Once
upon a time, motorcycle manufacturers produced just one type of bike:
the Universal Japanese Motorcycle (UJM). Each proud new owner started
with what was effectively a generic bike, then set it up with the
special parts that defined what type of riding that person preferred. If
you wanted a sportbike, you bolted on some low bars and rearset
footpegs and voila, you had a sportbike. Then the '80s happened, and
superbike racing drove the manufacturers to begin specializing their
production bikes. Thus was born the production superbike and the arrival
of the amazing GSX-Rs and CBRs that we fawn over today. While a modern
sportbike is often awe-inspiring in stock form, a few simple
modifications can make these already supremely competent motorcycles
even better. The tips and tweaks presented on the following
pages range
in price from free to thousands of dollars, but each one will provide a
notice-able difference in performance and will take you one step closer
to sportbike nirvana.
Exhaust & Carburetion
Not too many years ago, one of the quickest ways to increase the
performance of your motorcycle was to pull off the heavy and restrictive
stock exhaust system and replace it with a lighter, higher-flowing
aftermarket one. Well, there's no free lunch, and the after-market units
were significantly louder than stock--negating, through the ill will of
the general public, some of their impressive perfor-mance gains.
Two
things have happened in recent years, though. First, the OE systems
have become significantly lighter and capable of flowing almost as much
volume as aftermarket systems. Because of the improvement in stock
systems, you can no longer count on instan-taneous double-digit
percentage of power increase after mounting an aftermarket exhaust.
Similarly, replacement exhaust manufacturers have become more socially
conscious in their approach to making less noise with their systems
while still offering improvements in power delivery.
Although installing an exhaust...
Exhaust Systems
Aftermarket exhaust modifications fall into two categories: full
systems and slip-ons. The full systems replace the entire stock system.
High-end exhausts with titanium headers still offer fair weight savings
compared to the stock ones. Some headers have various tapers and
crossovers to enhance low- and midrange torque while still improving
top-end power. In fact, some systems offer minimal gains in peak power,
choosing to instead shape the power curve for more midrange and a
broader horsepower peak.
However, one possible
disadvantage of aftermarket systems is that they require the removal of
the servo-controlled valves that some OE exhausts use for better low-end
power. Although installation of a full system is a relatively easy
modification, many riders choose to mount slip-on systems. These range
from simply bolting a canister to the stock S-bend of the header or
replac-ing the exhaust from a mid-point back.
Since the
system becomes a hybrid of OE and aftermarket components, the power
gains are mini-mized. Still, if your bike has a heavy muffler, shaving
those few pounds can be the same as adding some horsepower. Also,
slip-ons don't require the removal of exhaust control valves such as
Yamaha's EXUP system.
Installing this Two Brothers...
After installing a new system,...
Jet Kits
All riders, not just racers, benefit from having a properly carbureted
bike. While an aftermarket pipe may make your bike more powerful, making
sure the carbs are properly jetted will result in more power and
improved power delivery--whether you have a hot pipe bolted on or not.
For example, getting optimum power and smoothness out of an inline-four
may require different needle or jet settings for the center carburetors
and the outer ones. Often, once the needles and jets are set correctly
for all the carbs, a bike wakes up, producing more horsepower in the
midrange, revving quicker and sounding significantly smoother.
Even
on bikes with stock exhausts, the midrange can be overly lean, making
acceleration in the range streetbikes spend most of their time feel
soggy. Simply raising the needles a bit will solve this problem. So,
don't think you only need a jet kit for piped bikes. If you have any
problems with your bike's carburetion, consult the aftermarket. A fix is
probably available.
Installing a Power Commander...
Fuel Injection Remapping
When sportbikes began to arrive in showrooms with factory fuel
injection, changing a bike's mixture was significantly more difficult
than with carburetors.
Now that the aftermarket has had
a few years to develop some solutions, you can buy systems with
alternative injection maps for both stock and modified bikes. For
example, systems like Dynojet's Power Commander and Yoshimura's EMS come
preprogrammed with fuel delivery curves for your bike. Both fuel
injection modules will also allow you how to alter these curves in the
low-, middle-, and high-rpm ranges through the use of buttons on the
units.
The real power of a fuel-injection...
The
real power, however, lies in computer software that allows for control
over fuel flow in increments as small as 500 rpm. This is the ultimate
tinkerer's tool! Also, many shops that offer dyno tuning also have
computers that can upload maps specific to your bike's characteristics
after dyno testing.
