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Hello Folks,
This past week I had a brand new carbon-spoked wheel fail. Without naming the manufacturer, it is a metal rim with structural carbon inner. Brand new; ridden perhaps 5 times. I was riding in a very hilly area. Coming down a long steep stretch, probably 1/3 mile at 10-plus degrees, my tire blew. When I got off of the bike to inspect the problem, the rim was hot, likely from brake application. Since it was a wet road, I hit the brakes a bit to keep the descent at about 30 MPH. Upon further inspection, I noticed that the rim had totally separated from the carbon inner. My thought, and that of my father, a structural design aerospace engineer, is that the heated rim expanded at a rate far different than the carbon and the expoxy was not structurally sound enough to keep the materials sealed. This separation is what caused the tire to blow. A buddy of mine relayed that this happened to him before as well - similar wheel, different company.
Has this happened to anyone else before? Should these types of wheels simply not be used for major hills? On a related question, wouldn't the heat on a pure metal rim cause damage to the tube as well? Hard questions for this flatlander from Florida.
PS. The manufacturer immediately sent me a replacement - trying to make it possible for me not to miss a race 2 days later. Great service from this boutique triathlon companies!
"A buddy of mine relayed that this happened to him before as well - similar wheel, different company."
i can only relate my personal experience, and that of industry spectator for 15 years. i have two such sets of wheels like you describe, in this case both from HED, a hed3 and pair of alps. i've ridden both in hot, hilly long triathlons and i've neither had this happen to me, nor have i heard of it every happening before with these particular wheels.
"My thought... is that the heated rim expanded at a rate far different than the carbon and the expoxy."
no, not very likely. it's simply a question of whether the epoxy was the appropriate type and if the wheel is well-made. keep in mind who originally engineered the hed3, the company whose job is supplying the raw material. as for what other companies do, i can't say. but your theory as to why the wheel would fail is not observed to be the case in "nature."
i can see, however, how you could've perhaps blown a tire because of excessive braking on a descent. you can also roll a tire by melting the glue on a descent. you'd also have certain concerns on hot, long hard descents with carbon braking surfaces. fortunately, living and racing in florida, you don't have to worry about that much.
Dan Empfield
aka Slowman
Of course there is a simple solution so that you never encounter this problem...Dont use your breaks. It prevents this from happening, saves on tires, saves on break pads, and it is better for the environment (fertilizing the side of the road after you mess your trisuit, and skid off into the bushes when you hit some gravel in the road). Works for me ;)
Stephen J
I believe my local reality has been violated.
____________________________________________
Happiness = Results / (Expectations)^2
I have had the exact same thing happen. It actually ocurred during a race on a steep descent leading into a sharp curve. I was able to brake to a stop but my race was over....
Dan,
Thanks for the reponse. Looking back on my post, I was not sufficiently clear. I did not mean to question the strength of the epoxy itself, but the strength in this application - for example, perhaps the epoxy on this wheel was not applied perfectly, had an air pocket, etc. Incidentally, I did not say my wheel was a Hed-3 - :) By the way, you never mentioned why you think a tire could pop with heavy breaking. Since I intend to return to this venue frequently, perhaps I can modify my riding on steep terrain. Thanks again.
Danielito - Did you ever figure out the cause of your wheel failure?
"I did not mean to question the strength of the epoxy itself, but the strength in this application... Incidentally, I did not say my wheel was a Hed-3"
if i remember right, you questioned the wisdom in bonding together two materials that might have dissimilar expansion rates when overheated. i brought up the hed3 not because i thought that was the wheel that failed, because i found that unlikely, but as an example of a product originally invented and engineered by dupont. i doubt they'd have countenanced the manufacture of a product in which their own carbon fiber would fail when bonded to aluminum.
but things do get hot down there. if it gets hot enough to melt sew-up glue, it wouldn't shock me if it got hot enough to melt a clincher tube. but perhaps i'm wrong about that, i don't know. i guess i suspect a sew-up tire might be somewhat more protected, because it's entirely encased.
Dan Empfield
aka Slowman
As described in previous posts, the heat generated by the brakes might be dangerous. (Damaged wheel, melted glue...). I've seen a lot of riders that don't know how to use the brakes - generating too much heat. (And a lot of tourists get problems with their car brakes in the Norwegian mountains for the same reason). In decents - do not use the brakes all the time! Instead of a constant, low pressure on the brake, ride downhill without braking (most of the time) and when needed (just before turns) brake hard for a few seconds to reduce the speed. The periods without braking is needed to cool down the wheel.
I'm with Dan on this. The CTE mismatch between aluminum and carbon-epoxy composites is relatively large (and is actually often used in manufacturing to improve laminate quality), so I can see where your dad was going. The initial culprit is more likely the bondline between the rim and composite sections of the wheel, though...either by poor bondline quality (too thick or thin, pockets, etc) and/or - and this is my prime suspect - simply too much heat via prolonged braking causing the temperature to rise above the design limit for that particular epoxy. Taken past that limit, the bond will soften enough to allow those CTE-induced forces (and others) to separate the two wheel components.
Carl Matson
I've had tubes blow after rim temps melted light rim tape and sucked the tube in the spoke hole.Never heard of the tube melting.I only use Velox and ceramic rims on Mtb.Cullen