Few aftermarket items can change your bike's performance as drastically, and in so many respects, as a set of wheels. The few pounds dropped would hardly be noticeable if they were from another part of your bike, but because that weight is unsprung and spinning, the effects are magnified greatly. Add in the fact that sexy wheels are out in the open for everyone to ogle, and you can appreciate their popularity.
Testing wheels is difficult-the benefits felt are very subjective-and there is a mind-boggling assortment of aftermarket hoops to choose from. For starters, there are many sizes and types of wheels depending on what kind of riding you do-or how you want your bike to look. A street rider has no use for 16.5-inch race wheels, as there is zero DOT tire selection for them (and don't hold your breath for that to change-the truck industry is still feeling the effects of the dangers associated with having available rim sizes just a half-inch apart). A racebike with carbon-fiber wheels will not pass inspection in most organizations, yet that may be the material most suited to track use. And a racer needs 16.5-inch wheels if he wants the latest in slick-tire technology.
That said, certain properties can be measured to define a wheel's characteristics. One aspect is obviously its weight-which affects both straight-line acceleration and suspension-but another is its Moment of Inertia (MoI)-the characteristic that determines how great an effect that weight has when it is spinning (see sidebar, page 43).
To settle on a base line of what wheel sizes to test, we contacted as many manufacturers as we could find and asked for 17.0-inch hoops for our GSX-R1000 test mule in 3.5-inch front and 6.0-inch rear widths. Each manufacturer was invited to submit two sets, one oriented toward the street rider, one for track use. And yes, we know serious track wheels would be 16.5-inch, but in the interests of comparing apples to apples....
We weighed each wheel using an AdamLab CPW30 scale (measuring to 0.02 pounds, or one-third of an ounce), and found its Moment of Inertia. To check fit and finish, we mounted each set to the bike and measured some important dimensions. We'd have loved to test for strength and elasticity, but turning $30,000 worth of wheels into junk would make mincemeat out of our budget. Finally, we rode the GSX-R at a track day with one of the lightest sets of wheels installed to see just what all the fuss is about (see sidebar, at the end of this article.)
And now, a healthy host of heavenly hoops harmoniously and humbly harvested and highlighted for your honorable henpecking. Honest!
Weight: front: 5.50 lbs.; rear: 10.38 lbs.
Moment of Inertia: front: 217 lb. in2; rear: 304 lb. in2
These five-spoke carbon-fiber wheels are easily the lightest 17-inch hoops in the test, and also have the lowest MoI of the 17-inchers. The front wheel, at just 5.5 pounds, is the lightest overall. Fabricated in South Africa, the carbon rim and spokes are bolted and glued to aluminum hubs (though magnesium hubs are available for even more weight savings). Fit is excellent. Our test rear wheel's cush drive was a bit sloppy, and while the wheels are for the most part magnificent, the outside of the rims appear very rough and unfinished.
Weight: front: 9.42 lbs.; rear: 14.02 lbs.
Moment of Inertia: front: 421 lb. in2; rear: 587 lb. in2
Price: $2180 ($1480 in black anodized finish)
Formerly Hi Point wheels, these Carrozzeria forged aluminum wheels are made in the United States. The front wheel is a one-piece design, and has one-size-larger bearings with an internal spacer. The rear wheel has two bearings on the brake side, and bolt-on brake and cush-drive carriers. The rear wheel's spacers are held by dust seals, like the stockers. The machining on our test wheels appeared a bit rough; otherwise, fit and finish are good. The wheels carry the JWL (a Japanese quality standard) logo, and the hoops shown here have a nickel-chromium-plate finish, an additional $700 cost for the pair.
Dymag Custom Carbon
Weight: front: 7.30 lbs.; rear: 12.38 lbs.
Moment of Inertia: front: 301 lb. in2; rear: 406 lb. in2
Unable to supply a set of GSX-R1000 wheels in time for our test, MaxMoto sent ZX-9R Dymags as a substitute. The British-made wheels feature carbon-fiber rims glued and bolted to cast magnesium spoke/hub internals. Note where the weight and MoI numbers fall in relation to the other wheels, and you can see how important the rim weight is for inertia. The front hub is a single unit, while the rear has a bolt-on brake carrier. The cush drive is cast into the Dymag's hub, and a sprocket is supplied. While the wheels look beautifully made, our test front wheel was a bit wobbly-halfway to the normal service limit.
