Another probably very easy question...

[DCBassman]

I'm looking at new wheels in the not-too-distant future, as I suspect these are well-worn brake wise. Having read about these wheelsets (Shimano WH-R500s), they are stated as having a wear indicator of some diescription.
I cannot find any information on how this works, not see anything obvious on the rims. That might mean of course, that it's too late already! I've seen an example of what happens when a rim blows out under tyre pressure - not pretty. But I don't want to change them unless needed.
Your knowledge appreciated!

 

[S-Express]

Not sure about R500s, but other Shimano rims have a small hole partly drilled into the braking surface, so that when the hole disappears, you know the surface is worn to its safe limit.

 

[Widge]

Yup......there is a tiny hole in the rim. I watch it all the time!

 

[DCBassman]

Not noticed any holes...possibly bad news! Too wet right now, will check and possibly panic...

Many thanks!

 

[Globalti]

I've got some almost new Aksiums for sale if you're interested. I think they have a groove in the braking surface.

 

[Milkfloat]

You can look at the rim profile and see if it is really concave. For me personally the rim below has a bit of life left, but I would be keeping a sharp eye out for splits (and bargain replacements).

 

[DCBassman]

That's a great help.

Just been outside in the pouring rain for a quick dekko under the cover. The hole is not on the braking surface as it is currently worn - clean hole through black paint.
The profile is palpably worn, but nowhere near that in the picture above, so it looks like I can have a little while longer to save me pennies!
Again, thanks for the knowledge.

 

[Spiderweb]

My R500's don't have wear indicators, holes or grooves and they are definitely not worn out.

 

[Tim Hall]

You can measure the rim thickness, either using some vernier calipers plus a couple of spacers of known diameter (the rim profile means direct measurement isn't possible) or an Iwanson gauge. I've just bought the latter for a few quid from Amazon. Received wisdom seems to be 1mm thick is a good time to change the rim. Or you can pump the tyre up to something well in excess of its normal pressure and see if the rim fails. Ear defenders are recommended.