A question regarding old aluminium frames.

[megachris]

Hey there.

I'm sure you've had these questions before and here I am asking them again! But.. I've decided on the spur of the moment to buy an older Giant Cold Rock bike from around '99 or something. Got it for pretty much nothing.. It's an aluminium ("tubed"?) frame and I enjoy the feel of the bike and I think it could be a decent commuter that would allow me to also cross over some gravel roads. When I bought it I kind of hoped it was steel, because I reckon it holds up better - considering my size. I've heard a lot of horror stories out there about alu bikes and it's making me think I ought not to fix it up and get it in working condition (unless maybe if I set it up for my partner as she has a good healthy weight)

Anyways I'm about 20 stone/125 kg/275 pounds give or take. Currently trying my best to lose weight. Would I be alright using it? Would my weight end up being a safety hazard on the bike? I mostly got it because I thought it would be a fun project to pimp out a bit, it's nothing too special. But unfortunately I've developed a fondness for this bike.

Best regards,
megachris.

 

[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.

 

[megachris]

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!

Thank you. Yes, I primarily commute on paved and gravel roads but also like to drive around in the woods where there's some roots and bump and that, very "light trails" I guess you could say. I cannot even think of doing any 'jumps' on a bike, I'd be looking like a whale coming up for air if I were to try all of that. I feel a lot more confident going further with fixing it up then. I had already thought the bottombracket needs a better replacement, and I'll be changing a few things here and there. I guess sometimes you read too much on the internet and spend too little time doing the things you want. Thank you for putting my mind at ease. I'll stop my search for an older steel hardtail then.

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

Have a good one!

 

[megachris]

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.

Thank you. Yes, I've recently been getting back into cycling and I enjoy it immensely. I have been able to go for a lot longer journeys through woodland and by the sea, it's been a joy really. I had been stuck walking mindlessly around in the same area. Thank you for the encouraging words

 

[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.

 

[megachris]

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.

Thank you. Everyone here has given me so much useful information already, loving the forum. I'm going to start fixing up the bike as soon as possible. I have definitely been overthinking the frame and weight thing a bit too much.

 

[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!

 

[megachris]

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!

Thank you. Learning something new every day, hehe. Everyone in here has put my mind at ease and for that I'm grateful.

 

[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.