Bicycle Mechanics - Is it possible to true a hop in a rim?
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05-24-12, 08:19 PM
my question is fairly simple. is it possible to true a radial hop in a rim?
both of my rims have a slight hop or dip in them from two rather strong hits to speedbumps and curbs. they are older box section aluminium road bike clincher rims laced to 36 hole hubs. they are both laser straight...... they just have these bumps and are not perfectly round.
is it possible to fix this? and if so how?
Most bike maintenance books show how to use blocks of wood and a rubber mallet round out a rim. This requires rebuilding the wheel and the results may not be satisfactory. Before trying this check to see if there are any small cracks in the rim near the spoke holes. If there are don't waste your time, just get a new rim.
05-24-12, 08:56 PM
Depends on the reason you have this hop in the rim if it’s really a spoke tension issue then yes it can, if it’s physically dented in from a hard hit most likely no, unless it is really slight it may be possible to get it slightly better than it is but this would need to be seen to really know just how bad it is.
In either case it does take some know how to do so and going at it blind with no clue on how it’s done may only make things worse.
05-24-12, 09:00 PM
Meh. No sense of adventure, JT. If the hop is bad enough the wheel is already unusable. It wouldn't hurt to try to play around with it some.
I've got a Raleigh DL-1 with the 28" Westwood rims. Hard to find and expensive. Before I replace the ones I've got, I was thinking about using a tie strap with a come-along to try to pull the rim out.
05-24-12, 09:12 PM
LOL I have a sence of adventure and using a block of wood and a mallet :troll:is fine just not on my bikes if it needs raplacing replace it :thumb:
It really depends on the rigidity of the rim, the severity of the hop, how local it is, and your skill.
Before starting consider that the rim is a hoop, and that any section of it acts like an arch. That means that flattening the arch would lengthen it, and raising would shorten it. That's what makes taking hops out so difficult, the rim has to flow along the length. High spots are fairly easy to resolve by simply tightening the spokes locally, and slightly loosening the spokes for about 60 degrees of arc to either side.
Low spots are trickier, If the rim is fairly pliable as many light rims are, you can loosen the spokes in the low area, and it'll rise a bit, and/or you might have to tighten the rest of the wheel very slightly. For a more sever low spot, loosen the spokes in the immediate area until they're fully slack, then slightly loosen the spokes to either side. Then take of your shoes, put center your foot over the low spot, and lift the wheel/push the area out. Push it slightly beyond the original radius, then you'll true it back later on.
Once you've resolved the worst of it, you true, and retension the wheel looking for the best balance between even tension and good trueness. You won't get both, so you'll have to use your judgement and look for the best balance.
This kind or alignment work was SOP many years ago, and any decent wheel mechanic could and would do it. Nowadays it's less commonly done, partly because of the current attitude toward "rescue" work, but also because modern rims are heavier and stiffer, making them hold the set or bend more that rims did in the past.
05-24-12, 10:00 PM
i have found myself doing a lot of this rescue work. generally fix a lot of crash damaged wheels. i put them in the stand and mark the biggest offender spot. inflate the tire rock hard and whack the rim on the corner of the bench. severely dented rims/flat spots i don't usually fix, but minor dents in the bead hook can be made better. some rims end up with some brake pulse but i explain everything to the customer before doing the work. they wont be perfect but it will get you back on the road
05-25-12, 07:39 AM
I've done it recently enough using the techniques mentioned here and it's fairly true. The very noticeable hop is gone but I can still see a slight flattened section on the rim. It has no effect on the ride quality but I can't get rid of the brake pulse.
There's several threads here about doing it. Some last a long time..others eventually lead to a split or crack developing.
05-25-12, 07:46 AM
Yes, hops & flat spots can be fixed, or reduced sometimes, depending on severity. FB's suggestions are good, and I will fix the minor ones by loosening in the flat area, then tightening on either size to "squeeze" the rim outward. There's also a specific tool for pulling out bigger flat spots once you loosen the surrounding spokes, but for my own wheels, once they get to that point, I'll replace the rim.
05-25-12, 08:06 AM
ALSO,, are you absolutely sure it is in the rim, && not a problem with the tire seated correctly. Try removing the tire , if you haven'y already done, so, & spin it looking for the hop.
05-25-12, 10:04 AM
the hop isn't bad enough to affect performance or the feel of the bike when i am riding, and even more importantly it does not affect my braking performance it just really annoys me that it is there and i am worried about it getting much worse.
i don't want to try anything that may damage the hubs as i am quite attached to them. (suntour sprint sealed bearing jobs that are smoother than any new bearing i have ever laid hands on) i think this may just be the best time to make the jump to a new pair of rims and ride them as hard as i want.
thanks for all the help folks!
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