Yet Another Cycling Forum
General Category => Freewheeling => Velo Fixe => Topic started by: Manotea on 03 April, 2016, 08:34:42 am
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(https://photos-4.dropbox.com/t/2/AACS6nSPHVSQUZl5GOUz7BK55VyBwxUosmMfyO_h9-JP1A/12/26765083/jpeg/32x32/3/1459684800/0/2/IMAG0113.jpg/EMrJlBQYrr0KIAIoAg/Qus-zIZq2cKVYy9hTKn5KFgXEIuBwVtz-0Jz8-xYVk0?size_mode=5&size=32x32)
Once might be unfortunate, but twice?
3Down 2016
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Shudder !
I hope that there wasn't too much ouch involved.
Can't you 'borrow' a bit of that handrail and get improvising ?
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Oh fuckity!
Hopefully you managed to control your deceleration enough to not do yourself any mischief?
Becoming your signature party trick now!
Bad luck.
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<gulp>
Wait until you are in private before removing bicycle clips from trouser legs.
Hope you're OK....
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blimey! i hope you stayed upright..
next time i would hammer in a steel/carbon tube into the steerer ::-)
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Eeeep! That doesn't look quite right.
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That looks quite wrong.
And scary.
Hope you didn't sustain injury.
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'Mr Bond. Once is happenstance, twice is coincidence. Three times it's enemy action!'
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Personal damage was limited to a sprained wrist and skinned elbow... Every landing you walk away from is a good landing :)
The stem collapsed without warning crossing the bridge over the river on the southern approach to Bray. I'd slowed to cross the bridge as the surface is made of removable tiles and a bit flakey, so I was only doing about 10kmph. It could so easily been a while lot worse...
Both failures occurred on second user bikes, though I suspect I've put a lot more mileage on them than the original owners.Correction: this bike was second user, the other I built up from a new frame and forks (both have the same frame and fork set). Discussing the previous incident with the shop, I was told I had too many spacers under the bars, which increased the leverage acting on the stem, which sounded plausible. On this bike the setup was in spec.
I'm liking zigzags idea of fitting a steel inner sleeve.
The alternate option is to switch to all steel bikes in future. Fact is my current bikes are getting a bit tatty/end of life so maybe time to keep an eye.out for suitable frames.
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Glad that you're ok after such an experience Mr T. I know I was a bit shocked when riding behind you when it happened the first time.
I hope you won't be trying another set of forks with an aluminium steerer. They get an especially hard life in fixed wheel service. Nice idea to look for a good steel frameset and enjoy the steel ride quality and reliability.
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Glad that you're ok after such an experience Mr T. I know I was a bit shocked when riding behind you when it happened the first time.
I hope you won't be trying another set of forks with an aluminium steerer. They get an especially hard life in fixed wheel service. Nice idea to look for a good steel frameset and enjoy the steel ride quality and reliability.
It may seen like a dumb question, but why might this be?
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Glad that you're ok after such an experience Mr T. I know I was a bit shocked when riding behind you when it happened the first time.
I hope you won't be trying another set of forks with an aluminium steerer. They get an especially hard life in fixed wheel service. Nice idea to look for a good steel frameset and enjoy the steel ride quality and reliability.
It may seen like a dumb question, but why might this be?
Certainly not a dumb question.
Climbing hills on fixed, especially steeper ones, means that the rider will be pulling and pushing opposite sides of the bars with each pedal stroke. Really straining at times to try and keep the bike moving forward. This means high, cyclic forces on the steerer. If it's an aluminium steerer it will eventually fatigue and break.
Unless you try and ride your geared bike uphill in the big ring all the time it's much less likely to be a problem than on fixed.
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As above ^
Handlebars also take a hammering, particularly for those who push a really tall gear (manotea, teethgrinder, jonah etc!).
Toofypegs has snapped more than one set of bars from memory?
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Thank you, both.
I guess my ignorance comes from having a mostly pan-flat commute on the fixer.
And an all-steel bike (in this instance).
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Can't see the original photo but I assume it was the fork steerer tube that snapped.
MV isn't here any more to remind people to replace forks with alu steerers (mostly carbon forks) approx every 3 years (time isn't really the factor, accumulated usage is, it's just 3 years for the average Audaxer/commuter is usually enough).
I have a set of Deda Black Rain forks (carbon with alu steerer) somewhere awaiting me putting enough miles in on the current bike to warrant a preventative replacement.
Glad you got away mostly unscathed Mr O'Tea.
