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asymmetric rim wear on drive side, why did it happen?

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asymmetric rim wear on drive side, why did it happen?

Old 06-03-19, 03:08 PM
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tomtomtom123
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asymmetric rim wear on drive side, why did it happen?

I was looking at my rear wheel today and I saw that the drive side rim wall has been worn down heavily. The wear line indicator has been worn down until I can only just barely feel it with my finger. The black paint in the wear line has been completely rubbed off. In contrast, the non-drive side wear line indicator still looks ok and still has blank paint. The right brake pad seems considerably more worn than the left brake pad. But I had the brakes adjusted so that they contacted the rim at the same time when squeezed. The bike is only 15 months old, and I only rode it an average of 35km per week. I'm using the original brake pads (maybe they're really abrasive). What could be causing this?

The rear wheel has radial spokes on the left while the right side has 2-cross lacing, so the tension on the left side is much lower. It's 20" 28H.

The front rim looks better than the rear rim. But the front left side is a little bit more worn than the front right side, which is the opposite condition of the rear.

My last bike, also 20", had rims that lasted 5 years, until the rear rim cracked when the wear line indicator on both sides was almost no longer visible, and I rode it more frequently and did several tours on it. But I did replace the stock pads on that one very early with more expensive ones. But it had 2-cross lacing on both sides. So I'm a bit worried about the new bike, and wondering if I should rebuild with a new rim.
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Old 06-03-19, 03:13 PM
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Is this northern or southern hemisphere?
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Old 06-03-19, 03:22 PM
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How does the bike ride when you ride "no hands"?
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Old 06-03-19, 03:34 PM
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I've never been able to balance the bike without gripping the handlebar, so I never tried.
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Old 06-03-19, 03:42 PM
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If it's any consolation, I've noticed the left front and right rear brake pads on all my bikes tend to wear faster. Seems like the same condition your experiencing. Though I've never worn out a rim (getting close on my foul weather bike). BTW: they are Campy pre-skeleton 10s brake sets. I always thought it is what it is.
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Old 06-03-19, 03:54 PM
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Originally Posted by tomtomtom123 View Post
I've never been able to balance the bike without gripping the handlebar, so I never tried.
The "no hands" question is to gain some insight into the basic alignment of the frame, and tracking of the wheels. Sheldon Brown has instructions on how to check your frame alignment with a piece of string, it works very well, as long as it's done carefully. I think that would be a good place to start.
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Old 06-03-19, 03:55 PM
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Could the half-radial pattern, with the radial left side, contribute to greater wear on the right side? I wonder if 2-cross on both sides would help even out the wear.
I feel that it's odd that the right side is almost completely worn away after such a short time. I might also ask in the folding bike forum if anyone's experienced the same issue with a Dahon bike.

I remember checking the alignment with a string when I first bought the bike, but I don't remember exactly what I did. I think I tied the string from the rear dropouts to the headset, and measured the distance to the string on both sides of the seatpost, and it was fairly centered. But it's a folding bike, so there is more flex, including torsional flexing, than a normal non-folding bike.

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Old 06-03-19, 05:07 PM
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Frame alignment may cause uneven tire wear, but would have no effect on the uneven brake track wear.

As to the uneven wear, my guess would be that some type of lubricant got on the non drive side and is causing the drive side to do the majority of the braking work. That seems like an excessive amount of wear in a short period of time.
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Old 06-03-19, 06:06 PM
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Originally Posted by dsaul View Post
Frame alignment may cause uneven tire wear, but would have no effect on the uneven brake track wear.

As to the uneven wear, my guess would be that some type of lubricant got on the non drive side and is causing the drive side to do the majority of the braking work. That seems like an excessive amount of wear in a short period of time.

