Should I be worried about our rims?
 

We have a 2005 Cannondale road tandem with around 7 - 8k miles on it. It has Mavic A719 40h rims and disc brakes. We run Soma Supple Vitesse 38mm tires at 85 psi. Max per the rim sticker is 37mm at 88psi.
Our team weight is around 290#.
During a recent cleaning, I noticed that 2 of the eyelets on the rear have failed. There are 16 unaffected holes between the two. We have had a couple of broken spokes over the years, but otherwise no issues. I looked with magnification and can’t see any cracking around the missing eyelets.
I am looking for opinions - is this a sign of imminent demise; can we ride it this way indefinitely as long as we keep an eye on it; and what exactly causes eyelet failure in the first place?
Thanks.

https://cimg0.ibsrv.net/gimg/bikefor...8b92d4ca4.jpeg

Spoke and nipple failure is usually a clear indication that the wheel needs to be rebuilt or replaced. The general guideline is to replace a wheel if 3 or more spokes or nipples have spontaneously broken. Since wheels flex during every rotation, metal fatigue eventually destroys them.

The rear wheel is carrying a much greater load than the front wheel and so rebuilding the rear wheel should take care of the problem. On a tandem I would run 4-cross lacing to put less stress on the spoke nipples.

Perhaps a minority opinion, but I think they're still doing their job just fine for now. Eyelets are essentially nipple washers that hold themselves in place by curling around both sides of the hole. If the outer part cracks off (which is not unheard of), they merely become nipple washers and would fall out if you unlaced the wheel.

Thanks, this is pretty much how I see it as well. If you look closely at the picture I attached, you can see that the business portion of the eyelet is still around the nipple.
The rim otherwise seems completely fine; no cracks and dead true. I am hoping it remains so for some time for several reasons, not least of which is Mavic stopped making the 40h version.

Good question about the cause of the eyelet failure. Seems irrelevant to the wheel's integrity, as it's not structural where it failed. I assume cyclic fatigue is the cause. You're right to look for cracks in the rim around the spoke hole. Without those, I wouldn't worry about it. What would concern me is current spoke tensions. It would be nice to see if they're still within spec. It's important that they're high enough so the spokes don't reach zero or near zero tension through the rotational cycle. This is what leads to premature fatigue of rim spoke holes and spokes.

Then again, if the tensions are too low, it's probably too late. Just keep riding it until additional spokes fail or rim cracks develop. However, I would not do this if I had a big tour or foreign travel planned for this rear wheel. Then it would be time to build up a new 40 spoke rim. Maybe Velocity? You should be able to find a stout replacement for it. Good luck!

Thanks for that reflection. No big tours planned. Just normal riding.
I looks like the Velocity Dyad 40h rim would be a suitable replacement.

If you’re willing to go to complete new wheel, there’s no reason a 290lb team needs a 40 spoke rim anymore.

With a team weight of 350lbs (sometimes higher unfortunately) we’ve had no issue with 28 spoke wheels, even off road.

Tandem wheels were built with a lot of spokes bitd when rims were aluminum and not that stiff. With the availability of strong stiff carbon and aluminum rims 40 spoke tandem wheels are overkill for many teams and many uses.

unless weight is a concern , I would look at the velocity clifhanger since you are running 38's at what velocity will call the high end of the pressure range (I think you said 85 psi)
velocity replaced some aillerons on our rt2 with the cliffhanger on the original white hubs and they are near bulletproof, we are running 42 wtb resolutes on that bike

I have had two cliffhangers fail and crack after only few thousand miles 32 hole rims. the redraws re[placed under warranty and he used washers and that seems fine. the front took about 3 times as long to start cracking. if you had more spokes it may be fine but 32 did not work for us. the front is getting replaced with a dt dwiss 540 plus the cliffhanger I think the min tire size is 48

What size tire , pressure and team weight did you experience the failure with?
op is running a 40h hub
interesting that their chart does show a 45 minimum given the 25mm internal width (not to mention they warranty replaced my ailerons with the cliffhanger knowing the tire range we run)