Common Motorcycle Tire Wear Patterns
Common Motorcycle Tire Wear Patterns
Valkyrie and VTX tires shown, but these principles can be applied to most motorcycle tires
© 2006 Chet Walters
Permission to reprint granted by request
Please note that you can see a larger, better detailed picture by clicking on the images below.
Bear in mind, that this is an "informal study" and the facts within, though compelling and accurate for the most part, are not exacting. By "not exacting", we mean that none of the photos were squared up except by eyeballing, none of the actual angles were measured and there was no allowance given for the artifacts produced by backgrounds, lighting angles and camera lenses. In short, this is not a very "scientific" essay thus you will find missing the usual (and usually suspect) plethora of confusing statistics & numbers that often appear in articles of this type. There's not much math here for one very simple reason -- there is no need for it. As we assembled the photographic evidence to support these theories regarding motorcycle tire wear patterns, the evidence so obviously supported the theories and so strongly disproved other theories we felt no need to provide minutia. True, that lack here may leave some unsatisfied. So be it. We invite those obsessed with such detail to supply same and we will be happy to add those facts to these since we have no doubt that the conclusions drawn by them will be the same as those drawn here by us.
The first question to be addressed is "What is tire wear?" Tire wear is the actual removal of rubber from your tire. Scuffing is what wears out your tires. Just like when you were a kid and skidded your rear bicycle tire to make marks on the driveway, the abrasion of scuffing is the only contributor to tire wear. If you never scrubbed anything off your tires, they would never wear out. It takes some pretty good stiff forces to come into play for pavement to scuff stuff off of your tires. This scrubbing of material off your tires becomes evident in what is called cupping, flat band upright tire wear which presents itself most evident on the rear tire and side flat band tire wear which presents itself most evident on the front tire. All of these wear patterns will be discussed and all are present to some degree on both the front and rear tire. But in the following discussion, it is important to remember that it takes a goodly amount of force where your tire meets the road to grind material off of your tires to produce tire wear. Too, we assume that you will run with properly inflated tires. Improperly inflated tires will cause all of these wear patterns to be greatly exaggerated and will cause you to lose many many serviceable miles. Check pressure often. Empirical evidence for Valkyrie and VTX tires shows that running 38/40, 40/40 or 40/42 (or slightly above/below) will greatly extend tire life. The Honda spec of 33psi for these bikes is way too low and is designed for maximum comfort and grip but minimum tire life. Increasing the pressures to some combination of the above will provide increased longevity and improved handling for these tires.
So, with that in mind, let us begin with probably the biggest bugaboo tire wear pattern in the motorcycle arena.
FRONT LEFT SIDE TIRE WEAR:
One needs really first to understand
what causes "side" tire wear to begin with, as this "side"
wear is evident on both sides of a front tire and also to a lesser degree on both
sides of the rear tire. Side wear is a band of wear evident on the sides of the
tires at the most common lean angle for that motorcycle. It is caused by the interaction
of the pavement and the tires in a turn. When you turn, your bike really wants
to go straight (Newton's First Law of Motion). You apply a force to make it turn
in your wise desire to stay on the curving road. The bike's desire to keep going
straight is the natural and inertial centrifugal force in this interaction and
the force resisting the inertia making the bike turn to follow the road is the
As one can imagine, there is quite a bit of force coming into play when your bike makes a turn. You are probably not a light weight (how about a generous 200lbs with gear?). Your bike likely weighs in at several hundred itself (A loaded Valkyrie goes near 800 or more). Add to that half ton, the actual acceleration of your vehicle (about 45mph in a typical casual turn). So you are running fine up the road until the road presents you with a curve. You pitch your bike into a typical lean, that half ton at 45 wants to go straight and you need it to go around the bend. The only thing preventing a crash is about a 2 inch contact patch between your tires and the pavement where the forces involved in a simple casual turn exceed 1 G in space age parlance. The scuffing where your tire meets the pavement is what causes the "side wear" bands to appear sooner or later and this scuffing is the only "force" that is capable of producing the wear that eventually becomes evident. If one looks at the pictures of the worn front tire and the worn rear tire, the squared off side band wear is evident at the typical lean angle for casual riding on typical roads. In comparison with the tread pattern of a new Avon tire, one will see a much deeper tread precisely at the point where the squared off side band wear will eventually appear (might the Avon designers know something about this wear?).
But the question remains - Why is this wear more evident on the left front in most cases? Actually, excessive side tire wear is only evident on the left front in countries where one rides on the right side of the road. Riding right means that the left side of your tire will have more (and likely faster) miles on it than the right side. Left hand turns have a larger radius than right hand turns in right side driving countries, hence you ride farther (and likely faster) turning left than turning right with subsequent increased side band wear on the tire's left side. The left side of your tire has more miles on it (in some extreme cases, twice as many) than the right side of your tire. And the side of your tire only gets mileage when you are leaned in a turn, otherwise, this area of your tire does not contact the pavement at all as shown in the photo. European left side drivers find that the right side of their front tires will wear out first. Quite the opposite effect for precisely the same reasons reversed. (If you're still not convinced, we will re-visit this issue later with more reasons)
REAR CENTER TIRE WEAR:
Trail is necessary for your bike to be stable going straight, but it is also necessary for turns since trail causes your front wheel to steer itself into the turn. Countersteer and trail's geometry effect resulting in a turn is discussed at Wikipedia in detail. Click here to visit. A good video of using countersteer for turns is found here (VIEW MPG). Note in that film how countersteer is used to initiate the turn (the bike momentarily turns in the wrong direction) then once the bike leans shortly thereafter, trail causes the front wheel to turn itself into the turn which is what actually steers the bike in the desired direction.