Neat and simple, perhaps this is the answer. Surprising that the effect would last so long (unless the lubricant is periodically accidentally re- applied somehow).
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Old 06-03-19, 06:30 PM
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There are a n umber of reasons why one pad wears more the the other. Most do mean that the rider wasn't as on top of the bike's maintenance though... Andy
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Old 06-03-19, 07:23 PM
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Hm... well with the new Dahon bike I only rode 2000km on it for around 15 months, mostly on city pavement, sometimes on the gravel paths through the parks. So the conditions weren't harsh. It wasn't very dirty, so I didn't clean it often, although in hindsight I should have cleaned more frequently.

My old Dahon bike lasted 5 years under more strenuous conditions, including loaded touring on mostly gravel roads. But I cleaned it more frequently because it got very dirty quickly.

The old Dahon bike had the original Chinese Kinetix (dahon) branded rims, with 2-cross on both sides, with my own brake pads. While the new Dahon bike came with French Mach1 rims, radial left and 2-cross right, and the stock brake pads. I didn't get any lubricant on the rims or pads, especially on the left side. If there was any, it would have dripped onto the right side when lubricating the chain. But the wear is on the right side of the rim.

(I thought maybe the radial on the left, being unable to resist tangential loads, causes more braking force to be applied to the right side, when compared to a 2-cross, but i could be wrong. The rear brake cable is pulling from the left with the cable bolt on the right. The front cable is reversed, maybe contributing to slightly more wear on the front left side instead.)

Anyway, since the wear line is almost gone, I think I'll have to replace the rear wheel. It seems a few shops offer to build wheels for just a little bit higher cost as buying a preassembled one, if I buy the components from them. Doing it myself would only save at most $30. But Dahon bikes are 28H rear hub and sourcing 28H rim is difficult. And the hub has indentations from the lacing pattern.

Most of the shops do 32 or 36 spokes. Doesn't it get very difficult to lace a 20" wheel with a higher number of spokes?

Any good reason why Dahon does 20" freehub wheels with radial on the left, and 2-cross on the right? I assume it's to reduce the dish on the left side, although if you cross the spokes on the left, that would effectively increase the length and angle of the spokes.
The preassembled one's I've seen so far with 28H are 2-cross on both sides. Some offers have 36H for "stronger build", can't tell if it's 2 or 3-cross.

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Old 06-03-19, 09:30 PM
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It's not the spoke lacing! There are millions of half-radial wheels out there that aren't wearing funny.

My hunch is that one side of your rear brake is making contact first, maybe it even rubs sometimes when not braking, and that's what is wearing it faster. Next time you adjust your brakes (you do that, right?) take note of whether both pads hit at the same time, or whether one side moves more freely than the other. Sometimes you have to settle for unequal brake pad clearance in order to adjust both to hit at the same time.
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Old 06-12-19, 07:28 AM
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I have 2.1" tires, so I can't see both of the pads touching at the same time. I have to squeeze the levers until one side seems to stop moving, then take a peek at at each side while holding the lever still.

I took the wheels and tires off to do some spoke tuning. Now that the tire is off, I can see that the pads were not engaging at symmetric angles. I also remembered that one side of the brake arms was less springy than the other side or physically slightly closer to the rim, so the adjustment screw was inserted more on that side. Perhaps there is unequal spring force so one side engages and disengages from the rim more slowly. The OEM brake arms look like Tektro 857AL, with the springs running behind the aluminum arms. The springs dug a small groove into the back of the arms, and I wonder if that affects the springiness. I decided to order a set of Shimano BR-T4000 brake arms which have the springs running outside of the arms.

Next time, I'll do the initial pad installation with the tires off, so I can see the rim wall directly, and get the angles and centering of the pads right. I also changed to replaceable cartridge pads, so I can more easily remove the pads to clean them. I'll also use spacers instead of using the adjustment screw if one pad is very far off the rim compared the the other.

The rear hub was not turning smoothly, and the right side cone was severely pitted. I replaced the cone and the balls.

