Everything you ever wanted to know about brakes (from a brake engineer)
Hubba Hubba
Message Title: Lots of Brake Info from an Engineer's View
Posted by: LUVKARS on 2002-06-03 at 17:37:07
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Message:
Just some generic brake info for ya.
THIS IS JUST GENERIC INFO, NOT FOR ANY SPECIFIC VEHICLE.
Just some of my experience from being an automotive brake engineer in
Michigan for awhile.
First some quick definitions: Brake Pedal ratio is the measurement of how
much mechanical assistance you are getting from the pedal. Example; an ratio
of 4.1 will give you 41 pounds at the booster input rod for a 10 pound load
at the pedal itself.
Dead or lost travel is how much pedal stoke is required before you actually
start stopping.
Dead Travel or Lost travel and overall poor pedal feel is made up of the
following:
[(travel as measured at the brake service pedal assembly pin (where the
booster connects)]
(imagine traveling from the pedal through the brake system to the rotor, all
lost travel must be multiplied by whatever your brake pedal ratio is.)
1. Tolerance between brake pedal pin and booster input rod. This can be
quite a bit for systems that use a pin mounted brake light switch. If you do
have such a switch do not remove it or take up the slack as your brake
lights will be on all the time. If you don't have a pin mounted switch just
get a tighter bushing. If you do..you s**t out of luck.
* will be felt during first few mm of travel
2. Slack in the brake pedal assembly itself. To see how good or bad yours
are, with the car off pump the brakes until hard (2-3 pumps) and then grap
the pedal with your hands and see how much it moves around.
* will be felt through first few mm of travel (I hope)
3. Dash flex. This can range dramatically from vehicle model to vehicle
model. Not much you can do about this.
*felt during medium and high decelerations stops on most cars, on Fords
dashes flex with the breeze
4. Lost travel in booster. This is designed to be there to allow for booster
expansion due to climate and use over time. Only adds half a mm (multilplied
by the pedal ratio).
*felt only in the first few mm of travel
5. Flex of booster shell. Can be a real problem on some designs. All you can
do is try and brace the booster or replace with a better product.
*felt on medium and high deceleration stops
6. Design tolerances in the Master Cylinder. Varies creately from one to
another. Simply, if you want less lost travel in the TMC (tandem master
cylinder), you have to pay for a more expensive one. A minimum lost travel
of about 1-1.5mm is required for proper and safe operation. However, I've
seen some with double that. (again multiplied by the pedal ratio)
*felt duiring first 10mm or so of pedal travel
7. The brake tubes and ABS unit. Maybe .0000001mm here. Don't worry about
it.
8. Brake hoses. Get steel braided ones, there worth it. Rubber hoses flex
quite a bit even under low pressure.
*felt almost all the time
9. Brake Caliper Piston Roll Back. This is usually the worst offender. Only
way to get rid of these is get better calipers. Roll back is how far the
piston moves away from the rotor when pressure is released. The bigger the
gap, the more you have to push on the pedal to get contact.
10. Caliper Defelection. The caliper actually flexing under pressure, like 9
you can only improve this with better calipers.
*felt during medium and high deceleration stops
11. Brake pad backing plate. If this is flimsy it will flex and not allow a
good contact between the rotor and pad forcing you to apply more pressure
and therefore more pedal travel. Fixed by replacing pads with higher quality
ones.
*felt most of the time
12. Brake pad material itself. If the material is low density it will
compress like a sponge. And if it's a low mu (friction) pad it will require
more pressure and therefore more pedal travel.
*felt all the time
13. Rare, but a problem on really cheap brake pads: The bonding process used
to bond the brake pad material to the backing plate. A poor process will
cause the material to "squirm" around.
Well those are the biggy, but not the biggest. The biggest is AIR in the
system.. Before you do anything else do a really good and thorough brake
bleed. And only use the fluid it says to use on the cap, DOT 3 or DOT 4 or
whatever.
How I would go about improving a system:
1. Bleed system
2. High quality pads
3. Get steel brake hoses
4. New fixed calipers from a know manufacturer
5. Some bracing for the actuation unit (booster/ master cylinder/ pedal)
Also, changing the brake pedal assembly to one with a lower ratio. Remember
all lost travel is multiplied by the pedal ratio, the lower the ratio the
less dead travel at the pedal pad. This also firms up the pedal as your
getting less mechanical assistance. Just be careful, because if you brake
booster fails it will take more force on the pedal to come to a stop.
