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I have what I think is Specialized Hardrock mountain bike.

Recently, when riding on a flat surface the back wheel has a noticeable up-and-down movement with each spin. It is like ridding a horse in the merry-go-round.

When inspecting the wheel spin, I don't see a side movement and can't visibly see the up/down movement, but I can easily feel it to the point that I do not want to ride the bike.

What are the options and costs? Consider I am not a fix-it-yourself bike person.

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Yep, the wheel probably needs to be trued. You may have some broken spokes, or just spokes that got stretched out by a bad bump. However, it's also possible that the tire simply isn't seated uniformly on the wheel -- inspect the side of the tire and see that the mold marks maintain a constant distance from the rim edge all the way around. In any event, probably not terribly expensive to fix at your local bike shop. –  Daniel R Hicks Nov 3 '13 at 19:15
    
Once I leaved my bike near a door. Then it had this "up-down" movement: someone hit the rear wheel with the door and defaced the rim... –  Alexander Nov 4 '13 at 8:18
    
I remember being quoted A$60 to true the wheels but it could be because my spokes are bladed so it'd be an extra effort for them to keep them inline. Anyway, I decided not to do it because it's about 1/4 the price of the wheels (more if I take account of my time going to the shop). –  imel96 Nov 5 '13 at 6:17
    
So what was the problem? Please satisfy our curiosity. –  Vorac Nov 8 '13 at 8:33
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3 Answers

up vote 6 down vote accepted

Your description sounds like the wheel is out of true, out of round, or some of the spokes are so loose that they're flexing as the wheel rotates. However, for it to be as severe as you describe I would expect it to be visible on spinning the wheel and watching it, even to a novice mechanic.

Whatever the case, you should take your bike to a qualified mechanic. The problem may be fixable, possibly as simple as tightening and loosening the appropriate spokes. This is a relatively difficult job for a novice mechanic though. It is also perfectly possible that you need a new wheel. An experienced mechanic would have to visibly inspect the wheel to be sure.

If it's a simple fix, it could be as low as $15 US. If you need a new wheel, I would expect it to be around $75-125 for a bike that age depending on what quality you would like to get.

I would also recommend checking with a couple mechanics. Some are quick to sell new parts when an older part is serviceable.

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Check to see if the tire is going up and down or the rim, or both.

If the rim, then all the advice from others holds and you need to have someone start checking spoke tension, etc.

If it is the tire that is out of round and not the rim, it could either be that the tire is not seated well (perhaps it went slowly flat and when it was re-inflated it was not seated correctly), or it could be an internal failure of the tire. Particularly with mountain bike tires that have some age on them I have seen the tire start to come apart - on the inside it kind of looks like a tear and on the outside it just looks like a bump or bulge.

if the tire is not seated correctly, you need to let the air out, seat it evenly and re-inflate. If the tire is failing, you just need a new tire. You may be able to do either of these yourself - depending on your skills.

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You could also have bent the rear axle. That is also not expensive, $10 maybe, but the rim will need to be trued as well.

Provided that you are "not a fix-it-yourself bike person", you should have a LBS that you trust, to turn to in such cases.

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But of course if the axle (and not the hub) is bent then the wheel will not go "up-and-down" as it rotates. –  Daniel R Hicks Nov 5 '13 at 12:25
    
@DanielRHicks, the OP says he cannot see neither sideways, nor up-and-down movement. Last time I bent an axle, the feeling was quite "up and down". The rim was severely bent, but straightening it didn't fix the problem. Then I went ahead and ... bought a new bike :D –  Vorac Nov 5 '13 at 12:40
    
But he can feel the up-down motion. A bent axle will not result in any relative motion at all, simply cause the wheel to tilt to one side (and the bearings to go bad). –  Daniel R Hicks Nov 5 '13 at 13:10
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