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.
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 Racing slip-on doesn't even require the removal of the fairing lower. |  |
| After installing a new system, wipe it down completely to keep exhaust heat from burning fingerprints and smudges into the pipe's surfaces. |
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.
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, 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 stacks bolt either into the airbox or onto the throttle bodies to massage the horsepower output. |  |
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.
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.
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.
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.
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.
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.
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.
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."
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.
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.
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.
