Titanium Frame?

[TlfT]

I was wondering if there was some consensus on avoiding Ti for an ebike build.

I weigh 90kgs, and have been standing and smashing on bikes for ~20 years. I am looking at an ORA made hardtail mtb frame. I was going to run it with a 4130 fork and use PAS to power a 52 chainring with an 11/36 cassette. Super commuter road use.

Please share any thoughts. Thank You

 

[BalorNG]

I think this is called 'false dilemma fallacy'.
'Buttery smooth' is a propery of design, not material choice, and it usually comes with degradation in handling unless you can shape the material (further design choice) in a way that would be extremely hard with Ti.
Ti is cool for bling value, but frankly an overpriced luxury item - there is little to be gained by going ti, really, carbon does everything better and is actually cheaper - unless, of course, the high price bracket is something to be desired to impress others.

 

[Chalo]

really, carbon does everything better

Except last. It is only plastic after all. And it only withstands the forces that have been anticipated and built for. When you start doing things the designers didn't have in mind (like adding a motor and mounting a battery), isotropic materials win.

Ti bikes often have straight round main tubes, which helps us attach things securely to them.

Every quality that makes titanium a better material for e-bikes than plastic is even more so for steel, though. Once you strap on 20 or more pounds of electrical gear, you've quickly negated any weight savings between a "heavy" five pound frame and a "light" three pound frame, so you might as well use steel. It's tougher, more fault tolerant, more repairable and modifiable, and simply better for e-bike conversions.

BalorNG is absolutely correct to note that ride qualities come primarily from design and not material. If you want a smoother riding bike, get a frame with long chainstays and slack frame angles. Rivendell Appaloosa is an example of a bike that will ride smoother than any non-custom Ti bike due solely to its shape.

 

[BalorNG]

really, carbon does everything better

Except last. It is only plastic after all. And it only withstands the forces that have been anticipated and built for. When you start doing things the designers didn't have in mind (like adding a motor and mounting a battery), isotropic materials win.

Ti bikes often have straight round main tubes, which helps us attach things securely to them.

Every quality that makes titanium a better material for e-bikes than plastic is even more so for steel, though. Once you strap on 20 or more pounds of electrical gear, you've quickly negated any weight savings between a "heavy" five pound frame and a "light" three pound frame, so you might as well use steel. It's tougher, more fault tolerant, more repairable and modifiable, and simply better for e-bike conversions.

Well, 'it does everything better if you are inclined to use exotic materials for weight savings' If not, than of course mild steel tubing has best cost/benefit.

And if you are building your own frame, using, say, off the shelf carbon tubes (which I'm doing right now) - you can have your stright tubes and should know what to expect from them.
For instance, I know they do not have 45deg layers so I'll add them were applicable, and have 0deg layers so have good resistance to crushing.

Carbon is actually pretty easily repairable, if you do not care about aestetics at least... but than you can use carbon to repair a steel/ti frame, too Harder with aluminium, if still possible.

Currently I'm thinking to make sandwich tubes (read about that from research artcles - fashinating stuff) using 3d printed cores (carbon fiber petg), off the shelf tubing as interior layer and carbon sleeve as outer layer.
This way you can shape the resulting 'tube' somewhat where needed, and get result that is both stiff, strong and light...

 

[BalorNG]

Once you strap on 20 or more pounds of electrical gear, you've quickly negated any weight savings between a "heavy" five pound frame and a "light" three pound frame, so you might as well use steel.

Yea, it makes sense when your bike is not a standard 'diamond frame bike' that is stiff and strong with little material. (Actually too stiff perhaps ).

When the difference is between 30 pounds of frame or 15 pounds of frame, going with different materials starts getting highly attractive.

 

[TlfT]

Right on, Thanks guys

My experience is Ti offers a smoother ride and more organic pedalling feel than 4130. I owned the Salsa Collosal in both 4130 and Ti. Pedaling the Ti kind of felt like pushing into a spring, like I was hammering into the rear triangle as opposed to just the BB. That thing floated ... but I cracked the drive side stay.

I got screaming deals on both framesets, warranting and selling the replacement Ti netted me $550 profit and a leftover enve fork.

..

If you said Carbon is superior to Aluminum in every way I would agree, but carbon doesn't really flex across the frame as much as it dampens vibrations. I personally feel like carbon does the same thing as low tire pressure whereas steel or ti generally offers more significant frame flex over uneven or undulating terrain.

