Tandem, Ryde Andre (box type) rims, 25,000 miles, riding with 2” tires at 55 psi. I have recently noticed that the front cantilever brake pulses at 1 spot in the rim. The rim is fairly true without a hop at the place in the rim. With calipers I find that the rim is 10 mils wider at the spot relative to the rest of the rim. Have people observed such rim bulges? The brake pulsing is a bit annoying. I am tempted to put the rim in a vise with leather protection and squeeze it a bit, but aluminum doesn’t response nicely like steel.

Use a parallel jaw tool like this and work in small bits.

Before you do anything, look for hidden cracks in the rim sidewall. Brake wear and fatigue could contribute to a failure.

At 25,000 miles on a tandem, I don't think that the wheel owes you anything. Especially if you have rim brakes. Yes, you could ride it with a damaged rim, but you'll (a) struggle to get it unnoticeable and (b) increase its risk of failure. It is more likely to be inconvenient than dangerous, but if you have to do it why not do it before you need to?

I'd swap rims. Get another Andra and you could just swap the spokes over.

I’ll add to check the sidewall of the rim for concaveness as well. Put a straight edge on the rim from the top to the bottom. If the rim is okay, the sidewall should touch the straight edge from top to bottom. If the rim is worn, you’ll see a gap in the middle.

do your brake pads extend below the rim? if so (and it Looks like they do!) then that is, most likely, a cracked, Worn Out Rim.
it sure looks like a crack in that pic.....
the tire pressure can force the cracked area outward... 25k miles is a lot for a pair of rims to endure., and tandems experience much higher loads...

Concaveness can vary, depending on braking technique, pad alignment, rim style, and pad service intervals.

brake type can also change it.

Look on eBay for "dental calipers" Small and inexpensive and will measure down to .1mm so you can check thickness of rim wall

https://usdentaldepot.com/caliper-fo...B3SD9m7VXGbCD4

Also known as a "Crown Thickness Gauge". Some really cheap ones may not be very good. The one you linked to looks decent.
I think I paid about $60 for the one I was required to buy in dental school. It's made in Germany, and very nicely made. I still use it... but I wouldn't spend that much on it again!

This ^^.


The shadow of the edge of this ruler illustrates the extent of the convexity concavity* of the rim flange due to brake wear.
*Thanks to OneClick for catching my stupid typo.

Also...

When the wear makes the flange thin enough, tire pressure forces it outward. Brake application presses it back. This back-and-forth flexing eventually causes the alloy to crack. At this point, the rim will begin to "thump". Bad things can happen if this wheel continues to be ridden. (This is a 20" wheel with an internally-geared hub, which is why the spokes appear to be at a goofy angle.)

Rim is toast for sure. Now while you're at it get a SA XL drum brake in there, better with the dyno too.
Mine has 32,000 miles with 8,100 on tour with the total weight 290 lbs. Near half of these miles I had a useless POS rim brake on the rear. 100% safe and reliable.
Actually, in Vietnam my fork broke 3 times near the top. I then got a tandem fork. LOL.

Yes! Great idea.

Almost everyone who says bad things about these hubs hasn't used one. I have the smaller front drum on a Pashley Mailstar (the Royal Mail's postal delivery bike) - not a bike I use much but the 70mm drum on the front can stop me as well as I need it to and we have a lot of hills here.

That spoke angle needs dimples and cupped washers.

p.s. the preferred term is "concavity".

You'd be surprised. I hit a bad pothole on 20" aluminum rims, it flared the rim sidewall out a bit, no out-of-round, I took an adjustable ("Crescent") wrench, snugged it up around the bend, bent it back easy, varying how far in I put the throat of the wrench, depending on exactly where I wanted the rebend to occur. Worked dandy. That was many years and a lot of miles ago. Rims are near end of life now due to brake sidewall wear, I want discs. Ever since I run the tires 10 lbs higher as protection against that, middle of inflation range (40-60, I went 50 instead of previous 40).

Front rim on a tandem with 25k miles? I’d sooner replace than take the risk of bending aluminum back. Life is short enough.

Having a concave braking surface is never a good thing. It’s an indicator that the walls are thinning and that the tire is pushing the rim outwards.

O Crap! That's not the "preferred" term... it's the *correct* term. I slipped a gear.

Andra rims have a built-in wear indicator - they start to split at a thin part in the middle of the braking surface before structural failure.

Typing this makes me feel like a wannabe grammarian, but here goes...

First, 10 mils (0.01") is a cause for concern? After 25,000 miles, I'd think that might as well be attributed to hitting a pothole somewhere along the way. Check for concavity and cracks, sure, but if it's not worn or cracked I'd keep riding it (with periodic inspection).

Second, I didn't see a picture from the O.P. A couple of other people have contributed pictures of damaged rims, but I'd think it'd be better to offer advice based on the rim in question, rather than some other rim which may or may not be representative of the item in question.

Um, "concavity" is preferred to "concaveness"; though a previous poster's use of the latter may have led you astray.

Most every wear indicator I’ve run across is mostly useless. This one would cause the rim to become concave before it started to crack.

"Toroidal bilateral concavity".

Congrats on your new rims.

No... seriously... it's been 25k miles.
You got your money's worth.

Thanks for all the information from everyone. Here are responses and a couple of pictures about the 10 mil rim bulge which is noticeable during braking.

-No noticeable cracks or other imperfections in rim. Attached in a closeup of a typical section, nothing strange.
-"Concaveness" is less then 1/64" (<15 mil), a picture showing the gap is attached.
-Rim wall is close to 0.10" minus 15 mil or so for the "concaveness". Plenty of rim remaining.
-The brake pads do not extend below or above the rim.

The rim region in question, which is wider by 10 mils, is about 1" in length. The extra width is symmetric. On a truing stand (park) the left and right rim sides hit the stand caliper at the same rim points, both sides are 5 mils wider. As some have said, perhaps hit a pothole. However, there is no hop in the rim at that point. Perhaps coincidental, the bulge is very close to the rim valve hole. Some people have had success with gentle bending, I'm inclined to try the same.

The only one I like is the single "dot" (blind hole) placed on the braking surface 180 degrees from the valve hole. Of course, it only samples wear in that one spot, but wear is usually spread evenly around the rim, and no structural deficiencies are involved.
The one I like least is the milled groove around the circumference in the middle of the braking surface.