Emz

Hi,
I am about to buy an Electra cruiser/comfort bike. Am shying away from the "hi-ten" steel models, in favor of the aluminum framed models. Thinking the aluminum ones must be much lighter.
Is that true?
I wish they would list the differents models' weights, but they don't.
On a cruiser type bike, how much weight difference would aluminum vs. hi-ten steel actually be?

Would that seem negligible on this type of bike, since its not a competion bike anyway?

I do not want a 40 lb bike, though.

thanks,
Em
Trek 850 <<heavy!
Tampa FL

NoReg

Well since nobody else tried this... Al is about 1/3rd the weight by volume. A good bike frame in al is probably a little lighter, I really don't remember from my Canondale days. The Nashbar MTB in steel is 2 pounds heavier than their MTB frame in alu about 33% lighter. A high 10s frame looks about twice as thick as the butt end of a regular frame, so it could be at least twice the weight. since it's not butted and probably a lot thicker to boot. I have some motorcycle datapoints where you can have 1/16" wall 1" 4130 tubing sitting in for 1/8" wall 1.25" DOM tube, so it seems like it's not far fetched that the cheap stuff would weigh a minimum of 2xs bike grade stuff as much as 3 times where the tube is butted.

So the real guesswork would relate to the thickness of the al in the high tens equivalent frame. One of the advantage the al has is that due to it's light weight it could be designed around increases in both wall thickness and tubing diameter to gain any strength required from not using a 7000 series as in the Nashbar. So it would seem there is a significant weight advantage to the AL, I would think it could add up to as much as a 50% weight saving for "bad" alu vs. "bad" steel.

Emz

thank you!
I appreciate it.

I will get aluminum then, for sure.
Em

aley

Fair warning, some of this is pretty technical. I just can't help myself.

High-strength steel has a higher strength-to-weight ratio than most aluminum alloys, but there's more to it than just the weight of the raw materials.

The term "high tensile steel" doesn't refer to a specific alloy; rather, it's a general description, and therefore hard to pin down exact material properties. In general, I'd expect that it's got an ultimate tensile strength of 70 ksi (kilopounds per square inch - in other words, if you had a one-inch by one-inch bar, you could pull on it with a force of about 70,000 pounds before it broke). That's about double what you see in mild steel such as A36, hence the term "high tensile" or "high ten."

4130 steel has an ultimate tensile strength (UTS) of about 100 ksi in normalized condition, which is a common heat treatment condition for tubes from a material supplier. When it's properly heat treated it can reach 130 ksi, although many bike frames are not heat treated after welding because of the tendency of the tubes to distort when they're heat treated. Typically it's welded with a mild steel filler metal if the frame is not going to be heat treated, so the welds are likely to be closer to 60 ksi. Heat treated frames can be welded with 4130 filler metal and can therefore reach 130 ksi at the joints.

In comparison, 6061 aluminum is around 38 ksi in the T6 heat treated condition. 7005 is in the neighborhood of 42 ksi. These frames are usually heat treated after welding, so the welds are approximately as strong as the base metal.

So what does all this mean?

In general, steel has a higher strength to weight ratio (specific strength is the engineering term) than aluminum. However, aluminum has a higher stiffness to weight ratio (specific modulus) than steel. All other things being equal, a steel frame made from 4130 or other high-alloy steels will be lighter than an aluminum frame of equal strength.

But of course things aren't all equal.

One drawback of steel frames is that there is a lower limit to how thin the tubes can be made. A larger-diameter tube will withstand bending loads better than a smaller-diameter tube, but to keep the cross-sectional area the same the large tube must have a thinner wall. Thin walls are easy to damage, so most steel tubes are smaller than aluminum tubes to keep the wall thickness high enough that they don't get dented. Since dents in the tubes affect the strength of the tubes in some loading conditions, this causes steel frames to be somewhat heavier than they might otherwise be.

Tube diameter also impacts the stiffness of the frame; if you have two tubes, one with an outside diameter double that of the other, with the larger one having half the wall thickness, the larger one is 10% heavier per inch than the smaller one, but it's over five times the stiffness.

In general, a well-made frame built from high-quality steel tube will weigh about the same as a well-made frame built from aluminum. The steel frame will be somewhat stronger, in that it will take a harder impact to break the frame and the frame will be more able to carry extremely heavy loads. Conversely, the aluminum frame will be significantly stiffer.

Comparing a high-ten steel frame with an aluminum frame, I'd say that if the aluminum frame is a good alloy (6061 or 7005 come to mind, although there are certainly others) and has been heat treated after welding, it's likely that the aluminum frame will be either lighter or stronger than the steel frame, and quite possibly both. In either case it will almost certainly be stiffer.