The price of the Ti frame I am considering is certainly right. I am just wondering if the change from a road to mountain spec frame will improve it's longevity or if the added stresses of e-conversion will overwhelm it. Fwiw, the Salsa I cracked and the mtb frame I am considering were both manufactured by ORA.

 

[BalorNG]

Just FYI, some fully suspension bikes use carbon elements instead of pivots - some softtails, and lauf leaf spring comes to mind.
Carbon serves just great *when designed* for that.
But you truly cannot know whether the bike you'll buy will actually achive that unless you ride it, so asking on the forum is futile, you need to ride it and see for yourself... preferably in blind test, but that is pretty hard

 

[TlfT]

Everything I see on Google says those Lauf springs are fiberglass.

I don't think carbon has that kind of flex. That's the beauty, light and stiff.

 

[Bigwheel]

You neglect to say what type of motor system you will be using? But in reality it doesn't probably matter because if you have had good experience with Ti in the past you should not have any issues with making a standard type diamond frame one into what you want. Should certainly be strong enough.

It does seem that most prefer to have as integrated a look as possible these days in regards to having the battery as inconspicuous as possible and hoses and wires hidden. That will be difficult to achieve if that is a factor. Here is an example of what you might expect to achieve?

 

[BalorNG]

Everything I see on Google says those Lauf springs are fiberglass.

I don't think carbon has that kind of flex. That's the beauty, light and stiff.

Good point. Fiberglass is indeed a better option for truly *high* flex like leaf springs, but carbon can still serve as a spring in effect depending on how you construct it - just google 'carbon composite spring', there would be a ton of hits. Again, everything has to do with design, you can design an aluminium frame to be very compliant (but it will not serve for very long...) titanium extremely stiff (very easy actually, just overbuilt it ), but a combination of both tough, light, flexy where approriate, stiff where appropriate comes from *design* and can be achieved by careful shaping of the material, butted tubes, varying cross section and shapes of the 'tubes', etc. This is truly 'high art' and if you design your bike from scratch, using hydroformed tubes for instance will be MUCH more expencive than making your own carbon frame using 3d printed mandrels (provided you know what you are doing, of course).
This is really interesting subject, but again, unless you REALLY know what you are doing, just using steel (bike-specific cro-mo tubesets) might be the best option.

 

[sleepy_tired]

On a technical level Fiberglass can easily be stronger then Carbon fiber composite. Most Fiberglass that gets used is E-glass, which is a inexpensive form originally developed for use in the electronics industry.

Higher 'engineering' grades of Fiberglass, like S-glass, is stronger and more robust then carbon fiber. (edit: well many carbon fiber things you run into. Higher grades of carbon fiber won't get beaten by S-glass)

What makes carbon fiber special, and why it gets used in things like race cars and bicycles, is that it is incredibly stiff. Carbon fiber can be very very thin and still be stiff for the application. So they can make it just barely strong enough while still providing very good stiffness and thus maximize the weight savings.

This thinness is both a curse and blessing when it comes to bicycles. Because it's so labor intensive and requires lay-up of multiple layers it is very easy to get wrong and very difficult to make things consistently at large scale.

Bicycle manufacturers typically do a poor job of working with carbon fiber compared to "real industries" like car or airplane manufacturing. They use the cheapest materials and cheapest labor and produce a lot of very inconsistent bikes. Issues like squeaky bottom brackets or color shift "shimmy" on frames are indications of far greater problems under the surface. They get away with it because customers can't tell good from bad and with bicycles it doesn't matter that much anyways. There just isn't much going on with a bicycle.

Were as with aluminum they depend on great big factories to crank out frames at a massive level using industrial processes and automation. Which produces very consistent results. They make frames for dozens of bicycle companies under contract and use the same machinery and processes that is used for any other industry that needs high quality tubing. This produces extremely consistent results. If there is a flaw in the design or manufacturing it's going to affect hundreds of people, not a single person. So problems get solved.

Which means that you don't have to worry about, say, clamping a torque arm to a tube and finding a thin area and cracking the shit out of the frame. Sure if they design the carbon frame for mounting things or bouncing off of rocks it can be plenty strong and resist a lot of force. But if it is not something the designer anticipated then it starts boiling down to how lucky you are that day.