Originally Posted by
xroadcharlie
I had no idea how head tube angle and trail could change how a bike handles until I switched bikes with a friend last night. It may also account for some difference in ride quality.
I was riding my Giant Sedona comfort bike and my friend has a Specialized low entry cruiser style bike. The steering on my Sedona, Which I believe is based on a mountain bike frame is so much more sensitive my friend almost had trouble keeping it straight. And I noticed immediately how more relaxed the handling of the cruiser bike was. I'm guessing these two bikes are at the extreme ends of spectrum for handling. I'm good with both bikes, but was shocked at the effect different fork geometry can have.
I do find my Sedona less then reassuring on the rare occasion i approach about 35 kph. It feels unstable. I don't know the numbers on these bikes fork geometry, but I can see clearly the Specialized fork extends farther then on my Sedona.
bty, I really enjoyed the Specialized low entry cruiser. I might consider one next time. It makes getting on and off the bike SO much easier, especially with a trunk bag or panniers.
Well, it's really been decades since bike designers have known that trail affects handling, and that seat tube angle affects ride. I think the main reason a shallower STA improves ride is because it better places the rider's CG with respect to the BB. If your butt is farther back from the BB plumb line you have less weight on your hands. When you see or know a bump is coming you can lift your whole body up without pulling the bars, and hence your hands are not directly exposed to the jounce (sorry, automotive term) of the front wheel. In any case the jerk on your hands is smaller than with more weight on your hands. The push up at your butt as the rear wheel hits the bump can be reduced by long chain stays (just based on leverage), but I think the biggest insulation from rear end shock is lifting your butt and your hands (temporarily) out of contact with the bike. So long chain stays, a very laid-back seat tube or very high setback seat post, and a fork/head that allows a lot of elastic bending moment between the front wheel and the fork crown should together result in an improvement in comfort compared to the "crit geometry." Now how do you do all this without compromising lateral handling integrity and tracking accuracy? I can't afford to get an in-depth look at say, some Weigles, some Singers, and some BG Herses.
But I bought a Trek 720 to test this rear end stuff (47 cm chainstays) and trail around 55 mm. We'll see how I like it!
At least with my bikes this is how it feels, and I like it. OTOH, my Masi and Mondonico (actually two of those) are both rather comfortable and have STAs around 74 - 75 degrees, but very light, flexy main tubes. One of the Mondos has ELOS and the other has "pretty light" standard diameter, but it was not claimed to be SL when it was new. All three of those bikes have trail around 60 mm.