For a comfort/cruiser bike, I personally would lean toward a good steel frame (4130 chrome-moly, Reynolds 520, etc.) if it's available. If the steel frame is high-ten, though, I'd lean toward an aluminum frame. Given the desire for a comfortable ride I'd expect steel to have more give to it, but I wouldn't want to sacrifice frame strength for the sake of a cushy ride.

YMMV and all that.

NoReg

Valuable stuff.

I have previously asked on this forum what people mean by High-ten. The answer, hardly a flood, was mild steel, probably erw. Which is to say, something in the range of a somewhat work hardened mild steel. That along with "cruiser" led me to the above guesses. As you say, it's pretty vague nomenclature.

I'm not aware of any 4130 bikes that are heat treated post welding (which probably guarantees someone is doing it).

aley

I did a bit of hunting before I posted to try to figure out just what alloy "high ten" refers to. It's likely not a specific alloy, but rather a general description; tubing can be made of 1010, 1018, 1045 etc. These all have different carbon contents (.10% for 1010, .18% for 1018, .45% for 1045) but all fall into the category of low or medium carbon steels; mild steel is essentially the same thing as low carbon steel. Most inexpensive bike tubing is probably at the lower carbon end of the scale, since more carbon makes the tube more difficult to draw and therefore more expensive. It's possible that some tubing referred to as high ten is HSLA (high strength low alloy), but I doubt it - HSLA steel is more expensive than low carbon steel, and most manufacturers want to take all the credit they can when they use more expensive materials.

I honestly don't know whether anybody is doing postweld heat treat on 4130 or other chromemoly frames. If they're not going to go through PWHT, they're typically welded using ER70S-6 filler (or sometimes austenitic stainless steel, E308 or E309), which gives a ductile joint that resists bead cracking fairly well. ER70S-2 can be used, but it's less ductile and can crack occasionally at the weld.

Of course, once it's welded it all looks about the same.

charles vail

Get something in 4130 steel it has better fatigue resistance than any aluminum. When you are talking about weights you have to remember that the difference between a well built steel bike and a aluminum bike is only a couple of pounds and maybe even less than that. I'd put up with the increased weight any day for all the good properties that steel offers, whether it is high tensile, chrome moly or the latest super strong stainless tubing. You don't need to heat treat any high quality steel bike after welding or silversoldering with lugged joints, since its way stronger than aluminum and stiff enough. Steel bikes have a springy ride quality which is something aluminum can't have, if you want it to not crack! All this talk about frame weight is deceptive since the differences are so insignificant compaired to how much extra fat most riders carry, not to mention tools, water, etc. If you think about the difference when you add the weight of the components and the rider, its something in the order of 1% or less.

Emz

hey thanks, everyone who chipped in with thoughts, facts, etc.

Thank you for educating me. Now I'm tending to want the steel. The point made about any "overage" in rider weight pretty much cancelling out any weight advantage the alu frame might have, is well taken.

I have recently lost 41 lbs., but at this point I guess I am still fatter than the bike as I want to lose at least 20 more!

I'm happy to learn this.
Em

DannoXYZ 

You have to use your "strenght-to-weight" comparison here. Due to the difference in density, you have to triple the ultimate-strength numbers of aluminium for equal-weight samples. So strength-to-weight (actually strength-to-density)....

low-tens: 70kpsi / 0.284 lb/in^3 = 247
4130: 100-130kpsi / 0.284 lb/in^3 = 352-458
6061: 38kpsi / 0.100lb/in^3 = 380
7005: 42kpsi / 0.100lb/in^3 = 420

This relates more closely with real-world frames since most alloy frames aren't that much lighter than steel versions. And their failure rates aren't that different. If the alloy frames are made at 1/3rd the weight of steel, then yes, you can use the lower strength numbers for comparision. But due to the extra material used on alloy frames to bring their weights close to that of steel, their strengths are also tripled as well.

And how many aluminium frames have you snapped? How about some real-world standardized testing to failure under controlled laboratory conditions: EFBe frame-fatigue test.

Take a look the top 3 longest-lasting frames.... 2 aluminium ones and 1 carbon. They survived the entire 200,000 stress-cycles without any problems. That same load applied to other frames snapped them well before that number was even achieved. Guess what the bottom 3 frames were made of? STEEL! They didn't even last half as long as the aluminum ones... Actually probably even worse than that because if they had tested those aluminium frames to failure, they might have lasted 5-8x longer than the steel ones that broke! And the alloy and carbon frames that did not break also weighed significantly less than the steel frames that did break.

dbohemian

I would like to add that with all things as complicated as metallugy and stress, nothing is ever that clear cut.

