires I have no problem locking up the brakes if I want to with the stock system (except pads=Porterfield R4S). I think part of the upgrade path is a confidence boost since the stock system feels kinda funny even when in excellent condition.

With respect to brake upgrades, I'd probably get more excited about pursuing one if there were a more contemporary setup (multi-piston calipers for example) that was adaptable.

Have fun,
Kevin

This also goes back to the BMW 320i brake caliper up grade. People will always say it is an improvement, but did they run tests before and after? Hey, if I spent the money and did the work I would think and say it made a difference too. Maybe you stop shorter because you're wallet is lighter.

Now like others have said, if you add power (more engine) and weight (-6, roll cage, etc) you'll need the added brakes. But a stock 914 will stop fine with a well maintaned system.

Paul

Heh. Yeah, spending a bunch of time and money on a car has a strong placebo effect

With respect to the 320i upgrade......I just have been playing around with it.....I was running stock calipers with porterfield r4s pads front and rear. I also have a 19 mm master cylinder. brake pedal is rock hard, very easy to lock up brakes whenever I want. The problem is when driving it very hard on the track, NHIS, I was getting fade after the 3rd session. Bleed brakes, it is better but still there. During autocross, I can lock up at will. You get pretty good at guessing just where the limit is....although I corded a set of Hoosiers..... :dhead:

I picked up a set of calipers, 320I for about $35.00, rebuilt them and just through on autozone "lifetime" pads...about $25.00. My thinking was that now I have more brake area, I should have cooler brakes....Went back to NHIS, although in the rain....no fade. There was a performance difference.....I have more brake pedal travel. I am not sure that I like this. I am used to high rock hard pedal, now it is somewhat soft. The brakes do lock up, but I can modulate them right on the edge very easily... I think that my rears are going and I might have too much venting clearance on the rears.. If I pump once, I have a higher harder pedal. My next step is to get some track pads for the 320I calipers and replace the rear pads. Then we will see. I might also mount my old fronts with the porterfield pads in the rear just for fun. I also have a tilton adjustable valve for rear bias.

Is it worh it? for the $60.00 that I have into it...yes, the ability to modulate the limit is good, do I need to do something else, yes, I need to add brake ducts to cool the fronts. The jury is still out on the improvement to the rears.....HIH herb

Finally.. all my years of "drivel" about brakes is paying off.

I have argued for years that bigger wasnt better.

Bottom line is this: The stock ones work just fine for a 4cyl car (SCCA has mandated stock brakes on the production 914 race cars for 33 years).. .I think they have a clue.

Its all about the heat. Just some minor brake ducting to stock brakes and they will last 25 minutes of severe abuse.



Great thread guy's.


B

The main thing about upgrading the calipers only is that you have a larger pad utilizing the same size rotor - thus INCREASING the amount of heat you will generate and fade at temp! This would relate to a degradation of performance once you really start using them (iotw - track use). While the lager pad is comforting, it definitely hurts you when you are on your 10th lap and your rotors are red hot and useless....

just my .02

I have said the EXACT same thing to local people hanging around my shop.... all you are doing is introducing more heat into a rotor (stock) that was "spec'd" by somebody with some engineering experience.

Granted.. they where NOT "spec'd" with real sticky 205/50/15 Hoosiers in mind..LOL

Thanks.

I forgot about that one.


B

Well i have considered and almost got the 320i brakes, but after doing some research, found out that it would be really counter productive.

Just have to learn to brake less!

I was given a set of BMW caliper that came off a 914 that was club raced. He went back to stock Calipers. There was NO benefit without a vented rotor. I did not even bother to put them on the car. I just sold them to someone looking for the “hot setup”

I don't think I could lock my wheels on my 914 but then again I haven't tried and the previous owner said the brakes will need work on them pretty soon. It does seem like the brakes on my car are quite weak and require a lot of force on the pedal.

When my 74 was a street car I put in a 19mm m/c and that alone made a huge difference.
I was still running 165 tires on the street (205 R1's on the track). I used to lock up the 165's
so much the car wasn't safe to drive on the street. I can't tell you how many times I thought
I was gonna have to buy the car in front of me (I was driving it without insurance-dumbass, I
know).

The R1's didn't lock up though.

-sean

depends on where you live also. try running a stock 914 hard through the marin hills of the bay area for a couple hours. my brakes were literally smoking when I hit the 7 eleven at the bottom. this was with SS lines, 19 MM master cylinder, and PBR pads. not exactly the place you want serious fading (cliffs with no guard rail).

The biggest problem people have with the stock brakes is not maintaining or fixing them correctly on a regular basis.

This means new fluid and lines and rebuilding the stock calipers more than just once every 10 years.

What no one has done that I have seen is do a proper rebuild/repair of the stock brake setup and then immediatly do the BMW conversion and run numbers to compare the two.

