Took bike in for service ...first pedal stroke wrote off bike

[the snail]

I would have thought the chain snapping would have resulted in the loose end of the chain flying very quickly through the chain guide of the front mech without any damage?

Not necessarily, if the end of the chain is bent/twisted, or tangled up, then it can catch in the derailleur. A woman I was riding with had that happen, and her rear derailleur snapped off. So I think a lot of the posts here calling the OP a troll/liar are pretty unfair and quite unpleasant. None of you really knows what happened to his bike, or whether it was the fault of the shop, the rider, or just one of those things.

 

[Lovacott]

Not necessarily, if the end of the chain is bent/twisted, or tangled up, then it can catch in the derailleur. A woman I was riding with had that happen, and her rear derailleur snapped off. So I think a lot of the posts here calling the OP a troll/liar are pretty unfair and quite unpleasant. None of you really knows what happened to his bike, or whether it was the fault of the shop, the rider, or just one of those things.

I don't doubt that a snapped chain could cause damage, but it's the scenario which seems dubious.

A "precision engineer" getting a bike shop mechanic (who he knows to be rubbish) to change his chain, then after collection (and noticing that the chain isn't right), he pops straight onto it and goes pull pelt?

The chain snaps on the first pedal stroke after which he puts the bike away without noticing any damage only to find later that the frame is "wrecked"?

And, because he only noticed the damage just after the bike shop had shut, he thought he'd open an account on this site and start a thread about it?

If my chain snapped and ripped out the front mech, I'd at least have a glance at it before putting the bike away and I'm pretty sure I'd notice a "wrecked" frame. I also wouldn't use any tradesman who I knew from past experience to be "rubbish" (especially if I were a "perfectionist, precision engineer"). And, if that "rubbish mechanic" had just fitted a new chain which I could see was wrong when I collected the bike, I wouldn't jump on it and go hell for leather straight off.

The troll outed himself in the OP.

 

[DRM]

Don't cables stretch any more?

It's the outers that are compressionless, that give better braking on a mechanical setup

 

[Dogtrousers]

I seem to remember @Shaun saying that the lifeblood of the forum was new threads. So even if they are colourfully embellished versions of minor spats with mechanics in shops, or "how do I remove a pedal" or "what is the best chain lube" or "why I think tubeless tyres are stupid/brilliant" it all helps.

There's always the ignore thread button if they get too irritating.

 

[Ajax Bay]

Don't cables stretch any more?

Cables do stretch (and don't compress) - see my edit; apologies.
I appreciate you are just casting a line, there, but you've reminded me of a discussion we had here a few years ago about whether one could safely use a gear cable as a brake cable (in the brake cable outer). I've reached back to rehash that - below.
Let's leave aside the extent to which outers compress (and all do, normal brake ones much more than others).
All materials stretch when a strain is induced therein. A brake/gear cable stretches every time it is operated and returns to its original dimension when the lever is released (removing the tension). They never breach their elastic limit so there is no plastic stretch, ever.
Stainless steel cables do not stretch any more than normal when new. They stretch the same amount every time (the same amount of) tension is applied, throughout their life, from brand new to 'ready for replacement'. The entirely predictable amount of stretch means that, for a gear cable indexing is unaffected (and gear cable tension is much less than brake cable tension in operation).
Can a gear cable inner be used as a brake cable?
Does a brake cable stretch a bit when applied? Yes, but so little as to have no functional effect (think about how the brake levers operate the cable and the cable operates the calipers).
And so, being thinner gauge, the gear cable would stretch too, and maybe a tad more, but, again, so little as to have no functional effect.
I decided I'd try to quantify the approximate difference in stretch if one used a gear cable in place of a brake cable, and whether that would affect the effective operation of the brake calipers (rim brake).
1) The length of pull on a brake cable with a STI (brake lever) is about 9mm max (ie from 'resting' position to lever touching the (drop) bar. Proper adjustment means that full strength braking is effected (with my pads and pad/rim gap adjustment) at 5mm (ie with 4mm 'spare'). Operating the rear calipers, would a gear cable stretch >4mm more than a brake cable would?
2) Wire ropes/cables do not possess a Young’s Modulus but an ‘apparent’ Modulus of Elasticity can be used and the various generic steel cable types have working Moduli of Elasticity. So using Hooke's Law:
Elastic Extension = FL/EA where F = load applied (N), L = rope length (mm), E = elastic modulus (N/mm2),A = metallic cross section (mm2)
F The 'full' (ie 4 fingers in opposition to the thumb) grip of an adult is in the range 250N-500N. Even from the drop bars (the strongest braking position for the hand (and for other reasons)) the full grip cannot be exerted so, say, a force of 200N can be applied. The mechanical advantage of the levers is 3 (vector distances from axis are 54mm and 18mm) so this implies an applied force of 600N on the cable (ie max cable tension).
L 1300mm is a typical rear cable run for a normal bike (580mm TT c-t-c) and cables under tape on drop bars. Hybrids/MTB cable run will be a little less. A drop bar STI front brake cable run is much shorter and therefore stretch is less (~40%).
E General Elastic-modulus of the cable construction
Spiral strand, type 1x7 EM = 126000
A The area of a 1.2mm dia gear cable is 1.1mm2. Brake cable is 1.6mm dia so area = 2.0mm2

