Hi all. New here.
Working as a mechanic in a small bike shop, I come across a variety of bikes as we’re not locked into selling/servicing any particular “big brand” bikes. Sometimes I’ve come across some pretty nasty failures. Failures of the type I’d prefer to not see on any of my own future frames, so I’m posting this question here to learn from the combined experience of the forum members.
Most recently we had a customer come in asking us to pull the parts off a frame with a failed top and downtube. They bought the bike from us and we’re faciitating the comms with the manufacturer regarding the failure.
I’ve only ever seen this type of failure from frontal impacts, so I got curious and asked the customer how they managed to do this and they were adamant nothing special had happened and that they basically just trundle along bike paths. Classic JRA claim.
The story was that they came home after a ride one day and noticed the paint peeling, and upon closer inspection they also noticed the creases in the tube.
What’s the general concensus amongst all you experienced and less experienced frame builders and industry people? Do failures like this happen from anything but overload or head-on collissions?
Less experienced concensus: Classic customer states.
The customer is outright lying. There is no way a failure like that can happen without a force applied from the front. The tube is strongest axially so it has been a decent hit in this instance. Warranty claim denied.
I’ve had a top tube buckle at the internal butt after the rider flat landed from about 4m. Admittedly the tube was under spec’d (I now run a better tube) but the force req’d is massive and not from JRA.
The last time I saw a bend like that was at college. My mate had got completely plastered one night and rode headlong into a waist-height wall! He was fine; the bike went to the scrap yard. Your customer’s full of …it
I’m with Sean on this – like 98.7% sure it’s not a JRA.
But, as a thought experiment, what would I expect to see if it really was a JRA?
Tubes would be buckled in the opposite direction – body weight is pushing down. Buckling probably be less than what we see here. The failure is showing the direction of travel.
If I were to cut the frame apart I’d expect to see some significant butting issues or the wrong wall thickness (e.g. the assembly factory mitered tubes backward or mixed up tubing. Both of which I’ve seen IRL).
Gauges/scratches at the butts. (RL experience here tells me that the tube would crack not buckle)
Braze-ons at the butt location. (Cooking the tube at the butt is a possibility but I’d guess that we see a crack not a buckle.)
Weld/brazing failure. But the location would be at the joint not down the tube.
Check their roof rack for damage from driving the bike into the garage.
I worked in shops for many years and saw a lot of JRA damage. With that much damage, the bike is likely unrideable so they were def not JRA and happened to noticed cracked paint. What condition is the fork/bars/shifters/wheel? It’s more likely a ‘just driving into the garage’ incident.
It’s worth a check but I don’t think this is from driving the bike into the garage.
As my technical drawing below illustrates
I think the immovable object was by the wheel.
… which makes me think there should be damage to the wheel, fork, tire/tube.
Thats some good FEA right there.
Do a tech drawing with an upright bike rack.
purely anecdotal, but I’ve seen significant frame damage (nearly identical to what’s pictured but in carbon) with an intact fork and intact front wheel. The rider in question admitted to riding off the asphalt at medium speed into a ditch. The front wheel stopped and he kept going. It could happen in a way that doesn’t significantly damage the wheel and fork. But, this is just one example of one thing I saw once. lol
Thanks for your input everyone.
All responses are what I’d expect, but I wanted to at least entertain the possibility that a few of you had some experience to the contrary.
In my mind I’m thinking that maybe repeated heavy braking could be an contributing factor. I find it hard to imagine braking alone could have been the cause, but maybe in conjunction with a minor tube deformation from an earlier “riding into a ditch” incident or other tube imperfection.
Anyways, it seems I probably don’t have to worry about tubes folding like this as long as I don’t completely under-spec the tube selection or damage the tubes in some way during construction.
That’s some serious CAD skills man!
Imagine what I could do if I moved from Product Manager to Sales Manager!
Just to add another potential scenario alongside the classic garage impact case: I was going for an MTB ride with a guy I’d just met and after a sizeable gap drop he tagged a rock on landing and it sent him into a ditch that stopped the bike dead and he went over the hangers. No damage to him but the aluminium Santa Cruz hardtail he was riding failed in a similar manner, the wheels were almost touching!
Agreed - the weakest element will take the most damage, and if that is significantly weaker than other elements then it could be the only part damaged.
10 years ago I would have said “The customer was lying, 100%”.
I was on a group ride, where a 1 month old, aluminum Schwinn hybrid broke at the TT/HT & DT/HT, because the rider had to slam on the brakes when a car ran through a stop sign. There were several witnesses, so we all accompanied him to the Schwinn shop. Where we were all accused of being liars, and the shop owner hasn’t spoken to me since.
I have lousy short term memory. So I may be the only person who has driven into a garage TWICE, with a bike on top. Of course, these were the two frames that I’ve built for my wife. The bikes were OK, but the cars and the rooftop racks sustained damage. The bikes, Reynolds 531, were tougher than the hardware holding the racks to the car. After the 2nd time, I bought a minivan.
Weakest Element; When I built frames for my sons, I used cheap fork blades. Knowing those two knuckleheads, I figured I’d rather replace a fork than a frame.
Let the manufacturer decide. Nothing worse than implying that the customer is lying, even if everything suggests that they are.
Classic buckling failure at the butt transitions, from major frontal in-line impact. Usually hitting back of parked car or large kerb, upside down on a roof rack vs garage, or very occasionally from major braking on a rotted frame.
I did this myself, half asleep riding back from college at dusk. Slammed into the back of a parked hatchback
On the plus side, it was repairing that much loved frame that got me into frame building.
Lighter model 531 frames were notorious for this failure, with a 100% intact front wheel and fork.
All the best,