Interesting observations that fit quite nicely with my own. I spent the better part of a year researching frame geometry and experimenting with my existing bike. I determined that I wanted to try a lower trail bike (the one I was riding then had 74+ mm of trail) and set my sights on a 73/73 seat/head angle frameset. I found it in the Handsome Cycles Devil and my initial impressions were that I loved the lower amount of trail (60mm)
As I've ridden the Devil I've continued to study bike geometry and play with BikeCad in anticipation of an eventual custom build. I thought about going with 26" wheels so I picked up a 1995 Trek 850 MTB for cheap, overhauled it and started riding it a bit. This thing has about 72mm of trail. After a couple of days on the MTB I got back on my Devil and the best way to describe the sensation was that the front wheel literally "flopped" from side to side as I turned it. It was, for lack of a better term, twitchy and not at all pleasant to ride. I know a lot of bike feel is just getting used to a particular bike and after riding it a bit it felt normal again.
However, a steep head angle has other drawbacks. It decreases wheelbase, increases the chances of toe clip overlap and can limit the size tires you run. Plus, with the fatter tires I prefer, it just looks funny. I also prefer a short top-tube and that just makes those issues worse.
I test rode a Surly Karate Monkey with a 71.5 degree head tube and a 40'ish mm trail fork. That thing was a stable as I can imagine a bike being. I wanted to find things to ride off and over, it was so confidence inspiring. The bikes I rode from 1995 to 2012 all had 71.5 degree head angles with rake being in the 40-45mm range.
After playing with BikeCad I've determined that a slacker head tube angle is the way I want to go. I'm thinking something between 70-72 degrees, depending on what a builder can do with fork rake. I'm also not sure about overall trail but I'm leaning toward higher numbers (65mm +) which is a complete reversal from where I was six months ago.
I think I'll put my old Multitrack back together and see how it rides. It has similar geometry to the Karate Monkey.
On a related note, I think I've pretty much nailed down my seat tube angle at 73 degrees. All the bikes I've ridden have had 73 degree seat tubes but I've been curious about slacker angles. The Trek 820 has a 72 degree seat tube and no matter how I position my saddle, my knee starts aching within a few minutes of riding it. I can immediately get on my Devil and the knee pain is gone until I get back on the 820.
The Cross Check was on my short list of framesets but I wanted to try a lower bottom bracket and longer chainstays, both of which my Devil have. I'm definately sold on the lower bottom bracket (Devil has 70mm drop compared to my old bike's 60mm) but the jury is still out on chainstay length. Right now I have the wheel all the way back in the dropouts giving me a CS length of 45.5 cm and a wheelbase of about 1045mm.....almost touring bike territory. I suspect I like shorter chainstays but haven't done enough experimenting with that particular variable to know for sure.
Last edited by corwin1968; 10-28-13 at 10:34 AM.