BMW FRONT CALIPERS-you may be wrong Options

[Krieger]

I keep hearing this idea that BMW calipers add more heat vs stock caliper. I am not a physicist but any 2000 lb car going 60 mph with stock brakes is going to generate a certain amount of heat. Take the same exact car with smaller calipers (yes smaller) does it generate less heat? I don't think so. It is going to generate the same heat. The only thing that may change is the brake distance and time required to stop. Perhaps this extra couple of seconds it takes to stop allows more time to cool the brakes a tiny bit more, oh but your heating them longer. BMW calipers will add the same heat but faster. That is it. Other points are: the BMW rotors that these calipers were originally designed for are really close in diameter and thickness to our 914s. I'm sure someone will eventually post them. These BMW 320's were quite a bit heavier than our 914s as well. BMW used this combonation for 5 years it must have been a decent.

[DanT]

Check with a BMW repair shop or someone with direct knowledge...

Older BMWs tended to have too small of brakes for the specific vehicle....
and led to a lot of warped rotors.

My good friend and automotive shop owner made a lot of money replacing warped rotors on BMWs because of too much heat being generated and not being disapated quick enough to keep from causing the rotors to distort (warp)

forget the BMW calipers and do a nice M caliper upgrade with vented rotors, and no, you don't have to do a 5 lug conversion to make it happen.

Heat or no heat....I would prefer the brake calipers that give me the shortest stopping distance possible for a given application....

My $.02

[alpha434]

Did you say that all in one breath? Joke.

It's a function of work/time. It only takes so much friction before the work done by the brakes defeats the work done by the tires and creates lockup. This is the maximum amount of work done before the brakes are useless. If your brakes are capable of doing this muchwork, then there is no need to upgrade. For a 914, the stock brakes are capable of locking the brakes, therefore there is no *NEED* to upgrade.

Reasons to upgrade the brakes.

1. You are aiming for a substantial unsprung weight reduction.

2. You go to wider tires, or something else that creates more fricton (operating at lower tire pressure, compounds etc)and can no longer lock the brakes at speed. (Need to do more work.)

3. Heat displacement. Larger brake bodies, or aluminum/ magnesium bodies offer the propensity to displace heat better. This is based on just a few variables. (More work= more friction= more heat.)

BMW brakes are an easy way to take advantage of points 1 and 3, but not 2. They aren't significantly larger to do more work. If they were, then it would be very easy to lockup the brakes, and would render the upgrade useless without a brake pressure adjusting unit.

These rules apply to ALL braking mechanisms, even my own be-all-end-all brakes. Someone get a link. (IMG:style_emoticons/default/wink.gif)

[Krieger]

I did this conversion 6 years ago, 11,300 miles, 5 seasons of autocrossing. I have never experienced any warping or brake fade. The rotors look great, I run Ferrado street pads and measured the rotors for wear this past May at .003". I have Tons of pad left.

[alpha434]

Soooo. Braking distance will not change with the caliper. The calipers that we have already do the maximum work to lock the brakes up at speed.

[brant]

wow...
you need better pads.

pads are a wear item
I get 20-25 hours for a set of pads.

rock hard pads last for ever, but give up significant brake performance.

brant

[Krieger]

So you don't think they do more work than the stock units if I am running wider tires? What pads would be a better compromise. I did get the thought but have taken no action. I heard the porterfields were good.

[alpha434]

Can you lock 'em up with the the stockers? Or the BMWs? Whichever you have now. If you can, then there is no more work to be done. If it's too easy to lock, then there is too much brake work to be done.

Where's Andrew for all this. We can start bouncing the numbers. Wattage, and whatnot. Brakework can be converted to horsepower.

[alpha434]

Pads are going to be important though. Better pads= more friction and worse heat conduction (good thing.)

[Krieger]

I can lock them up with the BMWs, but it takes a little work. Its not at the top of the pedal and I do have to push fairly hard. Never tried it with the stock ones.

[alpha434]

Good. Now just wait to see if you've got heat problems. If you don't (and you probly won't) then you're good 2 go. Leave it to good enough, or get one of the engineers around here to run to numbers for ya (I'm too tired.)

But here's an important point. Heat is a function of work. The BMW brakes aren't doing more work than stockers, therefore they aren't generating more heat.

[brant]

I stand alone on this club in that I really like the KFP's for track work.
but I also have used portefields in multiple street cars with some track experience.

I'm not the autox guru... but I don't think you can go wrong with the portefields. probably the Street version if you putting that many road miles on.

I'm guessing that once you change pads you won't have to work very hard to lock up at will...

more importantly, you will stop faster and be more resistant to heat fade since a competition pad is designed to work best under a competition heat range...

however, you will dirty your wheels a lot more and need to learn different brake techniques including modulation...

oh... you may or may not start warping your rotors too.

ha

[Krieger]

What are KPFs? Not for this car, but I'm building a 3.0 6 conversion that I will definately TT. Maybe I'll cycle more and build my my legs and leave my BMW calipers be.