These magic boxes don't just offer
EFI tuning, though. The Yoshimura EMS connects to an accessory hub that
can allow the rider to switch between three fuel curves while riding or
install a shift light or ignition-related accessories. Similarly, the
Power Commander features an expansion port for other modules that are
being developed.
These Factory Pro Tuning velocity...
Brakes
From all the attention focused on motorcycle engines, you'd think that
gasoline fuels the most powerful system on a bike. You'd be wrong,
though. Another liquid--hydraulic fluid--carries that honor. Brakes can
scrub off speed faster than an engine can increase it. Consequently,
maintaining your bike's brake system is para-mount to extracting maximum
performance from it.
Upgrades to some components can
give you more than just better stopping cap-ability and/or better feel
from the binders. Aftermarket discs are often lighter than stockers and
can therefore help acceleration and steering.
Installing new pads is a maintenance...
Brake Pads
Yes, you could run your brake pads to the absolute limits of their
service, but performance often decreases before you run up against the
prescribed wear limits. So ignore the wear marks--plan on replacing your
pads when a minimum of 2 mm of the pad material remains.
When
choosing new brake pads, you're faced with an array of options. If you
don't have the time or desire to research what pads will give you the
best stopping power in the conditions you ride in, simply buy the OE
replacement items. Bike manufacturers spend a lot of time developing pad
compounds for their sporting machinery, and you can't go wrong with
these pads.
While the difference in thickness...
You
want pads that deliver consistent stopping power throughout the range
of speeds you're traveling--not a lightswitch-like transition from
little grip to maximum grip. Consequently, race compounds may not be
ideal for street purposes. Talk to the manufacturer first, as some race
pads need to build up heat to work properly.
Most pad
manufacturers do a good job of describing the type of riding different
compounds are designed for. Just be honest about the type of riding you
do when deciding. If you're buying aftermarket pads and your bike's
original pads were sintered (which would in-clude all current models),
you should only use sintered compounds on your discs.
Stronger brake performance,...
Braided Stainless Steel Lines
Although you can't see OE brake lines expand when you squeeze the lever
like you could in the Bad Old Days, fitting a set of braided stainless
steel brake lines to your sportbike can have a dramatic effect on your
bike's stopping power. The initial onset of braking will be much quicker
since stainless lines don't expand at all. Because the lines are
sheathed in metal (usually with a protective plastic outer coating), you
don't have to worry about stainless lines cracking from age and
exposure to the sun. Also, the Teflon interior line is less prone to
becoming brittle than rubber lines. Oh yeah, and they look cool, too.
Most
of the major line manufacturers, like Goodridge, have pre-measured kits
available for almost every sportbike manufactured in the last 10 years.
You shouldn't have any problem finding stainless lines for your ride.
However, if you've modified your bike by raising or lowering the bars or
extending the swingarm, you'll probably want to have a custom-length
kit ordered specially for you. Some manufacturers offer
build-'em-yourself kits where you cut the lines and attach the fittings
at home.
Braking Wave rotors offer...
Aftermarket Discs
While brake pad technology has advanced to the point where compounds
providing quick stops don't necessarily mean you wear your discs out
that much faster, you may find a time when you want to replace your
discs. The good news is that aftermarket discs are usually lighter and
grippier than OE pieces.
What you get for your money is
pretty impressive. Almost all front discs are now floating models,
meaning the swept area of the disc is loosely mounted on a carrier. This
space between the pieces allows the disc to expand without warping in
high-temperature situations. Also, since the swept area and the carrier
now have un-related jobs, their construction can vary more widely. For
example, high-carbon stainless steel is fairly common for the abrasive
surface. Cast iron has also been used here.
You won't
find carbon-fiber swept areas on street bikes since they require heat to
work properly. Recently, wave-patterned discs have entered the fray.
Aside from the obvious lessening of unsprung weight, the manufacturers
say that the wave shape lets a disc expand without deforming under heavy
use. Laser-cutting of the disc is now a common practice, ensuring a
smooth surface on the swept area. The carrier can vary from mundane (and
heavy) steel to aluminum or even featherweight carbon fiber.
Sticky Metzeler M-1 rubber...
Wheels & Tires
What can be said about tires? They're black and round and keep the
wheels from touching the ground, right? Actually, they are your only
link to the asphalt when you're riding your sportbike. Motorcycle and
tire manufacturers spend more time studying how tires interact with the
road than any of us can imagine.
