Is my frame cracked?

mtblad

Today I started on stripping my orange five down ready for a respray and in doing so I have noticed either a scratch or a crack on the down tube. My suspicions of it being a crack are basically because of where it is, the line runs from the seat clamp gap to an inch or so down the down tube. Also I imagine it would be fairly unlikely to scratch a frame like that on that part of the frame.

Would you agree?

timothyw

Looks fine to me.

Usually when I've cracked a frame you can see through it.

steve_sordy

I have blown up the picture and I still can't see any sign of a crack.

fenix

I can't see a crack either.

Take the post out and look from the inside to reassure yourself ?

mtblad

Thanks Guys it may just be me I just found it odd where it was, its going to the orange factory next week anyway so I've emailed them this and they will be able to check further for me without the paint in the way.

The Rookie

By the way that looks much more like the seat tube than the down tube, if asking Orange to check it its better to ask them to check the right bit!

No crack there, I can't see anything at all that even remotely looks like one.

bonzo_banana

I can see the very faint weak squiggle there which could be a scratch or could be the very first sign of a crack forming in the seat tube. If its a crack forming its right at the very beginning which normally you wouldn't notice yet. Considering the location it is quite possible.

I guess you'd have to remove the paint there to look at the bare metal to confirm if its the beginning of a crack and if it isn't you've spoilt your paintwork a little bit.

Maybe think about how old the frame is and how much use it has had, frames don't last forever. Maybe you could say the beginnings of the frame cracking could be expected.

Maybe you could lower your saddle height a bit or move the saddle forward or back a smidgen to try to move or reduce the stresses on the seat tube a small bit?

In my experience seat tube, chain and seat stays are common failures on mountain bike frames because of the constant movement of the rider and the impacts of landing on the rear wheel but on road bikes you get a lot more cracks in the bottom bracket area because of the level of power input on what are smaller tubes combining together in the bottom bracket area. This is just my general experience and of course others may have a completely different experience, some brands seem to suffer more in different areas.

Fatigue is a thing with aluminium, aluminium frames always get weaker with time, they have no endurance limit and I believe many aluminium materials if not all become more brittle/harden over time even if not used. So what was a incredibly strong frame when new can be close to failure 10-15 years later even with light use.

mark~p

I have not had a great deal of luck with cracks. My commuting bike, used daily in all weather and not exactly cared for developed a clicking noise I could not trace. One day when I picked it off the bike rack at work I felt movement where the downtube meets the head tube. Further investigation when I got home showed this.



Technically it was under warranty but Focus took so long to do next to nothing other than agree it was cracked that I just bought a new bike. It was cheaper than months of train fares.

I then had two Cube Stereos that were cracked in the same place, both second hand and I should have found the first. This was not obvious as it was under a chain stay protector. That ended up as a write off, sell the parts, grin and bare it. The second was frame only and it was only after it had been stripped and then powder coated that it came to light.

Crack was in exactly the same place on the RH chain stay by a cable guide. This ended up as a 50/50 with the person who sold it.

Cracks can be really difficult to detect until they are catastrophic and modern paint/plasticote finishes that are flexible can hide all sorts of problems. Alloy does not give in the way steel does and is more prone to stress fractures at the joints. The frames are supposed to be heat treated to reduce this but I think that even with modern manufacturing methods there is still a lot of variation.

bonzo_banana

Cubes and Focus bikes have shorter frame warranties and lower weight limits. I think 120kg total load, not as bad as Btwin with their 100kg load but many of the US brands and Giant go to the full recommendations of the certification standard which is 160kg and Giant offer a lifetime warranty too as do many US brands on the frame. There are advantages to making frames lighter with more tube flexing, they can feel more sporty and comfortable but then the frames have a shorter life. As a heavy rider I've caused a few frame failures in my time. The UK man has an average weight of 82kg I think but in the US I think it is 89kg I tend to go more towards the brands that meet the maximum weight recommendations of the certification which tend to be US brands. As you can imagine past bikes include the Kona Hoss and the overbuilt Saracens, So actually that is a canadian brand and a UK brand but in my mind I think I'm more in tune with the US brands and Kona meet the high 160kg total weight limits. People forget that different bikes have different weight limits but its there for a reason and even if you are a lighter rider if you are intending to give the bike some abuse a bit of extra strength is worth having. You can't claim a bike is suitable for 160kg total load unless its been rigorously tested to meet and exceed that weight level as part of the certification process. All bikes are tested and certified nowadays unless its a personal import, aliexpress etc.

mtblad

Interesting points, just to update orange have checked my frame prior to repainting and they confirmed that my frame is fine. It turned out just to be a scratch in this case.

fenix

Good stuff.