An Experiment In Front End Geometry

Introduction: As the geometry evolves for 29″ers, riders have been getting increasingly more aware of front end geometry, especially as it pertains to forks. Offset and axle to crown measuremens are topics du jour, while head angle charts are consulted like the newspapers latest astrological section. What does it really all mean? Does this stuff matter all that much. (Actually, that is a totally valid question) What happens when fork “A” gets mated to frame “B”? Will my bicycle become a wheelbarrow or a twitchy track bike? Hopefully the following posts concerning my forays into this nebulous world of front end geometry will help to clear some things up for some of you.

On One Carbon Superlight fork

The Set Up: I decided that in order to figure out what might result from swapping out forks that I would use one bike. This bike would get several fork swaps throughout the summer and I would report on each forks effects on said “one bike”. That bike is the OS Bikes Blackbuck. I also decided that for the most part I would stick with rigid forks, since there will be less variables with rigid forks versus suspended forks. (Although I will use a couple suspended forks as well) Along with the different forks, I will also detail out the different equipment and fit changes I needed to make to keep my relative seated posistion correct. All forks will be fitted with the same Avid BB-7 disc caliper with a 185mm rotor. I will also be using a Titec H-Bar, Avid levers, and Ergon grips throughout the test with various Salsa CroMoto stems to help achieve proper fit. The head set will be a Chris King No-Thread head set.

OS Bikes Blackbuck

I will periodically update the test with new posts. The first in this series will be on the initial set up. Then we will get into the following fork swaps afterwards. I will also touch upon my past experimenting with an On One 29″er where I swapped out the stock fork for a Bontrager Switchblade. Stay tuned for the first part in this series coming soon.

In the meantime, please leave any questions or comments in the comment section. I’ll be sure to address each one if I can.


No Responses to “An Experiment In Front End Geometry”

  1. James Slemboksi Says:

    I’m excited to see what you come back with.

  2. XchokeX Says:

    I’d like to see the difference between running a stock suspension-corrected fork, such as on a Karate Monkey, with a non-corrected fork. If any of those exist outside of the XXIX fork.

  3. Guitar Ted Says:

    XchokeX: You will get to see that early on in this series. Stay tuned!

  4. Steve Says:

    I have an On One carbon fork matched up to a Soma Juice, which I believe is very similar in numbers to the KM. Even though you’re using a different bike I’ll be very interested to see how this pans out!

  5. Lee T Says:

    As Fisher fan, I am looking to get close to the handling of my HIFi 29er and Superfly (both G2s) with a Ferrous 1×9 rigid – anything in your test to point the way on that?

  6. Tbone Says:

    EXCELLENT idea.

  7. alistair Says:

    I realise this is a geometry test, not a ‘how much trail bumps does it smooth’ test … however I am interested to know the difference in ride characteristics between my standard avanti kiss/raleigh XXIX non suspension corrected fork and something like an on-one carbon fork.

    I really love riding the rigid front on my kiss but sometime it all gets a bit out of hand, I am hoping longer suspension corrected forks would absorb more of the harshness?

    Of course a new longer fork would mean a new frame, I guess I can handle that ๐Ÿ™‚

  8. Cloxxki Says:

    @Lee T,
    I think you are trying to do the impossible.
    To slacken the headtube angle to the G2 spec requires a looooong, yet rightfully inexistent fork. Or (the horror!) a 26″ rear wheel, and then some. But that would lower the BB.
    And then it will have to have the G2-spec 51mm or so offset. In the process, the top tube on your Ferrous will be effectively an inch or more shorter.
    Ferous can be a great bike in its own way. If you really prefer the G2 approach for handling, rid yourself of the frame and fork, and find a replacement that closer matches it. Like the Redline Flight. It a bit like the middle way between mainstream and G2, in a good way if I do say so myself (I was allowed to help design it, using my same philosophy which Fisher later tested extensively to come to in some ways even more extreme set of numbers.

    if your Soma was built to have 72degree head tube ange around a ~468-470mm long fork, it’s indeed the KM copy I remember it to be be. KM has the same figures as an On-One (same comment applies as on the Redline, just not the philosophy, I had my diry hands in it), just the On-One got a modest 4mm more offset to spice things up, so newbies and journalists would be amazed about its big wheeled quickness, and that worked.

  9. Guitar Ted Says:

    Steve: I think you might find my first report interesting. ๐Ÿ˜‰

    Lee T: I have to say that you may need to go into a different mode of thinking on your Ferrous. Stay tuned and see what happens with my rig through the various permutations and I think you will have a clearer idea of where to go on your rig.

    Tbone: Thanks. I hope you enjoy it.

    alistair: Excellent notion. I may include a box that ticks off a few ride characteristics of each fork. Why not? I’ll be riding them and writing about them anyway, right? ๐Ÿ™‚

    Cloxxki: I’ll be interested to read your reactions to some of these forks. Thanks for checking in, as always. ๐Ÿ™‚

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