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Thursday, March 10, 2011

Valuable Tech Notes and More: Long Chainstays?

Here is a fantastic article about Frame Geometry and how it translates into bike handling.

When I first saw the CAD drawing and measurements for my new bike, I was a little surprised to see the 410mm chainstays were a little longer than I was expecting. I hadn't specified too much comfort as I seem to have an iron ass, and I wanted something a little on the racier side. After making some comparisons to other bikes I like, I noticed it has become fashionable to have chainstays between 405 to 408mm in length. Manufacturers have been shrinking the rear triangle for "stiffness" or the belief in "stiffness".

In the article, Darren Baum, a master in titanium, lay it out:

In Darren’s opinion, longer chain stays help deliver a better quality ride. When you climb, the bike has more traction. When you go through a corner, the bike trails further and you can hop on the pedals earlier. The intended use of the bike is a big consideration however.

When chainstays started getting shorter throughout history (late 60′s, early 70′s), it was when riders started getting more powerful and the technology didn’t exist to make the materials strong enough for the desired stiffness. Therefore the chainstays were designed shorter in order to make the bike stiffer. A good bike was considered one that you could barely fit a Tally-Ho cigarette paper in between the rear wheel and the seat tube. This design had nothing to do with handling. It was all about making the bike stiffer. People started identifying this small rear triangle as a “race bike”, and therefore a race bike must handle better. This never changed as materials progressed.

These days the materials exist to make a long chainstay that is still very stiff. However if you have a longer rear end, the bike naturally needs to be manufactured with more material and therefore will be heavier. These days in the industry there is a race for the lightest spec’d bike. What does Baum do with their bikes? They recommend making the rear end as long as acceptable by the customer.

If you’re flexible and can bend forward, 412mm is what Baum will recommend. If the rider sits more upright, the chainstay might go as long as 420mm. If the rider is really tall (i.e. over 6’3″), and the femer is very long, 430mm might be required. The reason for this starts to relate back to seat tube angle and pedalling technique, however I think we might leave that one for another discussion.

The whole thing is worth a read.


Here is a little video off You Tube about the process Seven Cycles uses to build frames. A couple of shots include two of my frame builders.

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