Weight: front: 6.86 lbs.; rear: 11.62 lbs.
Moment of Inertia: front: 282 lb. in2; rear: 421 lb. in2
Used by the Yoshimura Suzuki team, these Japanese-made forged magnesium wheels are among the lightest in the test, grouped closely with the other forged magnesium rims. The front wheel is fabricated in one piece, and the rear has a bolt-on carrier on the disc side-the cush drive is forged into the wheel with a special, 530-series sprocket included. A minor-but important-detail: These wheels came in the nicest, safest packaging. Finish on our black powdercoated examples is excellent, and they mounted up nicely to the GSX-R. The JBs are marked with the JWL stamp.
Lightcon Twin System
Weight: front: 11.64 lbs.; rear: 19.56 lbs.
Moment of Inertia: front: 512 lb. in2; rear: 786 lb. in2
Heavier than the stock Suzuki wheels, the German-made Lightcons are claimed to be stronger and more durable. Cast in two halves and welded together, our test wheels incorporate an SLC finish (Surface Like Chrome, an electrostatic-applied powder) that adds almost one pound to each wheel. The rear's cush drive is more substantial than most, and the front bolt-on brake carriers have blind holes that require special screws-included along with a sprocket. The wheels are marked with TÜV (a strict German testing standard), JWL and DOT approvals (though other required DOT markings are not present).
Marchesini forged aluminum
Weight: front: 8.82 lbs.; rear: 13.80 lbs.
Moment of Inertia: front: 362 lb. in2; rear: 496 lb. in2
Typically Italian, these Marchesini wheels are beautifully crafted as well as functional-they are among the lightest of the aluminum hoops, as well as having close to the lowest MoI values of that group. The front wheel has bolt-on disc carriers, and the rear cush drive has beefy nylon blocks as opposed to the small rubber donuts typical of most other aftermarket rims. The rear brake carrier is bolted on; valve stems and a special rear sprocket are required but not included. Fit and finish are excellent-our samples are gold anodized.
Marchesini forged magnesium
Weight: front: 6.54 lbs.; rear: 11.12 lbs.
Moment of Inertia: front: 276 lb. in2; rear: 373 lb. in2
Appearing almost identical to the company's forged aluminum wheels but powdercoated rather than anodized, these two examples highlight the differences a simple material change can make in weight, MoI and cost. As opposed to the aluminum Marchesinis, the front is a one-piece design; the rear, however, has the same nylon-block cush drive and bolt-on disc hub-the special sprocket and valve stems are not included. The Marchesinis are the lightest and have the lowest MoI of the 17-inch metal wheels in the test, just edging out the JB-Power hoops in both measurements.
Weight: front: 7.46 lbs.; rear: 12.16 lbs.
Moment of Inertia: front: 327 lb. in2; rear: 437 lb. in2
While cast magnesium was once the standard for aftermarket wheels, the two Marvic styles are the only such examples in the test (Marvic-forged wheels will soon be available). As you would expect, the cast magnesium wheels in general are slightly heavier than the forged magnesium hoops. The Italian Pentas feature five solid spokes, and are one-piece castings-no bolt-on hubs front or rear. A fully machined version (the Penta 2) is available. Fit and finish are outstanding (these examples are powdercoated; unpainted gold chromate is available), though the rear brake-side spacer is a bit thin and could mushroom over time.
Weight: front: 7.16 lbs.*; rear: 11.84 lbs.*
Moment of Inertia: front: 295 lb. in2*; rear: 391 lb. in2*
Similar to the Penta wheels, the Piumas are one-piece magnesium castings, though with larger, hollow spokes. These examples, in 16.5-inch, are slightly lighter-we estimate the savings due to the diameter difference to be approximately 3 percent in weight and 6 percent in MoI. The powdercoated finish on these test samples is excellent, and-as with the Pentas-the Piumas are available unpainted. In addition to a thin brake-side spacer, the threads for the rear disc in our sample wheel were very rough, and we couldn't install the screws. Fit, otherwise, is fine.* 16.5-inch measurements
Weight: front: 8.40 lbs.; rear: 15.54 lbs.
