Now we’ll be able to tune our rides.

Gary Fisher

I am leading out with this quote uttered to me at Interbike 2006. It was the first inkling I heard that there would be several suspension forks coming out with different and longer offsets. The quote is important to how I think one needs to look at what has happened to the 29″er landscape. “Tune your ride”, has opened a veritable can-o-worms in the way we can look at our rigs and their potential these days. However; I think it is important to recognize that the recent “revolution” in fork/front end geometry isn’t really all that new.

Here is a super brief history lesson on fork offset and front end geometry for mountain bikes. It goes way back to the beginning of modern day mountain biking with things like variable head tube angles and multiple off set forks that were well known back in the 80’s to most enthusiasts. The work done on fork offset by Keith Bontrager in the late 80’s/early 90’s was a well known and popular alternative to the “standard” geometry of the day. It wasn’t until the advent of the suspension fork that front end geometry settled on the 38mm offset/71 degree head angle that became known as “NORBA Geometry” because of the professional racers that preferred the handling this produced. Things didn’t really change all that much for the shorter travel XC bikes after that point.

As I noted in my previous post, early 29″ers followed this same geometry formula for the most part and only a slight increase in head angle was first tried out. Then Gary Fisher Bikes came out with 29″ers equipped with Marzocchi forks sporting a 43mm offset. This was followed by what I consider the ground breaking move in fork offsets for 29″ers.

On One came out with a 29″er single speed bike that sported a 47mm offset mated to a 72 degree angle head tube. This pairing gave On One 29″ers a snappy front end that was the closest approximation of a 26″ers handling yet seen on the trail. It is also good to note that it also retained a good bit of “29”er-ish” qualities as well. Of course, this daring offset was on a rigid fork. What would occur if it were to be translated to the dynamic world of suspension?

Well, we now know what happened, of course. The questions now are about mixing and matching different frames to forks with varying offsets. Should it be done and what effect will it have? Will you “ruin” your ride? Can you make it better?

The answers are not as clear as it would seem. (Take a look at the comments section from the previous post in this series to see what I mean) You can get somewhat of an idea from these simplistic guidelines.

More offset = quicker/less stable handling Keeping in mind that our baseline offset is 38mm, (which a lot of 29″ers still use, by the way) and “more offset” is a measurement longer than 38mm. Also, you may want to take note of your bicycles head angle. You might not want to install a longer offset fork on a bike that already has a 73mm head angle, for instance.

Axle to crown measurements may affect your head angle to start with. The axle to fork crown measurements can vary slightly from one suspension fork, or even rigid fork, to another. If the net result of axle to crown difference from one fork to another is great enough, it can affect your static head angle as much as 1/2 to 1 degree either way. Keep this in mind when considering a fork swap. And remember, suspension is dynamic in all its important dimensions. Add rear suspension and it gets even more hairy!

After doing all the math, install the fork and ride! This is probably the most important advice here. You will only know if your experience has been enhanced by actually riding the bike. Chances are if you did your homework, you’ll be okay.

I’ve done fork swaps taking the fork offset to a shorter figure from a longer one and vice versa. My experience is that you can certainly tell a difference in how the bike steers and reacts in turns. Some of my experiences were negative, some were really successes, and others mildly interesting. None of them were what I would term as “failures” or experiments that “ruined” my handling. In each case, I had a notion of what the change might do based upon previous calculations. Trail rides sometimes revealed surprises that I didn’t expect. In the end, I think it is entirely possible to “tune” your ride if you do it with consideration and forethought.

Should you try tuning your fork/front end handling? Well, keep in mind that the human that rides the bicycle is a very adaptive creature and a very subjective one. I would caution against jumping in without very careful consideration. Forks are not cheap and making a choice without doing your homework ahead of time could be disastrous if you go the wrong way with things. That said, a fine tuning of your bikes handling can be done in many cases without jumping all the way into a new rig. Test rides are always the best bet, but if you can not score a test ride on someone elses rig, you’ll have to pony up for your own “research”. It can be fun and rewarding if you are careful.

Next post: 29″er handling vs. 26″er handling: How much is good to have on your 29″er?