references on frame design theory?

[CNote]

Who has references for reading material on frame design theory? I'm not so interested in the actual building process (mitering, brazing/welding), but moreso in the planning process (nailing down geometry). I'm curious to learn more about how aspects like trail, front-center, wheelbase, bb drop, etc. all interact to influence ride characteristics. Website suggestions are welcome, but if you can suggest something substantial in paper form, that would be fantabulous! Thanks.

[Dave]

This site has a lot of good info.

http://www.anvilbikes.com/story.php?catID=3

Remember that unless you're talking about frames made of the exact same materials, the differences in ride harshness due to minor angle changes are not that great. Differences in the material, it's size and shape can be far greater.

I donl't quite agree with the statements regarding the STA changing the weight balance, unless you add the qualifier that the saddle position is changed proportionately to the STA change and the TT length remains constant. It's entirely possible to have two bikes with significantly different STAs, but the same fit and weight balance, depending on the seatpost style and TT length.

I have one bike with a 72.5 degree STA and 54cm TT and another with a 74.5 degree STA and 52.5cm TT. The bikes fit the same, within 2mm. This can be proven by calculating the horizontal distance from the center of the BB to the HT/TT intersection for both frames. The big difference is in the seatpost style required. The frame with the steeper STA needs a seatpost with about 2cm more setback to position the saddle the same, relative to the BB.

[CNote]

Thanks for the link, Dave. This explanation is very concise and makes a lot of sense. I think the disclaimer he mentions about using seatposts with differing degress of setback kind of gets at the same point you are making about the STA.

[Dave]

One of the most useful things I've only recently discovered, is Cervelo's concept of a "reach" dimension. They use a c-t frame size and measure the the "reach" horizontally from the center of the BB to the top of the head tube/HT centerline intersection point. This allows you to compare the difference in the reach of two frames, assuming any given saddle position.

They also use an interesting "stack" dimension that allows the handlebar height, relative to the BB, to be compared easily.

http://www.cervelo.com/bikes/2005/SL-Team.html#Geometry

For most other brands, the "reach" can be calculated as the top tube length - (c-c frame size x cosSTA). In the example I gave of my two LOOK frames that apppear to have a different fit, 54 - (51 x cos 72.5) = 38.66 and 52.5 - (51 x cos 74.5) = 38.87. The difference in the reach is only 2mm, which means that once the saddle is in the same location relative to the BB on both frames, they will have the a nearly identical reach with the same stem length.