Terry,
I am Nicholas, I use Ken's Email though...
The more that I think about it the more that I think proportion is more
important than we have realised, i.e having huge front calipers may not be
the be all and end all.
Now,
Friction is proportional to the normal force (force at right angles to the
ground). If you drag an empty chair across the ground there is less
frictional force at the feet than if you sat Mal Colston in it and dragged
it.
So just say at rest your car has 50/50 weight distribution and under
controlled heavy braking 60/40. To get maximum braking force you should then
have the caliper piston areas in the ratio 60/40 (assume same disc diameter
etc...) and (braking in a straight line) both front and rears would be right
at the limit-of-adhesion before-locking-up at the same time (without any
need for a proportioning valve).
Under OH-MY-GOD-I'M-GOING-TO-DIE panic braking the weight distribution might
briefly be 70/30 so your 60/40 caliper areas would cause the rears to lock
up first and you would fishtail towards your imminent demise.
Just say you fork out big bucks for some super-dooper front caliper that
even Porsche engineers look at and start feeling all inadequate, and now you
have caliper piston areas in the ratio 90/10, then when you are braking hard
and controlled, the fronts will be on the limit of locking up and the rears
won't be any where near locking - i.e you are not using the rear tyres'
potential grip as much as you could, so you won't be able to stop anywhere
near as quick as with the 60/40 setup.
With this in mind I propose that there are six main things to consider with
Brakes - in no particular order,
1. Proportion
2. Suspension setup - low centre of gravity gives smallest weight transfer
and stiff suspension gives near instantaneous weight transfer to steady
state values - hence maximum braking sooner.
3. Clamping force (if you can't get close to locking the wheels you can't
get maximum braking)
4. Heat dissipation.
5. Pad compound.
6. Cost.
I am currently using B/Bird front struts, the B/Bird (and R31) caliper is
the same internally as the 200B, I am about to swap to the R31 vented setup,
there will be no increase in cold braking since B/Bird and R31 (and to a
great extent the 200B) have the same basic setup, but since the R31 has
vented disc and finned caliper heat dissipation should be hugely better.
If is still isn't up to my heat-dissipation requirements there is a DBA
sport vented, slotted and cross-drilled rotor available for the R31!
Why wouldn't you want to run the R31 setup?
BTW I will get my struts expanded to fit a 36mm Bilstein or DeCarbon insert
and I'll fit a Stanza 100mm spring seat, the R31 spring seat is far too big
for normal Dattos.
Don't knock the Urvan caliper just because it comes from an unfortunate
looking vehicle - it might do the trick someday if you need a 'bigger'
caliper.
As for M/C's, sounds like you have done a fair bit of research.
However by sheer luck and rat-cunning I believe I have stumbled on a good
solution.
I have the twin reservoir Stanza 13/16th M/C with remote proportioning
valve.
Use this M/C, bin the proportioning valve and modify a BMC Mini prop. valve
to give you fully adjustable proportioning. Mount it near your seat, set it
for the track, adjust it mid race to compensate for race conditions, then
screw the proportion forward to give you safe emergency braking for the
drive home on the public roads of this fine country.
Lastly,
Clamping force, assuming you have sorted out the proportioning and all that,
but you still need more clamping force. Now you have to play with boosters.
I read somewhere that AP modify Mini Cooper boosters by changing the valving
from 2 to 2.5. I presume that this means that the booster doubles the line
pressure for a given input force???
I know that boosters work using engine vacuum on a diaphram, but that is
about it.
I presume that the different Datto boosters are 'valved' slightly
differently and that swapping them around could be useful.
If anyone can find data on boosters we can add it to Errol and Trevor's
spreadsheet.
The combination of booster and M/C will determine 'feel' to a large extent
so there will probably be one 'best' setup.
Sincerely
Nicholas Abraham
1978 Datsun Stanza GX
----- Original Message -----
From: Terry Rudd <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, 7 January 2001 10:01 PM
Subject: RE: Brakes - Long and longer
> Ken,
> Very interesting read.
>
> Some points that stand out in your post are that the performance of the
big
> bore Girlock callipers off the early 200B are the best option
(performance,
> availability and cost) for a solid rotor upgrade on a 1600. I did my brake
> upgrade progressively from fairly stock everything, then fitted a 180B
3/4"
> dual master and booster. There isn't a major performance increase gained
as
> this is more a safety and feel upgrade and was required even for club
social
> day laps at Wakefield Park and Fairbairne Park. I fitted Ultimate pads,
> porterfield shoes with 1200 slaves which gave me brakes until half way
> through lap 3 at Wakefield and then everything would go dead as in nothing
> with a rock hard peddle but the brakes weren't excessively hot, well
> compared to some other cars that the brakes were just about on fire. We
> could never pinpoint what was wrong with mine, but as a result of fixing
> another small problem recently I have just figured it out - it was the
> return valving blocked in the Tokico master cylinder which was very tricky
> to discover.
>
> I then fitted the Girlock big bore callipers and rotors from a 200B SX
with
> Pagid pads which gave a huge increase in braking performance, without
doubt
> the biggest single increase of the total package. Then I converted the
rears
> to R31's and used Premium Bendix pads as Ultimates were not available. The
> disc rear gave the braking a moderate performance increase (about 50% of
the
> 200B fronts) but the big thing was the braking balance was brilliant which
> contributes to way the car behaves under heavy braking i.e. no locking or
> fading and pulls up from high speed in dead straight line lap after lap
with
> a very progressive feel.
>
> I based my observations on timed laps of Wakefield Park which is a tight
> little track that's suited to small cars. Over my stock setup I was able
to
> improve my lap times by nearly 5 seconds which is quite considerable. The
> only other modification that was done in conjunction with the front
upgrade
> was a wheel and tyre change to accommodate the bigger brakes - this would
> have contributed to some of the performance gains but no where near as
much
> as the brakes.
>
> I have just changed my master cylinder from a 3/4" Tokico to a 13/16"
Nabco
> sourced from a Sunny. I haven't done any track runs to check if there is
any
> difference and I have to replace some bushings in the rear suspension
before
> I go onto a track as I got an "advise" last time, but first impressions
are
> that this cylinder is not as good as the Tokico in most areas especially
> feel, but it works well but is very firm and feels a bit dead. I was
> surprised that there is so much difference between brands. When I pulled
the
> Nabco down to check it out and clean it up inside, I noticed it has a
> different built in bias (much bigger internal return springs but not as
much
> difference front to rear), I'd say the bias effect is ~10% rearwards
> compared to the Nabco so I'm still getting used to the difference.
>
> The next step for me would be to go to a proven ventilated front upgrade
> that is guaranteed to at least equal the performance and balance of the
> current setup. The options that you have investigated don't strike me as a
> must have so I'll keep looking and reading for a cost effective
combination
> that suites the 200B strut.
>
> regards
> Terry
>
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