Braking surface wear to rim

thank you i was confusing it with when i said eek as it flew off

Old thread I know....

Cycling home last night, spinning down a hill, I hear a loud bang, next thing I know I am on the floor!

Look at the bike and the side of my front rim has blown off.

Nasty, glad you are okay though, gotta stop using those steel brake pads!

Weirdly my brake pads are fine! going to blame all this on the previous owner (he says sitting in the corner rubbing his shoulder)

Wow! catastrophic rim fail !

glad you ok matey, could of been worse.
the brake wall must have been worn thin or something.

Old thread indeed. Well in the case of my rims i used the front with a brake for a short while then laced it up to a disc brake hub and have now gone fixed and brakeless so rim is all good. But yeah that pic up there is what i was worried about happening.

What rims are they Sam?

They were Mavic MA40s, actually feeling the rim afterwards, it feels like the rim is pretty scored, so looks like someone forgot to put new brake blocks on! Rims were the only thing I didn't change!

MA40s are one of my favourite rims. Never seen anyone destroy one in this manner before.
Glad you're OK

Yeah, they were lovely Rims, guess it's just a case of making sure you check them for wear and tear, particularly when building them up with new hubs and spokes!

It's a good idea to check your rims for grooves (bow chicka wow) every now and then to prevent this very thing happening. I tend to do this when I clean my bike after any seriously messy rides.

I just swapped out my front rim after only a year for same reason. Deep concave wear to the rim.
Clearly the awesome forces required to arrest my kinetic energy combined with evil aluminium grinding paste generated by wet Dura Ace pads were too much for a puny CXP33.

^ Hmm how much sexual inuendo can you squeeze into such a short post.

^ Hmm how much sexual inuendo can you squeeze *out o*f such a short post.

better?

This happened to me on Piccadilly with a loud bang on my last delivery of the day in busy Friday rush hour traffic. It can happen to any wheel with rim brakes. I now keep a closer eye to see whether the rim surface is becoming concave.

Thread dredge.

I've noticed a ticking noise when braking, generally only when braking lightly. I had a look at the rim today and there was a very small raised piece of metal, not much bigger than a bit of grit. It looked like it was always in the metal and I'm guessing it is an impurity from the casting stage that was harder and has therefore not worn at the same rate as the braking surface. Anyway, 10 seconds with some fine sandpaper and it was gone.
My concern now is that the rim has worn to expose this small lump. So what's the way to check wear and when is it time to replace a rim?

what rim is it?

It's a Mavic MA3

apparently those rims don't have a wear indicator. Place a flat edge against the rim and look down the side of it.
This post by Dammit shows a couple of photos, if they look like that, they need replacing.

Here's the tool you need to measure rim thickness. I bought one of these about a year ago and have used it on a dozen wheels already. Anything above 0.75mm is fine in the older rims. Some of the newer lightweights start off even thinner than this!

http://www.ebay.co.uk/itm/Prestige-spring-measuring-caliper-jewellers-gem-stone-bead-diamonds-15mm-New-/330616452190

Thanks guys. I'm pretty sure they're not worn anything like Dammit's examples but will have a check. If it does look like they're worn I'll throw away the brake and HTFU buy a new wheel.

Thread dredge to post this weird one. My Mavic a119 rims have worn either side of the central wear indicator groove leaving a fairly sharp ridge immediately either side of it. Don't think it's a structural problem but obviously makes the indicator groove a bit pointless. Glad I've got an Iwanson guage that shows them at just over 1mm at the thinnest point so probably due a replacement sometime soon.

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Machining the groove work hardened the surrounding metal?

Interesting thought, could be that.

I'm wondering whether it's affecting the braking performance a bit as the pads have to work themselves into a pretty odd shape to conform to the rim.

Are they not totally worn into that shape?