Cause of cupped front tire? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 11 Old 07-11-2015, 04:40 PM Thread Starter
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Cause of cupped front tire?

With about 8200 miles on the front Anakee III's on my K7 Wee, I noticed significant cupping. Seeing how I needed a new rear tire at that time, I purchased a set of Metzler Tourances. While getting the rear tire mounted, i mentioned to the tech that as soon as I got the rear tire mounted, I would be returning to have the (cupped) front tire replaced, even though it still had about half of it's tread left. He suggested that I check my steering stem bearings first, as a slightly loose set of bearings will cause cupped front tires. He mentioned that he had learned this from a Dunlop rep.

The tire tech was right- the bearings were slightly loose. Not enough to feel slack in the forks when tugging on them, but more than desired. I went to the local Home Depot, bought a foot of 1 1/4" I.D. black iron pipe and proceeded to make a tool to adjust the special nuts that adjust the bearings. (Thank you for the instructions, Black Lab!) The bearings were tightened, and after another couple of thousand miles, the cupping was gone! The tires has about 12K miles on it now, and it still has 4/32" of tread left.

To summarize, if you are experiencing cupping of the front tire, check your steering stem bearings! Most likely, they are too loose.
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post #2 of 11 Old 07-12-2015, 10:12 AM
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So how did you determine the bearing was loose?? Without having slack, did you determine by the ease of turning the handlebars or something?? I'm feeling a difference in my front but have not been able to move the forks to confirm. I've not noticed any real strange wear patterns in the front tire however.

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post #3 of 11 Old 07-12-2015, 05:10 PM
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I'd imagine when releasing the lock nut and trying the home made tool that the play was obvious. Subtle changes make a big difference in the steering head.
BMW dealer tightened the bearing on my 800ST and 6K miles later told me they need replacement. Ain't that a Co-inky-dink.
I went another 20K miles before I couldn't stand it and replaced them.
Inflation pressure can be a culprit too.
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post #4 of 11 Old 07-12-2015, 07:58 PM
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Dunlop Tire FAQ here

How can I keep my tires from cupping?

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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post #5 of 11 Old 07-12-2015, 11:09 PM
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Too tight will kill the bearings. The lower nut sets the bearing tightness. Too tight is too much. The bearings must not be so tight that they act as a damper. The upper nut is the lock nut. Plenty tight is good.

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post #6 of 11 Old 07-13-2015, 12:55 PM
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In a way, the lower lock nut sets the load on the bearing. But as soon as the upper lock nut is tightened it pushes the lower one down, increasing the bearings pre load.
I've installed several roller bearing kits. I will first over tighten & turn the bars full lock to lock a few times. Then back the lower one loose & finger tighten it. After tightening the upper lock nut down it comes out about right. A little experimenting may be required.

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post #7 of 11 Old 07-14-2015, 08:36 PM Thread Starter
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You nailed it. Lacking the factory shop manual recommended tension gauge, I used experience and feel to judge the appropriate tension on the bearings. Prior to adjustment, the bars and front end fell rapidly to either side when movement was initiated. A VERY small amount of tightening of the top bearing nut (not the locknut) slowed the falling motion without causing binding. It takes a bit of experience and judgement to know when you have it right, but basically, the forks will move smoothly, but not fall rapidly to either side when you have it right. Slightly loose is better than too tight!
My tire cupping has gone from very noticeable to imperceptible after snugging-up the bearings and a couple of thousand miles.

Last edited by theDoktor; 07-14-2015 at 08:39 PM.
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post #8 of 11 Old 07-14-2015, 09:57 PM
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I'd agree with your tire guy, however

Being as how you did not use the identical tire after the bearing fix, the question of feathering on the tread isn't completely answered. Some tread patterns lend themselves to more feathering than others.

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post #9 of 11 Old 07-15-2015, 07:30 PM Thread Starter
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It was the same tire- still is 4K miles later! And the tire wasn't feathered- more like scalloped. We're talking about very visible divots!

Last edited by theDoktor; 07-15-2015 at 07:34 PM. Reason: typos
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post #10 of 11 Old 07-16-2015, 12:31 PM
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Same tire, got it

Okay, thanks. I must have miss read your previous post.

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