Front End Geometry For 29"ers: Set In Stone- Part II

In my first post on this subject, I got some questions in the comments section that I wanted to address in this post, along with some other related topics having to do with front end geometry. It seems that this topic is very confusing to some, of great concern to others, and some could simply care less. To the latter I say, “Go on out for a ride.” This post won’t be of interest to you.

To everybody else, I would suggest you all take a moment to read this short post about “trail as it relates to front end geometry. Once you have that down pat, we can look at head angles and where we are at with fork offsets. To better understand that, take a look at this article on offset. It will help clear up for you why more offset equals less trail/more unstable handling.

Now with the advent of the longer offset forks for 29″ers, what does that do to those older 29″ers that had 38mm offset suspension forks on them? Well, for that I would direct you to my series that I did called An Experiment In Front End Geometry. Looking through those links there, you will begin to see that a pattern developes. One that I think is unique to big wheelers.

That is the natural stability of the 29 inch wheel. It tends to overcome what would would result in an unrideable geometry for most folks in 26″ers. Done up in 29″er wheels, it is a different set of standards. The “window of what works” is a bit wider with the bigger wheels because of this “X-factor”, which is wheel stability caused by the gyroscopic tendencies in a 29″er wheel. So with more offset, we don’t see the instability with 29″er wheels that we might see with smaller wheel diameters.

WTB WeirWolf LT

So how will that affect a bike that has a 72 degree head angle and a newer 46mm offset fork? (A question I see popping up alot lately) Well, it will be a bit different than it was with the old 38mm offset Reba, yes. A bit easier to steer, really. For many folks, a few rides in and they will never know the difference. For some, they will crave the older handling, and either stay with an older Reba, or get a bike with a slacker head tube angle, but in my opinion, these folks will be the exception rather than the rule. I just feel that the “stability factor” of 29 inch wheels will make the changes acceptable for most, and for many it will be an improvement.


No Responses to “Front End Geometry For 29"ers: Set In Stone- Part II”

  1. Cloxxki Says:

    Good stuf, as usual!

    Buddy of my comp(l)eted the 2008 TransAlp Challenge (the original) on his usual Scandal he always ran rigid, but for this occasion fitted with the Manitou ~47-48mm offset fork, at 80mm. Nearly the same as the stock rigid fork. I expected it to be a handful in the TransAlp, being overly quick. But he felt it rode just fine. Like it could not have better. Well, glad to hear.

    I think for everyone’s riding style, there comes a trail figure that will sufice for the tightest of trails, and hat hardest of racing over them.
    On the 1st generation Fisher, 71.5D HTA, fitted with plain Surly KM 468/43mm fork, and having a super-low and stable >70mm BB drop, plus some goofy 38d trekking bars, on the tightest and most widing trails of our national seies, I found myself dropping riders over 9 inches shorter than I, on their tricked out 26″ team bikes. So, how quick do we need a 29″er to handle anyway? Once you learn how to use your body to drag the bike through twisties, it’s not only plenty quick, but also mighty fun.

    Thart all sais, I have a build-in-progress of a Fisher Superfly frame, and custom steel fork, pretty much matching the height at 470mm, but adding 4mm of offset to the stock Fox’s, at 55mm. I wanted to try that combination of a way long front end (the head tube angle raked it out a bit compared to my other bikes), and pretty quick handling. Another friend had an even more extreme custom built that way, and it was magically good, but did feel as it was rather too quick than too slow. My trails are not great Alps or Rockies though, I fight sandy hills and singletracks. I mainly hope the long front end will give me a mental edge in descending at race speed. I lose out there now, I keep using the brakes. Better bikes keep me from doing that, I’ve found.

  2. Tim Says:

    I’m with you on this Cloxx. I have the same frame, w/ a Waltworks custom fork, 470/45mm offset. Shortish chainstays contribute to making this bike quick, and neutral handling.

    I think that this geometry rIdes great!

  3. Cloxxki Says:

    Chainstay length doesn’t say much. MOre depends on your seat tube angle an seat position, and COG. With my long legs, I tend to sit more aft on the bike (all bikes share the same CSL), but then, I do place my seat quite a bit forward.
    I can tell the quickness of short stys, but long is excellent if you keep both wheels on the ground. Comfort, stability, cornering.

  4. Tim Says:

    Yea, whatever works.

    I am not an expert, and as you state, body position for and aft between the wheels is undoubtedly the determining factor on how the frame handles.

    That particular geometry seems to feel quite natural to me.

