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Wednesday, October 5, 2011

Full suspension 29er geometry...what's "good", A brief history from Gary Fisher to the BMC SpeedFox 29

29ers are nearly ubiquitous these days on the trail.  When I first began riding them in 2001, they were fringe, at best.  There were only a couple of tires around, and the best option for us out here in the desert of western Colorado, the WTB Nanoraptor did pretty well.  There were only one or two forks, and they were hard to come by.

Especially back then, critics said (often, I believe without ever having taken a 29er out on a technical trail) they were too slow to accelerate, were suited only to tall riders, and, my favorite, couldn't make any of the tight technical turns on trails, like the ones we have here out at our local haunt, the Lunch Loop.

In those early days, we were limited to hardtails for a while -- perhaps a lucky individual would get "the angry inch" on  Moots YBB -- but we were cross-country riding for the most part.

Now sidelined Gary Fisher, came out with the Sugar 292 and 293, since Gary was the first to really embrace the big wheeled bikes.  These early full suspension designs were plagued with problems though -- poor cable routing, and questionable geometry among others, but it was one of those necessary first steps into the foray to get things rolling in the full suspension 29er market.

Even a year or two later, at the Interbike Trade Show in Las Vegas, the 29ers were seen still as fringe elements.  I liked to joke that they seemed to be getting as much attention and support from the component manufacturers as the "burro bikes" with their funny 12 inch wheels.

So now we're up to about 2005 or so, and some of the bigger names in the industry are beginning to build hardtail 29ers -- Specialized, Trek, Scott, Cannondale, etc.  Around that same time, Devin Lenz of Lenz Sport mountain bikes began making a 3" travel full suspension 29er.  Devin had been building mostly big-hit and downhill 26 inch bikes, and he took what he learned from that to make his 29er (he skipped the hardtail step altogether).  the geometry he built with was unique -- he maintain high bottom brackets (13.625 inches), very short chainstays (~17.3inches), and the more slack head angles (~69.5 degrees) most associated with his all-mountain bikes.  The result of these changes is that you hit your pedals less or not at all on technical sections (higher bottom bracket), the bike climbs well and is easy to manual/unweight the front wheel to get up ledges (short chainstays), and it descends with exceptional stability and makes it much less likely that you will go over the handlebars when coming off rocks or ledges (slacker head angle).

Devin is a small, one-man operation, and probably not on the radar of the big manufacturers, and frankly, I'm sure they figured they knew better.

When the bigger companies finally began investing in full suspension 29ers, this turned out to be true.  They listened to the "problems" 29ers -- they're slow accelerating, their wheelbases are too long, poorer cornering stability since you're higher up -- and they concluded incorrectly, I believe, what they should alter.  They didn't want to take a 26-inch bike and just scale it up to the bigger wheels, so the changes they made were to shorten the chainstays (which is good, but not all of them accomplished this because their suspension design wouldn't allow that), lower the bottom bracket height to "improve cornering stability", and steepen the head angle to keep the overall wheelbase shorter.

There are some small differences between the big guys, but for the most part they all share this very common, and in my opinion, poor geometry.  If you don't ride on any technical terrain, these bikes can work fine, but they can make stepping up your technical riding game difficult and/or painful.

Here is a brief breakdown of a few of the more popular bikes out there.  The three dimensions listed are the head angle, then bottom bracket height, and then chainstay length:

LenzSport Leviathan
13.625" ;

BMC SpeedFox 29
70degree ;
13.3" :

Specialized Epic series
70.5degrees ;
13.1" ;

Cannondale Scalpel 29
12.9" ;

Santa Cruz Tallboy
71degrees ;
12.8" ;

Ellsworth Evolve
72.5degrees ;
13.4" ;

There are a lot of other out there, nearly all very similar to the Ellsworth, the Santa Cruz, and the Cannondale.

The Specialized's geometry is not bad, but my point was to point out the sleeper in there -- the newer-to-the-market BMC:

It is as close to the optimal geometry for riding moderate to severe technical terrain in it's first iteration.  Even better is that their hardtail 29er - the TeamElite 29 -- still has this optimal trail geometry, where the big manufacturers really drop the ball -- they revert back to 72.5 degree head angles, and even lower bottom brackets (the Orbea Alma drops theirs to 11.95"!).  What does this ride like?  Imagine just putting fat tires on your road bike, so I hope you don't plan on riding on any obstacles, like dirt or rocks, or maybe branches.

So if you don't like going over your handlebars, you don't like cracking your pedals on every rock you pass, and you just want the most enjoyment on the trail, then do your homework.  Find a friendly geometry, and hit the trails with confidence.

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