markz
100 TW
High power needs steel i.m.o. especially if you are going fast! Anything else, then Alum is fine. I would not touch carbon with a 100 foot pole t.b.h.
Aluminum vs Steel vs Carbon E-bike Frames
- Thread starter st35326
- Start date
Chalo
100 TW
markz said:
It's all a matter of how much you use. An '80s aluminum Cannondale or Trek is more robust than most steel frames, let alone expensive lightweight steel frames. Lightweight steel frames can be among the most fragile and damage-prone of all. They're just not what most of us would consider retrofitting.
markz
100 TW
True true, have you ever found any info on tube wall thickness of various bicycles whether steel or alum?
Chalo
100 TW
markz said:
Bog standard straight gauge chromoly frames usually have 0.9mm wall main tubes these days. Fancy double butted frames can be as thin as 0.6-0.4-0.6mm, which is crazy thin. Mild steel frames are usually thicker walled than chromoly, with more variation between models. The thickest I'm aware of were Chicago Schwinn Electro-Forged models, which used 14ga steel (2.1mm) for the main tubes.
Aluminum varies a lot according to shape, but it's in the 1.5mm range for the large diameter round tube frames I've cut up before. I've seen aluminum freestyle frames with 3.2mm wall tubes. Cannondale 2.8 series butted frames from the early '90s were as thin as 0.6mm in some low stress spots, and their later CAAD series frames might even be thinner here and there.
markz
100 TW
Interesting read
http://www.sheldonbrown.com/chicago-schwinns.html
http://www.sheldonbrown.com/chicago-schwinns.html
Chalo
100 TW
Buk___ said:Take a look; then choose wisely
That's pretty cool.
The aluminum tube they used had the same dimensions as the first two steel ones, which means it weighed 1/3 as much. I think if the aluminum one had been matched by mass rather than dimensions, it might have fared better than the steel samples.
And of course, if the carbon composite sample was made to the same mass, it would come out somewhat better too.
Chalo said:Buk___ said:Take a look; then choose wisely
That's pretty cool.
The aluminum tube they used had the same dimensions as the first two steel ones, which means it weighed 1/3 as much. I think if the aluminum one had been matched by mass rather than dimensions, it might have fared better than the steel samples.
And of course, if the carbon composite sample was made to the same mass, it would come out somewhat better too.
Indeed.
Even so, you need to go to twice the thickness to match the strength, cutting that weight saving down to about 20%. But then, if you want to achieve the same stiffness, you need to triple the thickness; at which point you lost the weight advantage, and increased your costs by 3.
And if there is any flexure in the design, reduced your projected life due to aluminium's limited plastic range.
Chalo
100 TW
Because a tube's stiffness varies as the cube of its diameter (actually, the fourth power of its outer diameter divided by its inner diameter), the stiffness break-even point given the same wall thickness as steel is at 1.4 times the tube diameter. At that size, the aluminum tube weighs less than half what the steel tube does.
So then you can double the wall thickness and get double the stiffness, along with superior strength (because the total tensile yield strength is now about equal to chromoly but the sectional properties are better), and still come in a little lighter than the steel tube.
Aluminum bike frames have the reputation of being really stiff, but it's not because aluminum is stiff-- it's three times more flexible than steel, just like it's three times lighter. But that low density lets you scale up the size of everything and disproportionately benefit from larger dimensions.
Aluminum is really good at this stuff. That's why we make flying machines out of it. That's why bike manufacturers can make all sorts of retarded bullshit (like curved tube frames) and it still works out. Aluminum is just a lot fussier to work with than steel, if you need the strength that comes only through heat treatment.
So then you can double the wall thickness and get double the stiffness, along with superior strength (because the total tensile yield strength is now about equal to chromoly but the sectional properties are better), and still come in a little lighter than the steel tube.
Aluminum bike frames have the reputation of being really stiff, but it's not because aluminum is stiff-- it's three times more flexible than steel, just like it's three times lighter. But that low density lets you scale up the size of everything and disproportionately benefit from larger dimensions.
