BMW FRONT CALIPERS-you may be wrong Options

[tesserra]

Most of the heat generated in the brakes goes to the rotors not the calipers.
So if you upgrade to BMW calipers, with no rotor upgrade there is no greater heat disipation.
The advantage of the BMW rotors is that the pad surface area is greater.
This has the potential of making more heat sooner, up to the point of lock up, however that helps in performance.

[lapuwali]

And as far as the BMW calipers requiring less pedal effort. How do you measure this? How do you know this is true?

I know it's true because I know the basic physics involved. Bigger caliper pistons with the same sized master cylinder piston means more mechanical advantage from the larger hydraulic ratio. This means less effort at the pedal for the same force at the caliper AND longer pedal travel for the same travel at the caliper piston. At some point as you increase the caliper piston size or reduce master cylinder size (same thing), you require so much extra travel at the master cylinder that you can't deliver enough fluid to press the pads against the rotor, and improvement ceases rather abruptly.

At some point before that, the long travel and light effort starts to "feed bad", generally feeling mushy even when perfectly bled. The brakes feel touchy and hard to control. I know this, because I've felt it myself (not on a 914).

In the opposite direction, as you reduce the size of the brake caliper piston(s) relative to the master cylinder piston, the brakes feel firmer, and travel is shorter, but pedal effort rises. At some point, the brakes begin to feel "wooden" and seem to lack power. Beyond that point, even the strongest person won't be able to lock up the brakes no matter how hard they press the pedal. I know this, because I've felt it myself (again, not on a 914).

In the middle, there's a sweet spot, which is fairly broad. Some people prefer the softer pedal with more power, others prefer the shorter pedal and put up with pressing harder. The BMW calipers shift the feel to the "soft/long" end, where using a 19mm MC with otherwise stock brakes moves you to the "hard/short" end. The stock 17mm MC with stock brakes is somewhere in the middle. The difference with the BMW "upgrade" v. the 19mm "upgrade" is that the caliper swap shifts the brake balance as well as altering the feel. This is esp. bad if you're also swapping in a heavier engine, as that by itself shifts the static weight rearwards, and you're shifting the brake balance forwards.

[lapuwali]

Most of the heat generated in the brakes goes to the rotors not the calipers.
So if you upgrade to BMW calipers, with no rotor upgrade there is no greater heat disipation.
The advantage of the BMW rotors is that the pad surface area is greater.
This has the potential of making more heat sooner, up to the point of lock up, however that helps in performance.

No. As counterintuitive as it seems, pad area has NO effect on braking force (and thus no effect on heat generation). Greater pad area spreads the load over a greater area of pad, so the pad wears more slowly, and generally can absorb more heat before fading. So, bigger pads ARE a benefit. However, by themselves, they don't generate any more heat.

Again, heat generation is only affected by how much weight you're slowing, and how quickly you're trying to slow it.

[bondo]

I think Brad's big beef with the BMW calipers is not that they add more heat to the rotor.. but that they prevent heat from leaving the rotor, since the pads cover a larger % of the rotor. You have to admit that an uncovered rotor will transfer heat to the air faster than a covered rotor.

[914fan]

Let us not forget the availability of options for pads. With stock there is Pagid? and what? I have not found a decent pad for our cars that was not 60-80. For that money I can get Mintex or Hawk for my Jetta, and those pads are 2x larger. There is more demand for the bmw pads so thier price is lower. Also let us not forget that we can order rebuilt calipers for the bmw that do not cost us to refi our homes.

[Eric_Shea]

BMW Calipers are not AL (the one's we're discussing here). Although I am agreeing with Alien Life Form for a while here. Stock brakes in the proper working condition work just as good. Most conversion were done on tired stock systems and got fresh BMW systems... not a good comparison.

Stock brakes are every bit as good and the entire system (yes, p-valve and all) works perfectly for any narrow bodied car in any situation up to heavy road course work and even then some (Brant) would argue that you're not driving properly. The cool thing about stock brakes is... you already own a set and you can waste your money on other cool things you must have like huge sway bars and oversized t-bars (tongue firmly in cheek)

If you have a hard time locking up stock or BMW calipers you need new pads.

The best money spent is on this...

[Eric_Shea]

With stock there is Pagid? and what?

Everything else.

[Bleyseng]

I switched out my recently rebuilt fronts for a set of rebuilt BMW calipers just to see if it helped in AX.(Brakes were getting soft after double runs)
Yes, less brake fade and more control.

