009jim

I have alloy rims on my Giant CRX3. Last night I noticed that when braking instead of a smooth zzzzzzzzzzzzz noise I hear zzzzzzputzzzzzzzputzzzzzzputzzzz

I checked this morning and the wheels are true but on the brake wall there are occasional minute bumps. These roughly seem to correspond with the noise.

Looks like little bits of metal could have gouged the rim. So I got out my mini-grinder and very carefully removed the bumps. Haven't tested it on-road yet but it seems to be an improvement.

My questions are:-
How thick are these rims? Can you wear them out from braking?
What could these bumps be? From the brake pad? Or from the road?
Should I use different pads?

Bat56

You caertainly can wear through a rim. As for the bumps, most rims have a weld. I've never heard of someone grinding a rim. Love it.

I surmise that more braking power will either wear the pad (soft rubber) or the rim (abrasive rubber) faster than less power. I opt for less power.

zonatandem

Bits of metal can inbed into softer rubber brake pads and create a scoring effect on rims.

Turbo231

Maybe catch a rock or something? I have had a rim gouge when I got a rock in the pad and hit the brakes...sounded bad and looked bad.

Retro Grouch 

How many bumps? Are they evenly spaced and do they seem to correspond with the spokes or anything else on the rim?

How old are the rims? Modern rims have wear indicators built into them. One style is a groove machined around the brake track. Another looks like somebody took a spoon to carve out divots from the inside of the rim. On these as soon as you see a little hole in the brake track, it's time for a new rim.

Welded rims are smooth at the joint. Pinned rims often don't meet perfectly and have a little ridge at the joint. You can grind down the ridge if you want or you can just leave it alone and it will eventually take care of itself.

wroomwroomoops

What Retro Grouch said. Most of my rims have the ridge, and I used to carefully smoothen it out with fine-grained sandpaper (and then carefully cleaned the surface), because I believe that the ridge causes unnecessarily fast brakepad wear. I don't do this anymore, because I have standardized all our bikes onto hub brakes. Which is something I would recommend to everyone.

wroomwroomoops

Hey Grouch, I didn't know you were a recumbent biker. I see these recumbents from time to time, and they are fast as hell. How has the recumbent been serving you?

JohnDThompson 

Isn't that what the fashionable "machined sidewalls" on modern rims are?

Nick Bain

ride em till they blow a tire, no just kidding that would not be fun.

Spoonrobot 

Here's a direct link to an interesting PDF article on rim wear/life.

https://www.ctc.org.uk/resources/Magazine/20011163.pdf

009jim

Thanks "Spoonrobot". That PDF was informative. I am a little shocked to find I will need to measure my rim thickness. I think less-abrasive brake pads are on my shopping list. The ones I have are Shimano Acera. The original Tektro pads didn't seem to make these bumps. I have another set of Ashima pads I haven't used yet and the pack says that the rims should be cleaned regularly. I'm assuming that applies if I was to ride through some mud. It's not like I'm on the brakes all the time, but there are two down-grades on my way home where I am on the sidewalk and need to keep the speed down. Can anyone give suggestions for brake pads that are going to cause less rim wear?

wroomwroomoops

These will cause no rim wear whatsoever.

Seriously though, the last couple of replies in this thread:
https://www.bikeforums.net/showthread...pads-wear-rims
should help answer your question somewhat.

JohnDThompson 

They actually make tools for this, and they're not expensive. Search for "dental caliper" on eBay:

009jim

There are about a dozen or more bumps on each side but just a few in one area seemed to be big enough to make the noise. They don't coincide with the spokes. My bike was new in 2009 but I had a year off so I've ridden probably 3000 miles tops. There are no wear indicators I can see. They were really smooth when new - no weld to be seen. I'm trying to get some photos.

FastJake

There's your problem. I love a lot of stuff Shimano makes, but their brake pads are total garbage. All the ones I've used have been rock hard AND manage to get pebbles, aluminum chunks, etc embedded in them which will destroy your rims.

Get Kool Stop pads. They're the best.

009jim

Good references, thanks wroomwroomoops. I noticed enough comments on the koolstop pads to suggest they would be softer and therefore maybe wear my rims less. Other comments said that Shimano pads pick up grit and tend to gouge the rims (that what's happened to me, and I have Shimano pads!). One guy said he got 20 years out of a set of rims yet another guy replaced his every 18 months.

"FastJake" thanks for your comment too - confirms my conclusion.

pat5319

Remove any metal bits or grit from your brake pads with a sharp untensil, and check them often, VERY often if you ride in dirt or rain. Clean your pads and rim regularly as well cheap hair spray works great!, alcohol works as well- your brakes WILL work better!

Metal bits or grit imbedded in your pads HUGELY increase rim wear. I worked in shop that mainly sold mtn bikes and we replaced brake worn rims regularly.

wroomwroomoops

Silica (sand) is even harder than metal bits - in fact, it's harder than almost any metal you could commonly encounter.

Jeff Wills

Replace your rim before this happens:
https://home.comcast.net/~jeff_wills/...s/rites042.htm

009jim

This issue has got me worried now. I've ordered some Koolstop pads off Wiggle (they have free delivery at the moment). My previous bikes had steel rims and wear was unheard of. If you get a new rim laced up to your hub will it be perfectly true like mine is now? As I kid I respoked a few wheels and they weren't bad but not perfect.

Jeff Wills

Lacing a new rim to an old hub is the same as building a building an all-new wheel. It'll come out true if you're careful.

It's the same as any other wheel build- what will make the wheel durable is high, even, spoke tension. There's many tutorials on the web about the process.

Kimmo

Folks are failing to make a distinction between concentric and radial damage.

Anything that makes your brakes go 'zzzzzzputzzzzzzzputzzzzzzputzzzz' is not the fault of your pads, it's a result of the rim being damaged by rocks or careless handling off the bike, or whatever. There's a short gouge in the rim, with a corresponding raised bit that tears through the pads and feels like crap through the lever. This kind of damage is almost always minor. I usually repair it by carefully trimming off as much of the raised bit as I can with a snap-blade knife, then smoothing down what remains with a fine file (a nailfile would prolly do it). Sometimes the ramaining gouge can still be felt through the brake, but it should no longer have any meaningful effect on modulation and pad wear.

As for the damage that destroys rims - normal wear and scoring due to crap embedded in the pads - it doesn't make your brakes pulse, because this is concentric wear. So the 'zzzputzzz' isn't your pads' fault. Keep an ear out for scraping sounds from the brakes and check the pads once in a while.

009jim

I've ordered the "black" koolstop pads (recommended for dry weather riding), and the "red" ones (recommended for all conditions). Anyone care to suggest a preference?
Why are they called "thinline"?

FastJake

Red or black, I've had fine luck with both. Red is a little softer I believe.

"Thinline" compared to some of the larger fatter pads they make that don't fit in many of the road racing bikes with tiny tire/brake clearance.

Kanegon

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!