In engineering terms, the motorcycle is referred to as a “single-track” vehicle.  That means that both wheels of the motorcycle follow the same single track.  At least, that’s how it would be in a perfect world.  The constant effects of wear and stress can change the relationship of the front and rear wheels on your bike.  When that happens, we call the bike “out of alignment.”  That’s bad, because if either wheel is out of line with the bike’s frame either vertically or horizontally, or if the wheels are out of line with each other, it’s definitely going to affect the way the bike handles.  The bike will tend to “pull” in one direction or the other while turning or braking, may tend to wobble at high speed, or may feel as if you’re riding on ice instead of pavement.  Plus, when the wheels are out of alignment on a bike the tires will wear out prematurely, as well as causing premature wear on the sprockets and chain or the belt. 

Looking for issues in wheel alignment is particularly important if you are looking at buying a used bike.  Remember, steering and wheel bearings can wear out, and frames may be bent as the result of an accident.  If the bike you’re looking at has these problems, you may never be able to get the wheels in proper alignment without replacing bearings or having frame work done, and both of those services can become expensive!  So it’s always best to have a trained motorcycle technician evaluate a used motorcycle before you pony up the cash.

When checking your bike’s alignment let’s address first things first.  First, check your manual to see if your bike has a front wheel offset.  Okay, I know that I just said that in a perfect world every bike would have wheels in perfect alignment, but the fact is some motorcycles – including many customs, as well as some production bikes – are designed with a front tire that is off-set from the back tire.  This feature is because, due to the distribution of weight in the frame, it would be impossible for some bikes to maintain balance if the wheels were aligned.  By off-setting the front wheel, these bikes correct for the imbalance and manage to roll true.  But even these motorcycles have alignment issues. 

While some new wheel alignment tools use lasers to pinpoint out-of-alignment wheels, the old-school method of aligning a bike involved running a piece of string, tied to the front tire, around the back tire, creating two straight-edges.  By measuring the differences in distance between the tires and the string, a shade-tree mechanic could make adjustments with shims or spacers that would true up the alignment to within a degree or so, and certainly within the 100-thousandths of an inch of variation that’s considered allowable.  See, on a motorcycle, alignment is less of an exact science because of the mushroom-cap design of motorcycle tires.  Even if the wheels and frame are in perfect alignment, even a slight amount of tire wear will throw alignment off by a few thousandths of an inch.  Thankfully, the gyroscopic operation of a motorcycle is by nature user-forgiving, and besides a few experienced bike racers, most motorcycle riders will never notice a minute amount of misalignment; however, let that amount of misalignment increase and more than just the handling of the bike may be compromised.  On bikes with fixed-disc-and-caliper brake systems, a badly aligned wheel will rob the brakes of contact between disc and rotor, making it harder to stop the bike, and resulting in pre-mature brake wear.  

So how does a trained motorcycle technician go about “truing up” your bike’s wheel alignment?  First, the bike must be on its centerstand or on a service-stand that will hold the bike perfectly level.  Start in the rear of the bike, making sure that the rear wheel is centered on the swing-arm and so rolling in a perfectly straight line with the bike’s frame.  Some bikes have truing holes drilled in the swing-arm.  By using a simple tool with a moveable marker, it’s possible to find the distance between the hole and the center of the axle on one side of the bike, and then compare that distance to the same marks on the other side of the bike.  If there’s a difference, simply remove the axle nut cotter pin...loosen the axle nut...and tighten or loosen the axle adjustment until both sides of the axle are the same distance from the measuring hole.  On other bikes this measurement must be taken from the swing-arm pivot itself, but the procedure is the same.  After you’ve finished your adjustments, use a torque wrench to snug the axle nut back to factory specs, and replace the axle cotter pin.

Now, using an instrument called an inclinometer you can find out if the wheel is perfectly vertical.  It should read within one degree of a straight-up-and-down 90 degrees.  If it doesn’t, you may have a bent frame, a badly worn hub or wheel bearings, a damaged wheel, or some other major defect.  Don’t ride that bike until you’ve had the bike checked out by a licensed mechanic because you may be facing severe handling problems.  After you’ve finished adjusting the rear wheel, check your final drive belt or chain for proper tension.  Every bike is different, so make sure you know what your manual says about how to go about this procedure on your motorcycle.

If everything looks good, it’s time to move on to the front wheel.  Your technician will have a specialized measuring device to read the exact distance from the center of the wheel to the forks on both sides of the bike.  Again, in a perfect world these should be exactly the same, but the fact is, any variation within 100/thousandths of an inch is considered OK.  You can usually correct small variations using shims or spacers.     

Now it’s time to hang the inclinometer on the front wheel.  If it doesn’t read between 89 and 91 degrees, we may be looking at some real problems – the hub or wheel bearings are in bad shape, you’ve got bent forks or suspension components, or you may even a damaged wheel.  Again, stop poppin’ wheelies and get this bike in the shop – it’s really not safe to ride until your technician has found and fixed the defect.

When should you have your bike’s wheel alignment checked?  Your manufacturer may have a recommended schedule so simply check your owner’s manual.  But anytime you sense too much vibration from your bike, especially at highway speed, or if there’s shudder and shake when you brake, or if you can feel the bike “pulling” in one direction or the other, these could all be signs of a motorcycle that’s out-of-alignment.  Keeping your wheels aligned means keeping your bike as rideable, as maneuverable, and as in control as it’s supposed to be, and that’s one more way to keep the shiny side up, and Ride On!

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