ALLOY OR STEEL ?? pro`s and cons of each

[justlooking]

what is you preference on the bikes .. do you like alloy or do you like steel ?? what is you reason for the sort that you like ??
im just trying to work out the pro`s and cons on each

i have heard that some people have had trouble with alloy bike frames, but steel ones seem to be heavy ,,

 

[melodious]

The battery pack/motor combination added to the bike will add significantly more weight that far outweighs what frame material you choose. Steel is real.

 

[fizzit]

Yeah, a lot of people on this forum prefer steel frames because (depending on the alloy) they are generally less likely to stress fracture, can flex more and soak up more energy from bumps, and can be welded more easily. However, it can be very difficult to find a high quality pre-made steel frame if you are looking to go full suspension.

 

[spinningmagnets]

The one concession I will make to an aluminum frame is that, if you already have an aluminum framed bike that you like, you could add a kit that is a mid-drive or a rear hub as long as it is a low-power set-up, and you use two torque-arms.

If you use a high-powered kit, or for some reason you want a front hub, in my personal opinion...steel is the only option worth consideration. If you don't already have a bike for the electrification project, I highly recommend you only look for a steel frame.

Not all steel is the same. The Yuba frame is advertised as a high-ten (high tensile) steel, and the forks are advertised as cromo steel (chromium and molybdenum). which is the most desirable steel. A cromo frame will flex or bend instead of developing cracks (at the common power levels found here). This pic is what aluminum does when it is fatigued, it cracks instead of flexing or bending:

 

[brumbrum]

As said above, steel will bend before breaking, aluminium just snaps without warning. It is also nice to have steel when trying to fit thehub motor disc brake and freewheel in the rear axle space as you can bend the frame outwards quite a lot. You can get nice low price steel frames and some with horizontal rear dropouts so you do not need to worry about motors twisting out or having to use torque arms. 'One one inbred' frames are a very good solution and relatively cheap in the UK for what i have mentioned. I have run both a 16" and 20". In fact i have the 20" frame on ebay uk at present. i also have a bespoke made to measure waterproof frame bag that fits the entire inside of the same frame.

Andrew

 

[fizzit]

As said above, steel will bend before breaking, aluminium just snaps without warning.

This seems to get repeated around here a lot, but it is incorrect. Steel and aluminum alloys will crack, flex, or bend under stress depending on all kind of conditions. I obviously am not making things any clearer, but I think it's definitely worth noting. I have ridden several hundred miles on a severely bent aluminum frame before getting a new one.

 

[liveforphysics]

Aluminium or carbon makes temporary bikes.

Steel makes a lifetime bike.

 

[neptronix]

^--agreed.
As long as you keep the rust off anyway. :lol:

Chromoly does seems a bit more rust resistant though, so while a chinese steel bike will rust just sitting there on the racks at walmart, i've had oldschool treks with pits in them that never seemed to grow.

As far as ride quality goes, steel will win every time, aluminum is fantastic at transmitting vibration, which is exactly what you don't want!.. chromoly can come within very close weight of aluminum too. The main reason aluminum is used is because it's cheaper. But i don't trust it, it has a finite lifespan and when it fails, it's not pretty.

The things i'd do for a decent chromoly dual suspension bike..

 

[fizzit]

Sorry, but this stuff about aluminum frames having a finite lifespan just isn't true. If the frame was designed by anyone who knows the material and it is not crashed repeatedly, it will last much longer than it's owner. Same with a chromo bike, or a carbon one for that matter. Aluminum B-52 bombers that were made in 1962 are still being used and are scheduled to stay in service until at least 2040.

edit: An inexpensive chromo full suspension frame would definitely be awesome.

 

[melodious]

This has been linked before not too long ago. But it is a damn fine article. I learned a lot from reading it.

http://www.ibiscycles.com/support/technical_articles/metallurgy_for_cyclists/

 

[Punx0r]

There is some truth to the different typical failure modes of steel and aluminium. Aluminium is more susceptible to fatigue - it will eventually crack no matter how little it is flexed. Whereas steel will not crack, no matter how many times it is flexed, as long as the loading is sufficiently small (its fatigue limit).

See here for a randomly selected illustration: http://en.wikipedia.org/wiki/File:S-N_curves.PNG

There's a reason why springs are typically made of steel, and why aluminium airframes are covered in strain gauges and have a finite service life.

We muddy the waters, though by using bicycle frames in ways they were not intended. Steel made just be better at taking this abuse.

 

[spinningmagnets]

Aluminum B-52 bombers that were made in 1962 are still being used and are scheduled to stay in service until at least 2040.

Even a B-52 is inspected regularly, and sections with stress cracks have to be replaced. Aloha flight 243 had stress cracks and the "out of spec" aluminum sections were not replaced as soon as they should have been. The plane was able to land safely, although one flight attendant disappeared. The cost of inspections and parts replacement is made up by fuel savings. If the plane was made of Chromoly, I think it couldn't carry as many passengers, and it would burn more fuel. I could be wrong, but for bikes, I still feel Chromoly is a better choice.