Minimum pedal ratio is calculated using NHTSA FMVSS 135 which states the
maximum force required to stop a vehicle in a certain distance when the
booster fails.
Pedal feel can also be "tuned" with a different booster. I will not get
technical, but basically the booster sets the Force-Force curve (Force into
the booster vs. the force out). How this curve looks will dictate pedal feel
(assuming all else equal). A F-F curve has certain points that are
important, the 2-stage, cut-in, boost ratio and the run-out.
2-stage is what sets the intial point of boost (when it kicks in)
cut-in is what sets how much initial force
boost ratio is just as it sounds, it sets how much assit you get
run-out is the maximum assist
By lowering the 2-stage and increasing the cut-in you get a better intial
bite sooner. Just have to be careful you don't go overboard and have the
driver eat the steering wheel at every stop light (like an '80s Audi).
Difference between Feel and Performance
Just some more stuff:
I want to make it clear there is a difference between making a brake system
feel better and actually perform better.
The stopping distance of a car is not necessarily directly related to the
feel. A poor feeling brake system can have very good performance, i.e.
Jaguar. While a great feeling system can have lousy performance, i.e. Ford
Focus
The only way to decrease braking distances is to create more heat through
friction and conduct that heat more efficiently.
Basically, you need a bigger contact area between the rotor and pad (bigger
pads and rotors) with the best contact patch possible between the two. Also
higher friction levels with higher mu brake pads.
And most importantly.........REALLY GOOD TIRES!
And you need a way to get rid of that heat at a faster rate. More rotor mass
and/or better conduction (vented, etc...).
How a car stops is simple, it takes Kinetic Energy (energy created by
motion) and transfers it to Heat (infrared) Energy. It does this by the
mechanism of friction.
KE=1/2 the mass of the vehicle multplied by the square of it's velocity
Stopping distance is determined by the rate of KE to IE transfer, or also
know as WORK.
Simply, to stop sooner you need to transfer Kinetic Energy into Heat Energy
faster.
There are no other tricks...you need higher levels of friction and ways to
dissipate the heat quicker (you can also get more massive rotors which are
capable of absorbing more heat).
The big things to do to get shoter stopping distance:
1. Best Tires for the conditions (use common sense here, no Pilots in Feb in
Alaska)
2. Higher Firiction Brake Pads
3. Bigger rotors with better heat conduction properties or better heat
absorbtion properties
That's it!!!!!!!
The small things you can do that give you that extra advantage:
1. LOSE WEIGHT (the car I mean), less mass, less KE
2. Minimize rotational interia of wheels/tires. Get lighter wheels and tires
(all else being equal). Note: the farther away from the center of rotation
the mass is the great the interia, so a 17" wheel will have greater interia
than a 16" all else being equal.
3. Try and balance out the braking, if the rears can do more work it spreads
out the work. Less weight transfer to the front [edited 4/5] BY MOVING THE
BATTERY TO THE TRUNK, stuff like that.
4. Calipers with more pistons and more piston area, this gets you that
better contact between rotor and pad.
5. Pratice! Get to know how your system works so you can best utilize it.
6. Don't drive to fast, remember it the square of the velocity. The amount
of KE increase from 40KPH to 80KPH is not 200%, but 400%
X-drilling is meant to help with heat conduction and vent gasses. Actually
drilling holes in the rotor decreases the amount of contact area and in
theory will increase brake distances (we're talking mm here).
But how many of you are threshhold braking on the interstate or county
roads?
Also, venting built up gases under the pad was a big problem, but pad tech
has come so far that it's not something I would worry about (assuming your
using race pads for racing). Again it's one of those things that's there but
only makes a very, very, very minor difference (if any) most of the time.
Same thing with slotting, which was developed to vent gases and clean pads.
Things like 2-piece rotors, X-drilling, slotting, crygonics, heat treating
are all "at limit" technologies. In other words they only make a noticable
difference (if any) at the very limits. If you drive on the street in a
manner that actually utilizes these technologies regular your probably dead
and not reading this!
I like the idea of x-drilled, 2-piece rotors on my car....BUT for looks and
slight weight savings (I think of it the same way as wheel design). Unless
I'm talking about a true auto-x or race car, but in racing every little bit
counts and I can justify the costs.
IN THEORY The below is true, but like I said above pad tech has come a long
way.
Does it actually inprove the total brake force available, by preventing pres
sure buildup under the pad and ejection of wear particles from under the
pad.