For the street a waste of time IIHO

I have since gone to 911 vented rotors and bigger calipers since I hate brake fade on track days.

[jhadler]

Goign back to the pad question. The Porterfield's in my experience are excellent track pads. They stand up to heat VERY VERY well. With minimal fade. On the other hand, I don't think they're a very good autox pad, especially with a 914. The Porterfields are very grabby, even when cold, which is good for the track where your wheels are rotating at very high rpms, and have very high momentum. At an autox however, the wheels are rotating at much lower rpms, and hence less momentum. With the grabbiness of the Porterfield's, it makes brake lock-up much more likely, and they are harder to modulate at autox speeds. I've found, especially after going to lighter wheel and tire combinations, that a soft, simple pad is best for autox. Yes, you can still lock 'em up, but the difference between first bite and lock up is a lot larger with softer pads, and allows for much better modulation.

Just my $0.02...

-Josh2

[Lou W]

BMW Calipers are not AL (the one's we're discussing here). Although I am agreeing with Alien Life Form for a while here. Stock brakes in the proper working condition work just as good. Most conversion were done on tired stock systems and got fresh BMW systems... not a good comparison.

Stock brakes are every bit as good and the entire system (yes, p-valve and all) works perfectly for any narrow bodied car in any situation up to heavy road course work and even then some (Brant) would argue that you're not driving properly. The cool thing about stock brakes is... you already own a set and you can waste your money on other cool things you must have like huge sway bars and oversized t-bars (tongue firmly in cheek)

If you have a hard time locking up stock or BMW calipers you need new pads.

The best money spent is on this...

Ok, I just ordered "The best money spent on this" I'll bring it with me on Aug 12th Riverside Autocross and compare it to what everyone is doing.(IMG:style_emoticons/default/smile.gif)

[DanT]

BMW Calipers are not AL (the one's we're discussing here). Although I am agreeing with Alien Life Form for a while here. Stock brakes in the proper working condition work just as good. Most conversion were done on tired stock systems and got fresh BMW systems... not a good comparison.

Stock brakes are every bit as good and the entire system (yes, p-valve and all) works perfectly for any narrow bodied car in any situation up to heavy road course work and even then some (Brant) would argue that you're not driving properly. The cool thing about stock brakes is... you already own a set and you can waste your money on other cool things you must have like huge sway bars and oversized t-bars (tongue firmly in cheek)

If you have a hard time locking up stock or BMW calipers you need new pads.

The best money spent is on this...

...


Ok, I just ordered "The best money spent on this" I'll bring it with me on Aug 12th Riverside Autocross and compare it to what everyone is doing.(IMG:style_emoticons/default/smile.gif)

Yes, Hank's book is a great wealth of information...

Hank is along time friend...Every student (90 of them) for our GGR/Zone7 AX school held this past weekend recieved a copy as part of their registration packet weeks in advance of the school so they could come slightly prepared.

Our students have been getting a copy of this book for over 15 years

[Air_Cooled_Nut]

And as far as the BMW calipers requiring less pedal effort. How do you measure this? How do you know this is true?

I know it's true because I know the basic physics involved. Bigger caliper pistons with the same sized master cylinder piston means more mechanical advantage from the larger hydraulic ratio. This means less effort at the pedal for the same force at the caliper AND longer pedal travel for the same travel at the caliper piston. At some point as you increase the caliper piston size or reduce master cylinder size (same thing), you require so much extra travel at the master cylinder that you can't deliver enough fluid to press the pads against the rotor, and improvement ceases rather abruptly...

Common [necessary] knowlege for braking. More here:
http://stoptech.com/tech_info/tech_white_papers.shtml

[wilchek]

I just added BMW brakes and may have opened this can of worms. I can say this. I like the BMW calipers better but they are not the end all be all. I got them cheap and figured I would try them out. I don't think they will stop all that much better but five or ten feet is a lot when it is needed. I am looking for a set of almost worn our Porterfield R4S pads for the stock calipers. If I can find them I will run some scientific test (BMW VS. Stock). I do like the feel of the BMW calipers better and with the up graded pads they clearly work better. I think the pedal modulation is better. As for the heat, it is negligible under my type of use

I also plan I taking out the proportioning valve or adding less bias to the front. I am going to try and run some test of before and after results. This should show how much the proportioning valve makes a differerence and how much the back brakes help in stopping.

I think my friend put it best. "We play with these cars for fun, it is not an investment, expect to loose money and have fun doing it." I installed the BMW calipers mostly to learn, play around and to wind down from work.

