Bike Geometry

[Kathi]

I think I have some information on bike stiffness bookmarked on my computer at home, I'm at my ski condo until Thursday but I will try to find it for you when I get back home.

Stiffness has to do with the tubing and how it is used in a frame. I was very concerned about stiffness when I built my new frame. I had a Cannondale 1995 vintage aluminum frame and whenever I hit chip and seal type roads I had to decrease my speed. Many days I felt like I rode a jackhammer all day. I was told the frame was too stiff for me, a 100 lb person and I wasn't heavy enough to flex the frame. Then I went to an Aegis Swift. It was carbon and I think pretty stiff but I didn't feel the jarring of the aluminum frame. The bike has a "snappiness" that I hadn't experienced on any bike. Whenever I stepped on the pedals it just "gets up and goes".

When I was researching bikes and materials for my custom frame I was told that the snappiness that I loved on my Aegis is due to a stiff bottom bracket.

I demoed a steel frame, ti frame and carbon/ ti frame. The carbon /ti frame was the similar to my carbon frame. But I was worried that ti would be to stiff. Serotta was able to build me a ti/carbon frame with a stiff bottom bracket for snap but with enough flex in the tubing that I have a comfortable ride. Actually, quite a wonderful ride.

From what I remember from my research a too stiff frame can affect handling on corners and downhills.

Also, wheels can affect the ride. Most wheels are built for men but if you're not in their weight range they might be to stiff for you.

For me building a custom frame was a big issue. I wanted a ride like my cf frame, custom cf is hard to find in my size and I was afraid I'd end up with a too stiff frame. Fortunately for me, I found a company that could come up with the right combination of tubing, with the right flex and build me the ride that I wanted.

Here's an article on frame flex,

http://www.kirkframeworks.com/Flex.htm

[li10up]

So is it a true statement to say that the more your top tube is slopped the slacker your geometry is?

And the slacker the geometry the slower the bike? Is this correct? And if so, why is this?

[Eden]

So is it a true statement to say that the more your top tube is slopped the slacker your geometry is?

And the slacker the geometry the slower the bike? Is this correct? And if so, why is this?

On the first point I'm pretty sure the exact opposite is true - a more traditional frame bike usually has a more slack seat tube and racing bikes, especially compact frames (sloping top tube) have steeper seat tubes. Though it is true that slack seat tubes are usually found on bikes that are built more for comfort than speed.

Everything you wanted to know and more at the Wiki...
http://en.wikipedia.org/wiki/Seat_tube