Carbon vs aluminum

[OldGoatMTB]

Well, back when most frames were made of steel some purists would complain about the new aluminum frames feeling harsh, so what goes around comes around. Of course there may have been some validity since most of them had rigid forks and frames back then.

 

[GrandPaBrogan]

Well, back when most frames were made of steel some purists would complain about the new aluminum frames feeling harsh, so what goes around comes around. Of course there may have been some validity since most of them had rigid forks and frames back then.

Yes, I remember that!

The steel (chromoly) frames of old had a springy flex that gave them a lively sprinty feel. Who knows whether or not this actually contributed to a faster sprint... but it felt real good. The flex seemed to bode well with the way our body moves organically.

When the first aluminium frames came out, they were straight wall tubing and stiff by comparison. Early designs didn't bother with additional production costs of butted alloy tubes seeing as they were already comparatively light. In time, double butted aluminium tubes came of age and restored some flex. In the advent of fluid-forming process, aluminium tubes can now be formed with complex cross sections that can vary in shape or size and wall thickness throughout the tube length, where engineers can incorporate stiffness or flex movement where desired. Provided their interpretation is correct, the aluminium frame yielded favourable flexing.

Carbon frames can of course be made rigid or flexy these days as well... by altering the shape, size, wall thickness and fibre orientation of the tubes. The R&D and applied engineering to get this done to ergonomic perfection is eye watering... especially when the likes of McLaren and Specialized get into bed...

 

[GrandPaBrogan]

For me, aluminium is easy to live with; it just isn't any trouble. It's about a 500gm hit in weight. It doesn't need other materials for joints or threads. For ebikes it is a much better for heat transfer. The only damaged frames I've seen on trail, were cracks, fractures, holes in cf frames. Never from casing a jump, stuff like falling on rock; once a bike leaning against a tree fell onto a rock and cracked the down tube. One not so long ago was a failure in the head tube of a high end specialized - just out of warranty. Apparently it wasn't from any impact; the dude was told by a high end boat builder / engineer that he could repair it but he wouldn't use it mountain biking. Specialized told him it couldn't be repaired. Maybe it's luck - aren't all cf frames hand made like the old days of fibre glassing? For sure though, if I was offered a really good deal, I'd probably take a cf bike; generally aluminium is a fair bit cheaper too. I am an inverted snob - generally function over form.

Same here... as far as off-road bikes are concerned, I think that aluminium has more practical advantages over carbon. But as always, that's a subjective thing because desired advantages are different from person to person.

Yes CF frames are hand made - but not quite like the old days of fibreglassing... in fact, far from it. I can share these two pics below, it's 13 years old anyway and there shouldn't be distinguishing features in there as to what bike it is. In this instance, specific types of ‘dry to the touch’ carbon cloth that’s pre-impregnated with resin (so there's no loose fibres floating around in the air when sliced and handled)... are cut into patterns by computer and are layed-up by hand with an inflatable bladder in the middle (like making sushi). That's where the engineering comes in (the fibre directions and sequence of layers) and sometimes a carbon 'woven sock' is used in combination with carbon sheets. Then they are placed inside a metal mould... bladders inflated... then baked in a pressurised autoclave. Depending on the design (retail cost derived), a cheaper carbon frame can be glued together afterwards from various moulded members - OR can pop-out of the oven in one-piece if need be, but the cost of the corresponding metal mould would be murderous. The number of moulds and the autoclave curing time is the manufacturing bottle-neck when it comes to mass-production. You can have hundreds of workers laying-up and as many again working in post-moulded finishing, but if you only have ONE mould then that'll just yield 2 to 4 frames per day, depending. A word about CF... don't inhale dust or fine shavings - they don't break down or decompose. You get that in your lungs, it'll stay there for good. The cutting, filing, sanding, finishing section of a CF factory is the most hazardous department and the workers in there wear PPE like it's Chernobyl.