[Brad Roberts]

So.. If I add 6 piston Carrera GT calipers to the front of my solid rotor'd 914 will it stop?

Brant,

I didnt know Karbon people where back (IMG:style_emoticons/default/beerchug.gif)

Run BMW calipers!!

I hate the pedal feel. It does not build confidence in the driver having what appears to be a mushy pedal at all times no matter how much you bleed them.

As far as heat goes: All the math and physics in the world couldnt tell me what I learned at the track one day. Same style 2.0 powered 914's running within 1 second of each other. One had stock brake calipers front and rear with Porterfields and the other car with BMW's and Porterfields.

The BMW car had MUCH higher rotor temps (150deg+) than the other 4cyl car. I know there are a lot of variables, but if you have driven a stock 2.0 injected 914 around a race course, you would know that brakes are used very lightly in most cases.

B

[brant]

regarding Karbon brand,
ordered another set of front golds about 5 weeks back..
so they are still out there, just not easy to find.

and conway at carquipt has been a dealer in the past too.
I've bought from him previously.

brant

[Air_Cooled_Nut]

...I also plan I taking out the proportioning valve or adding less bias to the front. I am going to try and run some test of before and after results. This should show how much the proportioning valve makes a differerence and how much the back brakes help in stopping...

Ask any motorcyclest and they will confirm: Back brakes make a noticeable difference in stopping distances! Same goes for cars (IMG:style_emoticons/default/wink.gif)

I wouldn't recommend pulling the prop. valve on a street car as you don't want your back brakes to over-power your fronts. You want the fronts to do the lion's share of the braking.

[ChrisFoley]

I have always used cool carbon/KFP Magnum pads on my race car.
A lot of the performance brake companies don't even list a pad for the stock rear calipers.

[alpha434]

...I also plan I taking out the proportioning valve or adding less bias to the front. I am going to try and run some test of before and after results. This should show how much the proportioning valve makes a differerence and how much the back brakes help in stopping...

Ask any motorcyclest and they will confirm: Back brakes make a noticeable difference in stopping distances! Same goes for cars (IMG:style_emoticons/default/wink.gif)

I wouldn't recommend pulling the prop. valve on a street car as you don't want your back brakes to over-power your fronts. You want the fronts to do the lion's share of the braking.

B.S.
Motorcycle racers don't even use rear brakes except for "tail wipping" Which is the motorcycle equivelent of drifting, which has nothing to do with stopping. One of the guy's I know (he and his wife race crotch rockets,) dosen't even have rear brakes on his race-bike.

The rest is right-on. No more arguements.

[GBallantine]

I use the BMW caliper setup on my 2.0 litre 4 full race car along with early 911 rear calipers with Hawk Blue pads all around. I also use a brake bias control and a 19mm master with Wilwood 550 fluid. My experience is that the brake pedal travel is greater and feels much softer then stockl It really takes some getting use to, but does have the desired result.

GB

[lapuwali]

B.S.
Motorcycle racers don't even use rear brakes except for "tail wipping" Which is the motorcycle equivelent of drifting, which has nothing to do with stopping. One of the guy's I know (he and his wife race crotch rockets,) dosen't even have rear brakes on his race-bike.

The rest is right-on. No more arguements.

Once again, Chris, you're talking one tiny sample and generalizing it way out of proportion.

Yes, many bike riders only use the front brakes. I did most of the time when I was doing that. The weight transfer from a bike with a fairly high CG and a fairly short wheelbase (which describes most sporting machinery) does indeed often render the rear brakes nearly useless except in special cases, like getting the rear end out (which can actually be very useful for stopping and turning at the same time, I've seen more than a few top pros "drifting" around tight hairpins very successfully as a passing manuever). Some racers also prefer using the rear brake to some degree, anyway, even if the rear tire is very lightly loaded. Mick Doohan, an Australian that won several world titles, insisted on using the rear brake extensively. When a serious leg injury made using his braking foot very difficult, Honda fitted a thumb operated brake on the clutch-side handlebar for him so he could still use the rear brake.

Not ALL bikes have a very high CG and a short wheelbase. Harleys and Harley-like bikes, for example, frequently have a very low CG and a long-ish wheelbase, and often have a static rear weight bias, esp. with a rider, as the seat generally places the rider quite far back on the bike. This dramatically increases the usefulness of the rear brakes, and using both brakes at the same time will substantially reduce stopping distances.

Bikes are a great way to experiment with brake bias and how it's affected by static and dynamic weight distribution.