And drilling doesn't do anything for pedal feel. Also, drilling and slotting
will wear the pad and rotor sooner...don't be fooled by crap that it does
the opposite...it don't!
hotrod....brakes are as much art as science..there are just so many
different variables involving not only performance but feel and consumer
wants it becomes a real pain! To give you an idea, the last program I worked
on was a Ford, they increased the overall wheel diameter by 11.25mm, it
increased my dead booster (emergency stop with a failed booster) by 7 feet
and outside NHTSA's regulations.
What I've done on my cars:
'95 Z28, pads and hoses
'96 BMW 328is, hoses
'00 BMW 328i, hoses
'02 WRX, probably hoses, pads and maybe painting the calipers (for looks, I
have open spoke wheels). Possibly lighter rotors depending on how much
weight I would save...don't know how much the stock one weigh (and would do
it only when it's time for replacement rotors) then again maybe it's just my
racing mentality showing.
Just my 2 cents: too many people try to built race cars for the road..it's
just a waste of money.
Again, you have to know what you want to get out of your system and where
you're going to use it.
In the end if you got the cash it won't hurt, but you get to a point of
diminishing returns and you have to wonder! I think the WRX brakes stock are
pretty good for street brakes and I belief a good set of high mu pads will
be all I need (knowing that wear and dust will be a problem).
The thing with ads is that many times they're true but leave out the
circumstances there true under. Decrease braking distance 10ft with our
pads....after 20 stops from 150MPH!
2-Piece rotors
I have seen a lot of postings on 2-piece rotors. Some of the information
contained in them is correct some is mythical.
Some definitions.
2-Piece rotor: A brake disc rotor that has a separate hat (cap) usually made
from a light weight metal. There are two types of common 2-piece street
rotors. One uses a bolted hat and the other a pinned hat (also known as a
"floating rotor" design).
The bolted type is just what it sounds like. Usually an aluminum hat bolted
to a cast iron rotor. The only real benefit of this design is weight
savings. However, weight savings tend to be only 10-20%, all else being
equal, but with a 50-75% price increase.
The pinned type has usually stainless steel pins that attach the aluminum
hat to the rotors. This allows the rotor to "float" on the pins. The great
advantage of this design is that it allows the rotor to move freely. When
the rotor expands and contracts there is much less chance of binding or
distortion. As you can imagine this cuts down on warping and uneven wear
(DTV). The disadvantage of this design is really high costs.
As far as better heat conduction, not really. It does help a bit, buts it's
not enough to make it worth the extra cost. The nice think about the weight
savings is you can get larger rotor with out taking a weight penalty.
- it may help keep you wheel bearing cooler.
Lug Nut Torque
Next Installment:
Most of you already know about this, but some don't and some don't realize
how important proper torquing of the lug nuts are.
IF YOU DON'T OWN ONE GO OUT AND BY A TORQUE WRENCH...NOW
Over-torquing of wheel lug nuts is one of the prime causes of brake rotor
distortion. This can lead to permanent warping of the rotors, uneven wear of
the rotors and pads and lots of brake chatter (NVH).
With todays very stiff alloy wheels, like from BBS, SSR, Volk, etc., when
you torque down the lug nuts the wheel mounting surface will force what ever
it contact to take it's shape. Which means whatever that surface looks like
will be what the rotor looks like.
Get a torque wrench and check the torques on every lug nut and make sure
they are within the specs (which you should be able to find in your owner's
manual). And make sure that every lug nut is torqued down exactly the same.
Even if all 5 on a wheel are within specs, not having all 5 be equal will
introduce distortion.
And if you think that your light alloy wheel can't possibly be that stiff,
you wrong they are MUCH stiffer than the brake rotor or even the hub.
WORD OF CAUTION: Don't assume that the torque the lugs to the lowest range
in the spec is the best. Try and keep it nominal not at the extremes of the
range.
Much of the problems with rotor warp, brake chatter, disk thickness
variation can be traced back to over-torqued and uneven torqued lug nuts.
After coming back from the shop, get that torque wrench and check the lug
nuts yourself.
Hey one thing everyone forgot about as far as keeping brakes cooler:
Brake Air Ducts.
This is only for auto-x and racing.
Getting all that extra air on the brakes going down a straight gets the
brakes nice and cool for the next corner.
Cheap and effective. You can do it yourself.
Just need some flex tube, a few brackets and some mesh.