[lapuwali]

The whole point of BMW calipers (or any other calipers with bigger pistons) is to reduce the amount of pedal effort for a given braking force. This doesn't mean you will automatically generate more heat. Heat is a function of the mass of the car, the speed you bleed off, and how much braking force you apply (at the caliper, not at the pedal). If you generate no more force at the caliper than you do with the stock calipers, then no more heat will be generated, and the pads and rotors will last just as long.

Of course, if this is what you do, the whole point of using the bigger calipers in the first place is rather lost.

The main downside to bigger front calipers only isn't so much the potential for extra heat and fade, but the fact that the brake balance has now been moved substantially forward, reducing the percentage of braking supplied by the rear tires. You have four tires, you might as well use all of them to contribute to braking. If you don't, you're reducing the amount of braking possible by overloading the front tires and underusing the rear tires.

So, using BMW calipers on the front is fine if you prefer the feel, but it's not a legitimate performance upgrade, since the overall performance of the car is actually reduced.

[brant]

Karbon Fiber Products.

(I know carbon is spelled with a C)
they are the same pads that used to be called "cool carbon"

I don't know if the company was bought out or just decided to do a name change. They are carbon ceramic pads with a carbon heat shield built into the backing. when the name changed, so did the color.
what used to be an "orange" grade of compound became "gold"

I run gold front and rear on my wheel to wheel car.

I used to run Blue fronts and Orange rears on my old race car way back around 96'
I run gold fronts and Portefield R4 rear on my semi-street daily driver that I will be using for DE

My race shop believes they are superior for lightweight vehicles.
my own experience echo's this. I really like the Port's for above 2500lbs. They were far superior on the old 944Turbo I built. But the KFP's seem much better on the lighter cars like a teener.

brant

[alpha434]

The whole point of BMW calipers (or any other calipers with bigger pistons) is to reduce the amount of pedal effort for a given braking force. This doesn't mean you will automatically generate more heat. Heat is a function of the mass of the car, the speed you bleed off, and how much braking force you apply (at the caliper, not at the pedal). If you generate no more force at the caliper than you do with the stock calipers, then no more heat will be generated, and the pads and rotors will last just as long.

Of course, if this is what you do, the whole point of using the bigger calipers in the first place is rather lost.

The main downside to bigger front calipers only isn't so much the potential for extra heat and fade, but the fact that the brake balance has now been moved substantially forward, reducing the percentage of braking supplied by the rear tires. You have four tires, you might as well use all of them to contribute to braking. If you don't, you're reducing the amount of braking possible by overloading the front tires and underusing the rear tires.

So, using BMW calipers on the front is fine if you prefer the feel, but it's not a legitimate performance upgrade, since the overall performance of the car is actually reduced.

No. This is wrong. There is no more heat generated, and no more fade. With bigger pistons on the brake side, means for more travel from the pedal, because the size of the master cylinder will remain the same and will have to fill more area with fluid. Also, the front brakes do most of the work, the rears only hold the car straight during braking. If you're car tends to "float" during braking, then you need more brakes on the rear. It takes a HUGE difference to do that.

The advantages of the BMW calipers are better heat displacement from the Al alloy, and lighter unsprung weight (which isn't a braking upgrade at all.)

[grantsfo]

My car has BMW calipers with SC vented rotors in front with SC calipers and vented rotors in the rear. Brakes worked great during my last track day. Fronts were a little prone to lock up in some cases.

If I had a stock 4 I would stick with stock calipers and rotors.

[DanT]

I think they were discussing the older BMWs that used non-vented rotors. I believe they work with stock 914-4 rotors...that is the simplicity of the swap. But I don't think you gain anything since you can not disapate any more heat than with stock since you don't have vented rotors with that set up.
That is why I decided to go with M calipers and vented rotors with the magic billet hubs up front. Since my car is a track/AX car I don't want brake fade after a 30+ minute run session...

[URY914]

I'd like to see a before and after test run using a G-Tech to really put this to bed.

I don't see that the BMW calipers are that much of an improvement over stock. Maybe just MAYBE the BMW calipers will take longer before fade begins to effect performance. But I don't see this ever being a factor on the street. If you are overheating your brakes driving on the street you need to slow down or you live at the top of a very tall hill.

And as far as the BMW calipers requiring less pedal effort. How do you measure this? How do you know this is true? Also, locking up the tires and sliding is not a indication of "better" brakes. Your stopping distance is shorter when you don't lock them up.

IMHO the people that have done the BMW conversion say they can "feel" the differance because thier wallet feel the difference. The easiest/quickest/cheapest way to improve brake performance is to upgrade your pads, flush the system of old fluid and BLEED, BLEED, BLEED the system.

I run stock calipers and Cool Carbon pads. (IMG:style_emoticons/default/driving.gif)

[maf914]

If you are overheating your brakes driving on the street you need to slow down or you live at the top of a very tall hill.

One of the dumbest and most dangerous things to happen to me was failing to completely release the emergency parking brake on my girlfriend's Toyota before a drive on the interstate. After driving for many miles and apparently overheating the rear brakes and boiling the fluid I found to my amazement that the brake pedal went completely soft as I exited the highway on an off ramp. "Oh, shit! No brakes!" Thankfully it was one long off ramp. Pump, pump, pump. The damn thing finally stopped. Scared the crap out of me! Then I realized the brake handle was partially up. Duh! Talk about feeling stupid.