# Why aren't bicycles made with small i-beams?

**URL:** <https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597>\
**Category:** Factual Questions\
**Created:** [August 21, 2006, 3:04pm UTC](https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597 "2006-08-21T15:04:36Z")\
**Posts on this page:** 4\
**Page:** 3

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**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\
**Post date:** [August 22, 2006, 10:49pm UTC](https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597/41 "2006-08-22T22:49:56Z")

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[QUOTE=Dag Otto]  
Cite?

The [Cervélo Soloist Carbon](http://www.cervelo.com/bikes.aspx?bike=SLC2006) goes for $5,200, built with Dura-Ace. Similar top of the line bikes from Trek, Specialized, BMC, etc. are about the same price. Where are these ultra expensive bikes you keep talking about?  
[/QUOTE]  
I have seen bikes in shops going for $15k. I was shocked. I remember thinking “you could buy an new car for that”. This was several years ago, and I was assuming inflation. Don’t recall the brand becasue it was\* slightly\* out of my range. 😉

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**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\
**Post date:** [August 22, 2006, 10:51pm UTC](https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597/42 "2006-08-22T22:51:18Z")

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[QUOTE=scr4]  
Since when did this become a thread about _high-end_ bikes? The $90 Walmart bikes are made of hollow tubes too, and it’s reasonable to wonder why it’s better than I-beams.

And I haven’t come accross $30,000 bikes either…  
[/QUOTE]

Well, it doesn’t matter what they make the frame out of, a tube is going to be stiffer than a beam for a given cross sectional area.

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**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\
**Post date:** [August 22, 2006, 11:00pm UTC](https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597/43 "2006-08-22T23:00:58Z")

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[QUOTE=Happy Wanderer]  
I have seen bikes in shops going for $15k. I was shocked. I remember thinking “you could buy an new car for that”. This was several years ago, and I was assuming inflation. Don’t recall the brand becasue it was\* slightly\* out of my range. 😉  
[/QUOTE]  
Perhaps this was in the early days of Carbon Fiber frames? Has there been a downward trend in those prices?

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**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\
**Post date:** [August 23, 2006, 12:04am UTC](https://boards.straightdope.com/t/why-arent-bicycles-made-with-small-i-beams/369597/44 "2006-08-23T00:04:11Z")

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[QUOTE=Happy Wanderer]  
Well, it doesn’t matter what they make the frame out of, a tube is going to be stiffer than a beam for a given cross sectional area.  
[/QUOTE]  
An I-beam that has the same dimensions as the tube and the same amount of material will be about 1.35 times as stiff in its stiffest axis and only about half as stiff in the other.

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