Aluminum is really good at this stuff. That's why we make flying machines out of it. That's why bike manufacturers can make all sorts of retarded bullshit (like curved tube frames) and it still works out. Aluminum is just a lot fussier to work with than steel, if you need the strength that comes only through heat treatment.
Chalo said:
Okay. But then you could increase the diameter of your steel tube and reduce its thickness to 71% for increased stiffness from the same weight.
But you don't really want that extra stiffness with steel; you cannot avoid it with aluminium.
Chalo said:
So, what to do if you haven't got a local pizza place that'll allow you to stick you welded up frame in the pizza oven?
Chalo
100 TW
Buk___ said:
Yes, but no. At 50:1 or so diameter to wall thickness ratio, tubes become vulnerable to "beer can" crumpling failures. This is what limits the practical oversizing of steel tubes (or any tubes). Manufacturers push the limits, but that gives us the vulnerabilities of lightweight steel frames as we already know them.
Cannondale as an example used aluminum tubes up to 2.25" in diameter to make practical, usable mass market frames that could be built up below the UCI minimum weight limit for racing. No tricks you can do with steel will get you there. But steel is still my choice for DIY e-bikes and any other custom frame work.
It's possible to get aluminum frames solution heat treated and artificially aged on a custom basis. But it's expensive and likely to warp them. Plus, it's time consuming if you don't have a local source. So for the DIYer, it's best to use steel or else grossly overbuild with structural aluminum.
Chalo said:
Agreed. But 1.4 * 1.75 = 2.45; and 0.125 * 71 = 0.08875; 0.08875/2.45 = 27:1.
Aluminium is okay for manufacturers, but still has a limited shelf life and higher cost; and the weight saving doesn't add up to much performance or range gain for an e-bike.
999zip999
100 TW
Hundreds of old Diamondback mountain bikes trek ect all made of steel weldable strong drill grind and make something a TIG welder is best keep it clean. And shape your pieces to fit with a file.
Buk___ said:Take a look; then choose wisely
idid&itstillTi.
Mg iz gooden2also, singz beautiful.
Ti be suspiciously left out of the video comparison (& this thread) for good reason, cuz there iz no comparison.
also if CF gives u pause, throw in some BF.
http://www.specmaterials.com/boronfiberproperties.htm
macribs
10 MW
- Joined
- Jul 22, 2014
- Messages
- 3,702
Buk___ said:Take a look; then choose wisely
Carbon fiber as light as it is could have much thicker walls for the carbon fiber @1.17 min into the video. And what is actually "conventional carbon fiber" without giving us some specific data of thickness? They didn't even come close to match the steel, and done correctly by adding carbon layers to match strength of chromoly the outcome would be totally different.
For the carbon matrix dual layer with kevlar core, I think a more correct chosen carbon layer/thickness and even lighter foam core would give even better result on par with chromoly or slightly better while still win in the weight department.
Chalo
100 TW
They should have controlled the test samples either for weight, yield strength, or stiffness. But they clearly didn't make any of those values close to equal across the range.
craneplaneguy
10 kW
BEER CAN EFFECT
For those that don't know, (few here probably) is when you chug a can of beer, but before you crush it in your manly hands, while it's still perfectly cylindrical, you place it on the ground and balance on it (hard to do if it's multiple beers first) and it will easily support your full weight. While still balancing on it, bend down and flick a finger at it (possible if you're nimble) and it will instantly collapse, clearly illustrating the importance of keeping things in column. When I was building, selling, and repairing hang gliders and ultralights, and some guy would claim that the dent in his wing spar wasn't enough to matter......I'd use the beer can effect to set him straight.
This is a great thread.
For those that don't know, (few here probably) is when you chug a can of beer, but before you crush it in your manly hands, while it's still perfectly cylindrical, you place it on the ground and balance on it (hard to do if it's multiple beers first) and it will easily support your full weight. While still balancing on it, bend down and flick a finger at it (possible if you're nimble) and it will instantly collapse, clearly illustrating the importance of keeping things in column. When I was building, selling, and repairing hang gliders and ultralights, and some guy would claim that the dent in his wing spar wasn't enough to matter......I'd use the beer can effect to set him straight.
