Rims & wear.

[half cog]

So far as I know mavic rims are around 1.4mm wall thickness.I read somewhere that the point that they explode is around 0.6. The old ma40 may be thicker to start with but the new rims I bought for the tandem( mavic A319 )are def 1.4 mm thick on the brake surface.What you need is a digital vernier.Cut two short bits of spoke and lay them on a flat surface and measure both of them together across the width. Pop one piece inside the rim at the back of the brake surface and the other one outside and re measure. This will now include the brake wall thickness in the second measurement. Deduct one from the other and you have the wall thickness.Its the only way to do it to avoid the hook at the top edge of the rim.You cant go straight in with the vernier.With the tandem I scrap them at 1mm. You tend to wear brake surfaces quickly with two of you on the bike and cos its the misses on the back I tend to play over safe .The idea of 0.6 as critical does not allow for an out of true rim catching and developing an overworn section.Before I started using the vernier I have had them go so bad that you could push a thumb nail through the side .Even on my solo bike I would dump them at around 0.8/0.9 .Back in the early days of mtb I once had an entire sidewall come away. Big bang and omg.Best not to do it

 

[shogun]

When you consider the greater bead area of a clincher road rim courtesy of diameter, running at up to triple the tyre pressure, and the greater speeds descending on a roadbike (coincidentally when they seem most likely to fail), I would think sidewall thickness is actually more important on the road.

 

[half cog]

Interestingly enough I see spike3 has just posted a photo of a rim he has had blow up . Frightened the c--p out of the dog would you believe. The neighbours came out to see what it was when I did mine

 

[glpinxit]

I have some Campagnolo aero wheels (both Zonda and Vento) that have a small hole drilled in the braking surface to enable wear to be gauged.

 

[FINNEY1973]

Thanks Gents, most informative. If we are taking 1mm +- a bit each way then i'm at that point with these MA3's. The bead seat section is pretty much untouched but that can't be said for the mid section & rather oddly the inner rim edge. Used by the previous owner with poor brake block alignment.

I'll keep a more regular check on my wheels from here on in, must admit it's something i've tended to ignore, more out of ignorance than intention.

 

[TGR]

Hacksaw time?

Richard

 

[FINNEY1973]

Indeed Richard, I'll be getting a pair of Athena hubs out of the wheels that need a service & I think i've got another pair of MA3's somewhere. If they're the right spoke count i'll be getting next winters wheels built up so not all is lost.

Hacksaw at weekend and I'll post a picture to see the true extent of the wear. Thus far this 'free' Ribble needs new rims, new calipers, new cranks, new seatpost, consumables and the BB is stuck and I've had to 'brush' the frame with some of these http://www.ebay.co.uk/itm/161215394151? ... 1439.l2649 to get it half presentable so it's been arduous to say the least. Would of been easier to buy a new bike but where's the fun in that?

 

[TGR]

I am actually in a similar state with my ProRace - cheap clean and tidy and i thought it would be fine... nooooooooooooooooope!

New HS
New BB
New cables
New pedals
Wheels need tensioned and a spoke for the rear
and i am sure i am missing something else

Cheap bike gets expensive and still remains a 'cheap bike'.

But all good fun!

Richard