A question regarding old aluminium frames.

[megachris]

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[legrandefromage]

You will be fine. The frame will be fine.

There are no horror stories really, most failures come from using too long travel forks or jumps or pivot points on full suss frames. A simple 7005 series aluminium frame wont fail from just commuting

However, if the wheels have steel hubs, change them, the steel flange will cut into the spokes and then go 'ping' at awkward moments. Lots of Giants of this era had some pretty low spec parts which fail easily.

The bottom brackets start to go fairly quickly too so budget for a new one.

Mudguards are good, it prevents the brown strip arse!

 

[greencat]

I concur. I've carried 50kg on some of my bikes and towed rather more than that.

BTW good on you for giving it a go. It should help with the weight loss while at the same time not putting too much strain on your joints.

 

[mattr]

Also, it's not 7005 Alu but 6061. Any difference?

Slightly different alloying elements, and 6061 tends to be heat treated, 7005 is an air hardening alloy iirc.

In real terms it'll make little or no difference unless the frame is a lightweight race bred machine. Which this ísn't.

Which also benefits the other failure mode of aluminium frames, fatigue. The older and lighter the frame, the more likely it is to fail. This is an older, middle weight frame. So you aren't going to have any issues for a decade or so yet.

As mentioned already, you're more likely to have component issues than frame issues, but keep on top of service/looking after it and most things are fairly obvious.

 

[legrandefromage]

Its all in the grain structure of the alumnium

Heres something on the Zaskar

7000 series tends to be failures of the tubing itself

6000 series is welding failures as mentioned earlier

The filler rods for 6000 (4043) is a strong alloy but prone to cooling cracks as it contracts a lot. 5356 which is used on 7005/ 7020 is less prone to cracking.

6000 is not inherently stronger but doesnt mind being manipulated and is more ductile. 7000 just isnt as malleable.

Look at the differences in cast iron and stainless steel for how 7000 and 6000 differs in structure.

Extrusion is a mess of weak points, large crystals being stronger than the surrounding areas creating fracture points. Making these crystals small and uniform across the object be it a frame tube or crankset makes it stronger and more durable and it aligns the grain structure with the form of the tube. As extruded tubes tend to be used in the headtube - you guessed it, cracked heatubes.

Or a big lump of sugar (7000) and Brighton rock (6000)...

Then theres the mixing of the alloys within the welding pool, penetration etc etc!

hope this helps!

 

[Woz]

There's a lot of goog advice above.

My tuppance is to inspect the frame (typically around the BB, head-tube and seat cluster) and if all good build
and ride. While I'm not a fan of AL, I have to admit some of my longest day trips (+200 km on mixed paved
and unpaved) have been on old AL. There is something about AL that makes you feel that every pedal stroke
is going to the back wheel.