Moment of Inertia: front: 331 lb. in2; rear: 565 lb. in2
These wheels may look familiar-the same model is used on the Aprilia Mille R Factory. The Italian-made forged aluminum wheels are the only ones in the test that bear correct DOT markings (aside from the stockers), and the only wheels that use the stock cush drive and spacers. This keeps costs down and your drivetrain happy, but it incurs a weight penalty for the rear wheel and means your spacers will fall out when you change wheels. Our samples are powdercoated, and the finish is excellent. Fit, as you'd expect for stock components, is near perfect.
Performance Machine Gatlin
Weight: front: 14.56 lbs.; rear: 19.48 lbs.
Moment of Inertia: front: 509 lb. in2; rear: 688 lb. in2
Significantly heavier than the stock GSX-R wheels, that extra weight is in the right place-check the MoI numbers compared to stock. The U.S.-made forged aluminum wheels have bolt-on hubs, no cush drive, and a polished aluminum 530 sprocket is provided. As expected for a blingy set of rims from Performance Machine, the Gatlins' finish is extraordinary-the wheels are beautifully polished, and a chrome finish is available. Fit is good, though the rear spacers are a bit tight on the axle, and the sprocket sits slightly inboard from stock.
Performance Machine Revolution
Weight: front: 9.14 lbs.; rear: 13.16 lbs.
Moment of Inertia: front: 380 lb. in2; rear: 498 lb. in2
Much more performance-oriented than the company's Gatlin wheels, the forged aluminum Revolutions are the second lightest aluminum set in the test-though there are heavier wheels with lower MoI numbers. The wheels have bolt-on hubs, and a polished sprocket (with nuts predrilled for safety wire) and new disc bolts (in titanium!) are provided. Our front test wheel was a bit wobbly, but well within the usual service limit. Typical for the company, the polished aluminum finish is impeccable; a black anodized finish is available. Aside from the rear axle being tight in the bearing spacer, fit is fine.
PVM Forged Aluminum Y5
Weight: front: 7.96 lbs.; rear: 13.44 lbs.
Moment of Inertia: front: 346 lb. in2; rear: 489 lb. in2
Price: $1795 ($1995 with rear rotor)
The lightest aluminum wheels in the test, the forged German-made PVMs have bolt-on brake and cush-drive hubs, and accept the stock Suzuki sprocket. A special floating rear disc is included, though one of the button-head screws on our test wheel had a prestripped head, and we couldn't take the disc off for MoI measurements (the numbers would barely be affected in any event). The weight number listed is without the disk. Powdercoated-and we have no idea why we were sent a mismatched set-the fit and finish are otherwise excellent, and the wheels are JWL marked.
PVM Forged Magnesium Y5
Weight: front: 5.60 lbs.*; rear: 9.76 lbs.*
Moment of Inertia: front: 209 lb. in2*; rear: 290 lb. in2*
Price: $2995 ($3195 with rear rotor)
These wheels tallied the lowest weight (for the set) and MoI of the test, though we were sent 16.5-inch samples. Still, accounting for the difference in size gives MoI numbers almost identical to the Blackstone Tek results. These wheels are another example where the difference between aluminum and magnesium is highlighted-the magnesium examples appeared identical to the aluminum versions (bolt-on brake and cush-drive hubs, rear disc included), though the cush drive is different and a special sprocket is required. Likewise, fit and finish are excellent. Packaging of both sets of PVM wheels, however, could have been better.* 16.5-inch measurements
RC Components Seabring
Weight: front: 10.42 lbs.; rear: 15.42 lbs.
Moment of Inertia: front: 342 lb. in2; rear: 496 lb. in2
The only spun aluminum wheels in the test, the Seabrings are only slightly lighter as a set than the stock hoops, but posted substantially lower MoI numbers-an interesting result. The U.S.-made wheels have hubs bolted and welded together, a beefy cush drive similar to the stock setup (though we'd be worried about the coarse bolts provided without lock washers coming loose) but a bit smaller, and a polished sprocket is provided. The polished aluminum finish is superb (chrome is available), and fit was hampered by the rear wheel's spacers being too snug on the axle.
Weight: front: 10.28 lbs.; rear: 16.80 lbs.
