Hi All, My beater (ultra high mileage touring bike) has a set of fairly worn Sun R17 rims. To test how worn the brake track might be I inflated the tires to 100+ PSI (~30 PSI above tire rating) and compared the before inflation to post inflation measurement. The two measurements were the same. There are no cracks in the rim, but there are a couple of spots in the rear rim worn enough to show some white.

If I wanted to use the beater on a tour, I can swap in the wheel set from my regular touring bike.

I know the best method is to measure the rim's braking surface thickness, but I'm wondering about the validity of this little test.

TIA,
Brad

Brad;

What was the resolution and accuracy of the measurement? What is the Gage R&R of the measurement system (which includes you, the operator)?

Even if the dimension was exactly the same to ± 1 nanometer; which it wasn't - all that it shows is the there was no plastic deformation of the rim due to over inflation of the tire.

I would place a straight edge across the brake track on the rim. If there's a significant depression (greater than 0.5mm) I would replace them. If there is circumferential scoring, consider replacement.

Sun CR-18 rims are cheap and pretty durable. If you've built wheels, replacement is straightforward.

Under normal circumstances the rim flanges barely move with the added load of tire pressure pulling them apart. However wear thins and weakens the flange and eventually it'll weaken enough to flex outward.

Fortunately wear isn't perfectly even, so some areas will begin to sag before others causing a pronounced brake pulsing. So no pulsing is the best indicator that the rim is OK. However you can also get pulsing from other causes, so pulsing alone doesn't mean the beginning of the end. If you have pulsing, combine it with other clues such as a concave brake track, and/or clean the rims and shoes to eliminate other causes.

If a rim is doubtful, I use a "safety method" by over-inflating tires by 15-20% to stress the rim, then drop back to riding pressure. That provides a degree of assurance that I won't see flange failure while riding.

BTW- referencing Jeff Wills' test. the rear rim on my commuter is concave by about 1.5mm or so and shows no hint of pulsing or measurable spread under tire load, even at 20% above where I ride it. I was hoping to take it to the point of failure, but unfortunately a nice lady T-boned me last summer bending both wheels sideways beyond salvage. (I was OK, suffering only a bruised thigh and ego).

All I was looking for was the possible deformation of the rim. Measurements before and after over inflation had a range of 25.36-25.40 mm at eight points of the rim. The digital caliper claims accuracy to .003 mm and I did my best to keep the caliper perpendicular to the rim.

There is some light circumferential scoring, but no depressions close to .5 mm. I was going to move my Alivio/CR18 wheel set from the primary touring bike to the beater or just rebuild with some new CR18 rims had the over inflation resulted in any deformation.

I had to test for any brake pulsation this AM and I didn't feel anything, but it's cold and I may've not felt any light pulsations. Sad to read about the wreck!

Thanks for everyone's comments. I use these rims for 2015 and see how things go.

Brad

FWIW: this is what happened to my last CR-18: rites042 . It lasted through several Pacific Northwest winters, so this wasn't surprising (except for the bang! when it let go). FWIW: I didn't feel any pulsation until after I had started that ride. Ten miles later...

When I bought the Alivio/CR18 wheel set I was positive I'd upgrade it if I liked touring. I do, but the wheel set has been so reliable I think it would be foolish to do so. What may help is my winters are just not nearly in the same league as what you and many others face.

Brad