  5. Mike Says:

    Hi Guitar Ted,
    I’m planning on buying a 2008 Gary Fisher X-Caliber (completely stock-it’s new) that I’m getting for a good price. I was wondering whether what you would think taking out the travel spacer in the F29 fork and increasing its travel from 80 mm to 100mm would do to its traveling. From your experience with G2 bikes, would that make the handling worse or better?
    For what’s it’s worth, I ride mostly in wooded Wisconsin trails, like HPT in La Crosse, WI, or Nine Mile near Wausau, WI. Also, I liked the handling of a HiFi Pro 29er that I demoed.
    Also, one other question. Would you recommend running this bike tubeless, and if so, would the Bontrager tubeless set-up or Stan’s work better in my area, if you know either of the trails I mentioned.
    Thanks for any advice you can give me,

  6. Guitar Ted Says:

    Mike: Thanks for your comments.

    With 100mm of travel I think your handling will be a slight bit “floppy” in slower speed, picking your way through, types of situations. In higher speed single track, the suspension will often times be into its travel enough that the extra travel won’t be a big deal to your handling. Again, I think slower speed handling is where your choice would prove to give that X-Cal a bit of heaviness in the handle bars when they are turned a bit one way or the other. Climbing is especially where I would notice that.

    TLR Bontrager stuff is the bomb. I would use Stan’s sealant versus the Bontrager Super Juice, but everything else about the TLR Bonty wheels and tires is top notch.

  7. Mike Says:

    Thanks for you advice! I was kind of thinking it might worsen the handling some. I won’t bother with taking out the spacer, then. On our trails with a 29 inch wheel I don’t think I’d really need it, anyways.
    On the sealant, I don’t really think our trails really have much in the way of thorns, though there are plenty of rocks (granite is everywhere) at Nine Mile, though I don’t think they’d be the type that would puncture tires much.

    Would you recommend using Bontrager’s rim strips and valves, then, with the Stan’s sealant?
    Also, I probably won’t change the tires on it until they wear out if I like them (which could be two or three years since I don’t ride everyday–I’m a cross country runner at UW-La Crosse), so will Stan’s dry out where I’d need to take the tires off occasionally to clean them out? Is there any other maintenance things you need to do with tubeless tires? (I’ve always used tubes before, so I don’t really have any experience with them.)

  8. Mike Says:

    One more question. Where Bontrager’s Rhythm wheels and Jones ACX tires are both tubeless ready, would I need less of Stan’s sealant than they say in their instructions (2-3 oz.)?

  9. Guitar Ted Says:

    Mike: Yes, use the Bontrager plastic snap in rim strip and tubeless valves. The valves have removable cores, (You’ll need a small wrench to remove the core) Introduce the sealant through the valve once the core is removed. If you don’t fear punctures, the Super Juice is an excellent sealant and stays in a liquid state far longer than Stan’s does. 3-4oz. is a good amount, but I have used as little as 2oz. and it has worked. The Super Juice bottles are marked and make the installation of the sealant easy.

    Stan’s will work, same amount is recommended, and you can expect it to dry out in two to four months time. The tires will still inflate and hold air, but they won’t seal puntures once the sealant dries up.

    Another product I have successfully used is Slime Tubeless Tire Sealant. It is similar to Bontrager’s Super Juice, but it also seals punctures better and lasts longer than Stan’s.

    All three sealants work with Bontrager tires and TLR wheels.

  10. Mike Says:

    Have you ever tried a combination of Slime Tubeless tire sealant and Bontrager Super Juice?

  11. Guitar Ted Says:

    Mike: No I have not. I’m sure it would work, but I’m not sure you would gain anything by doing that.

  12. Rob in Ottawa Says:

    (kind of off topic) I love the photo of that tire, it looks so large in that photo. It makes me want to go out and buy a set of WW LT tires.

  13. AF73 Says:

    Guitar Ted,
    I have the chance to get a 51mm offset Fox F29’er for that came off of a G2 Fisher Superfly. I have an Ellsworth Evolve with a stock Reba 38mm offset 2007 fork at 100mm. The geometry of the Evolve is follows:
    Size Large
    72 Head Angle
    73.5 Seat Angle
    13.7 BB
    24.7 TT
    18.2 Chainstays
    20.8 Static Fork Length

    I have wanted the bike to steer better in switchbacks, as it is sluggish and take a bit more effort to transition and “carve” in the Utah singletrack i ride in. Would that Offset be too much, with my angles, what affects will it have both positive and negative?

  14. Guitar Ted Says:

    AF73: Your suggested Fox fork would be a huge swing to the other side of the handling spectrum, all else being equal. (Head tube angle the same) It would possibly become a handful on longer, techy descents where if you lose your concentration, you may eat it easily.

    I would say to try it. It might be your cup of tea, but I would be willing to bet a 46mm Rock Shox with a Maxle lite would be a better upgrade here.

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