The amazing increase
in sporting machinery's capabilities owes as much to tire advances as it
does to suspension and engine improvement. When it comes to wheels,
lighter is always better, but wheels also play an important role in how
your bike steers--even how stable it is in a straight line.
Choosing The Right Tire
If bikes have refined their focus, tires have become laser beams
directed at very specific activities. Race tires and street tires both
benefit from these advances. Race tires are designed to give maxi-mum
grip for an extremely limited time. To make things even more specific,
they are formulated to work at temperatures only achieved at track
speeds. Below those temperatures, they can be downright scary.
The
tire companies are even tuning their street tires for different levels
of sport riding. If you're the kind of rider who commutes, travels and
runs the twisties on the weekend, you'll be fine with the OE tires for
your bike. Suppose you're the type of rider that only canyon scratches
or attends track days. Well, the premium-model sport tires are what
you'll want to run. According to Jeff Johnson from Metzeler/Pirelli,
Pirelli's Diablo tires were designed for riders who spend about 30
percent of their time on the track and 70 percent on the street. The
Diablo Corsa has someone who spends 70 percent of the time at the track
and 30 percent on the street as its intended user. Rubber compounds have
gotten that specific.
The best places to find
information about who the manufacturers directed a particular tire
toward are the manufacturers themselves. They know that, if they're
designing tires for specific riders, they need to let those riders know
what the differences are.
Instead of worrying about
which tire is stickier, you should concentrate on things like the tire
profile. Are you the kind of rider who likes to slam your bike on its
side and rail through corners at maximum lean? A more triangular
profile, with its quicker steering and larger contact patch at full
lean, will be more suited to you. If you're a rider who trail brakes
into turns, hanging at the outside, waiting to see where the pavement
goes before committing to your final line, you should look at rounder
profiles that have a larger contact patch for braking while upright and
allow for easier adjust-ment of lines mid-corner.
Similarly,
you should look into what riders and tire manufacturers recommend for
the type of riding conditions you're likely to face. If most of your
favorite roads are pretty bumpy, you'll be looking for a tire with a
softer carcass to allow the tread to flex over the bumps. If rain is a
regular occurrence in your region, pay special attention to a tire's
silica content for wet pavement grip. Also, while the big, blocky tread
of some hyper-sport tires look sexy, you can end up doing the two-wheel
two-step with them in the wet. Some tires have a reputation for taking a
long time to warm up in cooler temperatures, so consider the season
when you buy new rubber.
Finally, only use tires that
are designed to fit on your particular rims. Putting bigger tires on
your rim may not give you the bigger contact patch you desire. Since the
carcass will be squeezed smaller to fit, the carefully designed profile
will be erased.
Aftermarket Wheels
In its
most basic sense, installing a set of aftermarket wheels is no more
difficult than remounting the stock rims after a tire change or brake
disc swap--except for the extra money and massive street cred.
Seriously, though, mounting up a set of forged magnesium wheels gets you
more than a big credit card bill. Adding lighter wheels can, arguably,
deliver the most bang for the buck of any motorcycle modification.
Even
though the OEs have wised up and started producing some exceptionally
light wheels, any reduction in unsprung weight (weight not supported by
the suspension) makes it easier for your suspenders to help the tires
track across pavement irregularities. Even saving a couple of pounds
here is a big deal. Replace wheels on a bike more than a couple of years
old, and you can could save as much as 10 pounds.
Next,
consider the weight of the wheel at its rim. As Kevin Cameron says in
Sportbike Performance Handbook, "A pound saved in a wheel rim...is worth
2 pounds anywhere else on the machine. A wheel has to be accelerated
twice; once in a straight line, and also in the second sense of rotating
around its own center." Since wheels rotate, generating gyroscopic
forces, a lighter wheel will turn quicker and accept steering inputs
more readily. Riders who like flicking their bikes into turns will love
the effect lighter wheels have on steering.
On bikes with traditional...
Suspension
Today, the average street rider has suspension technology and
adjustments that were only available to the factory racers a mere five
years ago. This is a mixed blessing.
Proper suspension
setup is key for fast, safe riding, but approach suspension tuning in a
willy nilly fashion, and you'll have an ill-handling beast in no time
flat. If you follow an orderly path, you'll not only improve your bike's
handling but also become a more perceptive rider in the process. The
beauty of these mods is that they are completely free.
On bikes with inverted forks,...