The brackets are used to mount the ends of the tube and the mesh to keep
larger rocks, sticks, leaves from clogging up the tube.
Just do a little planning before hand and the job will go by real easy.
One piece of advice, you don't want the tube opening pointing directly at
the brakes, but use a panel to direct the air. These just makes sure that
you don't have dirt, gravel and winter salt thrown directly onto the brakes.
just want to add a little warning about the rear brakes. Be VERY careful
when it comes to making changes back there. Upgrading the rears to increase
braking power, not just feel, can be a double edged knife.
More braking power to the rears will only do you good if; 1. the balance is
woefully off (I mean way off) or 2. you have increased the weight the rear
tires carry and minimized the weight transfer to the front.
Putting more powerful brakes on the rear alone do nothing more than casue
you to lock up or go into an ABS event sooner. You must increase the rear
tires load to benefit from an increase in the rear brakes power. Otherwise,
the rears should be looked at only from a "feel" standpoint.
Brake Performance Vs. Brake Feel
I think too many are mixing these two up from reading some posts. Especially
about the 4 piston Subaru fixed calipers. Just to clarify, in brief, the
differences.
Brake feel: pedal effort and pedal travel for any given desired
deceleration. Ease of brake pressure modulation, accuracy and precision of
modulation. Feedback through the pedal "describing" pad rotor contact
dynamics and pressure fluctuations.
Brake Performance: Level of brake torque produced and the resistance to
brake torque loss, better known as fade.
For performance I do not use the term stopping distance because that
involves more than just the brakes.
Benefits of "better" feel:
Brake feel is just like steering feel. The better the feel/feedback is the
more of the inherent performance you will actually be able to use.
Imagine a car that has 1.0g of lateral grip, but has lousy steering. Too
light, completely dead, nothing happens just off-center, poor linear
response and too much or too little ratio. Like a Mercedes AMG
How much of that great 1.0g are you ever going to be actually using with
poor steering?
Same with brakes. Improving feel will allow you to better use what you have.
However, it will not objectively increase brake performance. If you are
already getting the max out of you system then better feel will not get you
more.
The formula below is a decent way to estimate what, if any, increase you
have in brake torque after an upgrade:
Brake Torque Increase %=
[(caliper piston area new/old) * (effective radius new/old)* (brake pad
friction coefficient new/old)]
*effective radius is the distance from the center of the hub to the center
of the brake pad
*For sliding calipers multiply the areas by 2
Any answer equal to 1 means no increase. Any answer less than 1 means you've
gone backwards. Any answer greater than 1 means a torque increase.
This will NOT give you the actual brake torque, just the difference.
Now things like steel lines, stiffer calipers effect feel not performance.
Only force applied, torque arm and friction do that. You can change things
like lines, calipers, pedals and boosters to change the characteristics.
Such as, initial bite point and initial deceleration level, pedal travel and
effort, pedal force mulitiplication. However, these do not actually produce
more brake torque.
Common Brake Fluid Boiling Points
code:-----------------------------------------------------------------------
----- || Wet Boiling Point || Dry Boiling Point
Castrol SRF || 518°F || 590°F
Earl's HyperTemp 421 || 421°F || 585°F
Motul 600 || 420°F || 593°F
AP-600 || 410°F || 572°F
Neosynthetic 610 || 421°F || 610°F
ATE-Super Blue || 392°F || 536°F
Valvoline || 333°F || 513°F
Castrol LMA || 311°F || 446°F
Earl's HyperTemp 300 || 300°F || 568°F
Ford HD || 290°F || 550°F
Wilwood 570 || 284°F || 570°F
PFC-Z rated || 284°F || 550°F
AP-550 || 284°F ||
550°F-----------------------------------------------------------------------
---------
All brake fluids absorb moisture, some faster than others (except silicone
which is not recommended for anti-lock brake systems). Castrol SRF resists
moisture contamination (non-hygroscopic) more than any other fluid we
tested, therefore change intervals can be greatly extended. This reduces the
effective cost over a season of racing. Many drivers say that they can run
the same fluid all year long with only bleeding off the fluid in the
calipers for each event. This way a can or two will last all year. Other
fluids (hygroscopic type) require additional flushing of the system for each
track event to maintain the lowest percentage of moisture and the highest
boiling point.
FYI - The Castrol SRF is around $77/container versus $10-15/container for
the rest.
Silicone Brake Fluids
Fluids containing Silicone are generally used in military type vehicles and
because Silicone based fluids will not damage painted surfaces they are also
somewhat common in show cars.