Any material can make great frames, even Bamboo.

Concerning this cited test though.. Much like tweaking political statistics to reach a pre-concieved conclusion, this particular test has been suspect by many people in the field. Essentially the loads applied to the test were quite a bit higher than would be reached in real life riding. Aluminum frames, being as stiff as they are can actually deflect less and performed better in this test.

If the loads had been more real world appropriate we may have seen better performance from the steel and Titanium entries. As most people can attest to, steel and Titanium have proven themselves to be great performers in day to day use.

I am not debunking Aluminum frames here, just pointing out that this test may not have been the end all of frame testing.

For reference, return rates, that is all returned bicycles to manufacturers are a good indication of actual reliability.

Good steel or Titanium from quality manufacturers average a 1-2% return rate. Aluminum and Carbon typically range around 3-5%. In the early days of Cannondale return rates were above 20%. Poorly designed frames of any material can run far higher than the low end averages here.

Dave Bohm
Bohemian Bicycles

DannoXYZ 

Yeah, construction methods and welding-skill has a lot to do with it as well. In the end, the materials selection in a frame makes a negligible different in the outcome in terms of performance.

Design parameters of weight vs. performance vs. durability vs. cost always creates multi-dimensional graphs. I guess pick any two or three, but you can't have all of them in your favor. In the 10-years I worked in a shop, I've never seen a hi-tens frame break from wear & tear. Sure, they may be crushed by running into a garage or run over by a garbage-truck. They won't help you win any state-championships, but a 10-lb hi-tens frame's pretty much bulletproof.

charles vail

My straight guage 4130 and hi ten mix Centurion should last me a lifetime as should my old Raleigh of all chrome moly. Heck they are already over 25 years old with a bazillion miles on them and I am a lardo at 260 pounds!

Thank you Dave for your comments regarding that test, I have seen it and came to the same conclusion that the test method favored the aluminum frames!

Its no mystery that aluminum has lower fatigue resistance and for a frame to be durable you have to make certain compromises that result in tighter clearances and or extreme stiffness to reduce flex. I prefer steel and lugged construction both for its beauty and strength. I'm not concerned with winning races and if I were I would have a new bike every season and probably several. Instead, I want a bike that I can ride for the rest of my life. Steel allows that with confidence provided it is not neglected.
My bikes: https://www.myspace.com/eccentriccyclistcharlie

NoReg

I'm not totaly convinced bamboo makes a great frame. It's useable between some rather extravagant lugs. But is it seriously better than anything else? Even in a specific niche. It does make great rods, bows, and fenders!

DannoXYZ 

So how does the test favour aluminium frames? If alloy is so weak as you say, artificially increasing the load to hasten failure would have the aluminium frame snap even faster, wouldn't it?

This is your personal preference and that's fine. But doesn't answer objectively the questions proposed by the OP. Let's stick with numbers and figures that everyone agrees on. Engineers know about fatigue-limits and design around it easily. The early alloy frames that had issues were more about manufacturing processes and skill than intrinsic materials properties.

charles vail

I guess I agree with you in this respect,however why is it that many authorities suggest replacing aluminum handlebars and other components that are not commonly worn out (such as wheel rims) before they fatigue crack? I guess I just don't have confidence in aluminums longevity for frames and CF has me even more spooked. Old steel frames made as much as 60 years ago are still servicable today as evidenced by all the restorations being ridden these days and I can't help but wonder if our current crop of aluminum and CF will be around 60 years from now.

aley

Fatigue strength is a complex issue. It's long been accepted in the engineering community that steel has a stress level at which it has an infinite life span, and aluminum does not. Determining this point for a given steel alloy is not particularly difficult. However, when you get into real-world applications, it's not as clear-cut as it is in an engineering textbook, largely because of the difficulty of predicting the stresses that will be placed on a structure.

For example, 2024 aluminum has a yield strength (the point at which the part permanently deforms and does not return to its original shape when the load is removed) of about 42 ksi. If it's cyclically loaded at 40 ksi it would be expected experience fatigue failure at about 1000 cycles; if it's loaded to 30 ksi it would be expected to fail at about 80,000 cycles; 20 ksi and it should fail at about sixty million cycles. In comparison, hot-rolled 1020 steel has a yield strength of about 48 ksi; if it's loaded at 40 ksi it should last about 10,000 cycles, at 30 ksi it should last about a million cycles; and at about 28 ksi it should never fail in fatigue. What's important to remember is that these are statistical probabilities; any given test piece, even under carefully controlled laboratory conditions, can behave significantly differently.

