Tomblarom said:
Because I already done a heck of development and custom fitting to implement the locking mechanism of the intube battery. Wasn't expecting, this frame to be so fragile... I got it for cheap and want to give it a try. I expect it to break at somepoint, but want to compensate by enforcing from the outside.
Sounds like you might be suffering from the sunk cost fallacy.
If somebody came to you and said "Hey I have a used full suspension bike with a custom locking mechanism for the battery, but to be perfectly honest the entire thing is probably going to break in half one of these days"... Would you buy it from them?
If the answer to that question is "yes", then go ahead and spend the money to save it. Otherwise it could be time to move on. Shit happens. This could be why you were able to find it cheap in the first place.
Maybe you can find another used Brose-based bike with the same battery mechanism that doesn't suffer from this flaw.
Would you guys recommend welding an additional aluminium piece or does it weaken the exisiting structure too much?
If you weld on it then it's going to ruin that heat treatment. So were the reinforcement ends you'll have 3 types of metal: Extra thick metal were the reinforcement and welded material is, a short amount softened aluminum in the "heat effected zone", and then hardened original aluminum that wasn't heated past the critical point. This is going to severely weaken the frame in those areas. It's called a stress riser and instead of the stress of the tube being flexed across the entire tube it will be concentrated in that small area of softness.
All of this depends on the specific alloy of aluminum and things of that nature that are beyond me. If the alloy permits it a very good welder who is skilled with a tig torch that can identify and mitigate these problems can probably get it done properly and make the bike significantly stronger. But I expect that would be quite expensive.
If it was a cheap 'high tensile steel' frame you can get away with shenanigans like that with little issue. But on chromoly steel frames or aluminum frames designed to maximize strength to weight ratios it's much more difficult. Those heat treatments are critical to their thin wall strength.