I checked the rear fork end alignment by nutting bolts to each fork end and letting the tips touch at the center, but they're off by a few degrees. The rear is maybe off 2-3 degrees and the tips are misaligned by 2mm. The dropout is 131.6mm at one side and 131.0mm on the other. When I squeeze the fork ends to 130mm, the angle and misalignment reduces a little bit. When I insert the rear wheel, and tie a string from the dropout to the seat tube, the distance between the string to each side of the rim wall is only offset by less than 1mm, so I don't think there is an alignment issue between the rear wheel and the frame.

The front fork ends are off by a higher angle by around 3-4 degrees, which increases a little bit when squeezing the fork ends to reduce the 75.5mm spacing to 74.0mm, but the bolt tips are centered.





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Old 06-12-19, 07:42 AM
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Dual pivot brakes move inexorably to center regardless of where rim is. Frame has to be straight and wheels have to be centred perfectly. Or use single pivot. Or disc.

Bike will ride lots better when you center wheels. Worth doing in any case. Do not assume wheels are centred just because they were expensive.
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Old 06-14-19, 05:34 AM
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What I meant with the worn groove in the Dahon (Tektro 857AL) brake arm, is that during braking while the bike is moving, the spring digs into the groove and slowly makes it deeper. I suspect that when the spring gets stuck in the groove, it reduces the amount of spring force, so the movement speed of the arm is reduced. The groove on the right arm is much deeper than the left arm, so it's possible that when braking while moving, the pads are not engaging and disengaging at the same time, and the right arm is lingering longer on the rim.

When adjusting the centering of the brake pads while off the bike, the spring doesn't dig into the groove because I'm not applying as great of a force on the brake and the arms are not bending forward as when braking while riding. So even if I adjust the pads to center while I'm off the bike, when I am actually braking while riding the bike the pads may not be touching at the same time due to the spring getting pushed into the groove.

I've changed to the Shimano BR-T4000 brakes, which has an internal pivot, so it doesn't pivot on the boss and has less play in the direction of travel, and the springs run on the outside of the arms, instead of directly and behind the arms like on the Tektro.



The spring dug a groove into the back of the brake arm.
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Old 06-14-19, 07:43 AM
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Well, it took 13 posts to actually say what kind of brakes these are and what kind of bike this is. On the other hand, this allowed you to figure out the problem by yourself, which I think you kind of did. I guess that this is an indicator of how the human mind works: the rim is worn asymmetrically, so we think its the rim or wheel or lacing.

I think that perhaps that the spring you noticed was the issue, but perhaps it was digging in or gouging, and not just wearing. Could this be happening? Rather than an issue with wearing a deeper groove, I would suspect that the spring was gouging out material (too short a spring) and that this formed a mechanical stop. So when you squeezed your brake lever, one side would advance to that stop - just short of the wheel rim, but then would hang on the de facto stop that the gouging spring had created. This meant that the other side would contact the rim but not the stopped side.

If you feel like it, reinstall the offending brake, take off the wheel, and squeeze the brake lever. If one side moves and stops while the other swings over the full range, that would be definitive. But if both arms swing the full range, then this is not the issue.

Do the Shimano brakes work better?

Instructions for your brake below:

https://www.tektro.com/upload/Produc...5882KmmMwm.PDF
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Old 06-14-19, 09:31 AM
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I've already switched brakes so I won't test the old ones again.

I'm still assembling the other bike components for the overhaul, so haven't ridden it yet, but I have an easier time adjusting the Shimano BR-T4000 brakes. They retract quickly and almost evenly, and consistently. The old Dahon branded (Tekro 857AL) had difficulty adjusting the centering,because it would sometimes not contract or retract consistently. I suspect it's because the spring is rubbing against the back of the arm, and it's also pivoting directly on the boss, which are things that the Shimano brakes don't do. The Shimano also seems to have less play, because if its built in pivots.

One problem is that Shimano and Tektro have different shoulder bore hole depths for the boss shoulder, 4mm deep for Shimano, 10mm deep for Tektro. The shoulder on my boss is 6mm high, so I had to spend some time trimming spacers to fill the gap when switching to the Shimano. I documented the procedure in another thread.

https://www.bikeforums.net/bicycle-m...l#post20977241

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