Bike Frame Points of Weakness?? - especially aluminum frames

[John in CR]

I picked up a nice front suspension aluminum frame bike that I just got running today with a front drive hub motor. Now that I'm up and running my thoughts have already turned to how to make it better, stronger and more durable. I've already fully addressed the weakness at the dropouts, which I will share in another thread once I have some pics. With me over 100kg and the motor force applied to the front forks, I'd like to strengthen the front of the bike. Where specifically are the common points of failure, so I can figure out the most beneficial manner to add more aluminum?

John

 

[Zoot Katz]

A steel torque arm is nice.
A nice fat gusset behind the head tube is reassuring.
Your aluminium frame was heat treated after welding. Can you do that after making modifications?

 

[deardancer3]

My Opinion:

Depending on the bike manufacturer, there are few across the board failure areas from the better frames.

Frame failures have been studied by Giant, Trek, Specialized,etc, and the weak areas reinforced already.

So then it comes down to the quality of a design, how long it has been in use, quality of material, and quality of assembly.

Some frames have had high failure rates, and have been recalled. So just google your bike model and look for problems in your google statement.

However, many of us have noted inadequate brakes for the loads and speeds we are operating at. Hopefully you are not using big SLA batteries, so then if not, your weight is not a big deal. But do get a quality rack and do a good job installing it. We also have a higher rate of wheel failure, again due to higher speeds and higher loads.

Reinforcing a 6061 T6 frame or maybe a 7000 Alumninum series frame by what ever method, seems to be a little risky due to the stresses you might put on the metal. But other areas of the bike may prove worthy of attention depending on the bike and components.

routine inspection and safety checks are wher the big paybacks are for me.

 

[D-Man]

No signs of failure for me with over 3000 miles and heavy sla's/aluminum frame.

 

[Link]

Yeah, most frames are quite strong. Most common failure I've seen is that the front fork bends completely or snaps, but from landing badly after a 15ft jump. :? I don't think we have much to worry about, unless we fall off a cliff, eh, Mathurin? :wink:

 

[dogman dan]

I wouldn't sweat it unless you see stuff bending as you ride. I just retired a cheapie mongoose when I got another that had more strength around the seat post tube. I could see the old one flexing with 15 pounds of batteries and my big ass all loaded on it. The new bike has a big gusset there the other didn't have.

 

[docnjoj]

Unfortunately, U dont see alloy bend, just hear the snap! My trike is bolted together a la ultralights. In fact Sid from Tricruiser used to build them befor his car accident. They rarely weld the alloy that flies in the Ulites. Bolts and safety wire and rivets! Also helps to make em portable!!!
otherDoc

 

[TylerDurden]

Unfortunately, U dont see alloy bend, just hear the snap! My trike is bolted together a la ultralights. In fact Sid from Tricruiser used to build them befor his car accident. They rarely weld the alloy that flies in the Ulites. Bolts and safety wire and rivets! Also helps to make em portable!!!
otherDoc

How true... Now that I know how to weld (poorly), I'm more interested in using bolts and rivets. :lol:

 

[dogman dan]

Must have been hallucinating again. I did see flexing on really big bumps, and could get it to do the same by levering hard on the seatpost rack. The bending was in the frame tube that held the seat post tube. A long enough tube can bend easy, but the worry was, how many times till snap? I definitely stood for big bumps on that bike! Cast stuff, like fork dropouts, definitely snap with no warning.

 

[Jonathan]

Besides the torque of the motor which rips apart your dropout, I think the other biggest worry is encountering a pothole or bump @ high speed.

It's probably best to study how the large companies design their DOWNHILL MTN bike.
They normally place extra emphasis on the headtube, downtube and bottom braket due to the shock & stress that it take.

Other than that I would inspect the TIG welding on your bike for defect/failure points.

If you purchase a decent quality downhill bike I don't think you need to worry about these.