Alloy Rim : Brakes : Thickness : Wear : Life?
01-15-14, 05:51 PM
#26
Constant tinkerer
I've seen these before. Pretty sure it's a symptom of hard pads contaminated with bit of aluminum. The rim is getting ground off by the pad, and either little bits are making their way back on, or your grinding pads (brake pads) are just cutting into the rim in a certain way.
Check your pads.
Check your pads.
01-15-14, 11:31 PM
#27
Full Member
The year-old Shimano pads have deep grooves from the bumps, they're shot. I don't see any metal embedded in the rubber. Weird.
01-16-14, 12:43 PM
#28
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,671
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5767 Post(s)
Liked 2,541 Times
in
1,407 Posts
From all appearances there's plenty of material left, which you can often gauge by looking for a step to the unworn area.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
01-16-14, 04:30 PM
#29
Full Member
I think the rims are shot. Those bumps are harder than the than rim surface, I had to use a flat jeweler's file to grind them down. I took out the biggest blob measuring 2-3 mm and the wheel is much quieter now when braked. Good enough for my town bike. I'm just perplexed at these little silver blobs, it can't be a good thing and it destroys the brakes. Since they stick out so much, I'm more willing to accept the theory that they are bits of metal off the rim that came off and got reattached - but how? What kind of temperature are we looking at and how much pressure does it take? Any physicists or metal experts?
01-16-14, 05:01 PM
#30
Senior Member
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,671
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5767 Post(s)
Liked 2,541 Times
in
1,407 Posts
I think the rims are shot. Those bumps are harder than the than rim surface, I had to use a flat jeweler's file to grind them down. I took out the biggest blob measuring 2-3 mm and the wheel is much quieter now when braked. Good enough for my town bike. I'm just perplexed at these little silver blobs, it can't be a good thing and it destroys the brakes. Since they stick out so much, I'm more willing to accept the theory that they are bits of metal off the rim that came off and got reattached - but how? What kind of temperature are we looking at and how much pressure does it take? Any physicists or metal experts?
In any case, the easy way to redress the rim's surface is with some emery cloth trapped under brake shoes. Back in the days before machined sidewalls, I used to cut strips of emery cloth, punch a hole at one end and trap them under the shoe mounting bolt, and wrapped around the front. Then I'd ride against the brake to remove hard anodizing on the brake track. This had to be done slowly and the bike rested often because it heats up very quickly.
If you do the same, you can bring up a clean uniform brake track in minutes.
BTW- it works better as a wet sanding process, so do it on a rainy day if you can.
__________________
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
01-16-14, 05:19 PM
#31
Constant tinkerer
Unless the rim is too thin at the brake track it's still fine. I don't know safe minimum thickness offhand but you can look it up and measure your rim.
01-17-14, 09:04 AM
#32
Full Member
Thanks for all the suggestions. My first impulse was to just prying them off with a screwdriver, only to discover they were actually fused to the metal. I think I'm gonna bail on these wheels, those bumps are just too gnarly and hideous, too many to try to eliminate altogether. I've never seen them on any of my other well-used wheels, be it Weinmann, Mavic or Araya. I'm taking it as a warning of sorts, not to be ignored.
03-20-14, 10:37 PM
#33
Banned
Join Date: Sep 2010
Location: lower mitten
Posts: 1,555
Bikes: With round 700c & 26" wheels
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
Sorry to resurrect a 2 yr old thread, but I just discovered what the OP describes on my vintage Trek 850. What I see are tiny blisters that look like solder blobs emerging from the rim surface. Looks to be either a metallurgical phenomena or a built-in wear indicator. I mean, pits/depressions yes, but bumps and blisters? They look like bits (islands...) of harder alloy that did not wear down with the rest of the rim. There's no way this is some other material making its way to the rim and fusing with the alloy, there's not enough heat or pressure to do that. I've filed the worst down but there are too many and they're everywhere on both sides of this 18 year old Araya front wheel. The rear wheel hasn't started yet, but I can see how it might be inevitable. THEY LOOK LIKE TINY SOLDER BLOBS. Never seen it before, not even on my old Weinmann thousands milers.
Just as well, I was getting ready to upgrade the rear wheel to a Deore 8 speed setup. I've ordered a whole new wheelset instead!
Just as well, I was getting ready to upgrade the rear wheel to a Deore 8 speed setup. I've ordered a whole new wheelset instead!
Replaced my Shimano XTR pads with Avid 20R and problem was solved. Avids are much softer, quiet and rims are happy now
I run out of Avid pads, so I may try kool stops now.
03-20-14, 10:46 PM
#34
Full Member
Had same issue, but it was only one big " bump". It was created in a matter a couple seconds during heavy braking. I removed mine with 220 grit sand paper. I did some quick research and almost every source was pointing at hard Shimano brake pad compound. I use Shimano pads for around 20 years and they were always lasting forever. I was getting easily 2000 miles from them, but never got any issues with braking surface. My quess is that today's rims are using softer/lighter alloy and that may be the problem.
Replaced my Shimano XTR pads with Avid 20R and problem was solved. Avids are much softer, quiet and rims are happy now
I run out of Avid pads, so I may try kool stops now.
Replaced my Shimano XTR pads with Avid 20R and problem was solved. Avids are much softer, quiet and rims are happy now
I run out of Avid pads, so I may try kool stops now.
03-20-14, 10:52 PM
#35
Banned
Join Date: Sep 2010
Location: lower mitten
Posts: 1,555
Bikes: With round 700c & 26" wheels
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
Need to be very careful. That front wheel broke a spoke, locked up and threw me over the handlebar 3 days ago. I have 7 stitches in my mouth and face at the moment. I love vintage bikes, but I'm done with worn equipment. I'm always learning the hard way, and couldn't be sorrier. Those bumps were telling me something, wish I'd paid attention!
My wheels are pretty new, and the "bump" was created month or two after I bought it. Braking surface is not machined, so plenty of thickness. When I'm done with them - this will be my last set of rim brakes ever.
03-20-14, 11:05 PM
#36
Senior Member
Join Date: Dec 2010
Location: Above ground, Walnut Creek, Ca
Posts: 6,681
Bikes: 8 ss bikes, 1 5-speed touring bike
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 86 Post(s)
Likes: 0
Liked 4 Times
in
4 Posts
... What I see are tiny blisters that look like solder blobs emerging from the rim surface. Looks to be either a metallurgical phenomena or a built-in wear indicator. I mean, pits/depressions yes, but bumps and blisters? They look like bits (islands...) of harder alloy that did not wear down with the rest of the rim. There's no way this is some other material making its way to the rim and fusing with the alloy, there's not enough heat or pressure to do that. I've filed the worst down but there are too many and they're everywhere on both sides of this 18 year old Araya front wheel. The rear wheel hasn't started yet, but I can see how it might be inevitable. THEY LOOK LIKE TINY SOLDER BLOBS...
THEN start worrying. 
seriously though, i think i've seen that before in aged alloy bike parts. and although i know aluminum oxide is white, it's probably a result of the of the natural oxidation process of aluminum. it can get funky and moldy too.
Last edited by hueyhoolihan; 03-21-14 at 12:55 AM.
03-21-14, 12:39 AM
#37
Banned.
Join Date: Jun 2010
Posts: 434
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 29 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
I did this once. Had the exciting experience of the rim losing its grip on the tire's bead, the tube expanding and exploding. Walked home. But I'm not going to measure my rim's thickness.
Thread
Thread Starter
Forum
Replies
Last Post
fmt_biker
Bicycle Mechanics
11
05-01-14 02:16 PM
