CX and trail

[FastforaSlowGuy]

I've been oggling CX frames recently (no money, so I can look but can't touch). I notice head tube angles tend to be a bit lower. Bikes my size normally have around a 72* HTA on the road, and I'm seeing many with 71* in the CX world. I'm assuming here that designers are intentionally increasing trail to help the bikes make those very tight, low-speed turns that you get in CX? And consequently, high-speed handling should be a bit sluggish? Is that about right?

[RedRider]

The majority of cross bikes sold are used for commuting, winter riding, trail riding and never raced on a cross course. There are a lot of "cross" bikes that have a more relaxed geometry than you would find on a "real" cross racing frame.
A cyclocross fitting and the frame geometry are designed for a hard, 40 minute ride rather than that of your typical road bike.

[s_curran]

Generally, a cross bike will be a little less stable at speed and in quicker corners. Its not only the HT angle, but the BB height as well. A good descender will have a lower BB. There are plently of bikes now, even used for cross racing, that are closer to road angles though. Its all about preference. I ride a cross bike for everything. Its not perfect for anything, but it works well, and I know it like the back of my hand, meaning I don't ever really feel unstable at speed on it.

[crankles]

my cross bikes, built with racing in mind, have around 59mm of trail.

[pakora]

My Kelly that I race on has a 72 degree head angle and a high bb (and the smaller sizes were 73), while my Niner mtb (which I think has an unusually high hta based on what is now becoming popular) has a 72 degree angle with a 80mm fork (which is what I'm running, or the suspension-corrected equivalent).

On the same trails neither of them feel either sluggish or twitchy in turns - "just right". Yet another bike, my sscx civilian has a 73 hta but a very low bb, and descends or takes the straights very stably (I haven't taken it on trails or raced it enough to really compare the turning).

Of course I don't ride them on the road, and even the odd time the Kelly sees pavement, it's with big squishy tires. And of course I'm used to them. They all feel very different than my custom bike (which has a steeper angle and is twitchy at low speeds, but super stable in turns and at high speed), but horses for courses for me I guess.