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Aluminium shouldn't be used in forks, except maybe for the crown in an otherwise all-carbon fork. It's a most untrustworthy metal unless dimensioned to keep the strains really small, and you can't change the dimensions of a steerer without going for a completely new oversize standard of headset. Remember when Cannondale recalled all their Pepperoni forks in the 1990s? That was because they used an aluminium steerer (the replacements had a steel one).
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Aluminium shouldn't be used in forks, except maybe for the crown in an otherwise all-carbon fork. It's a most untrustworthy metal unless dimensioned to keep the strains really small, and you can't change the dimensions of a steerer without going for a completely new oversize standard of headset. Remember when Cannondale recalled all their Pepperoni forks in the 1990s? That was because they used an aluminium steerer (the replacements had a steel one).
So, on that basis, the ally steerer / carbon forks on the Bianchi which I've been riding since 2006 (albeit notsomuch since I got the VN) should be replaced?
Shame, they have an attractive aero section.
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I wouldn't trust them. The headset is probably 1 1/8", which gives a bit more security over 1", but you really want something hugely oversize for aluminium. The Cannondales were 1 1/4" and still broke.
A fork steerer flexes rather a lot because it has all the leverage of the blades acting on it.
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A fork steerer flexes rather a lot because it has all the leverage of the blades acting on it.
Does it?
Doesn't the crown bearing take that load?
Yes, the connection between the blades and the crown will be subject to that force.
But shirly the steerer is supported from below by the crown headset bearing.
I'd expect that bearing and the upper headset bearing to hold the steerer co-centric with the head-tube and resist most lateral and twisting forces.
I can't see much fork flex passing above the crown bearing.
I *can* imagine flex load if there is a huge stack of spacers above the top headset bearing, tho.
( This is all based on thought-experiment, not actual knowledge! )
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According to Jobst "not always right" Brandt, it's the flexing of the steerer (he calls it "steer tube" becausw he's USian) that causes false brinelling of headset races when there is no other bearing surface to accommodate this flexing (headsets with cartridge bearings, and those with loose races like the Stronglight A9, avoid this because the movement can be taken up by a large plain bearing surface).
http://www.sheldonbrown.com/brandt/indexed-steering.html
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There must be millions of aluminium framed bikes with aluminium forks. I'd always assumed they had ally steeer tubes too.
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Steel steerers are quite common on alu forks (e.g. the Cannondale example). It's a problem with a component of fixed dimensions that was designed for manufacturer in a particular metal; you can't just change to something lighter or less fatigue-resistant as you could elsewhere on the bike. Bike manufacturers keep reinventing the wheel every 20 years, though, and there seems to be little corporate memory of historical misadventures. Even oval chainrings came back despite manufacturers disagreeing which way the long axis should go (with the crank or perpendicular to it) and the joke of the Shimano High Power Biopace, which was pretty much a circle.
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Alloy wall thickness varies, and quality of bonding varies, so I wouldn't have the same amount of worry for all of them. I hope to get plenty more life from my Tofosi ones. I managed to get all carbon fibre forks for my favourite bike, though, and I do mean all. The carbon dropouts are a bit silly.
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Increasing the wall thickness of a tube doesn't improve its bending stiffness greatly, thobuts. It's better to go wider and thinner for the same amount of metal.
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Larger diameter and thinner tubes are more susceptible to buckling and crimping (stress risers leading to fatigue), which isn't great for an unthreaded steerer.
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As my Alu/Carbon fork Pearson is now ahem .. seven years old I think it's time for a new fork. I can buy a replacement from Pearsons, I don't suppose they make them themselves though. This should do instead, https://www.evanscycles.com/m-part-rigid-700c-carbon-road-bike-fork-EV146183 (https://www.evanscycles.com/m-part-rigid-700c-carbon-road-bike-fork-EV146183)
Never heard of M-Part, as ?Chinese? manufacturing goes how good are they?
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I think M-Part is Madison's house brand, if that helps establish trust. (I've had other small parts from them which have been fine, but there's not a lot to go wrong with the likes of chainring bolts.)
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Thanks for the clarification, will order an M-Part from Evans and take a look at it in the shop - If I don't like it I can just walk away to Pearsons.
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Note they are 375mm long and, presumably, for long drop brakes. If so, you could replace with surly pacer forks - the 45mm offset version would almost certainly be a direct replacement (pm me if you want some!)
I really don't like alloy steerers. Carbon monocoque or steel forks for me.
Mike
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Thanks,
will pm