In a perfect world, we'd walk to our climate controlled garage every year-sometime after the new models rolled out-to find that old faithful had been replaced with the newest piece of techno-finery. Not that we didn't love our previous ride, but sport riders have a fascination with newness so why not own the latest and greatest? Unfortunately, in the real world-where we have to pay for our machinery-we've usually formed a bond with our bikes by just about the time they have been paid off. After all, the motor's been breathed on; you've added an aftermarket pipe and carbs and your suspension's been upgraded. When you really think about it, there's not much you need to change on your bike.
Except tire technology
You've been eyeing the sticky buns your riding buddy put on his bike, and you know that the only thing between you and nirvana is the wider wheels to mount those sexy tires. Yet, when you shop around for some aftermarket hoops, you discover that the cost of the improved wheels would make a nice down payment on a new bike. And some wheels even require that the stock brake system be tossed for trick-but-pricey binders. While you could simply resign yourself to running older tire technology, you do have another option.
Although many folks will opt to buy those nifty aftermarket wheels, thrifty riders and racers have long enjoyed the benefit of wider wheels without coughing up the big bucks for replacement items. Their secret? Weld-up wheels. Widened stock wheels offer many advantages over aftermarket wheels. First, the modifications are usually cheaper than buying new wheels. Second, the other stock components that have to interact with the wheels are guaranteed to work since the only part of the wheel being modified is the rim. So, nix the expense of having axle spacers and caliper mounting brackets machined for those aftermarket hoops. Finally, many aftermarket wheels require the sacrifice of the cush drive to the sticky rubber gods. Getting stock wheels widened is starting to look pretty good, eh?
When it comes to weld-up wheels, Kosman Specialties is the leader in what is essentially a field of one. The company has been widening wheels for more than 20 years while other companies have come and gone. Why? Well, widening wheels is a labor-intensive operation that requires in-depth knowledge of machining, welding, and, most importantly, motorcycle wheels. Cut too far into some wheels, such as the hollow rims on Comstar wheels, and you've crafted an expensive, hard to replace piece of junk. Once the time, machinery, and experience required to modify wheels is considered, the price of $375 per wheel seems like even more of a bargain than just comparing the cost of weld-ups to aftermarket wheels. An additional 50 bucks can even turn your 16-inch wheels into 17-inchers.
Since motorcycle wheels aren't necessarily centered in the swingarm, measure the clearance between the widest point on the tire and the narrowest point it must clear on both sides.
Measure Twice, Cut Once
Since sending your wheels off to Kosman for widening irrevocably changes them, a little research is necessary prior to pulling them off your bike. After all, you don't want to find out that you've got clearance problems at speed. First, decide on the sizes of the tires you want to run. You will need to know what rim width they are designed to be mounted on and the width of the tire when mounted and inflated. Next measure the width of the tires currently residing on your wheels. Finally, measure the clearance between the widest part of the tire and the next closest parts of the bike. (Usually, the swingarm on the right and the chain on the left.)
Now, do the math. Find out how much broader the new tire is by subtracting the measured width of the current tire from the manufacturer's width of the new tire. Divide the result in half and compare the number to the clearances measured on the current tire. If the calculated number is less than both measurements, you've got room for the tire-just don't cut it too close. Make sure you have at least an eighth of an inch to spare.
Wait! Don't pull the wheels off yet. If the new tires are significantly larger in diameter, the room around the current tire (measured from the axle when the suspension is fully compressed) should be checked also and compared to the radius calculated from the new tire's outer diameter (r=circumference/2p). The clearance between the tire and the front fender-or any brace under it-is even more critical. Remember, there should be enough room for the diameter of the tire to grow at speed. Now, start wrenching.
Cutting down to widen up
Even if you have a lathe in your garage, odds are it's not this beefy. The stock flanges are machined off the wheel, leaving only the center. If the machinist miscalculates the slightest bit, the rim is junk.
Once wheels arrive at Kosman, they are checked for straightness. Some wheels may have a ding in a flange that can be machined off, but Kosman doesn't straighten bent wheels. (See the sidebar below) In order to widen rims, the customer's wheel needs to have its flanges removed so that the flanges from a donor rim can be grafted on. A machinist mounts the wheel to a lathe, and using a parting tool, cuts off the stock flange. Next, the cut is cleaned and machined with an interface developed by Kosman to accept the donor flange. According to Kosman, the shape of the interface is crucial to the construction and long-term integrity of the weld-up wheel. The customer's rim width is then measured down to a thousandth of an inch so that the width of the donor flanges can be calculated. The new flanges receive a mirror image of the interface on the rim-only with enough difference in size to create an interference fit that will hold the flange to the rim once pressed together. The machinist's final step is to press the flanges onto the rim and check for runout.
