This is a bit worrying

[MichaelW2]

I have heard of it on a very cheap bike. Still surprised me that it was possible.

It happens on high end bikes as well. Removing metal is as bad as adding poor quality metal.
The most reliable cranks seem to be the low-midrange cold forged ones from Shimano. They dominate the market but not the parts failure posts.

 

[presta]

x

I’ve never heard of one failing

I’ve never seen that before in all my sixty three years cycling

I have:

That's either been massively over-loaded, or more likely seen a high degree of cyclic loading

Ductile metal deforms before it breaks if it's overloaded, two halves that fit back together like a jigsaw puzzle are the hallmark of fatigue.

I have the crankset I took off mine before fitting the hope one if anyone wants to make an offer

Are Hope cranks NC machined like their hubs? If so, that's reducing the fatigue life, not increasing it.

 

[tinywheels]

I'm more than happy with hope products, used them for years.
never had a failure

 

[Kell]

I think, looking at that failure, it looks like the same issue as mine.

A crack developed, and developed slowly over a period of time, weakened the crank as a whole, and then the final straw would have been a complete and immediate failure. If you look at my thread (linked to above by @berlinonaut) then you can see the tell tale signs. the darker patch where the crack had developed over time, then the cleaner bit where it eventually snapped.

I'd argue (I think I did argue) that the crack was hard to spot as it developed from behind the chain ring. But then I also wasn't looking for it. Most likely cause would have been it happened when the chain came off. Clearly that couldn't have been the case on this bike as it's on the non-drive side.

I do remember some terrible creaking which I couldn't pin down which went on for months before failure. I was lucky, I'd say, in that when mine happened I was sat down, climbing a hill. A steep enough one that I was going about 4mph. Lucky because when I come down that hill I'm doing 40mph+. And also lucky that it wasn't the bottom part of it where, on occasion, I've stood up to power up the first third.

That bike looks even dirtier than mine TBH, so I suspect maintenance wasn't high on their list. But while mine is dirty, I do remove the entire drive train once a month (on average) to completely clean the chain, sprockets and chainring.

The upshot for me is that if I hear that creaking, it will be on my checklist now.

 

[Kell]

You can see the crack here in all its glory.

The darker patches are rouged (Thanks to @Yellow Saddle for the engineering clarification).

But I think you can see from this image, that it would have been almost impossible to spot from the front (as it developed from behind) and the behind was hidden by chainring and arms.

As I said in the other thread, actually looking out for it might have led to me spotting it, but hard to know one way or another.

As it happens, I've just replaced the replacement crank around a month ago as I over tightened the chain ring bolt that goes into it, and stripped the threads.

 

[Drago]

on the t-line, yes.

Blimey, they'll be doing proper brakes next!

Pre-ride checks folks. Old pilots and bold pilots.

 

[berlinonaut]

Blimey, they'll be doing proper brakes next!

Probably not. The people that complain about the brakes are usually people like you who don't ride a Brompton. Actually the brakes are proper. You may not know that but there are norms for bikes that they have to fulfill in tests before they can be sold within the EU. The Brompton fulfills these norms, ergo the Brakes can be considered "proper".
What sense would it make for a company to listen to the constant annoying noises that people make that have no experience with the bike, seem not to know the legal basics and are no customers and probably never will be? No company will listen to these kind of comments or spend the slightest bit time thinking about these people. Companies care about their customers, not about notoriously moaning non-customers.

 

[tinywheels]

That's you told Drago😁.

 

[wafter]

I have the crankset I took off mine before fitting the hope one if anyone wants to make an offer

So freewheeling extends the life of your cranks .
I thought there must be a reason why I do a lot of it !

Actually, I'd postulate it's the opposite as free-wheeling implies the input of more power previously to allow said coasting... ultimately the highest cadence, lowest torque approach is going to minimse your chances of eating the bars / tarmac at the lights!

To consider a Brompton expensive is a question of personal perspective. Many would agree, many wouldn't. I would however be interested on the foundation of your statement that Brompton uses "cheap cranks". Do you have any?

To be fair this does seem to be the case, and it's a typically British approach. We're great at innovation; while sadly also great at torpedoing that insight with cost-cutting, bodges, bending over for the accountants and generally screwing the customer as a badge of honour.. In terms of material (rather than design) failure, how many other bikes / groupsets do you know of with this quantity of crankset failures?

I know the UK has "bouyant" labour costs, but at the end of the day it's a basic steel folder utilisting old tech that retails for, give-or-take a month's worth of average wage after tax.. they should be cheaper than they are, but at the end of the day he UK is second only to the US in terms of screwing the other to line your own pockets.

 

[fossyant]

Blimey, they'll be doing proper brakes next!

Pre-ride checks folks. Old pilots and bold pilots.

Regular 'washing' (I know) is a way of checking for faults on any bike. But hey, ho we don't do that with a car.

Cranks with a cut out for what, a few grams on an alloy crank is nuts, on a chunky bike. I really don't like cut out cranks on bikes, but given the relatively spindly construction is a "no" for a Brommie crank.

I've 3 bikes with solid cranks from 25-36 years old that are solid aluminium, nice stuff Dura Ace, 600 and LX (not cheap construction).

I have a SRAM chainset on the MTB that get's mashed and rock hit alot, that's 8 years old, and no cut outs. And a 10 year old FSA compact on the CX bike, thats no cut outs. Those last two aren't spendy chainsets at all.

Why does a Brompton have cranks like that.....

 

[berlinonaut]

View attachment 706421
In terms of material (rather than design) failure, how many other bikes / groupsets do you know of with this quantity of crankset failures?