Moment of Inertia: front: 480 lb. in2; rear: 880 lb. in2
Among the highest weight and MoI measurements in the test (uhh, no surprise there), the stock cast-aluminum Suzuki wheels have a cush drive that (aside from the O*Z wheels, which use the stock parts) is much more substantial than any of the aftermarket units. The rear wheel's spacers are held in place by dust seals-almost all the tested wheels use oversized bearings and captive spacers with no dust seals-that tend to fall out easily. The front wheel requires no spacers. Our test bike's rear wheel was a bit wobbly, but well within the service limit. The stock wheels are marked correctly for DOT.
A typical aftermarket cush-drive...
A typical aftermarket cush-drive setup utilizes small rubber donuts. These must be inspected and replaced regularly, as they are much smaller than the stock parts.
Which recipe is right for you?
Not too long ago, things were simple if you wanted to upgrade your scoot with aftermarket hoops: Call up your favorite supplier of Italian cast magnesium wheels, wait several weeks for the wheels to arrive, bolt them on and go. Now, with a wide variety of materials and forming techniques to choose from, selecting the right wheel for the job can be a daunting task.
The stock wheels on your bike are almost certainly made from cast aluminum-though there will be a smattering of other materials mixed in to enhance its properties appropriately. Aluminum, plentiful and easy to work with, offers a good compromise of cost for manufacturing, and strength and elasticity for the road hazards a streetbike encounters. Casting is the most economical way to form bare aluminum into the convoluted wheel shape. Molten material is poured into molds-usually made from sand-and left to cool. Excess material is cut away, and important areas like the hub and tire interface are machined smooth and true.
Suzuki cush drive is larger...
Suzuki cush drive is larger and heavier, but much easier on your drivetrain.
Spun aluminum wheels take shape from sheet stock. The two halves of the rim and spokes begin as flat discs, which are then "spun" into shape on a mandril and welded together. The machined hubs are then bolted or welded to the spokes.
One way to increase a wheel's strength-or parlay that increased strength into decreased weight-is to forge the material into shape. Forging requires huge investments in tooling, as the process involves tremendous amounts of force-a chunk of raw material is pressed into the desired form between two or more dies, much as you would squish a ball of plasticene into a pancake between your hands. The formed part is then heat-treated and, as with casting, excess material is machined off. Forging results in a stronger finished product than casting, as the grains of the material can be oriented in a desired direction rather than randomly placed. Because the dies for forged wheels are so expensive, many manufacturers will have a limited number, and use small machined bolt-on carriers to adapt the various disc and sprocket hole patterns; check for this when looking for wheels, as it does add weight and sacrifice a bit of strength.
Substituting magnesium in the casting or forging process is an easy way to shed pounds from the wheel, as magnesium (the origin of the term "mag" wheels) is approximately two-thirds the density of aluminum. That light weight comes with several disadvantages, however. One is the cost of the raw material and the caution required to work with it-pure magnesium will burn quite nicely. Another is the material's strength and elasticity properties: Magnesium has a lower tensile strength-the material's resistance to being torn apart-than aluminum, as well as a lower modulus of elasticity-a measure of its ability to return to its original shape when distorted. While desirable in racing for their light weight, magnesium wheels are more susceptible to damage from hitting debris in the road than aluminum hoops.
Moving away from metals, carbon fiber is even less dense than magnesium, and much stronger and stiffer than either magnesium or aluminum. The fiber weaves can also be laid in a specific direction, enhancing strength. Fabricating carbon-fiber wheels is a tedious process-a wheel is a much more intricate shape than, say, a fairing-and the machined metal hubs must be bolted or glued to the wheel. One drawback of carbon fiber is that its extreme stiffness makes it less pliable under impact-rather than deform, it could delaminate or even break. In some cases where a damaged aluminum or magnesium wheel could be repaired in a press, a carbon-fiber wheel could appear fine but be unsafe to use. Even though recent advances in their manufacture have greatly improved reliability, carbon wheels remain illegal in many racing organizations.
When shopping for wheels, there are a number of items to check for aside from the material and method of manufacture. Commonly, any spacers should be captive in oversized bearings rather than loose. Make sure valve stems are included, and see if the wheel accepts the stock sprocket or needs something special-like the majority of wheels here. And if you are concerned about drivetrain wear, take a look at the wheel's cush drive-most of the wheels tested, unless otherwise noted, have a simple arrangement of rubber donuts that offers significantly less damping than the stock setup.
Because the process results...