The donor flanges are machined to the proper size to achieve the desired wheel width once the pieces get welded together. These three sections have been machined so that when pressed together an interference fit keeps everything in place prior to welding.
The welder tack welds the seams together in a crisscross pattern akin to tightening down a cylinder head. By equalizing the pressures on the components, the opportunity for the pieces to jump apart from the sudden increase in heat of welding is lessened. Once both flanges have been tacked together sufficiently, the seams of the flanges are welded on both the inside and outside of the wheel. Kosman stresses that the proper type of welding rod is imperative for strong wheels. (And no, we weren't told what rods the welders use.) However, Kosman was willing to let one secret out: key to the wheel's strength is making sure that the area around the weld is clean of potential contaminants, which explains why the machinist stripped the OE powder coating back approximately 5mm from both sides of the flange interface. After the welding is complete, the wheels are again checked for runout before they are packaged for shipping.
Once spot welded together (at intervals of every few inches), the seams-both inside and out-get welded. Don't try to make the wheels pretty by grinding away the outer weld. This will weaken the wheel. |  |
The new rubber slides right in with room to spare. The extra meat will be appreciated in Willow Springs' long Turn Eight. | |
The Wheel Thing
The 3.5-inch stock wheel (left) looks puny next to the 4.5-inch Kosman-ized wheel. Surprisingly, all that extra aluminum only added eight ounces to the weight of the wheel. Now, any of the sexy rubber available for the Aprilia 250 will slip right on to this EX500 wheel.
Weld-up wheels do not require any more special treatment than stockers-with one exception. Painting or powder coating usually don't pose a problem to the wheels. However, some riders may be tempted to grind down the visible weld on the inside of the rim to keep things pretty. Don't. The weld is integral to holding things together. Besides, those in the know will see the welds as a sign of a cool modification. Contrary to popular myth, weld-ups don't add "a bunch" of weight to stock rims. (We even heard one shop claim that weld-ups weighed nine pounds more than stock.) To put these rumors to rest, we weighed our EX500 wheels before and after their trip to Kosman. The front wheel gained only two ounces while the rear gained eight ounces-hardly a major increase. And the pleasure of running fat, current-tech rubber vastly outweighs the slight increase in unsprung weight. (Kosman claims that weld-up wheels actually weigh less than some cast aluminum wheels of the same diameter.) So, if you want to go wide with your old, faithful bike, consider weld-up wheels before plopping down the big bucks for custom wheels.
Post-log
One of the three front wheels Kosman modified exhibited the strange symptom of leaking air around the bead of Dunlop D207GP tires while remaining air-tight with GP Stars. Sport Tire Services representatives said that, in the last ten years, they've only seen two Kosman wheels with this problem. The wheel was returned to Kosman, and we will report on the results in the future. The other wheels have been trouble free with Bridgestone, Dunlop, and Michelin tires.
Sidebar: Hey, nice hump!
OK, so you may have been following that car too closely to react when the 2 x 4 emerged from underneath it. Or perhaps you were riding in the rain, and the pothole was filled with water. Either way, your bike's rims aren't so round anymore. Never fear, Tom Mackie (626/355-7058) can smooth your wheel's new hump.
The dial gauge illustrates how badly a curb twisted the front wheel on our CBR900 project bike. Once Mackie worked his magic, the runout was only 0.015 of an inch.
An afternoon trip to Mackie's shop in Sierra Madre, California, revealed a craft that should appeal to the Luddite in most of us. As Mackie puts it, "I simply massage wheels until they cooperate or break." The tools Mackie utilizes for his brand of massage therapy are a dial gauge, a grease pencil, a Porto-Power hydraulic press, a really big leather mallet, and some beefy mounting bracketry.
In a process that is more art than science, Mackie mounts your tweaked wheel to his work bench and checks it for the out-of-round sections with a dial gauge. After marking the high and low points with his cryptic code, the hydraulic press flexes your rim in the right direction. Problems with the faces of the rim are handled with a whack or three from the leather mallet. The wheel abuse continues-with occasional pauses to flip the rim-until the runout is less than 0.025 of an inch.
Now before you go and get worried about how he treats wheels, remember that the wheels start out as junk. If the wheel expires while strapped to his table, he charges nothing. According to Mackie, Honda wheels fracture more often than others. Similarly, magnesium wheels, which lack the flexibility of aluminum ones, also tend to go to pieces under the strain of straightening. However, with the cost of a new F3 wheel checking in at more than $500, paying for the shipping of a bent wheel to Mackie is a worthwhile investment. Mackie charges $45 per wheel and usually turns around repairs within a week.
RESOURCE
Kosman Specialties
7706 Bell Rd.
Windsor, CA 95492(877) 456-7626
www.kosman.net
This article was originally published in the June 2000 issue of Sport Rider
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