OTHER THEORIES DISPROVED:
STILL NOT CONVINCED?
If you are still not convinced that
increased mileage is what causes one sided tire wear on the front tire of motorcycles,
you'll have to come up with a theory that satisfies all of the evidentiary criteria.
A) It will have to explain the fact that when riding upright, the tire's side
wear bands do not contact the pavement (road crown, unbalanced/off center bike
weight and even wheel misalignment won't work). B) It will have to reverse itself
in countries where one rides on the left side of the road rather than the right
(road crown still sounds plausible here but it was eliminated in "A"
Besides the fact that the left radius is larger which means you will probably go faster causing more stress on your tire than you would going the other way, there is more visibility when making lefts than rights which will add to your tendency to make the turn faster as well. Failure to negotiate a left turn will have you going off the the road onto the shoulder or into a ditch. Failure to negotiate a right turn will have you crossing into opposing traffic. Though neither scenario is appealing, there is a subliminal advantage to left turns (riding shoulders and ditches is better than crashing into trucks head on) and this will have you going a bit faster on lefties too.
The increased radius on left turns means more distance is traveled turning left than turning right on the average riding day. That is plane geometry and plainly undeniable. Because of the natural tendency to make left turns faster (admittedly this is subjective and open to debate, but is plausible for reasons given) there will be more stress placed on your tires as they travel that longer left distance. Increased left side tire wear is evident, though, on both the front and rear tires but because the front tire shows less evidence of flat band center wear (which disguises the side wear bands on the rear tire), side wear is more evident to the eye up front and leaves you to wonder, "Why does the left side of my front tire wear out first?" Now you know.
Of course, if you live in Singapore, you'll say, "Why does the RIGHT side of my front tire wear out first?" And now you know as well!
Dual Compound Tires
Michelin Pilot Power 2CT (front
BT45 (bias ply rear)
NOTE ON TIRE SIZES - The standard formula may not work for bike tires...
SIZE DOES MATTER: 180 or 200 mm is the WIDTH of the tire. 60 or 70 is the ASPECT RATIO of the tire. The height will be 60 or 70 percent of the width of the tire. As always, divide by 25.4 to convert to inches. Hence 180/70 = 180 times 70 percent = 126 mm height 200/60 = 200 times 60 percent = 120 mm height. If dead on accuracy of the circumference of a tire is necessary for a speedometer, always measure the tire, never depend on this formula to give exact readings for a bike tire. More info on MC tires can be found here: http://www.webbikeworld.com/Motorcycle-tires/tire-data.htm
(this text may be accessed as a single page at http://www.rattlebars.com/carformula.html )
After installing a Metzeler 200/60-16 tire on the rear of my VTX I tried to set my Sigma digital speedometer² on my VTX using this formula...
width x .profile) x 2 then divide by 25.4 mm per inch plus wheel diameter = total
height in inches
Total height from formula above would be the diameter then x 3.14 for circumference. However, the sigma readings were way off when I rode her so I measured the tire with a tape. The formula for a Metzeler 200/60 - 16 yields 79.9 inches (2029mm) for circumference, but the measured circumference of the tire is actually 81.39 inches (2067mm). Using the measured 2067mm for the sigma gives dead on readings as checked by radar. Wazznt able to accurately measure the diameter since the tire is mounted but math reveals the formula should give 25.44 inches (646mm) as diameter and the actual measured circ would yield 25.92 inches (658mm) (81.39 / 3.14) as diameter.
I was finally able to measure a new mounted Avon 180/70 x 16 as 80.8 inches (2054mm) while the formula yields 25.92 inches as diameter and 81.39 (2067) as circumference. However, the Metz 200 is a little pinched on the five inch rim which causes the increased height. Measured width of the Metz 200 on this rim is 7.625 inches (193.67mm) while the Avon mounted measures 7.25 inches (184.15mm).
|Metzeler also reports that the tread depth on the 200 tire is 6.5mm while I was able to measure variance from 4.8mm at the outer edge to the deepest which is 5.4mm. Here is a copy of the size comparison from the Metz web site courtesy of Blue Elf of the VTXOA.|
some links and each calculator will yield the incorrect results vs the measurments
² The Sigma 800 Digital Spedometer which I have one each mounted on all my bikes is detailed on this page http://www.rattlebars.com/vtx/sigma.html
Questions? Contact Chet at Chetspages@rattlebars.com
Wednesday, June 18, 2014 22:17