Setting Sag
Proper sag is important because a suspension unit needs a certain
amount of room within its travel to work properly. If you have too
little sag, your bike will be prone to topping out the suspension as it
extends to its limit. Similarly, too little sag could allow you to
exper-ience the unpleasant jolt of bottoming out. Your bike's sag is
broken into two categories: "static sag," the distance your bike
compresses its suspension from fully extended when you climb on board;
and "free sag," the distance your bike settles from full extension under
its own weight.
In order to measure static sag, you'll
need two assistants. A metric tape measure will also make the
calculations easier than an SAE one. Before you mount the bike, measure
the suspension completely topped out. To measure the fork's static sag,
lift on the grips until the front wheel begins to come off the ground.
On traditional forks, measure from the stanchion wiper to the bottom of
the triple clamp. Measure from the wiper to the top of the axle clamp on
inverted forks. Mark this number "L1."
Pick a spot directly above...
Now,
have one of your assistants hold the bike from the rear while you get
in position on the bike. Your other assistant should push down on the
fork and let it slowly rise up until it stops. The new measure-ment will
be called "L2." The front end should now be lifted and allowed to
settle slowly down until it stops, forming measurement "L3." Exactly in
the middle of measurements L2 and L3 is the point the fork would want to
live in a frictionless system.
Armed with this
information, you can determine the static sag by subtracting the average
measurement calculated above from L1. To write it out as an equation,
it would look like this: static sag = L1 - (L2 + L3) / 2. For street
riding, suspension gurus generally agree that between 30 and 35 mm
(1.2-1.5 inches) is optimum sag. If you're track-bound, a stiffer 25 to
30 mm (1.0-1.2 inches) is preferred. If you have too much sag, you'll
need to increase the fork's preload. Conversely, if you have too little,
back off on the preload a bit.
Once you have the front
suspension dialed in, repeat the process with the rear suspension. The
key to getting accurate measurements out back is to pick a solid point
on the frame or bodywork directly above the axle. If you don't measure
straight up from the axle, you may get inaccurate numbers.
All you need is a screwdriver...
Setting Damping
Begin by setting your bike's damping adjusters to the factory specified
positions (listed in your owner's manual). They probably won't stay
there, but the settings should get you in the general area. Damping
adjusters measure their settings in one of two ways: clicks or turns. If
your bike uses clicks, turn the adjuster all the way in (clockwise) and
unscrew the adjuster the correct number of clicks. For turns, do the
same thing but count the turns instead of clicks.
To
test your fork's rebound damping, stand your bike straight up. Press
firmly down on the center of the triple clamp (not the handle-bar).
Don't hold the brake. The suspension should rebound back to its starting
point and not beyond. If it bounces back beyond the ori-ginal position,
then you need to add some rebound damping by screwing the rebound
adjuster on top of the fork inward. Generally, make adjustments in
single clicks or half-turns. If the fork rises back directly to its
original position, press on the triple clamp and time how long it takes
to rise back. You want the rebound to take about a second. Adjust the
rebound damp-ing until you feel the timing is right. Follow the same
procedure in the rear, pressing on the center of the seat. The shock's
rebound adjuster is usually on the bottom of the shock body.
Although
you can test your suspension settings anywhere, the best way to get an
accurate measurement of changes is to repeatedly ride the same section
of road. Dial in the front and rear suspension separately. To get a feel
for what direction you need to go with your compression damping, ride
your test road with the compression set to the factory specs to form a
base line. Next, go a couple of clicks firmer. Did the handling improve
or get worse? Now try a couple clicks softer than stock. Which of the
three settings do you prefer? Keep experiment-ing. Take notes. When
you're satisfied with the front suspension, continue the process with
the rear.
If you need more adjustments,...
The
challenge of setting up your suspension is that some symptoms can be
caused by completely opposite problems. For example, if the front of
your bike has a vague mushy feeling, you could be suffering from either a
lack of compression damping or rebound damping. Looking for other
symptoms will help you determine which setting to alter.
When
you're happy with how your bike's suspenders perform, try one last test
to make sure that you have balanced settings. Support the bike without
any stands and press firmly on the tank. The front and rear suspension
should compress and rebound in unison. If either end compresses or
rebounds differently from the other, try altering the settings slightly
to get the chassis movement in synch.
--Evans Brasfield
is currently writing 101 Sportbike Performance Projects, set to be
published by Motorbooks International later this year. The material in
this article was adapted from that manuscript.
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