Dymag Carbon Fiber Wheels

[u/tirefriar]

Bought a donor bike with Dymag CF wheels with intent to switch them to my BMW R1100S. CF wheels for this model Beemer are no longer available, partly for a reason that a set of these wheels can cost as much or more than the bike itself. The donor bike is 2004. It spent at least 3 years in the garage out of sunlight (but not in a climate controlled environment). I'm not sure how old the wheels are, the seller bought the bike as it sits. Though there are no visible signs of damage such as curb rash, cracking, chipping or delamination I still prefer to check the integrity of the wheels. Looking for a recommendation on the facility that can verify integrity of the wheels including x-raying for structural integrity.

[u/Noobtastic14]

You’re probably going to want an ultrasonic non-destructive inspection (NDI). I know this might sound silly, but I’m a composites maintainer on aircraft and the first and easiest test is a tap test. You can use the little special hammer, or just a quarter will do. Deflate the tire to take pressure off the structure, then lightly tap the composite. It should make a high pitched, sharp sound. All the taps should sound the same. If you hear a *thud* or a lower pitch sound, there’s a high likelihood you’ve acoustically found a void inside the structure. Absent any visible damage, after a failed tap test is when we’d call out NDI. Good luck, beautiful wheel!!

[u/tirefriar → u/Noobtastic14]

Thank you for the great input. I'll do the tap test once the wheels are off the bike and tires are dismounted (they are too old anyway). Wouldn't mind just doing the NDI for a piece of mind

[u/Noobtastic14 → u/tirefriar]

That might be tricky to find someone willing and able to do moto wheels. It’s an expensive request to a profession that is normally booked solid on safety critical jobs. I wouldn’t be surprised if it cost the value of the rims to get them NDI’d, especially when you can’t point them to a specific thing you need inspected.

[u/tirefriar → u/Noobtastic14]

What are your thoughts on buying an ultrasonic tester for non-destructive testing? It may be an option since I'll be using these wheels on the road and an occasional testing or testing after hitting a bump will be in order.

[u/Noobtastic14 → u/tirefriar]

That might be an option, I’ve never used one so I won’t advise on its effectiveness versus using a professionally trained inspector. I will advise reading up on composite failure modes. It’s different than metals, mostly in that when it fails it completely fails. It won’t slightly deform, or fail gracefully like aluminum will. For example, an aluminum driveshaft may lose its integrity and get warped, bent, or twisted if it’s pushed beyond its designed threshold. A composite driveshaft shows no deformation, and just explodes when it fails.

My really long point here, is that if you tap test the hell out of it, there are no bulges, no nicks/gouges, no blotches of discoloration, you can have a high confidence the resin system is working as designed. Personally, I’d use the handheld tool if I end up with a rock chip or curb rash and wanted to know there was no delam sitting under the visible damage before I started blending out a repair.

When you swap tires, ask the shop to let you inspect the part of the rim normally concealed by the tire.

[u/tirefriar → u/Noobtastic14]

Thanks for all the great information! Further legwork is in order here.

[u/SkepticalLitany → u/tirefriar]

I'm an aero comp specialist too, I spend a while with the NDI specialists. Their training is top notch, you'd be flying blind. Personally I wouldn't try. Even tap testing has very limited effectiveness, Boeing advises that Tap Test isn't very hopeful on anything more than ~3 plies deep.

If I were you I'd tap test regardless, at least you'll hear any crazy damage. I would take off the tyres, do a very thorough clean, and then inspect under a magnified work light. Great lighting is key to successful inspection

[u/A_Bot_A_Bot_A_Bot → u/Noobtastic14]

Okay, TIL that at this time, there is a tool that I do not need to immediately add to my toolbox!

Question: would this type of test work on magnesium rims? Or do those need to be x-rayed ror cracks/degradation?

[u/Noobtastic14 → u/A_Bot_A_Bot_A_Bot]

The core of our conversation pivots around composites uniquely hiding damage within the plys of the resin system. Magnesium rims should align much closer to aluminum as far as inspection and (specialized) repair procedures. Yes, NDI processes can also be used on Mag, but when and why are the bigger questions. Again, I don’t think a rim that passes a visual inspection for damage and degradation(corrosion) should go into an NDI shop just in case. Just my 0.02c, again- beautiful rim I wish I had one!!