Aluminum vs Steel vs Carbon E-bike Frames

st35326

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Of the dedicated bike frame what are the biggest advantages/disadvantages of the various frames as far as weight, durability and cost? Lighter weight means less battery needed but possibly sacrifices durability? I began thinking of this when reading an article about the differences between the Model S (aluminum) vs. Model 3 (Steel). The Author States: "key advantages of steel over aluminum as being the lower production equipment costs, the lower worker training/skill needed to work/operate steel, the lower compensation and cost savings of steel workers versus aluminum workers, and the lower repair costs."
 
st35326 said:
Of the dedicated bike frame what are the biggest advantages/disadvantages of the various frames as far as weight, durability and cost?
Steel is easier to weld and easier to work with. Aluminum is stronger per pound and easier to drill - but you can't really weld it without heat-treating the frame, which is annoying. Steel also "feels better" to me but that's totally subjective. Carbon fiber is harder to work with, but not impossible.
 
Well it kind of depends if you look at this from a DIY point of view or if you are looking at it from a manufacturer point of view.

For you and me whatever you master will work wonders. You can make a stunning ebike using steel. Either pipes, square tubing, sheets or whatever you can get your hands on. Steel is easy to work with, very forgiving when messing up when welding. Just find your dremel and redo. You likely will end up with a hardcore e-bike that will outlast any bike you got today, your battery box can be made to fit your needs. And that will help with keeping the weight down.

Aluminum is light weight material. Comes in various alloys and strengths. Most likely the strength of your aluminium will vanish as soon as you start welding. So curing and heating might be required. Parts can me more costly to get. Welding aluminum is not as tough as some people will tell you to. Take your time and focus on the puddle and you will be fine. Practice a night or two on thin scrap alu bits to make sure you get it before you start welding you frame. If you cure and heat the finished product up to correct temp you will get the strength back into the metal and if your welding is fine you will have strong, solid e-bike. Much lighter then if you used steel.

Carbon fiber is for everyone these days. You get hi quality material for very low price these days compared to what it was like 10-15 + years ago. Even one-off projects can be amazing using carbon fiber. If you got enough patience to make a perfect mold, then you can make your super strong, super light e-bike from carbon fiber. Use injection vacuum bagging to help getting a better end result. If you first make a mold, take some extra time to get mold perfect. Once you made your first carbon frame, you can keep using the mold and take orders from friends and co workers who will be amazed by your carbon bike.

A manufacturer will need to calculate set up time, man hour, material cost etc. So for them a different ballgame.

Me and you we can do whatever we feel we are able to take on. If you hate time consuming fiddely work like polishing to make a perfect mold, don't make a carbon bike. Result will look poor, strength might suffer and overall experience will be pita. If you fancy doing such tasks, you can create anything you can imagine with carbon fiber. If you can dream it you can build it.

Steel to save time and money. Alu if you care about weight and you got needed equipment.
 
All great input. I have TIG'd Aluminum in the past but nothing structural (more like cylinder heads and cast water necks).
I did find a data sheet of sorts comparing one square cubic foot of various materialshttp://www.coyotesteel.com/assets/img/PDFs/weightspercubicfoot.pdf

Aluminum weighs 168 pounds per square foot. Steel shows 490 pounds per square foot (huge difference) but Im assuming you'd need more Aluminum to rival steels strength .
 
Not sure what advantages you're looking for. If you have your carbon fiber bike fall over because you didn't put the kickstand right, you've probably destroyed it. Anything I've done with these bikes so far the cheap steel frame has really been the best. And if I wanted to weld the steel would be even better because home welding goes far better on steel than on aluminum. Might there be reasons aluminum would be better? I suppose, but I'm not sold.
 
Well the finish of carbon fiber can be delicate. But if your side stand caves on you, your carbon fiber will be totally fine. Ask any of the carbon fiber frame riders here. They have put their ride sideways plenty, some even crashed hard and no damage worth mentioning. Carbon fiber is "strong as steel".

Also you can get so many cool and complex shapes when you are working with carbon fiber. Anything you can dream up, and make a mold for will be doable in carbon fiber.

But there is a good reason steel is popular. Easily accessible, strong, easily machined and welded. Will last forever and will make any future repairs doable by yourself. Steel does noe warp as easily as aluminium either during welding so less complicated jigs are needed.
 
