February 06, 2011

Material story 2 – Stiffness and weight for titanium and steel. - 材料の話2

This time, I post a little about relation between stiffness and weight for titanium and steel tubes.

This relation can be gotten through calculation with some material information. I show some examples. (*Unit is mm, D- diameter, t- thickness, All tube length is the same.)

1. Ti (D-35, t-0.8) and Ti (D-35, t-0.9)
    Ti (D-35, t-0.9) has more +12%stiffness and +12% weight

2. Ti (D-35, t-0.8) and Ti (D-38, t-0.8)
    Ti (D-38, t-0.8) has more +19%stiffness and +9% weight

3. Ti (D-35, t-0.8) and Ti (D-38, t-0.7)
    Ti (D-38, t-0.7) has more +5%stiffness and less 5% weight

1. You can see it is +12%stiffness and weight if thickness is added 0.1mm. 
2. If you have +3mm larger diameter and same thickness, it is +19%stiffness and +9%weight.
3. If diameter is 3mm larger and thickness is 0.1mm smaller, it is +5%stiffness and -5%weight.
These cases are for straight gauge tubings. However, in fact, many metal bikes have double butted tubes on them. So it is a little more complicated. I show a comparison example (Ti and Steel down tubes) below.

1. Ti (D-35, t-0.96 *BB, Head tube side) and Steel (D-32, t-0.7 *BB , Head tube side)
    Steel (D-32, t-0.7) has more+16%stiffness and +19%weight.

2. Ti (D-35, t-0.78 *Butted part) and Steel (D-32, t-0.5 *Butted part)
    Steel (D-32, t-0.5) has more +2%stiffness and +5%weight.

(*The numerical value can be changed by the butted length. You first have to calculate the rate of butted part and straight part in a tube.)

It is actually possible to have a lot of tubing combinations in a frame. It means there are many patterns for the relation between stiffness and weight in a frame. Particularly, as for Ti tubes, there are many sizes and it’s possible to make any wall thickness (Also, there is prenty of capacity to change the wall thickness.)
We can actually have lots of comparison examples of tubing about the relation between stiffness and weight, but having and improving a certain standard stiffness on a frame is also important thing because it doesn’t make any sense for this comparison without any standard. The only way to understand about the standard is to study deeply about materials and have lots of experience in a real situation.


1. チタンで径が同じで厚さが0.1mm異なるチューブを比べると、厚さが0.1mm厚くなることで12%の剛性アップと重量増になる。

2. チタンで厚さが同じで径を3mm大きくすることで19%の剛性アップと9%の重量増となる。

3. チタンで径を3mm大きくし厚さを0.1mm薄くする事で5%の剛性アップと5%の重量減となる。


1. チタン(径35mm、厚さ0.96mm、BBとヘッドチューブ側)と鉄(径32mm、厚さ0.7mm、BBとヘッドチューブ側)を比べると、鉄が16%の剛性増と19%の重量増となる。

2. チタン(径35mm、厚さ0.78mm、中心付近)と鉄(径32mm、厚さ0.5mm、中心付近)を比べると、鉄が2%の剛性増と5%の重量増となる。



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