3) For 2.0mm2 area (brake) cable that gives an elastic extension of 3.1mm for a 600N load
For 1.1mm2 area (gear) cable that gives an elastic extension of 5.6mm for a 600N load
This means that the difference in elastic extension (stretch) between the two types of cable is 2.5mm.
Conclusion: The STI levers have a margin (ie spare travel) of 4mm so using a gear cable, in extremis, would not result in the lever 'bottoming out' on the bars.
Comments
a. And since the main braking effect is using the front brake (which has a much shorter cable run) riders using a gear cable in place of a brake cable in an 'emergency' should maintain an effective braking system.
b. This result may not hold for flat bar brake levers - someone else can do the working, if they're so inclined. And off course long run cables (eg for tandems or recumbents) would result in significantly more stretch with the implicit failure of an effective braking system.
c. I have made assumptions to get this result: I hope they are valid (for the level of accuracy relevant for this).

 

[winjim]

Cables do stretch (and don't compress) - see my edit; apologies.
I appreciate you are just casting a line, there, but you've reminded me of a discussion we had here a few years ago about whether one could safely use a gear cable as a brake cable (in the brake cable outer). I've reached back to rehash that - below.
Let's leave aside the extent to which outers compress (and all do, normal brake ones much more than others).
All materials stretch when a strain is induced therein. A brake/gear cable stretches every time it is operated and returns to its original dimension when the lever is released (removing the tension). They never breach their elastic limit so there is no plastic stretch, ever.
Stainless steel cables do not stretch any more than normal when new. They stretch the same amount every time (the same amount of) tension is applied, throughout their life, from brand new to 'ready for replacement'. The entirely predictable amount of stretch means that, for a gear cable indexing is unaffected (and gear cable tension is much less than brake cable tension in operation).
Can a gear cable inner be used as a brake cable?
Does a brake cable stretch a bit when applied? Yes, but so little as to have no functional effect (think about how the brake levers operate the cable and the cable operates the calipers).
And so, being thinner gauge, the gear cable would stretch too, and maybe a tad more, but, again, so little as to have no functional effect.
I decided I'd try to quantify the approximate difference in stretch if one used a gear cable in place of a brake cable, and whether that would affect the effective operation of the brake calipers (rim brake).
1) The length of pull on a brake cable with a STI (brake lever) is about 9mm max (ie from 'resting' position to lever touching the (drop) bar. Proper adjustment means that full strength braking is effected (with my pads and pad/rim gap adjustment) at 5mm (ie with 4mm 'spare'). Operating the rear calipers, would a gear cable stretch >4mm more than a brake cable would?
2) Wire ropes/cables do not possess a Young’s Modulus but an ‘apparent’ Modulus of Elasticity can be used and the various generic steel cable types have working Moduli of Elasticity. So using Hooke's Law:
Elastic Extension = FL/EA where F = load applied (N), L = rope length (mm), E = elastic modulus (N/mm2),A = metallic cross section (mm2)
F The 'full' (ie 4 fingers in opposition to the thumb) grip of an adult is in the range 250N-500N. Even from the drop bars (the strongest braking position for the hand (and for other reasons)) the full grip cannot be exerted so, say, a force of 200N can be applied. The mechanical advantage of the levers is 3 (vector distances from axis are 54mm and 18mm) so this implies an applied force of 600N on the cable (ie max cable tension).
L 1300mm is a typical rear cable run for a normal bike (580mm TT c-t-c) and cables under tape on drop bars. Hybrids/MTB cable run will be a little less. A drop bar STI front brake cable run is much shorter and therefore stretch is less (~40%).
E General Elastic-modulus of the cable construction
Spiral strand, type 1x7 EM = 126000
A The area of a 1.2mm dia gear cable is 1.1mm2. Brake cable is 1.6mm dia so area = 2.0mm2

