Practise this and try to stay fashionable!
Many motorcycle instructors,
from CBT up to Police Advanced, still quote the following
old chestnut :- "you brake 75% front and 25% rear
on a dry road; and 50%:50% in the wet".
This advice is also enshrined
in "Motorcycle Roadcraft" and the " IAM
Group Handbook". So it's a pity that, nowadays
its totally wrong. Progress changes things.
The 75 %:25 % rule made its
first appearance a LONG time ago. The early diagrams
explaining it, show drum braked Triumph Speed Twins;
so it's not unfair to assume that the 75%:25% rule has
been around for at least 30 years!
The old Speed Twins (and
their ilk) had little in common with today's motorcycles.
They had one twin leading shoe front brake of about
7-inch diameter (I can't find anyone who's old enough
to be certain), operated by a Bowden cable from a hand
- brake lever. The rear brake was single leading shoe,
about 6-inch diameter BUT operated by a sturdy 10-inch
long foot -brake lever; pushed by a leg honed to muscular
perfection by kick-starting the darn bike in the first
And the tyres? They were
no wider than the widest mountain bike tyres of the
1990's and poorly designed even compared to the car
tyres of the day (cars already had tubeless tyres but
all Motorcycle tyres were high aspect ratio, tubed crossply's).
The usual tread pattern was ribbed front and block rear.
The all-important contact patch was long and thin, not
least because the wheels were 20 inches or more in diameter.
But above everything else,
it's the design of motorcycle frames that has changed.
The old Speed Twin and its like were TALL. The vertical
engine, surmounted by a spine tube frame (with enough
gap to allow daily tappet adjustment) meant a high riding
position. The centre of gravity of a bike (with rider
aboard), in the 60's was probably a foot or more higher
than it is on most sports bikes of today.
And there were two sorts
of front forks: - "Rock hard" (race bikes
and those carrying heavy Rickman fairings) and "Spongy
soft"; prone to dive to the fork bottoms under
the lightest braking. The net result of either type
was that, under braking the front went almost rigid;
like a pushbike's forks.
If you've got locked forks,
a narrow (low grip) front tyre and a centre of gravity
that small planes have to detour around; its not
surprising that you're cautious of using your front
brake. If that brake is a grabby drum brake (they "self-servo-ed",
so the braking effort was not proportional to how hard
your hand squeezed the lever) you did as much as you
could with the "controllable" rear brake.
Anyway, a locked rear was controllable, even on a Speed
"New Tricks Motorcycle
Design" has moved on since the old dogs of the
1960's. In fact, it had already moved on far enough
to make the 75%:25% rule questionable by the 1980's
The BIG sign that 75%:25%
is wrong, is that most bikes these days (since the RD350
at least) can do "stoppies'' and not crash immediately
after. In a stoppie you push the front brake to its
limits, you brake so hard that the rear leaves the ground.
This is neither big nor clever; but it does prove to
the most hide-bound among us that the bike, at that
instant, was stopping using 100% Front brake and 0%
I'd now like you to think
about proddy racing because in Production Racing (apart
from Owen's missing alternator, sorry Mr. Scrutineer)
the bikes used should be the same as those you meet
on the road. Now, I understand that, in a race, most
competitors are trying to ride as fast as they can.
Theyre not there to put on a show of stunt riding
to impress the crowd.
Yet, horror of horrors; they
do NOT brake 75%:25%! Stand at the braking point at
the end of the straight (do not stand on the bend at
the end of the straight: it's where Reg Ford usually
smashes into the crowd). You will see many of the riders
lift their rear tyre clear of the deck under maximum
braking. Theyre doing stoppies, yes theyre
braking 100% Front and 0% Rear!
And theyre not doing
this deliberately to show off (apart from Jamie Whitham
at the end of a race!). Theyre doing it because
nowadays, it's the natural, instinctive way to brake
as hard as the bike can possibly brake.
So What's New Pussycat?
Modern motorcycles (as above,
this includes most road bikes designed since the RD350)
are radically different from that old Speed Twin. The
few that aren't, retros like the Zephyr and trail bikes,
probably still have to brake 75%:25%.
(Apparently, one of the first
things Geraint Jones teaches at his Moto-X school is
how to brake. You do this by learning to stop a Motocrosser
from 50mph on mud , using only the front brake. So,
even on the dirt, there's scope for more front brake
use - if you have the cojones!)