In contrast, "tubular" aluminium frames have no outstanding production bottle necks and so if you want to produce a hundred frames a day, the factory just has to increase staff numbers (easier said than done I know, but that what they do to meet production order deadlines). A company that produces a hundred-thousand aluminium frames per year is a small player in Taiwan or in China.

This is why tubular carbon frames are so expensive in comparison to aluminium. Now here's the crazy thing about CF frames - which I believe contributes unnecessarily to it's high production cost. Carbon fibre is more suitable to monocoque construction... that's the main inherent advantage of this material. Traditional bike frames on the other hand originated from steel tube construction from the 1920s. Making a tubular CF bike frame these days is like building an F1 car, but using carbon to form tubular roll cages instead - similar to 1960's F1 structural designs. Nothing wrong with that intrinsically, but it involves tedious serpentine designs that requires complex tooling and sometimes uses even more material.

CF material is more suited for one-piece monocoque frame designs like the one shown below... which is specifically intended for Ironman or Triathlon or Time Trial (non-UCI race applications).

There are two reasons why monocoque bikes aren't mainstream (and may never be). One is because a considerable proportion of cyclists think monocoques are ugly (not this one specifically but in general)... although, I for one think they're gorgeous for this application. That, and not everyone wants to be seen riding an ostentatious 'rocket ship.' Second is monocoque frames have been banned by the UCI in their sanctioned events including the Olympics. Many reasons float around as to why, but I believe it has something to do with preserving the 'traditional double triangular" side view shape of the bicycle. This triangular tubular image it would seem, has made such a deep societal mark in people's psyche that it has been deemed worth protecting... technology be damned.

.

 

[Rusty]

I have broken aluminum alloy, carbon steel and carbon fibre - each has its benefits and its negatives. Personally if I can't have carbon steel I prefer carbon fibre as aluminum alloy always feels harsh to me - also noisier.

 

[GrandPaBrogan]

I have broken aluminum alloy, carbon steel and carbon fibre - each has its benefits and its negatives. Personally if I can't have carbon steel I prefer carbon fibre as aluminum alloy always feels harsh to me - also noisier. View attachment 32137 View attachment 32136

Far out, Rusty... you gotta cut down on the RedBull energy drinks mate!

 

[urastus]

Same here... as far as off-road bikes are concerned, I think that aluminium has more practical advantages over carbon. But as always, that's a subjective thing because necessary advantages are different from person to person.

Yes CF frames are hand made - but not quite like the old days of fibreglassing... in fact, far from it. I can share these two pics below, it's 13 years old anyway and there shouldn't be distinguishing features in there as to what bike it is. In this instance, specific types of carbon sheets (pre-impregnated with resin so there's no loose fibres floating around in the air when handled) are cut by computer and is layed-up by hand with an inflatable bladder in the middle. That's where the engineering comes in (the fibre directions and sequence of layers) and in certain portions a carbon 'woven sock' is used in combination with carbon sheets. Then they are placed inside a metal mould... bladders inflated... then baked in a pressurised autoclave. Depending on the design (retail cost derived), a cheaper carbon frame can be glued together afterwards from various moulded members - OR can pop-out of the oven in one-piece if need be, but the cost of the corresponding metal mould would be murderous. The number of moulds and the autoclave curing time is the manufacturing bottle-neck when it comes to mass-production. You can have hundreds of workers laying-up and as many again working in post-moulded finishing, but if you only have ONE mould then that'll just yield 2 to 4 frames per day, depending. A word about CF... don't inhale dust or fine shavings - they don't break down or decompose. You get that in your lungs, it'll stay there for good. The cutting, filing, sanding, finishing section of a CF factory is the most hazardous department and the workers in there wear PPE like it's Chernobyl.

In contrast, "tubular" aluminium frames have no outstanding production bottle necks and so if you want to produce a hundred frames a day, the factory just has to increase staff numbers (easier said than done I know, but that what they do to meet production order deadlines). A company that produces a hundred-thousand aluminium frames per year is a small player in Taiwan or in China.