Silicone-based fluids are regarded as DOT 5 fluids. They are highly
compressible and can give the driver a feeling of a spongy pedal. The higher
the brake system temperature the more the compressibility of the fluid and
this increases the feeling of a spongy pedal.
Silicone based fluids are non-hygroscopic meaning that they will not absorb
or mix with water. When water is present in the brake system it will create
a water/fluid/water/fluid situation. Because water boils at approximately
212º F, the ability of the brake system to operate correctly decreases, and
the steam created from boiling water adds air to the system. It is important
to remember that water may be present in any brake system. Therefore
silicone brake fluid lacks the ability to deal with moisture and will
dramatically decrease a brake systems performance.
MINIMAL boiling points for these specifications are as follows:
code:--------------------------------------------------------------------- #
|| Dry Boiling Point || Wet Boiling Point
DOT 3 || 401ºF || 284ºF
DOT 4 || 446ºF || 311ºF
DOT 5 || 500ºF || 356ºF
DOT 5.1 || 518ºF ||
375ºF-----------------------------------------------------------------------
---------
Poly Glycol Ether Based Brake Fluids
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1.
These type fluids are hygroscopic meaning they have an ability to mix with
water and still perform adequately. However, water will drastically reduce
the boiling point of fluid. In a passenger car this is not an issue. In a
racecar it is a major issue because as the boiling point decreases the
performance ability of the fluid also decreases.
Poly glycol type fluids are 2 times less compressible than silicone type
fluids, even when heated. Less compressibility of brake fluid will increase
pedal feel. Changing fluid on a regular basis will greatly increase the
performance of the brake system.
FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under
this standard is three Department of Transportation (DOT) minimal
specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for
fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based
fluids).
Wet vs. Dry Boiling Point
WET BOILING POINT - The minimum temperatures that brake fluids will begin to
boil when the brake system contains 3% water by volume of the system.
DRY BOILING POINT - The temperatures that brake fluid will boil with no
water present in the system.
How does water get in there?
Water/moisture can be found in nearly all brake systems. Moisture enters the
brake system in several ways. One of the more common ways is from using old
or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from
the surrounding air. Tightly sealing brake fluid bottles and not storing
them for long periods of time will help keep moisture out. When changing or
bleeding brake fluid always replace master cylinder caps as soon as possible
to prevent moisture from entering into the master cylinder. Condensation,
(small moisture droplets) can form in lines and calipers. As caliper and
line temperatures heat up and then cool repeatedly, condensation occurs,
leaving behind an increase in moisture/water. Over time the moisture becomes
trapped in the internal sections of calipers, lines, master cylinders, etc.
When this water reaches 212º F the water turns to steam. Many times air in
the brake system is a result of water that has turned to steam. The build up
of steam will create air pressure in the system, sometimes to the point that
enough pressure is created to push caliper pistons into the brake pad. This
will create brake drag as the rotor and pads make contact and can also
create more heat in the system. Diffusion is another way in that
water/moisture may enter the system.
Diffusion occurs when over time moisture enters through rubber brake hoses.
The use of hoses made from EPDM materials
(Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR
use steel braided brake hose with a non-rubber sleeve (usually Teflon) to
greatly reduce the diffusion process.
DOT what?
DOT: Acronym for "Department of Transportation" -- an American federal
agency or "Department of Transport" -- a British agency
DOT 3: This brake fluid has a glycol base. It is clear or light amber in
color. Its dry boiling point is 401° minimum and wet boiling point of 284°
minimum. It will absorb 1 to 2 percent of water per year depending on
climate and operating conditions. It is used in most domestic cars and light
trucks in normal driving. It does not require cleaning the system and it can
be mixed with DOT 4 and DOT 5.1 without damage to the system. The problem
with it is that it absorbs moisture out of the air and thereby reduces its
boiling point. It can also damage the paint on a vehicle.
DOT 4: This brake fluid has a borate ester base. It is clear or light amber
in color. Its dry boiling point is 446° minimum and wet boiling point of
311° minimum. It is used in many European cars; also for vehicles in
high-altitude, towing, or high-speed braking situations, or ABS systems. It
does not require cleaning the system and it can be mixed with DOT 3 without
damage to the system. The problem with it is that it absorbs moisture out of
the air and thereby reduces its boiling point. It can also damage the paint
on a vehicle.
