An Experiment In Front End Geometry: Suspension Fork #2

We continue now with the fork testing with the Fox F-29 G2 offset for sporting 100mm travel. This is the second suspension fork after the Reba which I wrote up here.

Fox F-29 on the Blackbuck

The Fox fork is the longest travel fork, and thus the longest fork, that I will use in this test. Let’s take a look at the numbers…

Head Angle- 71 degrees
Axle To Crown- 510mm (unsagged)
Offset- 51mm
Wheelbase- 43 3/8ths″
Bottom Bracket Drop Range (EBB)-48mm-58mm
Approximate Trail*- 79 mm (unsagged

Changes Made This setup is outside the ability to adjust for correctly with the componenets I had worked with all throughout the test period. . I had to slide my saddle all the way forward, (I still didn’t quite get there). The handle bars were about at the correct handlebar height since the steer tube was shorter on this fork, so I didn’t have to run spacers on top of the stem. Note: I did leave the bars slightly too high to allow for sag and when sagged, the seat most likely was right where it should have been, but I had no way to measure this effectively. Suspension throws a lot of dynamics at you. At best, you can only “get in the ball park” compared to your rigid numbers which do not change

Handling Characeristics: The trail figure and head angle are somewhat reminiscent of a Fisher hard tail with G2 geometry. Did the Blackbuck become a G2 clone? Well, not quite. I think the Blackbuck is a bit steeper in the head angle than a true G2 hardtail and it showed. The bike was very sensitive to input and depending on the exact situation on the trail, down right sketchy. For example: A downhill turn with a tightening radius. Getting into the forks travel, braking hard, and trying to steer the bike more sharply with the increase in steepness of the head angle was tough. General trail riding needed very little handle bar input. Leaning, steering from the hip, and fine handle bar movements were all that was necessary to get around my local trails. Fast descents were not too sketchy, which surprised me a bit. The Fox fork was taking up the trail hits with aplomb, keeping me online. Climbing was at my limits of what I would deem acceptable in terms of front end height. The Fox fork raised the front end to a point that the front was feeling too light on steep climbs, especially on slower ascents.

A Note On The Forks Ride: The Fox fork was no real surprise here. It was really good in terms of stiffness laterally and the travel was smooth and predictable. Trail obstacles were erased with out drama. What did surprise me was how much better this fork worked with the Blackbuck in terms of getting all the travel on tap. Usually I find Fox forks great, but I also find that getting full travel is most often difficult to do without compromising other performance features of the fork. Not so with this particular Fox F-29, which was getting full travel and performing with proper air pressure. Nice! If I could try a Fox with the standard 46mm offset and set it at 80mm, I think it would match up with this bike very well.

Final Thoughts: I thought that this combination was just a bit much. Too much fork length, too much offset for the head angle, and too much bottom bracket height. It worked okay, but not great. I think that trying to achieve a “G2 handling” on a frame not designed for it by simply slapping on a Fox fork with G2 offset doesn’t work all that well. (Consider that if I had used an 80mm fork, the static head angle would have been steeper and made matters worse.) As a choice in forks for the Blackbuck, I would pass on this one. Perhaps something with shorter travel and less offset would be the ticket, and that’s exactly what I will put on the Blackbuck next!

*The trail charts I used all gave slightly different answers and of course, your tire selection will also affect the trail figure slightly. Take my trail figures with a grain of salt. Your mileage may vary!
Look for more on the series in a week or so.

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No Responses to “An Experiment In Front End Geometry: Suspension Fork #2”

  1. James Says:

    Looking at the Selma in a Small size the head tube angle is 71. Any fork suggestion to make it 72? Or would the 71 be a good thing?

  2. Guitar Ted Says:

    James: Looking for snappier steering? Try a 46mm offset fork perhaps. A Fox, Manitou, or the new Reba. Any of those should make the Selma steer pretty well. 🙂

    Going rigid? Well, there are options there too. If you wanted a steeper head angle, the 440mm axle to crown options would be about right to get you 72 plus degrees head angle depending on tire choices. Maybe even as steep as 73 degrees. There really isn’t anything out between 440mm and 465mm, so dialing in a specific head angle would require a custom fork.

  3. Dirt McGirt Says:

    I prefer 71.259 degrees. It’s optimal. Bottom line.

  4. Cloxxki Says:

    James, with this very fork you’d have a G2 front end, really. Those seem to work for some.

    Good reading as usual, GT.
    A friend has a Scandal, and I was pushing him to get a 100mm G2 Fox. I would nett similar angles to your bike I suppose. Then, we ride pretty lame twisty singletrack, it might work.

  5. plesurnpain Says:

    GT
    Great write up. You’re views are pretty much what I expected. I was offered the same fork for my XXIX, buth I was afraid of it having the effect that you talked about. The front end would probably be even lighter for me as I have a lon torso and stubby legs.I’ll bet you’d love the 80/46 Fox on the Blackbuck. Get in touch with me, maybe we can work something out.

  6. Lee T Says:

    Perfectly clear now why the G2 Fox won’t work on the Ferrous, as I was contemplating. Thanks for the geometry lesson!

  7. sthrnfat Says:

    GT – in your opinion, would an FS frame that would have a 71′ headtube with a 100mm fork (Jet 9) be too twitchy with a G2 Reba? Have the G2 Reba on another bike and would like it on the Jet to save some cash. I have a Standard Reba and the G2, so I could go with either fork.

  8. Guitar Ted Says:

    sthrnfat: Well, I think that depends on how and where you ride that set up. Sagged that set up would yeild a trail figure in the mid to upper 70’s. Not too bad, but on longer, techy descents, you might wish for something requiring a little less concentration to pilot. Keep in mind that through the travel of the fork, that trail figure will get even more nervous, so the initial numbers are really only a guide and don’t tell the whole story.

    Conversely, on twisty, flatter to rolling terrain, you might just love it.

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