This is a great thread.
MadRhino
100 GW
This is a neverending thread.
People believe what they want.
The fact is, if you are buying a cheap crap bike, better buy a steel one.
If you are buying a quality bike to build high power, it’s better be stiff enough to make a safe ride. Good steel bikes are hard to find nowadays. Much stiffer are quality MTB Alu or CF frames. Harder to build, but better rides in all aspects.
Those riding slow don’t care about fishtailing frames, but at 100+ kmh they can send you crashing in a tree or upcoming car, for a small bump in a turn.
People believe what they want.
The fact is, if you are buying a cheap crap bike, better buy a steel one.
If you are buying a quality bike to build high power, it’s better be stiff enough to make a safe ride. Good steel bikes are hard to find nowadays. Much stiffer are quality MTB Alu or CF frames. Harder to build, but better rides in all aspects.
Those riding slow don’t care about fishtailing frames, but at 100+ kmh they can send you crashing in a tree or upcoming car, for a small bump in a turn.
st35326
1 kW
[youtube]https://www.youtube.com/watch?time_continue=43&v=Itq7vOQbuts[/youtube]
Carbon can be engineered to be near indestructible or ultra light to really capitalize on its properties. One of the absolute advantages is that you can precisely dial in the properties that you need, be it structural, impact crumple zones, or just the relative strength-weight benefit etc etc.
Vehement Fear of carbon components is from lack of understanding and not being able to get past the early implementations and failures which is natural with any new technology.
Look to f1, koenigsegg et al who truly understand it's potential. Obviously they respect it's potential limitations but work around it or tailor to specific needs.
Check out this abuse
https://m.pinkbike.com/news/danny-macaskill-carbon-wheel-crushing-video.html
Vehement Fear of carbon components is from lack of understanding and not being able to get past the early implementations and failures which is natural with any new technology.
Look to f1, koenigsegg et al who truly understand it's potential. Obviously they respect it's potential limitations but work around it or tailor to specific needs.
Check out this abuse
https://m.pinkbike.com/news/danny-macaskill-carbon-wheel-crushing-video.html
MadRhino
100 GW
Yes it can, but it is very time consuming and expansive to do it at home. Due to costly development and manufacturing processes, suitable CF frames to build a powerful ebike are expansive and not so common. Most of us are conscious that CF has a great potential, but choose to build on other suitable frames that can be found and mod at lesser expanse.12-C said:
Chalo
100 TW
I would very much appreciate carbon fiber composite rigid frames built to a weight of 5 pounds or more. It would mean practical durability comparable to a sturdy chromoly frame, but with far greater stiffness and strength. Unfortunately, such a frame would cost more to make than a light racing frame while appealing mostly to practical minded riders who are not eager to pay huge amounts for a commodity tool.
Perhaps once graphene and carbon nanotubes become available in useful quantity and quality, carbon fiber will be sufficiently de-glamorized that it will move into the realm of affordable and practical materials. Or perhaps those even higher tech materials will prove to be cheap and plentiful enough even for those of us who demand durability and good value.
Perhaps once graphene and carbon nanotubes become available in useful quantity and quality, carbon fiber will be sufficiently de-glamorized that it will move into the realm of affordable and practical materials. Or perhaps those even higher tech materials will prove to be cheap and plentiful enough even for those of us who demand durability and good value.
MadRhino
100 GW
A few more years, and we can find used DH racing CF frames for a good price. Some are made very thick, and soon to be replaced for lighter, since the DH racing courses are getting better and more technical, and often won on crank work.
Tony01
100 W
markz said:
The limit for a stock schwinn is approx 8hp, with 4 gussets in the rear and a sleeved seat tube is around 11hp, and with major gusseting and bracing around 15hp. Unfortunately. However, I think that by cutting the rear end off and bracing in a swing arm pivot the frame becomes ideal for road and light off-road use. I have been wanting to try this for a while and I have just the right beat up schwinn sitting here with a frame crack already waiting to be attended to.
