Notes on brake "upgrades", What's worthwhile, what isn't. Options

[lapuwali]

A bit bored this AM, so I'm rambling a little...

The 19mm MC used with otherwise stock 914/4 brakes: this results in a reduction in braking force for a given pedal force (forcing you to push harder to stop), and the actual amount is 16%. Some people like the "firm" feeling this provides, but it doesn't mean "better braking".

The 19mm MC used with BMW 320i calipers OR Porsche M calipers (same size). This results in a 12% decrease in pedal effort for a given braking force. So, you will feel an improvement, but it's not a very big one. The downsides to this swap is the bigger calipers are heavier (unsprung mass, too), and of course you're doing a lot of work for a pretty small gain. You're also doing nothing to help brake fade. You're likely making it more likely, since you can now load a bit more heat into the brakes more easily. Happily, this also won't have a huge effect on front/rear brake bias, however, since the overall effect is so small.

A 17mm MC used with M calipers would produce quite a big change in pedal force v. braking force: 33%. However, this MAY cause a problem in that the 17mm MC is small enough that you couldn't move enough fluid with it before you run out of pedal travel to fully press the pads against the rotors. You'd certainly have to push it a long way to get the brakes to come on at all, and the brakes would likely feel touchy and mushy, but powerful. Rather like overboosted power brakes...

btw, "17mm" and "19mm" (and "42mm" or "48mm" for caliper piston diameters) aren't strictly correct. Even in metric countries, brakes are actually specified in 1/16ths of an inch, so 17mm is really 11/16, or 17.45mm, and 19mm is really 3/4 (12/16) 19.05mm. 42mm is really 26/16", or 41.275mm, and 48mm is really 47.625mm. Germans just list the sizes in the nearest metric size, whereas the Japanese perversely use both systems: 10mm for some parts, and 0.50" for others, for example.

[Eric_Shea]

Cool thread.

Thought provoking stuff before my pragmatic view:

* Larger wheels and tires generally = larger contact patch - Talk amongst yourselves.
* Excellent new tire and pad compounds - Talk amongst yourselves.

My pragmatic view:

Stock 914 brakes were over-engineered for their day, just like any Porsche brake system. This mark is known for the best brakes in the business.

Today's tire compounds are leaps and bounds over what was available in the 70's... so are today's pad compounds.

If you have a 914 with stock fenders you're 'probably' good to go with stock brakes. If you are racing said 914 in a 'serious' road course environment you'll want to look into brake 'system' solutions. There's evidence of this within this thread (John Rogers).

If you're autocrossing you'll generally be good with stock brakes but it would do you well to get good pads. There's evidence of this within this thread (Trekkor).

BMW brakes are not an 'upgrade'. If you think they are, you had really shitty brakes on your car before you put them on. The exact same 914 with BMW brakes and stock brakes will stop in the same distance. Your tires (contact patch) will be the limiting factor. He/She who locks up his/her wheels faster stops last... sliding is not stopping. 914 brakes can lock the wheels with the right pads (even with most wrong pads).

If you've successfully increased your contact patch through the use of flared fenders and wider tires you could probably benefit from a larger brake system. If you haven't, you're probably just trying to be cool (IMG:http://www.914world.com/bbs2/html/emoticons/cool_shades.gif)

Flared 914's, with the exception of all but the largest wheels and tires can be successfully stopped on a regular/race basis with a set of A or S-Calipers. Anything larger is probably bragging rights. These cars raced for 24 hours back on June 13th and 14th of 1970 with 908 calipers (basically an S-Caliper with fat-ass pads). They were around 220hp, lightened a bit and had 7-8x15" wheels and race tires of the day. They won their class in that little race called "LeMans"! (IMG:http://www.914world.com/bbs2/html/emoticons/w00t.gif)

What do you plan to do with yours? (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

Talk amongst yourselves...