The load on a bike frame is dependent on the rider's weight and riding style, which are essentially impossible for a framebuilder to predict. If a heavy rider puts a 20 ksi load on a particular part of a frame by hopping a curb, then one might argue that a steel frame will withstand hopping an infinite number of curbs, while an aluminum frame will fail after hopping "only" eighty million or so curbs.

Of course, if routine, foreseeable riding conditions cause that kind of load on a frame, then the frame won't hold up long in the real world. If a frame is designed such that hopping a curb loads it to 20 ksi, then when the rider fails to see a large pothole and hits it at full speed without unweighting the frame it's at some significant danger of bending the frame. Since bent frames naturally don't result in happy customers, framebuilders quite reasonably build them so that normal riding keeps the loads at a lighter level. This pushes us further out in the fatigue range for any material; the chart I have handy for 2024 aluminum stops at a billion (10^9) cycles and about 16 ksil. I would argue that it's unlikely that most bike frames experience a billion or more full-reversing load cycles even at this level of stress, so it's unlikely that they will ever fail due to fatigue.

The point of this long-winded explanation is that fatigue probably shouldn't be a big concern in the mind of someone looking for a frame. If you like the way a frame looks, if it was built by a reasonably skilled framebuilder, and if you like the way it rides, it's probably a good frame for you.

charles vail

I wonder why frame manufacturers put weight limits on their bikes? I am 260 and really liked the looks of the Swift folder in aluminum, both for the price and availability but it seems I am too heavy to ride this and have to buy a steel one for 33% more $......and wait for a few months to get it. I suppose these limits are put there because liability lawyers and insurance companies insist but it makes me wonder! The carbon fiber limits put on by various companies are also many times under 200 pounds,so I suppose,I'll stick to steel and multi spoke wheels,with practical width tires and accept the fact that I will go 1-2 mph slower.

DannoXYZ 

Well, I doubt the weight-difference would result in any actual speed-differences on the road anyway. It really only makes a difference in acceleration (sprints) or going up hills. Please refer back to the OP's original requirements:

He mentions only weight as his goals, nothing about speed or durability. We're even getting several comparisons mixed up:

1. aluminium vs. steel frame of equal-strength = 1-2 lbs lighter in aluminium
2. aluminium vs. steel frame of equal-weight = alloy much stronger
3. aluminium vs. steel frame of greater-strength = 2-3 lbs lighter in aluminium

I'm talking about #1 & 2 and you're talking about #3.

dbohemian

Companies put weight limits on lighter weight aluminum and carbon components not because of insurance companies and lawyers but because they are not as durable in actual use for heavy weight riders as the steel one.

Engineering as ALEY pointed out is a complicated subject and there is always a give and take. Light weight in any material equals a reduction in durability and since many carbon and Aluminum bicycles are designed to take advantage of their reduction in density they also reduce the ultimate strength and longevity.

I see a lot of big people riding lightweight components and in my view it is just an outright mistake. When you are lugging around the kind of weight many of us are it is not wise to use the light component. In addition if the light component was equal in performance it would be one thing but many of these items are much more flexible for instance and can reduce ones enjoyment. Let alone a failure in a carbon MTB handlebar for instance can lead to serious injury.

DannoXYZ. Your recent conclusions about Steel VS. Aluminum are just plain wrong. I don't want to insult you, but as I have said before, generalizations like that nearly always are wrong. I find material science to be a fascinating subject. A thorough study (and I am not talking the non-factual crapola that gets thrown around on internet lists) will sadly open up more questions for you but it will be fun.

Here is an article written by Scot Nicol of IBIS fame who knows a heck of a lot about material science.

https://www.bohemianbicycles.com/materials%20science.htm

It is very simplified of course (It is not a 500+ page engineering text) but it is great for those interested in materials science and is still entire pertinent today.

Dave Bohm
Bohemian Bicycles

DannoXYZ 

I'm not sure which conclusions you don't agree with, if you'd point them out, I might have more specifics to support my assertions. My main vague generalizations are on the opposite extreme to balance out Charles's view that "steel is always better" and I've tried to point out that the actual issues that contribute to the differences between steel vs. alloy frames are mainly outside of the materials' properties themselves.