 

[fizzit]

I agree that a well made chromoly frame is better for e-bikes, where weight doesn't matter as much. It just seems that some people on here have the idea that if your frame is aluminum, you'll be riding down the street one day and without warning your bicycle will become two unicycles.

Oh and if a jet plane were made of steel, it could not even carry itself

 

[John in CR]

Your bike has a motor now, so the few pounds that AL could possibly save is irrelevant, and that's assuming you have the ability to properly heat treat the AL alloy to get it up to full strength for there to be any weight savings. It doesn't consider the parts which must be reinforced by steel, or the far higher risk of catastrophic failure with AL. Thing about how poor a steel design would have to be before you start seeing failures in headsets, swing arms, handlebars, etc.

 

[amberwolf]

It just seems that some people on here have the idea that if your frame is aluminum, you'll be riding down the street one day and without warning your bicycle will become two unicycles.

http://www.endless-sphere.com/forums/viewtopic.php?f=1&t=42401
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=13450
http://www.endless-sphere.com/forums/viewtopic.php?f=7&t=23470
( http://www.pinkbike.com/photo/5947707/ )
but see http://www.pinkbike.com/photo/5595646 as cause :wink:


then again, steel breakstoo
http://www.endless-sphere.com/forums/viewtopic.php?p=610957#p610957

 

[fizzit]

No offense Amberwolf, but one of your links is a cheap full suspension costco bike, one of them was a $25 ebay handlebar, and the other one hit a concrete wall in midair with a rider on it, and broke at the weld. Breaking at the weld indicates that it's a workmanship issue, which is just as likely on a steel bike. I just googled "steel frame crack" and found about 1,600,000 Results in .41 seconds

If you buy cheap crap, it will break, and if you abuse your stuff, it'll break.
Well-designed aluminum frames are lighter and stronger than Chromo and will last as long as any other frame. Like PunX0r said, if you are constantly abusing your frame in ways that it was not designed for, a steel frame may take the abuse better.

With that said, my aluminum bike frames are definitely not used as intended but they have lasted longer than any other parts of the bike

I had a used 1999 raleigh made of 7005 aluminum, a fairly hard alloy. I hit the side of a car at 20mph and it looked like this:

After that, I rode the bike for two months before getting a new one. Note also that I drilled holes in this frame to mount the motor reduction on it.

 

[neptronix]

When researching for MTB frames for my first ebike conversion, i found that many MTB frames had problems with cracking and such. Heard folks on MTBR talking about old aluminum frames being dangerous, due to their finite life spans.

Now don't get me wrong, there are some REALLY good aluminum bikes out there which are overbuilt to the point where they could last well over 10-20 years, but those are far and few as low weight is the name of the game in recreational bicycle design - dozen year durability is rarely a design goal for a mountain bike.

What if they sold a steel dual suspension MTB? maybe it'd last forever and you'd not buy another one after it breaks from 3 seasons of riding :lol:

High end road bikes aren't often designed for durability either.

http://www.bustedcarbon.com/

If you thought aluminum is bad, look at this gallery of horror!!

 

[Chalo]

The bikes I have had longest (20 years and more) and which I have ridden farthest are aluminum. But I have also cracked a few aluminum bikes.

If I had a choice between a well designed six-pound frame made from steel and a well designed six-pound frame made from aluminum, I'd take the aluminum one for almost any application. Pound for pound, it's much stronger and stiffer when used appropriately. But aluminum and steel frames don't usually weigh anything like the same for any given style, size, and quality level. So that muddies the waters a bit. A six pound steel frame is probably a better choice for an e-bike than a three-and-a-half pound aluminum frame.

Steel frames are more repairable (though this advantage is grossly overrated for most people), and a steel frame can have mounting points attached by welding or brazing. Usually aluminum frames can't be welded onto without weakening them severely.

These days, aluminum frames tend to be made with all sorts of goofy hydroformed shapes, which serves a marketing purpose but not a valuable engineering purpose. Steel bikes are more often made from straight round tubing, which greatly simplifies clamping or strapping things on.

For at least a couple of reasons, steel forks are generally a much better idea than aluminum forks. This is especially so when they are fitted with flatted axle front hub motors. Forks have fixed diameter steer tubes, so for any given frame, it isn't possible to use a larger steer tube size to exploit aluminum's advantages. Even good quality structural aluminum is not as ductile as comparable steel, so crashes can result in more dramatic and dangerous fork failures.

The cast aluminum used in suspension fork sliders is not comparable to the wrought aluminum used in frames! The cast stuff is much weaker and more brittle. The fact that suspension fork tips are easy to break is a good reason to avoid suspension forks, not to avoid aluminum frames.

I say, if you can find an inexpensive aluminum frame that doesn't use curved, tapered, ovalized, squished, or hydroformed tubing, has nice thick dropouts, and isn't too light, it would be a fine basis for an e-bike. That just isn't most aluminum frames available today.

It's probably easiest to get a set of features appropriate for an e-bike conversion if you select among inexpensive to moderately priced steel framed bikes. But that's no reason to rule out an appropriate aluminum frame.