I like what Hunter has said about the big brake upgrade but remember
this. He is talking about a Porsche here. Yeah you could genalize some
of it to apply to an M3 but not all of it. What about the upgrade to a
BIg Brake Kit? On a Porsche, why would you want to upgrade. It is like
Greg said in that the 928 uses the calipers of a 993 Twin Turbo. I
cannot fathom why someone would want to upgrade but I know that people
do. I have the Porsche kit on my car and I can tell you that the car
feels well balanced during braking at the track and on the street. As
for a 928 being similar in weight to our beloved M3's it might be but
there are some major differences that can affect this braking balance.
One of them is that the 928 is lighter in the rear than our M3's causing
more of a need for a biasing kit. One thing that you have to remember
about the M3 and the Porsche is that the M3 has a braking deficiency on
the track and the Porsche does not. The M3 loves to cook the brakes
after a couple of laps. Put on a brake kit and now your problems are
fixed. There are plenty of people running one kind of brake kit or
another on their cars, and most of them have never had a problem out of
them. They also do not have the problem of cooking the rotors again.
Do this if you want to see what the difference is: Take a pyrometer and
measure the temps of the M3 brakes and that of one of the Big Brake
Kits. If you are lazy then you can trust Neil Miller as he has already
done this. His findings is the the stock brakes were somewhere in the
mid to high 700 degree range and the M3 with the Porsche kit on the
front was in the high 200 degree range. Now tell me which is bad for
our cars. Now I also know that this does not mean everything as there
are other examples we need to get a firm conclusion here. I do have
them but I can tell you that the Porsche kit is the best engineered kit
on the Market. The rotors, calipers and pads were all designed by
Porsche, the company with the best brakes in the business. What else do
you need to say about that!! Now we can benefit from this engineering
on our cars thanks to Quido and Movit.
Re brake postings recently, the Porsche Club of America's Panorama magazine has
unusually excellent articles about preparing vehicles for the track, and over
the past 6 months in particular there have been two articles which were very
informative. I suggest that anyone interested in these contact the PCA to either
get a membership or at least reprints of these articles. I'm sure I can't quote
the article verbatim to the digest, but I think I could give you a few key
points the author of the latest article, titled "Braking Systems, Technology and
the Track". As someone on the digest pointed out about a year ago, Porsche
brakes are perhaps the best production vehicle brakes on the planet (although
the Brembos on Ferraris might be a very close second). However, given the weight
of production cars, even Porsche brakes often fail in near-racing situations. As
background, the author has experience putting his 928 on the track, which is
comparable in weight to our M3s (at 3,400 lbs), so I think some of his comments
might be worth noting.
Re stainless steel brake lines, apparently non-DOT approved lines do not have
strain relief ends which would allow the connections to flex (SS brake lines are
very rigid compared to the factory rubber lines, which bend by themselves and
don't need strain releifs). The author says that he has seen more than one of
these types of failures, and apparently race teams replace these regularly. He
suggests either DOT approved lines or keeping the stock lines.
Re pads, the author runs PF90s on the street (although he doesn't mention the
rattling I get when I put them on my M3 for track use). Just another data point.
Although there have been uncountable posts re the "best" pad for the track, he
adds mentions that going to full race pads will allow the pads to put severe
thermal stress on the other braking components (most importantly the rotors).
For example, he tested pads with an CART style compound which required only two
laps to generate enough heat to crack the rotors. But there's no doubt that
street pads (that is, softer compounds) do not help, either -- he cites a test
of one street pad which, after 20 laps, was worn from new to backing plate.
Re rotors, after putting in ultra high performance (and fresh) brake fluid
and good track pads, the stock rotors now are that much weaker than the rest of
the system and thus that much more prone to failure. One tip he gives is that
new brake rotors need to be "bedded" [my quotes] in just like the pads; 150 to
200 miles of regular driving before tracking the car helps put the rotors
through some heat cycles which apparently are needed to further heat temper the
cast iron rotors. Otherwise the rotors wear much faster.
Re big brake kits, the author says that in some of his tests, upgrading the
front brakes alone can lead to MORE front brake failures (!?). As I have
questioned re big brake kits, the author states that when the brake balance is
disturbed (by adding more braking torque on the front, for example), the front
now starts to do a lot more of the work, and the rear is underused. Porsches
apparently have fixed pressure regulators on the master cylinder or ABS unit
which can be quickly swapped out to readjust the front/rear brake balance. For
example, the author, after upgrading the front brakes on his 928GT, removed the
18 bar (265psi) rear limiter and put in a higher unit (they range from 18 bar to
55 bar, the higher for more rearward weight bias and thus more rear brake bias).
By doing so he says that the difference between front and rear rotor and pad
wear was reduced, and the heating of the front brakes was greatly reduced, along
with stopping distances and changes in pitch. I have always wondered how you can
get by with installing huge Brembo rotors up front on an M3 and then expect to
have proper, efficient braking balance. According to this guy, you can't, and
the adage "most of the braking work is done by the fronts", while true, doesn't
really address whether the car is stopping efficiently or safely (if additional
pitch is introduced).
An excellent example of why brake balance front to rear is key is Michael
Schumacher's wreck at Silverstone. Pictures in German magazines clearly show
that when his rear brakes failed, the front tires were locked and worn through
the cords, while the rear tires were in perfect condition -- he didn't have rear
brakes, and his car wouldn't stop. Clearly your M3 doesn't depend upon its rear
brakes as much as Schumacher's Ferrari, and if you lose half your braking system
you'll crash too, but the fact remains that you can't ignore front/rear brake
balance after making brake modifications.
Given that some have posted recently that they buy $100 sets of front rotors, it
seems to me that replacing 6 sets of rotors every season is more cost effective
(over 5 years) than buying a $3,000 big brake kit, which its extremely expensive
rotors which will need to be replaced every two years anyhow. One of my
acquaintances in Germany knows some insiders at BMW Motorsport, and one of my
goals while I'm here is to come back to the US with the absolutely best braking
system available for my M3/4. I'll let you know how I make out.
1998 M3/4, PF90s at all four corners on the track, and polyellipsoids at