[Destroy]

Topic pretty much says it all.

Several online order sites say not to use Ti skewers on frt susp fork or rr susp bikes.

Anyone know why?

 

[Grumpy]

Topic pretty much says it all.

Several online order sites say not to use Ti skewers on frt susp fork or rr susp bikes.

Anyone know why?

Titanium is more flexible then steel. When a bike wheel resists twisting (a large component of) that force is converted to an increase in tension in the skewer. In a suspension fork/frame the structure of frame/fork is less able to resist the force so an even larger component of the force is handled by the skewer. Set at the same pre-load tension the ti skewer will flex more (or resist elongation less) then the steel skewer. So the rider will see more wheel flex and, as a result, less directional stability. Simple as that.

 

[shiggy]

In addition, the flex/elasisity of the ti skewers can let the wheel work loose and move in the dropouts.

 

[Destroy]

Ahh..makes sense, Thank you. I always thought titanium was stronger and lighter than steel, but I guess not.

 

[Krause]

It can be, but like said they just have different properties, so in some applications like a skewier and a high tension bolt it just isnt always as good.

 

[Grumpy]

Ahh..makes sense, Thank you. I always thought titanium was stronger and lighter than steel, but I guess not.

Yes that is true it is both lighter and typically stronger (there are ssome exotic steel alloys that rival ti). confused?. The problem is that structural properties are complex and not a single parameter. Titanium is typically stronger and lighter but strength is typically measured by "yield strength" (or sometimes UTS (ultimate tensile strength)) The yield strength is the point where you apply stress (bend) until the material doesn't return to it's original shape (ie permanently deforms). Titanium alloys are more flexible but at the same time are also more resistant to permanent bending.

The specification for elastic bending of a material is called the "Young's Modulus" and is is simply the ratio of stress/strain (IOW a ratio of how much force cause how much bend) Here steel is typically much stiffer, ie having a much higher YM

To confuse matters even more these properties can be measured by unit weight or by unit volume. Steel is stronger then kevlar or carbon fiber by unit volume, but not by unit weight. In other words two cables 2cm in diameter; the steel cable would be stronger than the kevlar cable (UTS). But two 100' long cables each weighing 5kg the kevlar cable would be stronger.

That is why you hear so many confusing and seemingly contradictory "what is stronger" facts about Steel VS aluminum VS carbon fiber vs titanium. Each material has specific positives and any can be shown to be the "strongest" or best in one or more specific property(s).

 

[Grumpy]

In addition, the flex/elasisity of the ti skewers can let the wheel work loose and move in the dropouts.

I had also thought of the possibility of the additional flex (strain) causing fatigue (particularly with aluminum) in the frame or fork but I don't know if the increase is significant.