I have an idea for a bike in carbon....but never tried it before.Would a frame of carbon wrapped arround foam be ok? :roll:
 
The main advantage of carbon is weight, which becomes a bit of a joke when you strap a 15 pound motor, and 10 pound battery on the bike.

But not so much a joke, if you live 3 flights up.

If you can park in a garage like I do, then I could give a flip how much my bike weighs. So steel is my desire. I do care if I can weld kooky modifications to it. The bike ends up weighing 100 pounds, so what, 25 pounds of that is a 3000w capable motor. Plenty to overcome my fat ass, and the crap I welded onto the bike. And make carrying 50 pounds of battery no problem if I wish. Its a "motorcycle with pedals" now.

Aluminum I can't weld, so I don't go for that, except on my off road bikes that get no modifications. Those bikes end up around 60 pounds. And I don't have to go up stairs with em.

That said, it would be fun to make a carbon bike, but you'd want to build some steel into it for a hub motor, like a bolt on rear dropout or swingarm. I just find it fun enough to chop up old bikes for the frame tubes, and frankenweld them into something new.

My best effort was this bike, which unfortunately had its battery blow up, and burn my garage down.Finished cargo mixte..jpg
 
I think maybe people are looking at carbon the wrong way... Yes, you can build an ultra light frame with it, which is pointless for a heavy ebike. But you can also build a frame that is the weight of an aluminum frame, but more indestructible than the heaviest steel frame. The advantage isn't just the low weight, its the strength to weight ratio thats important.

Not necessarily who you would associate with cutting edge carbon, but Lamborghini is a leader in using forged carbon parts, and have it to the point they are used in the piston rods and other high temp structures that would have been impossible a few years ago.
Soon mass manufacturing will be bringing cheap strong carbon monocoque frames squished out of molds as the new normal.

rod.jpg
chips.jpg
 
Excellent point sir, I tip my hat to you. Strength to weight ratio, elegant spoken. Very efficient. A sentence of only 4 words. Yet so meaningful.
 
Making a good frame yourself is costly and time consuming. CF frames that are thick and can stand high power are few, and expansive. They are not old enough to find them at a good price on the used market.

Making mods to a steel frame is cheap and easy. The same mods on an alu frame are more complicated but can be done neat and quick. Doing neat mods to a CF frame does require equipment and experience.

It is a long and expansive process, to develop a light FS bike frame that does ride good and safe at high speed. Their design is improved at every new version of a model, over years of racing team work. Alu frames had reached optimized level long ago, thus can be found cheap on the used market. Today, most FS racing bikes are CF and I believe CF is the future, although we still can see some CF frame failures during the DH races. We, as DIY ebike builders, can’t afford risking frame failures. I find better to wait for the CF bike frame manufacturing to reach optimized design and process. Some DH racing CF frames are reliable enough already, but there is still the problem of cost and mods.
I prefer building and riding alu for now, for it is the best compromise for weight/cost/reliability when you build an ebike to ride hard and fast.

The major players are getting involved in ebikes now. They have the experience and staff to develop and improve design and manufacturing process. If they start building bikes that are out of the legal rules to target off road performance, we should have very good Ebike specific CF frames pretty soon.
 
For ebikes, just go steel if you can, if not, aluminum is fine, stay away from carbon bikes unless you already have a carbon bike and you do a mild conversion.
 
It would be fun though, to build the strongest carbon frame in the world so far. Definitely do it if its mostly for the fun.

Lightness is always a plus for off road riding, if I did not make that clear. The handling of the bike is the thing that really matters on singletrack. So what Mad Rhino said applies for off road for sure.

But for street riding, the heaviest steel frames, including 25 pound motors, are still light compared to motorcycles as large as 125cc. The thing I like to do to steel, is stretch them to the same length as motorcyles, so they handle better at higher speeds. Might still have some speed wobble at 40 mph, but its now so much more controllable. The wobble gets worse if you carry large batteries, or cargo in the back.
 
dogman dan said:
It would be fun though, to build the strongest carbon frame in the world so far. Definitely do it if its mostly for the fun.

It all depends on your definition of "Strong." Do you mean strong like concrete?

