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Do you mean "cupped?" As has been stated in this thread, bad or imbalanced tires are the most likely culprit. A badly cupped front tire would almost certainly be noticeable at higher speeds.
Yes, they're "cupped" so sounds like best bet is to get a new tire - thanks!!
 

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cupping should indicate tyre pressure issues, or tyre out of balance, or defects in the steering. get the tyres replaced and dynamically balanced. Then try it without luggage, then with luggage
 

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My theory on tire cupping, feathering or scalloping will lead me down the rabbit hole here..

So.. here it goes anyways.

We can sit back and blame it on a number of things but as far as I'm concerned.. on this bike.. its wear, plain and simple. Under inflated tires, hard cornering and weight bring the problems on faster than the normally would. I've had 5 sets of tires on my bike and every one of them did the exact same thing. Some of them lasted longer than others but they all feathered or cupped. My current set of RSIII's have less than 2500 miles on them. Almost all of it two up and spirited riding.. they are shot. The rear is starting to look like a sand paddle and the front isnt so bad but has a funny shape across the crown so it will get swapped out anyways.

You can do anything you want to stop it from happening but if you have a tendency to ride hard, its just a fact of life.... of the tire.
 

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I‘ll take a stab at it based on my understanding because @Darbinco didn’t shy away from it. And I agree with him. Worn or misaligned suspension parts can wear tires in unusual and maybe even predictable ways as well as poor pressure control or balance. But, tires wear. And motorcycle tires wear quickly and are not rotated to help them wear more evenly. And the K is a heavy powerful bike that punishes tire compounds.

And as far as scalloping of the front tire...at some point I reached the understanding that the diameter of the tire constantly changes as the contact patch moves from centerline toward sidewall so that the contact itself has varying tire diameters within it. That coupled with counter-steering has a natural tendency for uneven wear referred to as scalloping or cupping. Some tires may resist this result more than others, but I believe it is more the riding style than the tire itself that magnifies the natural wear tendency. Then again, my understanding could be subject to change and evolution. Darb...is this similar to the rabbit hole to which you were referring??
 

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I agree with @Darbinco and @J-Luv on front tire wear. The only thing I would add is temperature. If you ride hard when it is hot (>90 degF), you will wear out both tires in fewer miles. Watch any MotoGP race and you will see how worried they are when the temperature goes over 90 deg F.

Back to the original post, my 2015 GT with a Top Box is rock steady without any shake, rattle or roll (or left pull) at all speeds up to what my cojones will allow. I can put it in cruise at 90+ and take my hands off the bars. (Yes, in Texas we have roads with legal 85 mph speed limits)
 

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Darb...is this similar to the rabbit hole to which you were referring??
Yes Sir!
Theres also a theory out there that the leading edge of the tread block wears faster than the main or following edge of the block because it hits the pavement first and most easily sheared edge of the tire. That tread block will also be thinner at that point than the rest of that block on the tire. This wear pattern gives the tire a feathered look and feel. While I do have some doubts on the overall theory I can look at my front tire and see some truth to it. The back is a bit different. When the daylight swings back around tomorrow I will try and post some pictures of it.

I agree with @Darbinco and @J-Luv on front tire wear. The only thing I would add is temperature. If you ride hard when it is hot (>90 degF), you will wear out both tires in fewer miles. Watch any MotoGP race and you will see how worried they are when the temperature goes over 90 deg F.
Heat absolutely plays a part in tire wear. The hotter the tire the softer it gets. You dont have to be a MotoGP racer to tear up a tire in 90+ deg temps on a twisty road.
 

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On another note..
Dunlops website states

You may not be able to entirely avoid cupping. Tire cupping or irregular wear is a somewhat common occurrence on all vehicles. On a four-wheel vehicle, you are advised to rotate your tires periodically to even out wear. Unfortunately, you do not have this luxury with a motorcycle because front and rear tires, unlike those on most four-wheel vehicles, are not interchangeable.

However, there are steps that can be taken to minimize cupping and uneven wear on a motorcycle: Maintain your motorcycle and particularly your front and suspension. Avoid hard braking whenever possible. Braking causes the tire to grab and wear in one direction. When braking is applied to the front tire, the load transfer over-flexes the tire and increases the tendency for cupping and uneven wear. Maintain your tire pressures. Under inflation and overloading of motorcycle tires are significant causes of cupping and uneven wear, particularly in association with hard braking and/or trailer use.

Once a tire begins to show signs of uneven wear, even following these steps may not improve the condition.

Tire companies can, and are, helping to minimize cupping and uneven wear but you, the rider, must do your part. Following the aforementioned guidelines will help avoid uneven wear.
 

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My SWAG;

Tire cupping is impossible to completely eliminate. Tire cupping can be caused by a large number of issues and is to be expected on all tires, on all vehicles. The concerning factor is the degree of cupping. Tires are designed for 'load'/'speed'/'traction' but none of those variables take into account suspension, riding style, road, air pressure, etc...