When someone replaces out a system that has not been fixed properly in 5 or 10 years with the BMW conversion parts, they have no real benchmark.

this tech article doesn't expressly discuss coefficient of static vs. sliding friction but does give a good roundup of mechanical advantages of break/caliper combos:

tech article

Thanks Jeff for your comments... technical article but it substantuates many of our fellow teeners comments. master cyl. size comment is also a item i have thought about before as it only pushes fluid (although more of it) that only changes ratio of leverage and therfore does NOT increase braking capacity, it only makes it easier to reach maximun braking force. my thinking on this subject started several years ago when i mentioned that i was concidering a six conversion in my 914..... several members of our pca club stated that it was cost prohibitive as you HAD to upgrade the brakes with the six! i then asked why? my 2000 lb. car could lock up brakes as a four, adding 150 lbs. of six motor would be no different than ridding with a passenger, you are stopping weight..... brakes do not know what motor is in car, they were unable to dispute this and moved on to wine and cheese topics0

Yeah I wouldn't be surprised if the previous owner never did anything with the brakes over the 9 years he had it. I'll have to look into that.

When I purchased my 914 the calipers were stuck, rotors were warped, and the master cylinder (17 mm) was leaking. I went through the entire stock system front to rear. I never drove a stock 914 so I don't know how the brakes compare to mine. I have oversize tires & wheels with flares. After all the fresh stock brake work I couldn't reach lock up. (well by the time I did I was shitting rubber nickels) I Don't think I should skid and slid But I would like the opportunity to modulate the peddle myself. Something about that appeals to me.
I'm not an engineer. But I do consider myself a reverse engineer steming from my 20+ years in the collision business. This is my spin on things. A larger dia. tire becomes a heavier spinning force. (remember I have over size tires & wheels) It takes a more powerful equal and opposite force to stop the rotation. This can be achived in a small but effective way by increasing the volume of fluid (19 mm master cylinder) and the pad area (BMW calipers)on the stock smaller diameter rotor. For those that race and auto cross the vented rotors may help with boiling. This is a practical upgrade for a simple 5 bolt conversion or larger aftermarket 4 bolt wheel upgrade. Also didn't the 6 cyliner cars come with wider wheels and larger tires? Maybe that's why they have bigger brakes and vented rotors. When you take a small car like ours and start adding cages, coolers, and sound systems etc. you may want to consider increasing the diameter of the rotor when increasing wheel and tire diameters. Hence the big rotor, big brake sales pitch. The applied leverage will increase considerably. Light weight wheels will help but the increased diameter will still effect the leverage. Ok Start the flames.

No flames here, just other observations!
Your comments have merit.

My setup on my 2.0- stock rotors, calipers, 19mm MC, and usually Pagid Orange pads, gives me good stopping power for short sessions on the track (@20 minutes), although there may be some fade at the end of a particularly "spirited" run. In longer events like enduros, they tend to overheat if used in the same manner as a short session. This would (and will) be remedied by a cooling kit to the rotor.

(Disclaimer - not an engineer, the following may not make sense )

To address the original question of bigger brakes "stopping" the car more quickly, the magazine cars with the blown up HP numbers need these larger brakes to counteract the exponentially higher forces involved in the attainment of higher speeds. The ability to reach that threshold between maximum stopping grip and locking them up (no grip) quickly is key here. The larger rotor and brake pad area provides a greater surface of friction by which to slow whatever mass you may have. Also a 2000 lb car moving at 130 mph is X-Times more difficult to slow down than the same car going 80mph ( I dont have the exact equations in front of me). While initially your smaller setup may be able to handle the demands placed on it, your heat sink (rotors) can only absorb so much heat (caused by friction) until the given size of and type of material can no longer serve as intended. Ceramic brakes, as an example, have a much greater ability to not absorb heat, and thus display far less (if any) fade over time. Usually these will be very large as well, given that the cars they belong on go very fast, and need a larger area of friction by which to slow the vehicle.

Hope at least one line in this post makes sense....

While we're on the subject of brake upgrades -I hope that everyone understands that the 19mm master cylinder is not an upgrade. When it comes to hydraulics bigger is not better.

Yep.. you can install a 21mm MC with stock brakes.. all you will get is a rock solid pedal that takes both feet on the brake pedal to make the car stop.


Rich,

You have very valid points. Anything with a much larger contact patch will require more rotor/more brake pad. My wifes car has 7+8's on it with stock brakes... it doesnt stop as well as I would like for it to stop.. but it stops fine for her.

B

Brad: I didn't think there was a 21mm unboosted master cylinder.

Spent a lot of time on the Pelican 911 board, and this has been hashed out fairly well, and no one ever was able to verify the existence of this MC.