I always love seeing what some of the instant experts have to say about things I've studied in school and worked with, such as carbon fiber. Nothing happens when the carbon fiber bikes fall over? They don't delaminate inside? The don't suffer long term structural degradation? They don't break first along the bonding of the separate tubing? Let's not forget the coming apart at 40mph part. Imagine how I feel sitting here with the awards I won and remembering the one guest speaker who fixed those carbon fiber frames for a living and made the point HE would never own one. But he highly recommended getting into patching them, more business out there than people to do it.

If you want to make a carbon fiber frame you'll break the normal rules for making a strong composite structure. Rather than getting your matrix under 40%, you'll push it over. Along with using one or more plys of fiberglas on top. This is to protect the finish and the carbon fiber itself. But a resin rich composite also breaks easier. Darn.

And with having read so many stupid comments on bike forums way back when, let me point out that no, it is NOT safe to let the Dreamliner or the F-22 "Fall over." If one did "Fall over," it would be immediately grounded and inspected, I would expect considerable damage would be done. So much for proving carbon fiber doesn't break when it falls over by mentioning aircraft. I"m not making this up, people spout this nonsense on bike boards, probably to this day. If someone held up a carbon fiber panel for an airplane you could throw things at it that would punch a hole that would not go through the steel panel that carbon fiber replaced in the process. Even if the carbon fiber is overall stronger. Oh, I'm sure you don't believe that, any more than you believe that you could stand on an aluminum can and then just touch one side and have it collapse. Oh, how the instant experts must be scoffing at that one. But think of how the bullets that would penetrate the carbon fiber and the steel panel would be stopped by the concrete. I guess we can figure out the best thing to make a bike out of, eh? (Wouldn't that be a kewl thing to be riding around on at the beach?)

Oh, more that I'm sure will get the instant experts hackles up. So you think chrome moly is far better than mild steel, eh? Do you know which holds up better over time? Which takes longer to become brittle under vibration? Which one takes a second impact, say after bouncing off the wall a racecar is then hit by another car, and takes that second impact BETTER? But you just feel so sure that chrome moly is better because you've heard talk, eh?

I'll let the instant experts insist on the right answer to this: Two round steel tubes, made of the same metal. (1020, whatever.) They are the same length and the same weight, but one has a thinner wall. Which is stronger?
 
I'm a devotee of home made carbon stuff, It's a very easy material to work with, and if overbuilt it is bomb-proof. As I'm running a very heavy motor, wheels and forks on a vehicle intended to take passengers and cargo—the weight of the frame is almost irrelevant. My building process used carbon over an aircraft ply skeleton (sort of). The result is incredibly stiff, and so far, very strong. the frame weighed about 25 lbs. I think that for experimenters carbon fiber is great. I'm also fond of Kevlar, I use it for strong points, and I've found that kevlar cord soaked in resin can be very hand for joining dissimilar materials. You can literaly tie things together with multiple wraps of resin-soaked cord and then clean up the aesthetics with Bondo or foam.
 
This is what most of us D.I.Y. builders would be better off doing, like you over thin wood, or a foam core that can be left in or scrapped out once the composite has cured.

I also believe that for e-bikes we do not need the expensive and very time consuming task of making a mold, unless you want to go into business and sell the frames.

Now what about fiberglass , is it still cheaper than carbon fiber or has carbon fiber come down in price enough to use it instead ?

Have you thought about the mix of Carbon and Kevlar cloth ?
That was used along with carbon fiber pre peg , in a Rigid Wing Hanglider, the Bright Star Millennium , that was made up in Santa Rosa ,California some 20 years ago.

I like your project , would like to see a chronicle / thread on your build.

tigcross said:
I'm a devotee of home made carbon stuff, It's a very easy material to work with, and if overbuilt it is bomb-proof. As I'm running a very heavy motor, wheels and forks on a vehicle intended to take passengers and cargo—the weight of the frame is almost irrelevant. My building process used carbon over an aircraft ply skeleton (sort of). The result is incredibly stiff, and so far, very strong. the frame weighed about 25 lbs. I think that for experimenters carbon fiber is great. I'm also fond of Kevlar, I use it for strong points, and I've found that kevlar cord soaked in resin can be very hand for joining dissimilar materials. You can literaly tie things together with multiple wraps of resin-soaked cord and then clean up the aesthetics with Bondo or foam.
 
are you talkling make or buy?

Really, it all depends on the frame builder as you can get a lot of overlap depending on what the frame builder wants.

From a buy perspective:
Steel is maybe 2lbs heavier (or more for a heavy duty frame). tends to ride better, doesn't fail catastrophically, and can be repaired when damaged.

