Monday, October 17, 2011

29"er Geometry: Old School, New School, or No School?

Front End Geo
Twenty Nine Inch Bikes were always at odds with folks riding 26"ers early on because they felt soooo different. Besides the overall feeling of the wheels, the main complaints centered around handling issues related specifically to the front end of the bike. The reason for this was pretty plain. The fork trail figures for 29"ers were different than they were for 26"ers, merely due to wheel diameter change. A bigger diameter wheel, with no other changes to the front geometry, (besides the obvious axle to crown measurement, but not necessarily so), caused the trail measurement to increase, and thus made the bikes steer differently. Most would say "sluggish", or "slow" handling resulted.

So, the first geometry for 29 inch wheeled bikes specifically would generally just be a tweak to the head angle, which when steepened would get that trail figure back shorter a bit. Trouble was, doing that too much would cause more issues with toe overlap in smaller sizes. That is why to this day you'll hear folks say the 29"ers are "only for tall people". (Of course, that's not at all true now.)

Since companies were reluctant to set up rigid forks with more offset when they couldn't get more offset in suspension fork crowns, thus making bikes handle totally differently, the standard operating procedure was to steepen the head angle. 72 degree head angles were commonplace with 38-40mm offsets. Some companies were doing even steeper angles in the head tube, up to 73 degrees. Of course, even in the "early days" there were exceptions, like Fishers with 43mm offset Marzocchi forks and Raleigh XXIX+G bikes that came with 70 degree head angles! 

It seems even early on  divergent paths to 29"er geometry were being pursued to adapt the big wheels to preferred handling traits. Some liked the so called "sluggish feel" of bigger wheels, and some wanted the bigger wheels to handle "just like 26 inch wheeled bikes".

G2 Geometry
 When I first met Gary Fisher at Interbike in 2006, he mentioned to me that "...soon we'll all be able to tune or bikes." He was talking about getting new fork offsets for 29"ers specifically, and suspension forks in particular. What he knew right then was that Fisher Bikes were about to unleash a "Pandora's Box" of front end geometry weirdness on the masses.

Of course, I am talking about "G2" geometry. The centerpiece of which was the longer offset suspension fork crowns made for it by Fox Shocks, which before this point were not in the 29 inch wheeled market place. This allowed Fisher engineers to relax head angles, and smaller bikes were no problem with regard to toe overlap. Subsequently, many more manufacturers started to ask for a longer offset crown from Rock Shox, and Manitou. The offsets were nominally set at 44-47mm, but, as is true to this very day, 38mm offsets were still being produced for 29"ers.

Regardless, this allowed most company designs to go back to 71 degree head angles, with some going to as slack as 70 degrees. This resulted in the older designs being called "Old School Geometry" for 29"ers, and this new offset era being called "New School" geometry for 29"ers. Of course, nothing could be further from the truth.

In fact, as you can see by reading this, what we have is not a sea change in geometry, or even an "evolution" as much as we have more choices. More ways to "tune our bikes", just like Gary Fisher said way back in '06. Companies are even getting into the game to differentiate their designs and ride feel. Rigid forks are being built out of carbon with 38mm offsets like those from Whiskey Parts, Ritchey, Syncros, and others.

So, when it comes to front end geometry, it would be most accurate to say there is "No School" geometry. The numbers are all over the place, and it doesn't look like that is going to change anytime soon.

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