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Getting rid of a wheel hop questions

Old 09-15-13, 05:36 PM
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Getting rid of a wheel hop questions

So I was able to true my mnt bike wheels pretty well but I don't know how to get the round better. I have a couple areas where the rim dives inwards towards the hub. How do I fix that?
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Old 09-15-13, 05:48 PM
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Originally Posted by squatchy
So I was able to true my mnt bike wheels pretty well but I don't know how to get the round better. I have a couple areas where the rim dives inwards towards the hub. How do I fix that?
The principle is the same, but your success will depend on the cause and nature of the hop. If the hop was the result of you're truing efforts, or is long and gradual, then spoke work alone will do it. Basically you would loosen (slightly) the spokes where the rim is low, and tighten the spokes where it's high.

However, if the hop is very sudden and in a small area, then the rim itself is bent, and not just flexed. So while you might succeed with working the spokes, it will take large differences in tension to overcome the rim's natural tendency to stay bent.

Fixing hops used to be much easier back in the days of light, flexible, shallow profile rims. Many of today's rims are very rigid, and if they have a deep profile, they're especially rigid radially. This is good news/bad news. The good news is that they're easier to build, and more resistant to getting hops. The bad news is that it's that much harder, or impossible to correct hops if they happen.

In your case, not seeing the rim, I can't predict how it'll respond, but you might try a test. Setting the gauge or feeler close to but not touching in the low area, loosen four sequential spokes there one turn, and see how the rim responds. If it rises 1/2mm or anywhere close to that it's a good sign and you can go ahead with a normal tighten/loosen process. OTOH if they barely respond at all, odds are it'll be difficult to resolve the hop by spoke worl alone, without ending up with large differences in tension.

Hops can also be resolved bu brute force, bending (unbending) the area back to the correct curvature, but this requires a decent amount of hand skill, and decent wheel building touch.
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Old 09-18-13, 06:03 PM
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so I was able to straighten it pretty good. I then started to get it round and had a hard time because it messes up the true. It's an old school mavic rim from 92-94 so it should true up better than new stuff. I think I bent the back as the hops are fast not gradual. I don't know what to use as a baseline to determine weather I should pull the hop tighter to the hub or loosen it in the low spots to let is move away. Also all my spokes seem to have more tension on the cassett side and I didn't even plan for that. Is that normal due to the offset??
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Old 09-18-13, 06:07 PM
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DS has more tension due to the dish. Else the rim would be centered between the flanges like the front.
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Old 09-18-13, 06:15 PM
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Originally Posted by squatchy
so I was able to straighten it pretty good. I then started to get it round and had a hard time because it messes up the true. It's an old school mavic rim from 92-94 so it should true up better than new stuff. I think I bent the back as the hops are fast not gradual. I don't know what to use as a baseline to determine weather I should pull the hop tighter to the hub or loosen it in the low spots to let is move away. Also all my spokes seem to have more tension on the cassett side and I didn't even plan for that. Is that normal due to the offset??
Usually, a little of each at the same time. Imagine your wheel is oval, by pulling in the bulge, you are also forcing out the low spot, so it should "average out" to round. So you need to loosen the low spokes to allow the rim to go outward.
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Old 09-18-13, 06:59 PM
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Originally Posted by squatchy
I then started to get it round and had a hard time because it messes up the true.I don't know what to use as a baseline to determine weather I should pull the hop tighter to the hub or loosen it in the low spots to let is move away.
Working on round should not generally greatly affect the true, as long as you always turn an even amount of spokes. Of course if you tjurn more spokes on one side than on the other the rim will go out of true.

The tension of spokes is interrelated - if you tighten some you will increase the overall tension. So if the high spots are getting too tight you should then have enough tension in the low spots to work on those spokes. If they are loose even though other spokes are tight then you know the rim is physically bent there. As the spokes can only pull in you would have to physically push the rim outward at that point. Again as noted - doing so requires some skill and a good touch.
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Old 09-18-13, 07:26 PM
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Originally Posted by cny-bikeman
Working on round should not generally greatly affect the true, as long as you always turn an even amount of spokes. Of course if you tjurn more spokes on one side than on the other the rim will go out of true.

....Again as noted - doing so requires some skill and a good touch.
Yes, and no. For you and I and experienced wheel builders radial and lateral movements are pretty independent. But for less experienced folks, working on one tends to mess up the other. That's because of the asymmetry in the rear wheel.

The right spokes are at least half again as tight as the left, and have a more radial line of force. So if one were to tighten both right and left adjacent spokes the rim would move in but to the left. Then there's spoke twist which will be more pronounced on the right spokes, so someone lacking feel will think he's doing more than he is.

As you point out, experience and good touch make a world of difference.

My advice is to be very patient and work slowly by degrees toward the goal. Also set a much higher priority on radial correctness, because it's much easier to make lateral adjustments at the end. When the wheel is radially correct, use the left spokes spokes more than the right (almost exclusively of tension is near target) to true the wobble.
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Old 09-18-13, 11:09 PM
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The way you fix hop is to replace the rim (assuming the reason for the hop is that it's bent from a pothole or curb).
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Old 09-18-13, 11:43 PM
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approximately $25 at your lbs, problem solved.

If you're nice they may even tell you how they fixed it.
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