Classic Rando vs Offroad low trail geometry

[J L]

What are some smart adjustments to frame geometry that make a bike more suited to riding in the dirt? More specifically I am speaking from the perspective of starting with a classic low trail french fit rando bike and shifting from there. In the past 5 or so years I have seen a growing number of bikes that are "fat tire low trail dirt road bikes". Many of them share lineage but they aren't the same as the bikes of yesteryear. I don't come from a mtb background and I wonder how much the proportionately shorter top tubes and single oversized tubing are optimizations or simply modern aesthetics blending in. Is a sloping top tube etc, better?

I guess with anything the answer is it depends. I'm just curious about people's comparison by experience.

Jason
SF, CA

[Clayton]

for rigid specific, take a look Jeff Jones bicycles. interesting thinking and the bikes ride superbly.

Clayton Scott
SF, CA

[Mike Schiller]

I've thought about this a lot.  I have two low trail ( 40 mmish) monstercross bikes and love the way they ride off-road.  I ride all kinds of trails, just short of steep chunky stuff.  For more serious off-road and sandy conditions I have a B+ ( 3 inch tires) bike set up with dirt drops.  It has a 72 d HTA as it was designed for XC riding.  I am using a 46mm rake Fargo fork now but I'm having a 55 mm custom fork built for it which will put the trail around 60 mm.  I've seen a few builders tackle this issue and most ended up at 60 mm of trail but with slacker HTA's and more fork rake.

Once I get the new fork later this month I'll see how this works out.  

Also this bike has a longer top tube and shorter stem ( 70mm) to be more compatible with the leverage of the wider dirt drop bars.  So far this results in near telepathic turns on singletrack trails, 

~mike

Carlsbad Ca.

[Brad]

Are your numbers for trail or fork offset (rake)?

[Mike Schiller]

I stated in my posting which were rake and trail.  ??

mike

[rcnute]

Seconded.  I like high handlebars, a shorter top tube and don't like all the wheel flop on most newer MTBs.  I like a slacker front end than a road-y bike though (tried mountain biking with trail in the mid fifties and it was too quick handling for me).  

Ryan

[satanas]

One thing about the Sequoia I have been impressed with is the handling offroad. It's got a 71.5° head angle, 50mm offset and 359mm radius stock tyres, now replaced with something ~5mm bigger.

This gives trail in the high 60s, which works well on a variety of terrain. The limiting factor isn't the drop bars but rather the lack of front suspension on really rough descents, and the resulting hand fatigue. The slightly bigger tyres help noticeably with this.

Later,
Stephen