In this thread we've found about 4-5 cases while on the other hand there are over 1.000.000 Bromptons out there. I would not call this a spectacular failure rate. Even less so when having in mind that the cranks should be changed after 5.000 miles and most (if not all) of those that snapped were way over that limit.
How many bikes do you know that have over 1.000.000 samples in the wild?

Would you complain if you bought a Diesel car, ignore the change interval for the belt, and complain when it collapses (and trashes your motor) that they were using "cheap parts"? Possibly not...

I know the UK has "bouyant" labour costs, but at the end of the day it's a basic steel folder utilisting old tech that retails for, give-or-take a month's worth of average wage after tax.. they should be cheaper than they are

They should be cheaper than they are but at the same time you complain that the parts used are not expensive enough - while at the same time there is the t-line available with way more expensive parts but you did not go for it but bought a second hand C-line. Isn't that a bit of a weird combination?

 

[Profpointy]

I’ve never seen that before in all my sixty three years cycling.

Whilst I've never bust a crank, a friend who was a keen cyclist had broken several so had steel cranks on his fixie on which he expected to break cranks regularly grunting up hills in mid-Wales on his 20 mile daily commute

 

[wafter]

In this thread we've found about 4-5 cases while on the other hand there are over 1.000.000 Bromptons out there. I would not call this a spectacular failure rate. Even less so when having in mind that the cranks should be changed after 5.000 miles and most (if not all) of those that snapped were way over that limit.
How many bikes do you know that have over 1.000.000 samples in the wild?

Would you complain if you bought a Diesel car, ignore the change interval for the belt, and complain when it collapses (and trashes your motor) that they were using "cheap parts"? Possibly not...

I'm not claiming it to be a spectacular failure rate; I am however questioning whether it's not still significant since no other brand appears to have a reputation for crank breakage in this way. Granted Shimano have an issue with some of their higher-end Hollowtech cranks failing; but this is through a bonding issue rather than outright material failure.

I suspect the number of cranksets in use from Shimano is orders of magnitude higher than the million Bromptons you reference.

My issue is with Brompton essentially specifying the crankset as a consumable, when no other manufacturer seems to consider them in this regard. On the one hand I respect their candour, on the other it could be argued that they're only doing so to cover their arses for supplying parts that fail before many would expect them to.

I imagine they've consciously kept the arms slim to keep mass down, which in turn has reduced their stiffness and predisposition to failure. One might postulate that they've pushed this relationship unacceptably far, considering that stiffness rises (and stress falls) to the fourth power of the beam thickness and reducing stress massively increases fatigue life.. so for a modest increase in size, mass and cost they could have made the cranks last basically forever.

I don't consider your Diesel engine example legitimate since a cam belt is clearly a higher-stressed, cheaper, obviously consumable part which you'd struggle to increase the service life of through design changes (other than swapping it for a chain!). I'd suggest a more appropriate example would be having to replace the pistons in an engine after 50k miles on the manufacturer's advice; when everyone else's pistons last for the lifetime of the vehicle.

They should be cheaper than they are but at the same time you complain that the parts used are not expensive enough - while at the same time there is the t-line available with way more expensive parts but you did not go for it but bought a second hand C-line. Isn't that a bit of a weird combination?

Again, a straw-man argument that simplistically, naively assumes the cost of an item is directly representative of its quality.

I'm suggesting that the bikes offer poor value when compared to others - being over-priced for what they are and suggesting that either the price should be lower, or the components better quality than they are.

I bought the bike I did as it was as much I could afford, and I expect it to be fit for purpose. I didn't buy a T-Line because unfortunately, somewhat obviously I don't have over four thousand pounds to spend on a bicycle 🙄


EDIT: Further from some brief fag-packet calculations, increasing the thickness of the crank arms by 20% in both planes would have more than doubled their stiffness; which for a given crank load would have more than halved stress. From the graph of no. cycles versus load for a decent alloy posted in Kell's other thread on the subject, halving the stress would potentially increase the service life by a factor of hundreds or even thousands - making the cranks essentially "fit and forget" like everyone elses; rather than something that requires regular replacement at a cost not insignificant to the value of the bike itself.

 

[berlinonaut]

since no other brand appears to have a reputation for crank breakage in this way.

I didn't know that Brompton has a "reputation" for snapping cranks...

My issue is with Brompton essentially specifying the crankset as a consumable, when no other manufacturer seems to consider them in this regard.

Maybe you should read the manuals of other bikes. I'd say most have a recommendation to exchange Aluminium parts as Aluminium parts do have a limited lifespan. Just that no one cares until his or her own crank or bar snaps.
To be precise: When you say "no other manufacturer" recommends a change of cranks - how many manufacturers did you check? And how did you check them? As it - obviously - is impossible to check every single manufacturer on earth your statement is per se obviously untrue as you can not have a serious foundation for it.

I don't consider your Diesel engine example legitimate since a cam belt is clearly a higher-stressed, cheaper, obviously consumable part which you'd struggle to increase the service life of through design changes (other than swapping it for a chain!).

Well: Chains do exist and they do have a way longer lifespan.

I'd suggest a more appropriate example would be having to replace the pistons in an engine after 50k miles on the manufacturer's advice; when everyone else's pistons last for the lifetime of the vehicle.

You obviously never had a 2-stroke engine

I simply do not get why you are so upset. Change intervals for Aluminium parts are common in the bike industry for decades. Literally since they became available on "consumer" bikes. Like it or not: This is totally normal. Just you seem not to have realized it until now.

 

[tinywheels]

get the popcorn in guys