Titanium always a little flexy?

[bicycletricycle]

Over the years I have really come to enjoy a nice modern stiff steel bicycle. It started with an IF built Tournesol with double oversized tubes and now I have two Chapmans built similarly. I like the way the bikes handle, they just feel more stable. I know that a million variables go into this and this language is inexact but I have ridden a lot of bikes and that is how I feel about it.

Anyways, I know have 2 nice titanium bikes, A Tournesol and a Spectrum. Both are 2nd hand customs and I do not know the tubing specifications but they are both built with relatively large tubes. Both are also much Flexier than my steel bikes.

Question- What would it take to make a titanium frame that is as stiff as my oversize steel frames? I know some modern titanium frames have very large main tubes (especially down tubes) but on a large tired bike it seems like it might be tough to fit a large enough chain stays in.....

Anyways, what say the braintrust?

[Peter P.]

Steel is denser than titanium, which is why a smaller diameter steel tube provides a greater resistance to flex than a same-sized titanium tube.

But that resistance to flex ramps up quickly with small increases in diameter.

The problem may be the availability of titanium tubes in precisely the correct diameter to provide that equivalent road feel. Builders are likely selecting from "standard" tube sizes offered by the manufacturer. And I sincerely doubt the titanium frame builders are provided with the material numbers necessary to make a comparison, and tube testing would prove too costly.

Also, changing wall thickness offers minimal changes in tube stiffness so don't dwell too much there.

As I see it, your only alternative is to have a frame built with tubes larger than what you currently have until you are satisfied. That could prove to be an expensive search if you go through multiple iterations.

[Ken Robb]

You could order a custom Legend from Serotta as stiff as you want--------OOPS! Never mind--too late. :-)

We used to have posts from guys who thought their Legends were too stiff. Mine was perfect--a 60cm with just a little "snappy flex".

[NYCfixie]

Any metal (Aluminium, Steel, Titanium) can be made to be flexy/cushy/comfortable/etc. or stiff/harsh/uncomfortable/etc. as you want with a "custom for you" build. You answered your own question by stating you do not know the tube specs of your 2nd-hand customs.

My Lynskey R255 rode great for fun Sunday rides but was "flexy" in the BB area under my fat arse. I gave it to my sister-in-law (she and are are within a mm of each-other for reach and saddle height) who is at least 50 pounds lighter than me and she just loves it because she finds it neither stiff or flexy but rather neutral.

My Seven Axiom SL was custom built for me (and my fat arse) in all the right ways and I find it to ride like a dream. I had my sister-in-law try it when she was out East a few months back and she hated it. The fit was fine but she found it much too harsh (we use the same wheels and tires).

I had a '89 Cannondale road bike which rattled my teeth even at my young age when I owned it as new. I have ridden newer, similarly fat tube, Cannondales and they are so much better. It is amazing what they can do with Aluminium these days.

And, talk to IF. They can build you a sweet comfortable riding bike or a stiff race bike that will rattle you teeth both made out of steel.

It is not the metal material as much as what tube size, wall thickness, and how they put it together that matters.

[cadence90]

Great question.

It would be very interesting to read what Seven, Spectrum, and other experienced builders who offer custom stiffness-tuned frames in both steel and titanium, have to say about this.
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[zank]

My last steel bike had a max DT (34.9 mm) and TT (31.8 mm), 31.8 mm ST, 30/16 mm oval tapered chain stays, and 15.9 mm tapered seat stays.
My last alumimum bike had a 42 mm DT, a 34.9 mm TT, a 34.9 ST, 30/16 oval tapered chain stays, and 19 mm tapered seat stays.
My ti bike has a 38.1 mm DT, a 34.9 mm TT, a 34.9 ST, 22.2 mm chain stays, and 19 mm seat stays.
The ti bike feels like it has the stiffest drivetrain. I remember when I went from my steel bike to my aluminum bike and the standing stiffness of the aluminum bike was the biggest difference. Both felt similar otherwise. I felt the ti was even a bit stiffer out of the saddle and in a sprint (my paltry 1200 watts). The non-tapered stays must play a role. Same wheels and tires (Belgium plus with 28 mm Pro Ones at 60 psi). I think the ti is a little smoother on our horrible roads, but I think the rims and tires play a big role in that. Corners solid. I can't feel any wiggle. Feels similar to the Max.

There are plenty of tubes to pick from in all three materials. You can make a great bike with any of them.

[bicycletricycle]

I am sure that the main tubes of a titanium frame can be made to be as stiff as one wanted. The chain stays seem to be the limitation to me, especially if you want big tires and low Q factor cranks. The space in between the chainrings and tire/fender is very constrained.

I guess a machined yoke of some kind could help.

[bicycletricycle]

Thanks for the detailed response, did you have to dimple the 7/8” ti chain stays?

