Sportbike Modifications

Dollars at the rear wheel

By Simon-Pierre Smith

The long dreary Northwet winter has finally arrived, and your mind has been wandering to the coming spring. Christmas money from Aunt Maude is burning a hole in your pocket and you're looking to buy a little performance before the sun hits. Before I tell you where to spend your ill gotten gains, I'll paraphrase a line out of the repair manual for the venerable Honda CB360T, "Before purchasing performance parts, one is well advised to consider putting the money toward a machine with more potential." I'm intentionally leaving riding gear out of this list of goodies. We all know that flip-flops, a t-shirt, and a baseball cap are all the riding gear we need, assuming they've gotten the Nikwax treatment.

Power

Let's start with the big Kahuna, a full on Superbike motor. This typically involves high compression pistons, a lightened and balanced crank, titanium rods, high lift and duration cam, valve springs, some clutch modification, and removal of unnecessary items like a starter, alternator, and balance shaft. This would cost around $6,000 for a GSXR 1000. The trouble, for a street ride, is the high compression. Most people ride enough to want to be able to gas up with 92 octane. One easy fix is to swap high compression pistons for ones with bigger bore and lower compression. Not legal for some race classes, like 750 Superbike, the bigger pistons have all the poop and probably a longer ring life. While a lot of money for an occasional thrill, the Superbike motor is the pinnacle for easy wheelies.

Above: This SV650 motor shows high compression pistons to give power and oversized studs to hold it all together.

Aunt Maude didn't cough up $6,000? Blame Enron. A cheaper route is the traditional "pipe and a remap" Supersport method. A typical high end exhaust like Akrapovic will run upwards of $1,500 and give less weight, good ground clearance, and a hearty power boost. There are lots of pipe brands in the world, but some shops won't deal in certain brands because they fit poorly. When a 10-minute bolt up turns into a 2-hour cut, bend, and re-weld, you've lost money. The "re-map" of the fuel injection needs to be done whenever any modification is made to adjust to the change in airflow.

Do you want raw wheelie loftability without spending a couple of mortgage payments? The best bet is a gearing change at about $60. The smaller the front sprocket, or bigger the rear, the more torque is applied to the rear wheel. Sure, you'll hit the rev limiter before you hit top speed, but do you really need to go 180 MPH? Impressing people outside the bar happens in first gear. If you can wait until your stock sprocket is worn, then the change is essentially free.

Another cheap wheelie mod is available for some Suzukis. They come with a built in ignition retard that drops power in the first 3 gears. This is to prevent novices from flipping the bike out from under themselves. A simple mod tricks the ignition box into thinking it is always in 4 ^th gear. Old timers will fondly remember the good old days when the single wire on the GSXR 1100 that runs from the shifter drum to the ignition box could be snipped, giving a 1 ^st gear power boost. Crafty Suzuki left that wire off the wiring diagrams. Now expect to pay about $150 for the fake out box.

Suspension

Let's again start with the big dollar option. A high end set of forks like Ohlins will give you less weight, more rigidity, and damping tailored towards the racetrack for about $3,000. A good Penske shock will do the same in the rear for $1,100. You'll still need a couple track days to get all the adjustments set the way you want them, and you may need to do some tweaking from track to track. To be honest, the change will not be noticed on the street.

OK, Maude the Miser has stiffed you again. A basic truth about bikes is that most don't need a different suspension, they're just sacked out and misadjusted. With old overworked oil changing viscosity, seal leaks letting oil out and water in, and goop and grunge clogging up oil passages, a good cleaning and rebuild is all you need. Expect to pay a few hours labor for cleaning, polishing of tubes, seal replacement and reassembly. Make them give you a good middle of the road setup and work from there. Don't be afraid to twiddle knobs. Compression damping, rebound damping, ride height, and preload, just keep track of what you did and what effect it had. Don't be worried that what worked for a friend wasn't what worked for you. Tires, rider weight, and riding style all make suspension tuning an individual task. That's why they come adjustable.

Looking for a fashion mod? Trick yellow titanium nitride (TiN) coatings can be put on your forks for about $300 plus the same amount for labor. The benefits of lowered seal friction are nothing compared to the cool factor on the street.

Looking for better wheelies? For free? Adjust your ride height way up, both front and rear. This improves weight transfer to the rear, lofting the front wheel. You can also crank up rear spring preload, rear shock compression damping, or even get a stiffer rear spring. Just remember that the further you get from a balanced bike, the more likely you are to toss it in a corner. It also increases stoppies, which reduces braking ability. Your flip-flops will not protect you.

Weight Loss

The nice thing about most weight loss items on a bike is that they rarely add stress to wearing parts, and also tend to look good.

Aunt Maude's Visa only gets hit for $1,500 for a good set of magnesium wheels. This gives noticeably better acceleration, handling, braking, and cool factor. Look for about 6 pounds of rotating and unsprung weight loss. Throw in a set of Titanium axles for about ¾ pound and $250 ea. Some people worry about galling of the threads and bearing areas with Ti axles, but I've never had a problem.

Next step down on the cost scale is bodywork. Racers always pull the heavy and valuable plastic fairings and put on light, expendable fiberglass. You can too. Prices for Kevlar and carbon keep dropping, so fair weight gains can be had, though the finish can be rough and paint is required. Finally, look at handfuls of little things. Lightweight aluminum sprockets, thinner chain and sprockets, aluminum fasteners for NON-CRITICAL applications, aluminum clutch plates, smaller turn indicators, etc… Just put a price per pound limit and then spend away. It should be possible to trim 15 lbs off a stock bike just with a fairing and a few little doo-dads.

Above: The lightweight wheels make you cool. The Marvic sticker lets the world know about it. The after market brakes look snazzy, but money spent on weight loss improves braking and acceleration.

Bonus Modification

This isn't a performance mod, but can save you a ton of cash, as well as looking cool. Put on some aftermarket billet side covers and nylon frame saver pucks. For just a few 100 dollars your machine will look race prepped and be a good $1000 better off in a low side. Just don't rub the frame savers on a belt sander. Save that for your knee sliders.

Many thanks to Eric Dorn of EDR Performance and Dave Hodges of GP Suspension for encouraging this fantasy world where we spend money on bikes.