DOT 5: This brake fluid generally has a silicone base. It is violet in
color. Its dry boiling point is 500° minimum and has no wet boiling point in
federal DOT 5 specifications. It is used in heavy brake applications, and
good for weekend, antique, or collector cars that sit for long periods and
are never driven far. It does not mix with DOT 3, DOT 4, or DOT 5.1. It will
not absorb water and will not damage the paint on a vehicle. It is also
compatible with most rubber formulations. The problem with it is that it may
easily get air bubbles into the system which are nearly impossible to
remove, giving poor pedal feel. It is unsuitable for racing due to
compressibility under high temperatures. If as little as one drop of water
enters the fluid, severe localized corrosion, freezing, or gassing may
occur. This can happen because water is heavier and not mixable with
silicone fluids. It is unsuitable for ABS.
DOT 5.1: This brake fluid has a borate ester base. It is clear or light
amber in color. Its dry boiling point is 500° minimum and wet boiling point
of 356° minimum. It is used in severe-duty vehicles such as fleets and
delivery trucks; towing vehicles, and race cars. It can be mixed with DOT 3
or DOT 4 without damage to the system. It maintains higher boiling point
than DOT 3 or DOT 4 fluids due to its higher borate ester content. It is
excellent for severe duty applications. The problem with it is that it costs
more than other fluids and there is limited availability. It also absorbs
moisture out of the air and thereby reduces its boiling point. It can also
damage the paint on a vehicle.
What causes a mushy pedal?
DOT 5 fluid is not hygroscopic, so as moisture enters the system, it is not
absorbed by the fluid, and results in beads of moisture moving through the
brake line, collecting in the calipers. It is not uncommon to have caliper
temperatures exceed 200° F, and at 212° F, this collected moisture will boil
causing vapor lock and system failure. Additionally, DOT 5 fluid is highly
compressible due to aeration and foaming under normal braking conditions,
providing a spongy brake feel.
I'll call it, "Mini brake test"
Me and 2 friends performed a little brake test this morning.
I have a friend that works at Teterboro Airport and was able to gain access
to a nice flat and large area. Not a runway.
To make it interesting we brought my 2000 BMW 328i with sport package.
Atomsphere Conditions at the time (benefit of being at an airport):
Temp: 54 F , Humdiity 55% , Barometer 30.28in and rising , Wind 6 MPH East,
partly cloudy
Surface was perfectly dry and smooth. Surface was concrete.
The vehicles:
2002 Impreza WRX Sportwagon with manual transmission, SSR Competition
wheels, 225/45ZR17 Bridgestone Potenza S-03 PP tires, Tein H-Tech springs,
rear 20mm anti-roll bar. All else stock, including brakes.
2000 BMW 328i with manual transmission and the sport package, all stock. The
tires: 225/45ZR17 Michelin Pilot Sports.
The WRX tires have 650 miles on them, the BMW tires have 7000 miles on them.
All pressures where set at the recommended settings as posted on the
driver's door jamb.
WRX has 720 miles on the pads, the BMW has 7000 miles on the pads.
Test procedure:
10 consecutive stops from 60MPH (using the car's speedometer, so chances are
it wasn't exactly 60MPH). That's all I had the time to do.
Consecutive means the time it took to turn around get back to the start and
then 30 second wait.
3 drivers. Myself, worked as a brake engineer and have expierence on well
over 100 different vehicles. Driver 2, Ralph, is a "car guy" and knows how
to drive. Driver 3, Carmine, good driver but not a "car guy."
All numbers are rounded to nearest whole number, so no 120.5 feet, That
would be listed as 121 feet. I do this because of the nature of the test and
the measuring equipment. Which consists of 10 cones spaced 15 feet apart and
a tape measure.
The BMW's DSC (ESP system) was turned off, so both cars had ABS only
working.
For time reasons I was the only driver to do all 10 runs. Ralph and Carmine
just did one each in each vehicle 15 minutes after I was done to add
subjective data.
The results (all in feet):
-------------------------WRX----------------------BMW-------------------
Run 1.......................121............................117
Run 2.......................121............................116
Run 3.......................121............................116
Run 4.......................123............................117
Run 5.......................125............................117
Run 6.......................125............................119
Run 7.......................128............................121
Run 8.......................133............................121
Run 9.......................133............................121
Run 10.....................133............................121
Take these numbers for what their worth. Please keep in mind the difference
in tires and miles on them. And the "test equipment" used. Disclaimer: This
is for entertainment purposes only.