Compound. A motorcycle tire (appropriate for our bikes) has variables compounds, it literally changes as you move across the width of the tire.



The center compound is hardest, the edge compound is softest. This is design meant to ensure that you get the highest mileage out of the tire but without compromising cornering grip. Note that the tread grooves span the multiple compounds of the tire. This means that all things being equal, those grooves are going to wear differently across their span based on where on the tire you ride (what compound), the air pressure in the tire, how you ride, etc.. Spending a lot of time under load on the edges of the tire is going to put more heat, deformation, and wear into that part of the grooves (starting at the leading edge of the groove which undergoes the most deformation). I suspect that the problem starts here. Tread grooves are a compromise between legal, performance, and aesthetic concerns. That compromise is where everything starts and together with actual tire design (compound) and manufacturing quality, probably come together as the single biggest factors in uneven wear.

The rest is mental mastirebation. (can you be more speculative than just a SWAG)

The second thing that happens is while you are riding is that you are moving the contact patch around the circumference of the tire. (the tire is rolling and the contact patch is hopefully in one place relative to the road). As the tire deforms it transfers the load into the rest of the tire, ideally this would be a perfectly uniform distribution... but its not. Tires can be perfect balanced but not perfectly true and even if they are balanced and true, that doesn't mean that they are perfect structures. Tires are built using an additive process out of non-uniform (imperfect) materials. While tires may appear to be round they are not and while the sidewalls have a rating, they may not be uniformly stiff (and are not) all the way around the circumference. All tires vibrate while driving - whether you notice it or not. This sets up both a natural frequency (based on being imperfectly balanced and imperfectly stiff around the circumference). Add to this the moving deformation of the contact patch and you have not just heat but also variations in forces across the circumference of the tire. This will contribute to non-uniform wear.

The byproduct of hard riding or even long steady-state riding is that you will begin to create wear patterns in the tire. In the case of the former (as @Darbinco pointed out) is putting heat into the tire (as a byproduct of friction) which is going to cause those variable compounds to wear unevenly. During extended steady state riding sessions you may get some uneven wear just from the fact that the tire is imperfect and any variation in construction is going to set up a natural resonance in the tire which in turn could cause uneven wear.

On top of this, any suspension related problems (bearings, alignment, weight distribution, air pressure etc) are going to create their own issues, more often than not accelerating uneven wear.

Once the wear pattern starts (cupping is typically a pattern) it just accelerates slowly over time. It could be a case of some tires having the perfect storm of tread pattern, construction, compound that makes them worse than others for a particular bike (cup faster than others). I would suspect that all tire designers know this and some of them are biasing towards one target vehicle class, riding style, etc over others meaning that even given the same load class and tire wear that the target use case is different. A Goldwing vs 1600 GT as a loose example so some tires are just going to do better on some bikes.

/end of SWAG
 

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Yes Sir!
Theres also a theory out there that the leading edge of the tread block wears faster than the main or following edge of the block because it hits the pavement first and most easily sheared edge of the tire. That tread block will also be thinner at that point than the rest of that block on the tire. This wear pattern gives the tire a feathered look and feel. While I do have some doubts on the overall theory I can look at my front tire and see some truth to it. The back is a bit different. When the daylight swings back around tomorrow I will try and post some pictures of it.



Heat absolutely plays a part in tire wear. The hotter the tire the softer it gets. You dont have to be a MotoGP racer to tear up a tire in 90+ deg temps on a twisty road.
Here is my rear tire after a trip last year in the summer after some hot days in some twisties (2-up)...

139882


And this photo was taken after a few hundred more miles in non-twisties to get home. This is the only tire I've ever done that to but our riding conditions are typically not above 90. The heat certainly had an impact.

You can clearly see one edge took the brunt of the wear.
 

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Mine looks similar just not as much wear. This is a good example of what it looks like before they get to the point of Cams tire. Whats strange though is the little fin thats starting to appear is the leading edge. Which is opposite of what the front tire is doing... it seems anyways. While theres still life left in my tire it rides terrible and will be replaced in the spring.
139885
 

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All motorcycle tires cup due to the physics involved in how a bike tire works (as outlines in several posts above). While running under inflated tires may aggravate cupping, it’s not the root cause. I’ve never had a set of tires that didn’t eventually cup and I check my tire inflation every two weeks. Regarding the OPs vibration..I’ve never experienced cupped tires vibrating while riding upright. The cupping only caused vibration (and tire roar) when cornering.
 

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Whats strange though is the little fin thats starting to appear is the leading edge. Which is opposite of what the front tire is doing... it seems anyways.
You are right...and that is because of the rear tire experiencing the forces in the opposite direction compared to the front. The front bears the force of braking. The rear bears the force of acceleration.
 
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