New Avon Cobra Chrome - any good

barbagris said:

ime this is little to do with the width. The sidewall reduction using a 150/70 gives the same axle drop (hence rake/trail change). And this makes a huge difference to handling esp with an E-Max on the rear.

I have a theory (though it will not be cheap to test - involving custom rims) that massive width differences front to rear affect handling more than one might think. It's all to do with crown radii.

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Speedy said:

It does, it does. The contact point on the wider rear moves toward the corner's radius center point more than the contact point on the front wheel moves as the bike angle relative to the road increases. Thus a line from front contact patch to rear contact patch changes angles as the inclination angle increases with the effect of reducing the effective turning radius. So the more you lean the more you have to steer.

Then there is the effect of the change in the center of gravity relative to the contact patch centerline which the shift in contact patch line inward moves the CG outward creating a moment that wants to stand the bike back up. The net effect is it takes more and more rider input the greater the lean angle. This effect can easily be felt at slower speeds on crowned streets or near a curb even traveling straight ahead.

On the plus side, the old girl stands right up when exiting a curve which makes her feel more svelte than she actually is. I suspect the Touring models are easier to ride fast then the standards.

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Speedy said:

It does, it does.

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CrzystghndKC said:

if you have an Avon tire that has worn out too early you may have a claim.

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barbagris said:

What would be your opinion on how this continual change of relative patch movement affects wear.
I suspect it's like continual Indian Burn and exacerbates wear the more you go over.

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Speedy said:

I think the effect is that the front wears faster because of the increased lean angle needed to travel around a given radius corner.

Tire wear rate is determined by the interplay between many factors. On our R3's the biggest factor for the front tire is de-acceleration, for almost all riders. As the load on the tire from weight transfer and the friction between road and tire increase, the deformation of the tire profile progressively flattens the contact area, increasing its length and width. The resultant tread squirm wears away the tread surface.

Why does the tread squirm? Simple geometry. A rounded tire and tread profile has different diameters as you move away from the centerline. If the tire measures 28" in diameter at the center but 27" measured 1" from the centerline and both are in contact with the road surface, then the tire center travels 3.1416..." further per revolution than the area 1" away. Something has to give, and does. The tread deforms and does so the most where the co-efficient of friction is lowest. Thus the edges of the contact area will squirm more than the center which has the highest loading. The result is cupping on the perimeter of the contact area as the surface undergoes "slip-stick" continuously.

A similar phenomenon occurs when cornering. In this case the geometry is more complicated because the contact patch is not straight. It is curved and the curve radius changes with lean angle and load. So the leading edge of the tire makes contact with the road at a angle to the direction of travel, curves to meet the direction of travel at the contact center point and then curves back at the trailing edge. The load and the co-efficient of friction change as well. The combination of angular contact and tread deformation result in squirm which cups the tire.

Tread patterns, tread compounds, multi-compound construction, curvilinear profiles, aspect ratios, road surface type and material, load, road crown, road surface temperature, acceleration rates, motorcycle geometry and more come into play. Therefore, almost everyone has a unique experience with a motorcycle tire.

It is nearly a small miracle that tires can do what they do and last as long as they do. I am amazed by what 150 years of engineering and materials science can accomplish.

Click to expand...

Speedy said:

I think the effect is that the front wears faster because of the increased lean angle needed to travel around a given radius corner.

Tire wear rate is determined by the interplay between many factors. On our R3's the biggest factor for the front tire is de-acceleration, for almost all riders. As the load on the tire from weight transfer and the friction between road and tire increase, the deformation of the tire profile progressively flattens the contact area, increasing its length and width. The resultant tread squirm wears away the tread surface.

Why does the tread squirm? Simple geometry. A rounded tire and tread profile has different diameters as you move away from the centerline. If the tire measures 28" in diameter at the center but 27" measured 1" from the centerline and both are in contact with the road surface, then the tire center travels 3.1416..." further per revolution than the area 1" away. Something has to give, and does. The tread deforms and does so the most where the co-efficient of friction is lowest. Thus the edges of the contact area will squirm more than the center which has the highest loading. The result is cupping on the perimeter of the contact area as the surface undergoes "slip-stick" continuously.

A similar phenomenon occurs when cornering. In this case the geometry is more complicated because the contact patch is not straight. It is curved and the curve radius changes with lean angle and load. So the leading edge of the tire makes contact with the road at a angle to the direction of travel, curves to meet the direction of travel at the contact center point and then curves back at the trailing edge. The load and the co-efficient of friction change as well. The combination of angular contact and tread deformation result in squirm which cups the tire.

Tread patterns, tread compounds, multi-compound construction, curvilinear profiles, aspect ratios, road surface type and material, load, road crown, road surface temperature, acceleration rates, motorcycle geometry and more come into play. Therefore, almost everyone has a unique experience with a motorcycle tire.

It is nearly a small miracle that tires can do what they do and last as long as they do. I am amazed by what 150 years of engineering and materials science can accomplish.

Click to expand...