Boardman bikes
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barq
Senior Member
- Location
- Birmingham, UK
I haven't tried one, but I had exactly the same reaction to the top tube. I thought it might just be the MTBs where box sections aren't unheard of, but no...
Does anyone know what the alleged advantage of the diamond section is?
as I believe I've mentioned numerous times on BR, disk brakes and radial* wheels shouldn't go together - as on the top-end hybrid of the boardman range. People have justified them - nicklouse earlier having pointed out that the wheelsets probably will have been tested thoroughly, and supersonic also correctly pointing out that they are double spokes and 2-cross as opposed to completely radial, but Sheldon Brown says on his wheel building guide on his website that disk brakes require much more torsional strength than rim brakes, and the more crosses the more torsional strength. As I say, I suspect halfords have only put those things on to look flashy.
* they are in fact two cross but still.
* they are in fact two cross but still.
barq
Senior Member
- Location
- Birmingham, UK
I hadn't spotted that. As you say, radial spokes only transmit torque once the hub rotates in relation to the rim - and that wind up causes fatigue. Ok, so CBoardman are using 2x spoking. But that seems to take them further away from the best conditions for transferring torque. The ideal is when spokes are perpendicular to the axle/spoke-head line. 3x is nearer that ideal, 2x is further away. So with their design braking forces aren't delivered as directly as they could be and so there is more hub/rim wind up. My prediction would be that the wind up would eventually manifest itself in a higher number of broken spokes than with an equivalent 3x wheel. 
hubgearfreak
Über Member
barq
Senior Member
- Location
- Birmingham, UK
HJ
Cycling in Scotland
- Location
- Auld Reekie
hubgearfreak
Über Member
barq said:
I understand the middle one
, but what's the objection to the others?[/QUOTE]as for the first, then search frame material, or steel is real in google. this isn't the place to re start a discussion that's been done to death.
as for the last, i simply don't see the need....if i wanted a mountain bike, i'd have one, i have 2 nice old racers for longer rides and an everyday commuting/shopper bike. it is made of 531, with a sram7 speed hub. i simply don't believe that a bike designed for town use needs 18 or however many gears hybrids have, at least in lincoln
Chuffy
Veteran
- Location
- On the banks of the Exe
bonj;42631][QUOTE=hubgearfreak said:
But aluminium's lighter...?[/QUOTE]
Yup. Lighter, but with a finite fatigue life. An aluminium frame will eventually fail. Steel doesn't have the same drawback. How much of a problem this is in real life is a moot point. I probably won't put enough use into my aluminium bike to get it to a point where it fails, so I'm not too worried. Mega mile monsters might see it differently. Anyway, it has been covered on a multitude of other threads.
HJ
Cycling in Scotland
- Location
- Auld Reekie
Chuffy;42658][QUOTE=bonj said:
Are you saying that steel doesn't have finite fatigue life? Have you found a way of over coming entropy change?
My last bike had a steel frame and the head tube snapped.
Chuffy
Veteran
- Location
- On the banks of the Exe
Are you saying that steel doesn't have finite fatigue life? Have you found a way of over coming entropy change?Hairy Jock;42995][QUOTE=bonj said:
My last bike had a steel frame and the head tube snapped.[/QUOTE]
I'd need to do some truffling about to check, but the gist of the steel vs aluminium debate is that aluminium can take less stress than steel and will fail before steel does, for an equal amount of stress. No, I didn't mean to imply that steel had an infinite fatigue life (in the strict sense of the word) sorry if that was the impression I gave. I'm doing this from thread memory by the way, so iirc applies throughout. Like I said, this has been covered in a number of threads elsewhere.
Did you really mean to call me bonj? Please say you didn't....
Chris James
Über Member
- Location
- Huddersfield
Not sure what you mean by the entropy change comment.
Steel has a fatigue limit, at stresses below this the steel will not grow fatigue cracks regardless of how many times the stress is applied. I haven't read the wikipedia article below (can't be bothered!) but I dare say it will go into this in some detail.
http://en.wikipedia.org/wiki/Metal_fatigue
So if a bike frame is designed from steel with sufficient tube thickness and diameter to ensure that this fatigue limit is never reached then theoretically the bike will last forever! Of course it is not that simple as fatigue is not the only failure mechanism. Corrosion and corrosion-fatigue would both affect steel frames and the method of construction and design can result in the frame being locally stressed to start with.
Equally an aluminium frame can be designed such that the stresses is sees result in a such a long fatigue life that it will effectively 'never' fail by fatigue. But to do this they need thicker and oversized tubes than for steel. Aluminium alloys are also much less strong than steel alloys used for constructing bikes. So, for the same strength frame they need more material.
So even though aluminium alloys are much less dense than steel, the resulting frames are often similar weights. The aluminium frames will tend to have larger diameters and thicker sections, resulting in a stiffer bike. Hence the stereotype of a harsh ride on aluminium and a whippy 531c frame.
The upshot of all this is that good bike frames can be made out of lots of materials. No bikes last for ever and light frames are unlikely to have the longevity of a more heavyweght design, regardless of the material it is constructed from.
Steel has a fatigue limit, at stresses below this the steel will not grow fatigue cracks regardless of how many times the stress is applied. I haven't read the wikipedia article below (can't be bothered!) but I dare say it will go into this in some detail.
http://en.wikipedia.org/wiki/Metal_fatigue
So if a bike frame is designed from steel with sufficient tube thickness and diameter to ensure that this fatigue limit is never reached then theoretically the bike will last forever! Of course it is not that simple as fatigue is not the only failure mechanism. Corrosion and corrosion-fatigue would both affect steel frames and the method of construction and design can result in the frame being locally stressed to start with.
Equally an aluminium frame can be designed such that the stresses is sees result in a such a long fatigue life that it will effectively 'never' fail by fatigue. But to do this they need thicker and oversized tubes than for steel. Aluminium alloys are also much less strong than steel alloys used for constructing bikes. So, for the same strength frame they need more material.
So even though aluminium alloys are much less dense than steel, the resulting frames are often similar weights. The aluminium frames will tend to have larger diameters and thicker sections, resulting in a stiffer bike. Hence the stereotype of a harsh ride on aluminium and a whippy 531c frame.
The upshot of all this is that good bike frames can be made out of lots of materials. No bikes last for ever and light frames are unlikely to have the longevity of a more heavyweght design, regardless of the material it is constructed from.
hubgearfreak
Über Member
sorry, i did say
hubgearfreak said:
