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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

Stuff you should know about bicycles.

Old 03-20-07, 11:14 AM
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Stuff you should know about bicycles.

Singlespeed/fixie or not, the more you know about what's between your legs the better.

It's also not easy to find a database that has everything important in one spot. Sheldonbrown's site is fantastic but it's still missing a lot of general bike information. I'd like to use this thread as a way for people to learn things they never knew, brush up on things they forgot or simply contribute and help others. Seeing Ken's post about trail made me realize there's still plenty for me to learn too, so I'm interested in benefiting from this too.

I'll start out with some things I know, frames first. If you guys can keep the posts informative and in a similar organized structure it'd work out better than a bunch of chatter.

Bike Frames - Materials
There's 3 materials being used, steel, carbon and aluminum and each has their own properties. Within those types there are different methods of joining and something called butting. Most people seem to have a softy for steel so I'll start with that after some basic concepts about materials.

In order to understand a materials properties you need to know what they mean. A yield strength is the stress (force divided by area) required to pull the material apart at a very rapid rate. Yielding generally means failure in brittle materials (glasses, cast iron ect.) but in ductile materials (rubber, steel and a lesser extent aluminum) the ultimate stress when the material finally breaks is generally higher than the yeild stress and happens after a great deal of elongation of the material.
Modulus of Elasticity or E is a simplified relationship between the applied stress and the % elongation or strain of the material. Higher modulus's of elasticity means the material elongates less for a given increase in stress. It generally means stiffer and brittle materials often have higher E values than ductile ones.
Fatigue is the tendancy for materials to fail after a large amount of repeated stress cycles. For instance, sitting on your bike seat puts a predictable amount of stress on your frame and wheels, getting up relieves the stress and completes the cycle. Different materials have different fatigue resistence. This is especially true among the many alloys of steel with some designed to take far greater fatigue than others.

In general steel has a higher fatigue resistence, and far greated yeild stress than aluminum and carbon. This results in the oversized tubes of aluminum and carbon to get the same strength as a traditional steel frame. Steel is also much denser, and the heaviest of the 3 materials but light frames can still be built with modern steel.

Steel frames
Steel is a dense metal with thousands of different alloys for different applications. Common to most bikes are high-tensile steel, chrome-molybendium (chro-moly) and various Reynolds, Diadacci and Columbus tubing.
High tensile steel is actually the crappiest despite the fancy name. It's weak and the tubes are generally found on poor quality bikes, because of their weakness they must have thick walls and result in a heavy frame.
Chro-moly is a very common material that has hundreds of sub-alloys but is generally quality stuff especially when double and triple butted. I'll get to butting later.
Tubing companies like Diadacci, Columbus and Reynolds have varying grades of tubing that can be found on their website. Some of these tubes will actually gain strength when exposed to the high heats of welding, creating and even stronger joint. The general rule with Reynolds is the higher the number the thinner and lighter the tubing. These are all quality brands and a bike with one of their stickers will be quality.

Butting is referred to any long shape such as a tube or spoke that has more material on one end than the other. Double butting means the ends are one thickness, say 2.0 mm and the middle is thinner, say 1.6 mm, such as a spoke. Triple butting means the first end, middle and other end are each different thicknesses.
Because different parts of the tube are under more or less force from various loading conditions (potholes, sprinting, normal riding ect.) tubes and spokes can be butted to thicken members where more force is, resulting in lesser stress. This creates frames that are equally or often strong than unbutted frames but much lighter. Some claim it also changes the feel of the frame but I don't have enough experience to comment on that.

Joining Methods
The tubes on any frame must be joined, with steel the three methods of choice are welding, fillet brazing and lugging. Brazing is used in fillet brazed joints and lugged joints and involves melting a metal with a low melting point such as brass or silver (silver has a lower melting point) and filling in the joint with the material. This works to fill in the gaps in the lug and to chemically bond the steel to the braze material. Welding melts a weld material along with some of the surrounding tube to create a molten area which cools.


Welding steel frames should only be done with a TIG welder (check wikipedia for more information on this) as it is the strongest and lightest weld for the application. Welded connections are very strong when properly done. Signs of a good weld include a very uniform flow and the smaller amount of weld material the better. Welding uses very high heats and can often leave minor residual stresses in the material from the differential cooling of the joint and surrounding tube. This can weaken the joint but generally isn't a problem. A method of dealing with this is the use of "heat sinks" often peices of brass touching the metal near the joint to aid in cooling and prevent the build up of too much heat.
The bad thing about welding is that if a tube is damaged it cannot be removed and replaced, unlike fillet brazing and lugging. Also, fatigue stress on a welded joint is higher because of the sharp changes in profile which leads to a shorter life for a welded joint. However, joints can be re-welded but it isn't pretty.

Fillet Brazing is when tubes are joined by a large amount of brass or brass silver mix brazed around the joint. When properly done it makes the joint look as if it was one peices with a slow curve from the verticle peice to the horizontal. Fillet brazed joints are very strong, but heavier than welded. However, because of the smooth transition the fatigue life is extraordinary and longer than either of the other methods for joining tubes. Fillet brazed frames are generally touring frames that will see a long rough life but take skill and time to do properly. They are often more expensive than lugs for that reason.

Lugged frames were the frame of choice until the innovations and wide spread use of TIG welding in the 1990s. Lugs are generally cast from a mold as small peices of metal that allow tubes to be fit into them and then brazed with silver or brass to complete the joint. Lugs can be beautifuly crafted and have ornate cut-outs referred to as pantographs. Signs of a good lugged frame are thin, sculpted lugs that have been filled down by hand to reduce stress concentrations in the transition from lug to tube. A simple lug that is point and filled very thin at it's end is the sign of a quality frame builder. Pantographed lugs, or lugs with cut outs are also a sign of quality.

Some of the best lugged frames came from Italy (Colnago is my favorite) and Japan but many custom builders in the US have become reknowned including Richard Sachs, argueably the best. Quality lugs are brazed with silver that is underneath the entire lug with no gaps left between lug and tube. This creates a stronger and longer lasting joint. Evidence of how long lugged joints and fillet brazed joints last can be found in frames from the early 1900s still in use, as well as the thousands of 3 speed cruisers from the 40s and 50s also still in use.

All Steel Frames exhibit a vulnerability to corrosion. This can be easily delt with by the use of products such as "Frame-saver" or applying boiled linseed oil to the inside of the frame. These along with any other method to coat the inside of the frame with a layer to prevent water from contacting bare steel and drying (to form rust) will do very well but may need application every few years.
Steel also has the ability to be cold set and to be bent back after minor damage. It's fairly simple to respace a 126 mm frame to 130 mm using your bare hands as long as the frame and dropout alignment is checked with the proper tool. Often small bends can be bent out of steel after minor traffic accidents.

Typical damage includes bubbles or creases on the bottom of the down tube and top tube from a head on collision. Despite what anyone tells you, it's impossible to tell how long crashed frame can be ridden for. It depends on the tube thickness, degree of damage, rider weight and use and can't really be predicted. What is almost certain is that a frame with this kind of damage won't fail suddenly. Over time, the fork will bend back closer to the frame and eventually the front wheel will contact the downtube. At this point the frame can no longer be ridden and should either be scrapped or have the tubes replaced.
The point is that a steel frame with minor damage can be ridden. It may not have the same geometry as before and it's life will be shortened but unlike aluminum and carbon fiber it generally will not fail suddenly. IF YOUR FRAME IS DAMAGED, HAVE A PROFESSIONAL LOOK AT IT, DO NOT GO ON THIS ADVICE ONLY.



Aluminum Frames
Aluminum as a material is about 1/3 lighter than steel but approximately half as strong. Various alloys gain increased strength, the best being alloys with with scandium but 7071 aluminum is also very high quality. Aluminum also has a much lower modulus of elasticity or E. In order to compensate for these properties any aluminum bike will generally have very large tube diameters with thin walls. A large diameter tube gives higher strength under bending due to an increased moment of interia. By doubling the height of a cross section the stresses from bending are decreased by 8. For more on bending stress, check wikipedia.
Aluminum frames, along with titanium can only be joined through welding. Unlike titanium, aluminum frames are often described as stiff and do not damp road vibrations as much. This is skeptical and will always vary from frame to frame, that is simply the reputation aluminum carries. I may add something on material dampening later

Aluminum frames are typically easy to manufacture, light and stiff. Instead of relying on expensive alloys as in steel, large double butted tube diameters can be created inexpensively to create lighter frames than steel. Often carbon fiber chain stays and forks are combined with an aluminum frame to dampen road vibrations and further reduce weight. These are quality frames but will not last as long as steel or pure aluminum frames. Any added joints are weak points that will eventually fail.

All aluminum frames cannot be cold set or bent back. Often the tube will simply crumple under damage and are ruined. DO NOT RIDE A DAMAGED ALUMINUM FRAME. The extra thin wall thicknesses and the fact that aluminum is not as ductile as steel can lead to sudden dangerous failures.

Things to look for in a good aluminum frame are mainly double butted tubing and small, uniform welds. Good aluminum welds, as in steel and Ti are with minimal material and have a uniform flow to them, as if you had stacked little flat ovals all the same size of weld on top of each other around the joint.

Carbon Fiber (CF) is made up of thousands of tiny strands of carbon fibers fixed together in a resin or epoxy. The smaller the threads, the denser the packing configuration and the stronger the CF will be. By using very tiny strands of any material, you vastly increase the yeild strength by changing the grain and molecular makeup to reduce the effect of dislocations in the atomic structure. Very thin steel wires are known to have yeild strengths in excess of twice their bulk counterparts. Bulk carbon would be fairly weak, but using very thin strands increases it's strength.

What makes CF so revolutionary is that the properties of the material can be altered simply by layering the strands in different directions. This means if you have a component only in direct tension you can design for that stress. With steel, Ti and Aluminum you have fairly equivalant strength in each direction (tension is usually highest) that isn't really being used. With CF you can layer all the strands parallel to the direction of loading, giving the component very high tensile strength but very low shear and compressive, as well as torsional strength. This uses less material for the same strength and a completely customizable material. Not only that but Cf frames can be almost any shape imaginable; leaving plenty of room for aerodynamic frame designs.


That's all for now. I'll write more on Ti frames later. Also look for frame geometry info.

Forging is a process where a hot peice of extruded or cast metal is repeatadly smashed with huge force into shape. If you have ever seen one of those sweet old WW2 or industrial america videos of a factory where something red hot is being smashed by some huge machine, that's forging.

Forging gets the metal on the outside of the item stiffer and stronger than the metal deeper inside. This is especially useful for items under bending and torsional stresses which are highest at the outer most parts of the cross section. By forging something you are effectively making the material at the outside more resistant to the higher stresses it will see.

Last edited by Hocam; 03-22-07 at 08:39 AM.
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Old 03-20-07, 11:17 AM
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You should make a webpage. Forum threads are a very very very difficult way to look up information. Maybe you should add it to the 'fixiewiki' or whatever...
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Old 03-20-07, 11:18 AM
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you forgot bamboo titanium and wood
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Old 03-20-07, 11:24 AM
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Stuff you should know about bicycles:

They're fun. Ride safe. The rest is details.
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Old 03-20-07, 11:26 AM
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Stuff you should know about bicycles:
www.sheldonbrown.com
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Old 03-20-07, 11:48 AM
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Good bit of info there. Well done Hocam.

Yeah a web page would be good.

Sheldon has good stuff but can't do / write up everything. I think a good idea would be an extention to his site edited / veted by him with article / info from other pepole, like Hocam's little bit of info above it could be submitted and then Sheldon could vet it edit it talk to Hocan e.t.c like any editor would and add it to his site. This could allow good info to gain the exposure that Sheldon's site brings do to it's reputation and google rating plus it would allow it to expand but still giving Sheldon ultimate control and allowing people who have specialist knolage to fill in gaps. I think he would make a good editor as he has an good wrting style (to me anyhow). Don't get me wrong Sheldon know loads but he and no man can be an expert in all fields of bike related info / engineering / meteorology. Kind of make an enCYCLOpedia. (please shoot me)

I just think it would make a nice extension.
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Old 03-20-07, 12:23 PM
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Thanks, I have 0 in the way of webpage building but I'll send it to fixie wiki as well as keeping it here. If it grows enough to be a sticky on this forum that'd be great, but fixie wiki would be awesome too. I could try sheldon too.

Originally Posted by Dead Roman
you forgot bamboo titanium and wood
You're right, I did forget titanium. From what I've heard, wood and bamboo are usually facades on carbon fiber, but I'm not sure about it.

Also added more on steel and a small section on aluminum.

Last edited by Hocam; 03-20-07 at 12:47 PM.
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Old 03-20-07, 12:58 PM
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very nice!
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Old 03-20-07, 01:07 PM
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You also forgot Magnesium
https://www.paketabike.com/
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Old 03-20-07, 01:13 PM
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Originally Posted by Hocam
A large diameter tube gives higher strength under bending due to an increased moment of interia.

I'm not an engineer but that doesn't sound right to me.
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Old 03-20-07, 01:28 PM
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Originally Posted by dutret
I'm not an engineer...
...
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Old 03-20-07, 01:32 PM
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Originally Posted by dutret
I'm not an engineer but that doesn't sound right to me.
Yeah it's right. That's why all the frames with ultra thin tubes are also larger diameter
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Old 03-20-07, 01:35 PM
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uuhhhh dupe

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Old 03-20-07, 01:37 PM
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Originally Posted by Fixxxie
Yeah it's right. That's why all the frames with ultra thin tubes are also larger diameter
Because of the moment of intertia? Then why are they stronger under constant uniform forces as well as short ones?

EDIT: actually I don't see how the moment of interia is different for bending forces on them either. just spinning around their central axis.
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Old 03-20-07, 03:05 PM
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is there any place to get stress train curves of all the different types of tubes commonly used in bikes or even just a single graph that shows a few different materials all on one graph- ideally i am looking for a stress-strain curve plot of steel vs. aluminum vs carbon vs Ti
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Old 03-20-07, 05:26 PM
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Originally Posted by dutret
Because of the moment of intertia? Then why are they stronger under constant uniform forces as well as short ones?

EDIT: actually I don't see how the moment of interia is different for bending forces on them either. just spinning around their central axis.
What is a short force?

Moment of inertia doesn't really have much to do with spinning area's around in the context of stress.

Bending stress is found by multiplying the applied moment (M) and the distance from the centroid of the area to the point where you're finding the stress in the cross section (y) and then dividing it by moment of inertia (I).

So

Stress induced by bending = My/I


The moment of intertia for a round tube is: (PI/64)*(D^4 - d^4) where D is the outer diameter, d the inner and PI is approximately 3.14. If we plug D = 25mm and d = 23mm we get a moment of inertia of 5438 mm to the fourth. That gives an area of 75.4 mm squared. To compare, if we do an outer diameter of 50 mm and inner of 49mm that gives an area of 77.8 mm square and a moment of inertia of 23,817 mm to the fourth, a 437% increase in moment of inertia for a 3% increase in weight.

This translates to 54% less bending stress. Using tubes with an oval cross section will see even more gains with this analysis.


If anyone has any other questions please ask, I want you to help me clear up any mistakes I may have made and clarify everything
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Old 03-20-07, 05:30 PM
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...bikes are cool...
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Old 03-20-07, 05:31 PM
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I want to hear what you have to say about carbon, mostly because I associate it with 10,000 dollar road bikes that you see in boring bicycling buyer's guides.

But it'd be fun to try a carbon frame once.

And why don't more people use titanium for frame material? Does it have a ****ty ride feel to it or what? I saw a video on youtube where these guys run over various bicycle tubings with their truck (steel, carbon, titanium), the titanium doesn't even get a dent...
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Old 03-20-07, 05:32 PM
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Originally Posted by lbthomps
is there any place to get stress train curves of all the different types of tubes commonly used in bikes or even just a single graph that shows a few different materials all on one graph- ideally i am looking for a stress-strain curve plot of steel vs. aluminum vs carbon vs Ti
The problem is that steels vary in yield stress on the order of 36,000 psi to 190,000 psi and more. There are brittle steels, ductile steels, steels made for various purposes like corrosion or fatigue resistance. Aluminum varies to some extent as well but not quite as much as steel. If you do google searches for "4130 steel stress vs. strain curve" you might find some stuff. The same goes for 7071 aluminum ect.
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Old 03-20-07, 05:42 PM
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how does one meld carbon fiber together?
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Old 03-20-07, 08:46 PM
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Originally Posted by Kilgore_Trout
how does one meld carbon fiber together?
Carbon fiber is produced like a fabric. The cloth is shaped around something (a balloon is sometimes used) and glued together with resin. I don't know anything about engineering, though. In fact, I hated it so much I changed majors after the first semester...
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Old 03-20-07, 09:15 PM
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Originally Posted by Kilgore_Trout
how does one meld carbon fiber together?
Carbon fiber is a fabric, bikes are made out of carbon fiber reinforced plastic. The fabric is laid down into a mold and covered with a resin. The finished frame is a single piece.

More economical or older CFRP bikes use tubes made of the stuff glued together with steel lugs. Jamis makes a hybrid steel/carbon bike.
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Old 03-22-07, 08:41 AM
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Added stuff on carbon fiber. PMing sheldon now.

I don't really know much about magnesium but if I get real bored next week I'll do some research on material properties and such.

Ti is comming eventually too.

If anyone has other stuff to add, go for it, I was trying to make this a joint-thread with everyone putting in info they've picked up over the years.
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Old 03-22-07, 08:56 AM
  #24  
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Old 03-22-07, 09:27 AM
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Originally Posted by Hocam
What is a short force?

Moment of inertia doesn't really have much to do with spinning area's around in the context of stress.

Bending stress is found by multiplying the applied moment (M) and the distance from the centroid of the area to the point where you're finding the stress in the cross section (y) and then dividing it by moment of inertia (I).

So

Stress induced by bending = My/I


The moment of intertia for a round tube is: (PI/64)*(D^4 - d^4) where D is the outer diameter, d the inner and PI is approximately 3.14. If we plug D = 25mm and d = 23mm we get a moment of inertia of 5438 mm to the fourth. That gives an area of 75.4 mm squared. To compare, if we do an outer diameter of 50 mm and inner of 49mm that gives an area of 77.8 mm square and a moment of inertia of 23,817 mm to the fourth, a 437% increase in moment of inertia for a 3% increase in weight.

This translates to 54% less bending stress. Using tubes with an oval cross section will see even more gains with this analysis.


If anyone has any other questions please ask, I want you to help me clear up any mistakes I may have made and clarify everything
Ok I can see how I coresponds to my more vague common sense view of tube shape and stiffness. Knowing stuff is cool.
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