You can understand, why tubular carbon frames are so expensive. Now here's the crazy thing about CF frames - which I believe contributes unnecessarily to it's high production cost. Carbon fibre is more suitable to monocoque construction... that's the main inherent advantage of this material. Traditional bike frames on the other hand originated from tubular construction since the 1920s. Making a tubular CF bike frame these days is like building an F1 car using carbon tubular roll cages similar to 1960's F1 structural designs. Nothing wrong with that intrinsically, but it involves serpentine designs that requires complex tooling and sometimes uses even more material.

CF material is more suited for one-piece monocoque frame designs like the one shown below... which is specifically intended for Ironman or Triathlon or Time Trial (non-UCI race applications).

There are two reasons why monocoque bikes aren't mainstream (and may never be). One is because a considerable proportion of cyclists think monocoques are ugly (not this one specifically but in general)... although, I for one think they're gorgeous for this application. That, and not everyone wants to be seen riding an ostentatious 'rocket ship.' Second is monocoque frames have been banned by the UCI in their sanctioned events including the Olympics. Many reasons float around as to why, but I believe it has something to do with preserving the 'traditional double triangular" side view shape of the bicycle. This triangular bicycle image it would seem, has made such a deep mark in people's and society's psyche that it has been deemed worth protecting... technology be damned.
.

Awesome information GPB. If a company made such a bike - built for maximum strength and function - and I could afford it, I'd buy it. I think Pole bikes are aluminium monocoque and have an awesome reputation. They may be the company to do this with cf? Out of my price range though. Another interesting thing with pole bikes is that they bond the frame parts together with glue! Imagine - that would be a way to repair aluminium frames. Glue a section of aluminium over the damaged section - the glue would hopefully not create a weakness as welding would.

 

[I want my 2 Dollars!]

I coat my carbon and alloy mountain bikes with dirt and mud..... So far no breakage in 30 years of riding.... Not counting the flesh and blood parts and the occasional shock bolt (long ago).

 

[Rusty]

Far out, Rusty... you gotta cut down on the RedBull energy drinks mate!

Never touch any of those poisons.
The carbon MTB bars I was playing catch-up on an easy trail after dropping my glasses and snagged a fallen tree with my left shoulder - nosed in to the wall then fired off the track on the right - tree trunk was hit about where my brake lever was. Was about 20km into the ride and rode that repaired set-up for 60km with a fractured wrist/thumb, damaged shoulder and a couple other injuries.
The Renthal MX bars were at my last Pro race. Rear stepped out and clipped the bank heading into an uphill corner/jump - which I went off facing the opposite direction and 30 something shocked racers. Actually my worst wreck on anything and I only got the bars back from my sponsor - ripped the forks clean off the bike.
With all the broken frames & swing-arms, collapsed wheels, broken hubs and so much more (crashing after the fact and not damaged due to a crash) my sponsors always said, if it holds up under Rusty it will hold up for anyone.

 

[GrandPaBrogan]

Awesome information GPB. If a company made such a bike - built for maximum strength and function - and I could afford it, I'd buy it. I think Pole bikes are aluminium monocoque and have an awesome reputation. They may be the company to do this with cf? Out of my price range though. Another interesting thing with pole bikes is that they bond the frame parts together with glue! Imagine - that would be a way to repair aluminium frames. Glue a section of aluminium over the damaged section - the glue would hopefully not create a weakness as welding would.

The rear suspension design of the Pole Bikes from Finland is very interesting. I’m a fan of short chainstays too! They look very well made and designed.

The wings on commercial airliners are glued together too. The key is to have a large enough surface area for the glue to bond... and for the special glue to have sympathetic characteristics as aluminium itself so that it can allow the metal to minutely bend, expand, and contract accordingly under load and temperature changes. If done correctly, the glue construction should be better than welding.