Originally Posted by zank

My last steel bike had a max DT (34.9 mm) and TT (31.8 mm), 31.8 mm ST, 30/16 mm oval tapered chain stays, and 15.9 mm tapered seat stays.
My last alumimum bike had a 42 mm DT, a 34.9 mm TT, a 34.9 ST, 30/16 oval tapered chain stays, and 19 mm tapered seat stays.
My ti bike has a 38.1 mm DT, a 34.9 mm TT, a 34.9 ST, 22.2 mm chain stays, and 19 mm seat stays.
The ti bike feels like it has the stiffest drivetrain. I remember when I went from my steel bike to my aluminum bike and the standing stiffness of the aluminum bike was the biggest difference. Both felt similar otherwise. I felt the ti was even a bit stiffer out of the saddle and in a sprint (my paltry 1200 watts). The non-tapered stays must play a role. Same wheels and tires (Belgium plus with 28 mm Pro Ones at 60 psi). I think the ti is a little smoother on our horrible roads, but I think the rims and tires play a big role in that. Corners solid. I can't feel any wiggle. Feels similar to the Max.

There are plenty of tubes to pick from in all three materials. You can make a great bike with any of them.

[mt2u77]

Young’s modulus for Ti is roughly half that of steel. To get an equal deflection for a given load, you have to roughly double the area moment of inertia (I.e. make the diameter bigger and/or walls thicker— diameter changes are by far more impactful).

Turns out to be a 20-25% increase in outer diameter assuming wall thickness stays constant. (Roughly. Back of the napkin here.)

The equation for area moment of inertia for a tube is: I = pi(D^4 - d^4)/64. Big D= outer diam, Little d= inner diam.

I’m sure this gets much more complicated in real life depending on the type of loading/twisting, joints, etc., but this is a decent first order approximation.


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[zank]

With titanium, I ovalize rather than dimple. Titanium likes soft bends. Anything resembling a crease is prone to cracking.

[93KgBike]

I always thought titanium was for smaller frames, for that reason.

If you're big like me, or bigger, then steel for road bikes. It's the best.

For mountain bikes, I'm still partial to aluminum.

Although if I where still a young racer, which I'm not, carbon fiber makes sense.

Oh, in answer to your question, it would take more titanium, and/or larger diameter tubes.

[bicycletricycle]

Originally Posted by zank

With titanium, I ovalize rather than dimple. Titanium likes soft bends. Anything resembling a crease is prone to cracking.

I wonder if you ended up ovalizing them down to 16 millimeters? If so, perhaps some increased stiffnessin the main tubes could compensate for the decreased stiffness in the stays. I know some brands are using 1” stays but they still have to be cold worked into a less ideal shape to fit.

[cadence90]

Originally Posted by zank

My last steel bike had a max DT (34.9 mm) and TT (31.8 mm), 31.8 mm ST, 30/16 mm oval tapered chain stays, and 15.9 mm tapered seat stays.
My last alumimum bike had a 42 mm DT, a 34.9 mm TT, a 34.9 ST, 30/16 oval tapered chain stays, and 19 mm tapered seat stays.
My ti bike has a 38.1 mm DT, a 34.9 mm TT, a 34.9 ST, 22.2 mm chain stays, and 19 mm seat stays.
The ti bike feels like it has the stiffest drivetrain. I remember when I went from my steel bike to my aluminum bike and the standing stiffness of the aluminum bike was the biggest difference. Both felt similar otherwise. I felt the ti was even a bit stiffer out of the saddle and in a sprint (my paltry 1200 watts). The non-tapered stays must play a role. Same wheels and tires (Belgium plus with 28 mm Pro Ones at 60 psi). I think the ti is a little smoother on our horrible roads, but I think the rims and tires play a big role in that. Corners solid. I can't feel any wiggle. Feels similar to the Max.

There are plenty of tubes to pick from in all three materials. You can make a great bike with any of them.

Excellent, interesting comparison, thanks much.

Are you building in titanium also now? I thought I had read that here somewhere, but now I can't find any mention of it.
.

[cadence90]

Originally Posted by zank

With titanium, I ovalize rather than dimple. Titanium likes soft bends. Anything resembling a crease is prone to cracking.

Some years ago I did a bunch of production drawings for Jim Kish, mtb and road chainstays and seatstays, of various sizes, tapers, and S-bends. Besides getting the dimensions correct, of course, the major criteria was to stay absolutely within the ovalization parameters. No creases, dimples, crimps, etc. allowed at all.

Ovalized look a lot more elegant, too, imho.
.

[Kirk007]

To each his own, and there's so many factors that could come into play here. I'm 6 3" currently 220 and I've had a ti bike that I thought was too stiff (Lynskey 29er). I currently have a Spectrum made for me that I ride interchangeably with a Peg Marcelo and a Hampsten carbon bike. All ride very well. The Peg seems harsher which I would interpret as stiffer. But the Spectrum and Carbon are not flexy in the least. When I was at the barn Tom's comment was to the effect that he could make a ti bike as stiff as I wanted. Anyway each bike feels just a bit different but none feels faster than the other. This summer will see which I feel better on at the end of 4-6 hour rides.

I don't buy that you can't get a ti bike that is suitably stiff for a big guy and big tires. My Spectrum takes Compass Bon Jons easily. The only thing it gives up to a steel bike is that it's lighter. And the Spectrum rando frame that I have for sale feels about the same - smooth not flexy.

I just picked up a second hand Hampsten by Moots YBB and we'll see how that feels as its older and the tubes aren't as stout as the Spectrum but first ride impression with the YBB active and 35mm Bon Jons it seems like a good frame for gravel and dirt in particular.