Modern bikes are lower -
by about a foot (compare even a "modern" GPZ500
with an old 750 Triumph - the GPZ is more powerful,
too). Modern bikes tend to be shorter, by around 5 inches.
And have smaller wheels, these days fronts are 16 to
18 inches they used to be 18 to 21 inches. And wheel
widths (hence the contact patches) are at least twice
as wide as they used to be. The modern tyres are stickier
- even in the wet and theyre radials (or bias
belted), so they deform to grip the road far better.
Added to that, the low sidewalls help the bike's centre
of gravity stay low.
And front suspension, even
if you don't have upside down fork legs, is ten times
better at absorbing ripples that might upset a tyre
You'll notice I haven't mentioned
the brakes. I think the grabbiness of 1960's brakes
and the need to stand on that big footbrake lever, is
one of the root causes of the 75%:25% rule. That was
how people found they had to brake, so they assumed
it was the best way to brake.
Since then, Triumph have
died, been reborn; died again and been reborn as a far
better bike. Rules for braking written to suit the 1990s
SpeedTriple would differ a lot from those written for
the Speed Twin of the '60s.
But the masters of motorcycle
design are the Japanese. Now, believe it or not, they
tend to design things to do their job. Very occasionally
they screw up, but most things they get right. Mudguards
keep the mud off. Footpegs don't bend under your weight.
You can reach the levers and the switches at the same
time. (The old Triumphs, sad to relate, didn't manage
any of these things.)
So we'd expect modern Japanese
bikes to have brakes suited to their function - stopping
the bike as quickly as possible. So, how do they set
up their brakes?
Front Two 320mm disks, each
gripped by 4 or 6-piston callipers.
Rear One 220mm disk, gripped
by a 1 or 2-piston calliper.
At a conservative estimate,
the front brakes are 5 times as powerful as the rear
(remember the diameter of the disk has a big effect).
And I'd bet that the foot lever is now as short as the
So why have the Japanese
fitted brakes so out of line with the 75%:25% rule?
Are they foolish? Is it some sort of "look at the
size of my brakes, darling" fashion accessory?
Or is the 75%:25% rule just plain wrong these days?
Answer: the 75%:25% rule
really is "just plain wrong" these days (for
most modern bikes on most dry roads).
What's the truth? The truth
is, there is NO truth. Any fixed apportionment of braking
effort, front to rear is wrong. In cars, they teach
taper braking - you bring the pressure up gently, to
avoid a skid until the weight transfers forwards; at
which point you can brake hard; and you let it off gently
as you roll to a halt, to avoid a jerk when you stop.
Bikers, too, need to learn
taper braking. But as we have separate front and rear
brakes, we also need to learn to taper the force from
rear to front and back to rear again as we slow.
(Owners of Moto Guzzi and
Honda linked brake systems can leave now - but remember,
as you depart, that racing Guzzis always removed the
linked brakes - they aren't quite as good as separate
systems, right at the limit.)
An ideal stop goes something
You apply both brakes gradually
and with almost equal force for the first phase of your
The weight will transfer
forwards as the front suspension compresses, and your
There's now more weight on
the front (up to 100% if you're braking at 1g - and
modern road bikes can brake at up to 1.2g).
You now let off most - or
all - of the rear brake and increase pressure on the
front, which now has most or all of the grip. This middle
phase of braking can be 100%:0% - if it is less than
85% front, you probably aren't braking anywhere near
your bike's limits.
The bike slows and the forces
you are exerting through the brakes and tyres diminish
(the energy in the bike is proportional to the square
of your speed).
The front begins to rise
back up on its suspension.
(If it's an emergency, you
now breathe a sigh of relief and a small prayer of thanks).
You taper off on the front
brake - to prevent a slow speed lock up - and increase
the rear brake pressure once more.
Even stopping from 100 mph,
the last 5mph are slow riding, and you should only use
the rear brake for slow riding. So you do the final
phase of stopping 0% front and 100% rear.
If you MUST quote a fixed
apportionment of effort - I'd say it is 85%:15% - which
is in line with the way Japanese bike designers set
up the brakes.
But the truth is, situations
will vary which is why we should forget 75%:25%. Motorcyclists
need to learn to taper brake; to balance front and rear
brakes in a sensitive, reactive fashion - not to follow
an outdated mathematical tenet.
And, to slip in two quick
plugs - you can learn how at the Nurburgring Perfektion
Training courses or on London Advanced Motorcyclist's
Machine Control Days.
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