Because the process results in a stronger material, forged wheels generally have numerous, thin spokes. Whereas cast wheels have unmachined portions, these forged items are completely machined to specification. Note the small bolt-on hub used to adapt the common forging to a variety of disc patterns.
Cast wheels generally have...
Cast wheels generally have a limited number of large, hollow spokes. Note the portion of the rim that must be machined smooth.
Carbon-fiber wheels still...
Carbon-fiber wheels still need to have metal parts in the structure, and these must be bolted or glued--or both--in place.
Moment of Inertia can be calculated...
Moment of Inertia can be calculated by rolling the wheel down a slope and measuring the time it takes to roll a set distance from a stop.
Moment of Inertia
How we measured it and why it's important
We're all familiar with Newton's second law, in practice if not in theory, and for objects moving in a straight line, the concept is fairly easy to grasp: If the object is lighter, it will accelerate easier. Once the object is spinning around an axis, however, things get a bit tricky.
We've discussed the concept in an earlier Art and Science (April 2001, online at www.sportrider.com/0402), but here's a quick recap: For spinning objects, the characteristic that relates force and acceleration is Moment of Inertia (MoI). Expressed in pound-inches squared (lb. in2), an object's MoI depends not only on its mass, but also on how far away that mass is from the axis it spins about-in our case, the wheel's axle. As an example of how the distribution of mass is just as crucial as the mass itself, during our test of Buell's XB9R Firebolt ("Occam's Razor," Oct. '02), we found that, while the Buell's front-wheel assembly was 4.5 pounds lighter than that of a Yamaha YZF-R6, their MoIs were identical-the huge weight savings is offset by the Buell's larger single disc and heavier rim area.
Moment of Inertia is important for two reasons. First, a wheel with a lower MoI requires less force to spin up at a certain rotational acceleration, and this can even be seen on an inertia-type dyno, which will read more horsepower for a given bike with a rear wheel that has a lower MoI. Second, MoI determines a wheel's gyroscopic characteristics. A lower MoI reduces the gyroscopic effects, making it easier to turn the spinning wheel from side to side-for the front wheel, this makes turning the bars easier, and for both wheels this makes the bike lean quicker.
John Bradley's The Racing Motorcycle: A Technical Guide for Constructors (Euro Spares, 415/665-3363, www.eurospaces.com) details a method for measuring a wheel's MoI, which we employed for our test. Each wheel was mounted to an axle and rolled down an incline of a known slope. The amount of time it takes for the wheel to roll a set distance from a stop is used (along with the wheel's weight, the slope angle and the axle diameter) to calculate the wheel's MoI. We did five tests, discarding the highest and lowest results and averaging the remaining three values for each wheel. The numbers listed include the rear wheel's cush drive and hardware (but not the sprocket) and a small axle used to conduct the test that has negligible influence.
We sampled the Blackstone...
We sampled the Blackstone Tek carbon-fiber rims at a track day--the benefits of the lighter rims manifest themselves in many ways, but there are also some drawbacks.
A few pounds make a huge difference
As part of our test, we took our GSX-R1000 to a Hypercycle (818/988-8860, www.hypercycle.com) track day at the Streets of Willow and mounted up the Blackstone Tek hoops halfway through the day. We immediately felt a big change in the effort required to turn the GSX-R-it flipped from side to side with less effort, and feedback from the front end was much better on turn-in. The change can best be described as being similar to hopping off a GSX-R1000 and onto a GSX-R750-it's that big a difference. One change definitely not in the GSX-R750 direction was the 1000's acceleration with the wheels installed-the big Suzuki gained speed more easily, and felt like it picked up a few ponies with the swap.
The lighter unsprung weight of the Blackstone Tek hoops also made a difference in the bike's suspension. The GSX-R tracked better over the Street's rough patches, and felt more compliant in general. With more time on the wheels, we'd want to make some suspension adjustments to account for the decreased unsprung weight.
On the downside, the normally solid Suzuki was noticeably less stable in fast transitions, and we encountered some brake problems with the wheels mounted. A slight pulsation under heavy braking from fast speeds with the stock wheels turned into a major chatter, and it felt like there was less feedback under braking.
Lap times during the test were inconclusive-a stiff wind came up once we had the Blackstone Tek wheels installed, and our man went a hair slower than with the stock rims.
Hoop It Up Extras
For additional images and information for the February 2004 wheel test, simply click here.