3) For 2.0mm2 area (brake) cable that gives an elastic extension of 3.1mm for a 600N load
For 1.1mm2 area (gear) cable that gives an elastic extension of 5.6mm for a 600N load
This means that the difference in elastic extension (stretch) between the two types of cable is 2.5mm.
Conclusion: The STI levers have a margin (ie spare travel) of 4mm so using a gear cable, in extremis, would not result in the lever 'bottoming out' on the bars.
Comments
a. And since the main braking effect is using the front brake (which has a much shorter cable run) riders using a gear cable in place of a brake cable in an 'emergency' should maintain an effective braking system.
b. This result may not hold for flat bars - someone else can do the working, if they're so inclined. And off course long run cables (eg for tandems or recumbents) would result in significantly more stretch with the implicit failure of an effective braking system.
c. I have made assumptions to get this result: I hope they are valid (for the level of accuracy relevant for this).

I think your main problem would be bodging the gear cable nipple into the brake lever. Assuming you managed to do it I can imagine it moving around and slipping about quite a lot, especially under heavy braking.

 

[Ajax Bay]

Nipple incompatibility. I agree. Use as a get you home option only (and on the back brake). And
@FishFright mentioned in that 2017 thread that he'd seen a nipple pull straight off. I don't know what tension the cable manufacturers test the cable nipples to but I'll bet the brake ones are more secure, by both design and manufacture.

 

[DaveReading]

Don't cables stretch any more?

You missed a trick - you should have asked if they stretch any longer.

 

[Smokin Joe]

So I think a lot of the posts here calling the OP a troll/liar are pretty unfair and quite unpleasant. None of you really knows what happened to his bike, or whether it was the fault of the shop, the rider, or just one of those things.

Perhaps we don't like being taken for fools?

 

[Lovacott]

Perhaps we don't like being taken for fools?

There was never a bike in the first place.

When the OP made the original claim, it had a couple of holes and with every question asked of him, he created more holes and then dug them deeper and deeper.

A good example is when asked "Why take it to a rubbish mechanic" he replied that only a Giant dealer would know how to replace Giant internal cables?

Like Giant have something mystical going on inside their frames that is privy only to Giant dealerships?

This thread was started by someone looking to take the piss and he was sussed out very quickly.

Requests for photo's are more than reasonable and needn't compromise someone's anonymity. He could have easily given his story some credence with a simple cellphone snap of a ripped off front mech.

Instead, he went very quiet.

100% Troll.

 

[Scoosh]

MOD NOTE.
The OP hasn't returned for a while and the thread has been useful in giving valuable information about the differences between brake and gear cable outers and inners, so thus is probably a good time to Close it.

Thank you all for your input.