Aluminum and carbon can be a couple pounds lighter, and tend to be more responsive when pedaling. Carbon bikes tend to be very, very strong, but can not take point loads and are not abrasion resistant like the metals are. Aluminum tends to ride stiffly and like carbon it can fracture without warning.
 
Dauntless I don't know your background, your education, your experiences etc. But what I read between the lines in your post is a feeling of being superior. For all I know you might be. If that is the case please be superior without trying to put other people down.

You are not the only person on this forum that have worked with carbon fiber. Other has as well. I have designed, produced and made racing parts, extreme white water crafts, etc. I have used infusion vacuum bagging, autoclave etc and I mean it from my heart when I say a DIY carbon fiber frame is perfectly doable for most of the ES crowd.

If you feel otherwise that is fine, but your truth is far from universal. Any carbon frame won't split. Won't delaminate or cause you pain and suffering. An e-bike frame in carbon fiber is far from lycra racing thin walled super light frames. When you have control over the process you can make sure there are no trapped air inside the mold. You can take your sweet time to do it right because you are not on the clock to make a profit - your goal is to make a high performance long lasting frame. And you put in as many hours as need be to get it perfect. If you take good care of your carbon frame I am sure you can easily pass it along to your son or even your son's son. How well cf will hold up to time I don't know, but we got cf parts made some twenty years ago that is still around.

As always TLC goes a long way, and what you put in is what you get out.
 
Ti is tough. Tough to work and tough to break. But the tough to work part might be a show stopper for many DIY's.
You can get many of the Ti's advantages by using various alloys. Magnesium alloy comes to mind. Super light weight, very strong and easy to machine. But as with Ti magnesium is also expensive to buy.

Remember KTM did magnesium swing arms in the late 80's for their MX line. Tough as nail or should I say steel but without the weight penalty.
 
HEre is my recipe. NEW alum frame, full suspension, STOUT rear trangle, oversized air shock, 36 fox Talas, rc2. BBSHD. 14ah battery in custom case underslung. Onboard lock 1lb. carbon 38mm outside, 30 inside, 47mm marathon plus. ALL UP weight, 41 lbs. Goes 28 with doable cadence. 25 good cruise. I set up the suspension plush. Fattish tires will roll well, and cushion well. Flat tread, will corner like a go cart.

I could not do better on weight, if I went carbon. I have an aux battery, that fits on seatpost. I can go well over 100 miles on charge.

I don't need any doo dads or trinkets welded or bonded. I have done all kinds of trick stuff. Cables internal all the way back. 10mm axle rear. Onboard lighting.

Aluminum is the sweet spot. But, don't cut significantly, But, you could add/bond.

My carbon wheels, wide and light, and cushy suspension, will make it literally, a Cadillac, yet sporty. There is not a thing I should add. This does not cover a cargobike, but covers street personal cruiser.

Found frame for 200 new on ebay. Cant get that, but watching craigs, you will find a good alum frame. Might be limited to 27.5, but a little grinding, and 29ers are possible.

I am about to fit the carbon wheels. I am excited. The bike will then be a hotrod.
 

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For DIY, steel wins. You can bend it, weld things to it, braze things to it-- all without weakening it substantially. It's usually formed into round tubing of customary diameters, which is very convenient when trying to attach things.

There's nothing wrong with aluminum if you can use the frame as is, without modification. But you can't reshape it or weld it without severely weakening its structure. And more often than not, the manufacturer has used gimmicky hydroformed shapes that reduce the specific strength and stiffness of the frame while making it much more difficult to mount things onto it.

"Carbon" (plastic) frames are, well, plastic. They're light and disposable, and easy to damage. You can fix them (to some extent), or add onto them, with glue and string-- because they're made out of glue and string. Bamboo frames have the same benefits and drawbacks, but can be much cheaper if you're making your own.
 
I like building with steel because it is easy to work with and very, very cheap. $200 welder, $60 for grinder and supplies, $10 map gas and.... $30 worth of local steel for my project.

However it is very heavy. I'm looking into cf myself. I'd be looking into aluminum too however, there is nothing new in it. It's been done and overdone enough. And I don't wanna shell out for a spool gun and gas. If I'm gonna spend more money on tools it's gonna be on cf fabrication; which is the future IMO.
 
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