Topic: Ever have a rim explosion on a Mountain Bike ?

[754]

 I did tonight.. Blew about 8 inches of the side of the rim out..
 Fleeping loud.. Wtf .man that sucks..

[brandEn]

You OK? Where you on it when this happened?

[754]

I had just filled the tire too much probably.. Was at 48ish I think. The rim had damage, and I tried fixing ita while back. There was a warning sign I guess, had noticed before that when reinflated that the rim dragged. It did that tonite, rode about 150. Feet, then stopped to back off brake.. Then it blew.  Good think it wasnt still inside the shop, my ears would still be ringing..

[brandEn]

Good thing you weren't hauling ass down some steep single track!

[City Boy]

Geez 754,now you have me worried.I have a Supercycle and CCM downhill models and a Raleigh mountain that I keep 50 psi in all of.So far the odd broken spokes but no rim failure.What was the nature of the previous rim damage?

[Duke McDukiedook]

Yeah, you have to be careful about rim repairs or rims that wear past the wear mark on rim brakes.
You have quite a bit of pressure riding on your rims.

[754]

Ok its a gary fisher Joshua, will gpet pic and rim name later today.
 Rim had a slight wow on it near valve core. My pads were thin and I went on ride that had a long downhill, paved. Exit near bottom, so I am and of brakes scrubbing off speed, when I hear the pad start graunching on the rim. I got stopped and rim was only lightly scarred. I changed pads.
 It seemed a bit worse, and I thought maybe it got warmer and distorted a bit. Then I tried  tweaking  the rim with a c clamp and shims ON the bike. I did not know the cross section of the rim, I thought it was thicker on the shoulder like a mc rim, but it is hollow. Ended up pushing a low spot into the shoulder. So I dismounted wheel and tire, fixed it up as good as I could.
 But it was lumpy, that was August...
 Yesterday I added air, maybe 60 lbs , off the guage , let a bit out to around 48.  During this I heard a snoik noise, like when bead finally seats...I thought that aint good. Push it outside, wheel is dragging, like it got wider.....I noticed that before after topping air up. Leave on bike maybe 15 minutes later.. Dragging..I get off try to slack brake a bit more... Then boom..
 I suspect the earlier noise was the rim cracking maybe between spoke holes, on the inside under rim liner? Rim was for sure compromised, by earlier events.

[Duanob]

Wow I've never had that happen in the 40 or so years of biking and having many many bikes of all types. Must have been a defective rim. I've never heard of rims wearing through the sidewall from rubber brake pads but I guess it could happen. How old is the bike?

As said before, it could've been a disaster if you flying down some steep single track. My buddy and I were at the Whistler downhill park A-line when his tire blew, he ran into a tree and broke his hand and wrist in several places. He had to be hauled off the mountian. Not a good day.

I have discs on all my MTBs. I've thought about discs on my next road bike. I'll set it up more of a cyclecross with road tires.

[754]

IT didnt wear thru. I. Think I may have started a crack or stress riser.  I would not have done what i did to the rim, had I known what the cross section looked like. I was in process of changing to disc up front, all I need to do the rear is a wheel.

[grumpy]

It happens. I've done it. Worked in bike shops for about 20 years...
Grit gets under the pads and acts as an abrasive while you brake. Happens especially in the wet.
Rim walls are pretty thin to begin with so it doesn't take much to wear them down. Plus - grabbing a handful of brake concentrates a HELL of a lot of force onto that tiny area under the brake pad.
Worn rim + a ton of lateral force = boom.

There are worse things: broken down tubes, snapped crank arms, broken forks, snapped stems, broken handlebars, disintegrating front wheels (from getting a pedal or derailleur jammed in there at 35mph)... I've done them all.

 

[Duanob]

There are worse things: broken down tubes, snapped crank arms, broken forks, snapped stems, broken handlebars

That's why I don't go carbon fiber on some pieces.  One little nick in the skin and BAM you're on your face!

[754]

Here it is,

[Duke McDukiedook]

There are worse things: broken down tubes, snapped crank arms, broken forks, snapped stems, broken handlebars

That's why I don't go carbon fiber on some pieces.  One little nick in the skin and BAM you're on your face!

Crabon, I had a crabon seat post break on me in the middle of a ride. Fortunately I was not too far away from a bike shop that fitted me up with a nice aluminum post.

[grumpy]

Yep - classic blown side wall

Although that one blew up reeeeeal gooood.

[faux fiddy]

One time in a peloton a guys rim started making a noise all of a sudden....tick tick tick as it went through the brakes, and it was taking him off the road and down into a ditch at about 25 mph. I saw a splash but he was too far down to see. Another rider checked on him so I stayed in. Found out later rider was okay .

Heat treated stuff was fairly new to me at the time, but the disadvantages were obvious in   that they shatter.   I saw the rim afterwards, and the largest piece was about 4" long and it was just a bunch of pieces hanging from the hub.

[underachiever]

If you've got a Joshua it's a least 10 to 12 years old. What happens to wheels which use rim brakes, not that it takes time but use, is that the sidewall of the rim, the braking surface, wears thin during use. As the sidewall of the rim gets thinner due to abrasion from the pads, eventually the rim wall gets worn enough that the side of the rim may become concave. If the rim or wheel isn't replaced soon what will happen is the pressure from the tire inflation will cause the rim to bulge, usually in one area which presents as a sudden dragging against the brakes. You may think that it's an alignment issue but the rim has pushed out and eventually if it continues to be used will end up looking like the above picture. I see one or two every year. We try to encourage customers to get them replaced before they blowout. Interestingly, they usually occur on rear wheels because most people don't use their front brakes nearly enough. A sound, double-walled mountain wheel will support 100psi slicks without any trouble.

Tony

[faux fiddy]

If the rim or wheel isn't replaced soon what will happen is the pressure from the tire inflation will cause the rim to bulge, usually in one area which presents as a sudden dragging against the brakes. You may think that it's an alignment issue but the rim has pushed out and eventually if it continues to be used will end up looking like the above picture.Tony

This was what I must have seen at speed, hence the tick tick tick.  The continued use lasted about three seconds before catastrophic existence failure.