23mm... yes

http://forums.pelicanparts.com/showthread....ght=21mm+master

I "meant" 23mm. 21mm came to mind first.



lol


B

Well I did the comparision, Perfectly working stock brakes. Stock pads, stock rotors, new fluid 17mm M/C. 195/60-15 General tires. Car was exciting to bring to a stop. meaning I was always happy to finally get it "whoaed up". Put in 19mm M/C realized that I needed to hit the gym and get stronger legs. Car did not stop any shorter. period!!!!cold brakes
Put 914/6 front calipers with center section removed. at least now I had matching hydraulics. Car didn't stop much shorter nearly no difference. cold brakes
Put 320i calipers on the front stock BMW pads, stock 914/4 rotors. stock rears. with same stock proportioning valve. braking was better ie. shorter stops with cold brakes. I started to adjust proportioning valve to get more pressure to the rears and the stopping got shorted by a few feet. I kept cranking the proportioning valve until the rears started to lock and then backed it off a bit.

Bottom line I don't race, just drive on the roads 65 to 80 MPH and feel more confident about the car stopping right now!!!! no locking of wheels because skidding ain't stopping. car tips the scales at 1950 lbs empty. I just scored on some factory 4 lug FUCHS with 165/70 Kumho tires on them I will try and recreate the stopping test with the skinny tires I'll keep you posted.

Yeah.. righ back at you!

But seriously... some people don't like the 23mm and they fell that the 19mm isn't enough.

There's an ATE reference guide somewhere that lists a 21mm Mercedes MC from ATE, and everyone thinks they've located one, when it's actually just the 23mm.

I WAS HOPING you maybe new something we all didn't...

Interesting Joe..

Good info. Real world testing.

The BMW calipers should stop you better... they are bigger and have a larger pad contacting the rotor compared to the stockers.

I think you would have gotten the same effect by running a better brake pad in the front/all around.

B

I think fitting bigger wheels and tires is the easiest way to shorten stopping distaces. Less work for sure.

When I changed from street tires on 5.5" rims to 205/50 R-rated autocrossers on 7" rims it was like I entered a new dimension.

Tires and wheels make the greatest impact by far.

Paul

Actually you nailed it on the head!

Impacts are the greatest way to reduce stopping distance.

Sixty to zero in 0.003 seconds!

Oh, I get it Carl- "impact".
A joke right?


Paul

I reckon this argument holds some water in getting more force to the rears by adjusting it or fitting a Tee. I agree that in all these cases by fitting new callipers (one would hope the system is bled after ) and pads the braking system as a whole is receiving some maintenance so its BOUND to work better.

Guys,

All this debate is very interesting. I find that what works over long events/stages is 23mm master cyl, 3.2 carrera discs on the front with BMW 733 calipers (ie 4x40mm pistons) which bolt straight on, EBC green stuff pads, and on the rear Girling 4 spots (ex Volvo 240 4x38mm pistons) with SC discs and the same pads with a wilwood in between. Then you have reliable stopping when you are racing brakes down a mountainside.

How

Better pads all around would cost about the same as the 320i calipers. My machinist friend did the mod to the ears of the caliper. FREEBIE

In connection with the other post about tires when I get the bigger rubber I will again adjust bias or replace witha T.

HOWARDR, Do you have those brakes on a street car? What size tires & wheels are you using? Sounds like enough brake to stop a freight train. Or are you just funnin wit us fokes?...

Actually there is an ATE 21mm,
I know because I had one once.
I couldn't make it fit the steering rack without the same mods that are done to the 23mm so I sold it to a local guy here.

It comes in the Euro 1977 3.0 (precursor to the SC with an aluminum block)

its non-power.
I don't have the part number any more, but look up a replacement MC for this car and I think it will show a unique part number.

I could have been mistaken, and it could be a 23 but I don't think so and I measured it when I used to own it.

brant
brant


-----------------------------------------------------------------
Brad: I didn't think there was a 21mm unboosted master cylinder.
Spent a lot of time on the Pelican 911 board, and this has been hashed out fairly well, and no one ever was able to verify the existence of this MC.
-----------------------------------------------------------------

Rich,

Its a street car also used for competition. It now has genuine stopping power and can be really hammered without fade. I have 15 x 7 wheels with 205/55 Yoko 32 R race/street tyres.

Now that we have established that whatever brake that is used is ok.....

The agreement seems to be that cooling is needed for the best performance...

What are you guy doing about this?? I have foglight grills, no lights and was thinking about using these holes for brake ducts...are there any kits? herb

there are brake ducts for 911/914-6 front ends. you put a scoop on the bottom of the a-arm and it ducts air to the backside of your brake rotor. ill see if i can find a pic

here

Remove the sheet metal "dust covers" from the back side to let more air.

Paul

Eventually I'm planning to use those ducts, but connected to the a-arms with the Smart-Racing swivel manifold thingies, and then routed to the intakes on my front spoiler.

Willow Springs (and The Streets) is a minimal braking track so this isn't high on my list right now...until I start travelling to farther away tracks (next year???)

Racer Chris / Tangerine Racing has nice ducts for stock /4 calipers

cheers,

Jeroen