Metal Fatigue on rim.

roadmanmad

Last Sunday, while out for a spin on my primary night training bike. I recieved a big puncture. Whatever it was went straight through the beading. Called in the rescue team and headed home. On Tuesday night I was attempting to fix said pucture when i noticed crack in the rim of the wheel.

The training wheel was a very basic race wheel, ambrosia rim with sora hub. I ordered a new wheel as I brought the wheel to my expect bike shop to show the issue. The wheel is 7+ years old and has done 5-7k miles approx in that time.

Under examination there were at least 6 visible stress cracks all around the rim. The wheel would not have last much longer.

It could be interpreted as a very fortunate puncture. I have never seen this level of cracking in a wheel.

This may be of interest to those who are doing a lot of mileage.

kona

roadmanmad wrote: »

Last Sunday, while out for a spin on my primary night training bike. I recieved a big puncture. Whatever it was went straight through the beading. Called in the rescue team and headed home. On Tuesday night I was attempting to fix said pucture when i noticed crack in the rim of the wheel.

The training wheel was a very basic race wheel, ambrosia rim with sora hub. I ordered a new wheel as I brought the wheel to my expect bike shop to show the issue. The wheel is 7+ years old and has done 5-7k miles approx in that time.

Under examination there were at least 6 visible stress cracks all around the rim. The wheel would not have last much longer.

It could be interpreted as a very fortunate puncture. I have never seen this level of cracking in a wheel.

This may be of interest to those who are doing a lot of mileage.

This is not metal fatigue,this is what happens to rims, where the braking surface is the rim(non discs) and is taken into account by manufacturers.
there is a wear guage built into every rim(maybe every decent rim!)
its usually, either a dot or a line which is below the braking surface.
when this difference in depth, evens out, its time for a new rim.
you can prolong the life of your rim by keeping it clean and using quality brake shoes.
lucky puncture is right!!!

Capt'n Midnight

if your brakes put too much pressure on the rims it dont' help
also if you let the brake blocks wear down too much till the metal shows, tbh lots of brake blocks are very badly designed with metal barely below the groves in the blocks

doozerie

The tell-tale sign that I reply upon that my rim won't last much longer is that the braking surface develops a curve - as the side walls get thinner with wear from the brake blocks, the pressure of the tyre against the walls of the rim will grow stronger than the rim wall can withstand so effectively the rim will widen (hence the curve).

From then on you can't predict when the rim will fail. I have had some rims develop a crack along the side wall mid-ride, at which point you've gotta just hope that it will hold until you get home (although riding it at all at this stage is risky). I have also had a rim "burst" apart before any cracks ever showed, and that is dodgy 'cos you can end up with a strip of your rim poking out and trying to both impale your leg and also wrap itself around your frame while the wheel is still turning (wheel didn't turn for long either so basically the wheel seized up and I skidded to a halt).

You should check your rim regularly for signs of wear like this 'cos the consequences of leaving it too late could be serious.

doozerie

Forgot to mention that another sign that your rim may be on its way out is if you feel a jerking motion when braking. This can be a consequence of the rim widening as the walls have weakened - the widening/bulging of the rim is typically not consistent all round the rim so the bulging portion(s) catches in the brake blocks. Of course, this can be caused by other things too, but it is a common symptom of the rim being worn out.