A major difference is simply design. Comparing fat-tube alloy frames vs. small-tube steel frames isn't possible simply because you've got a cartesian product of four combinations: 2 materials X 2 designs. Looking at just two of the cross-products leaves out the design-parameters of tubing-size from the comparison. That can have a bigger impact on the results than the actual materials used. A lot of Charles's arguments are valid IF and only if you made alloy tubing of exactly the same dimensions as steel. And if you did so, you'd end up with the wet-noodle frames like the Vitus979 or the disastrous Peugeot Comete that was recalled.

Anyway, thanks for the reference to Scot Nicol's post. This one quote from that article pretty much sums up why I'm talking about something completely different than Charles:

This sums up the results of the EFBe tests. Comparing this kind of aluminium tubing vs. the lightest steel frames possible simply isn't fair really. Here's a table of properties similar to that listed in Nicol's article gleaned from MatWeb:



It's not just about the density (weight) of a material that matters, but in combination with other properties like yield & ultimate strengths or stiffness. If you compare strength-to-weight of aluminium vs. steel vs. titanium, they're very similar. Thus matching real-world example where frames of these three materials are very similar in weight. You're not gonna find an aluminium frame that weighs 1/3rd that of steel or a titanium one that's only 1/2. Simply because the strength-to-weight of these materials are so similar, by the time you design frames of similar strengths, they're gona be similar in weight as well.

What does look promising is the other materials like the new stainless stuff or beryllium. These have significantly higher strenght-to-weight ratios which really will allow you to build a frame that's 1/2 teh weight for the same strength. But again, it's not the native materials properties that's the cause of most failures, but rather that of design and manufacturing.

dbohemian

Hi Danno,

I agree much more with your recent post. The thing we were leaving out of our discussion was the geometric considerations of tubing (larger dimensional tubing) which you are correct, can have a much larger effect on design properties than just the material.

Also consider, as you have already brought up that we are not talking about your grand-dads steel here. For quite a bit of time we have had steel material like 853 and OX Platinum that skirt the 150ksi range in yield strength and there are certainly materials out there like the Carpenter Technologies steel in the new 953 that pushes 200ksi (and believe it or not there are super-steels that push a lot higher for a yield strength).

Using these newer metal materials one can design frames differently than those of old. Steel is currently the fastest advancing metal material in existence.

But it is kind of hard to argue about lightweight, long lasting aluminum frames that will cost a 10th of what these super steels cost (i.e the new 953 sets wholesale at $875.00)

I think we have come to a consensus on this with a lot of good information disseminated.

charles vail

Doesn't this super steel suffer from beer can thin guages that can dent too easily? Whats wrong with a heavier guage that won't dent so easy.....not to mention possibly rusting through and will have sufficient strength for any rider and only suffer an additional 2 pounds of frame weight? All the emphasis on super lightweight and high strength amount to very small performance gains IMHO! For racers.......it could make the difference......for me I would prefer a robust, utilitarian machine that can be ridden for a lifetime, day in and day out and one that can be repaired easily and not cost too much. Even if I were to purchase a custom work of art, I would want reliability and durability over every other feature since the differences are really not all that great. One other point, isn't it easier to build a frame from non heat treated 4130 steels of a slightly heavier guage? That super strong stuff is so springy!

dbohemian

I agree with you 100%. Sacrificing reliability for any other factor on a non-race machine is just not worth it. At least in concept, the new breed of high-strength steel should allow one to make bicycles that were just as reliable, dent resistant and such of the frames of old but weigh significantly less. Sometimes the hurdle to this is that the tubing companies don't always draw the tubes in a spec that will allow this. Light sells and constantly there has been a push to lighten up with all the corresponding draw-backs you mentioned. It isn't all bad news though. There are tube sets from True Temper, Columbus (Heavy Metal set) that use the new materials but are drawn in a thicker wall, giving all the benefits you mentioned.

Building in different steels isn't all that much different. Yes, in a production environment where frames often have to be cold set to a significant degree, or torch control (TIG or Braze) is poor or inconsistant. non-heat treated steel is easier to deal with and more resistant to production abuse but in a custom environment like mine, any deviation that large would not be tolerated and would be scraped. The same procedures need to take place to make a quality bike frame, be it standard 4130 or something much more exotic.

DannoXYZ 

David, how much do you charge to replace the top or down-tube on a steel frame? Including re-paint or re-chrome?

Emz

hi guys, as the original poster of this thread, I wanted to say thanks. This makes for some very interesting reading and shines alot of light on things for me.

For the moment, I have decided to stick with my heavy-ish old steel-framed Trek, as my own body is (still) overweight, and I came to the realization that asking my bike to be "better" than me is a kind of hypocrisy. (at least for me, where I'm at with this whole thing)
EM