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?
Tags: steering performance
The Big Wheeled Ballyhoo 
January 7, 2008 at 9:11 am |
It seems like weight distribution is being left out the discussion because it’s hardest for manufacturers to quantify in their product specs. I had a similar first experience to many 29″ detractors when I took the first ride out of the box and the bike handled like a shopping cart with a wheel missing. After flipping the stem and pulling all of the spacers I was finally able to get enough weight over the front end to get it hooked up in the corners. If I hadn’t taken the time to figure that out, I might have given up on big wheels. Tuning of front end geometry needs to be done with the understanding that many riders simply aren’t going to get the same saddle to bar drop, and thus weight distribution, on 29″ as they’re used to on 26″.
January 7, 2008 at 9:31 am |
Art: Good points. The thing that you are referencing is about fiting the rider properly. I wouldn’t be so quick to point a finger at the manufacturers though. This is the duty and responsibility of the bike shop that sells the bike.
That manufacturer sells the bike in a state that is tunable- ie: tall stack of spacers, stem in high rise posistion, so you the end user can have it fitted to you and your particular riding style as closely as is possible with a stock bike.
That said, it seems strange to me that one of the most common complaints against 29″ers is that the front end height is too high and that they come out of the box with such a long steer tube and riser bars many times. Something a little weird about that, but the practice is common place in the 26″er mountain bikes you see for sale in local bike shops too.
Oh, and if you bought your bike from an online source, that fitting responsibility then falls to the buyer. One more reason a good local bike shop is of great value to consumers.
Another thing: Weight distribution shouldn’t necessarily be the same for a rider going from 26″er to 29″er bikes. It could be, but it might not be in many cases. Lots of variables to consider there.
January 7, 2008 at 10:00 am |
I don’t mean to point fingers. It’s just a fact that the interplay between bike fit and handling is, for lack of a better word, quite squishy. And squishy doesn’t make for good add copy. Think about the big deal that gets made about how much things weigh. In the case of something like a saddle, this is a just about pointless, but people tend to focus on absolute quantities that they can compare.
I also didn’t mean to imply that weight distributions should be exactly the same between 26″ and 29″ bikes. At the smaller end of the size spectrum, that would require such long chainstays that the extra wheelbase would negate any advantage gained from moving the cg forward. In my head at least, the discussion about 29″ fork offsets and head angles all boils down to figuring out a way to get the correct handling out of a bike when it doesn’t have the weight balance we’re all used to.
January 7, 2008 at 10:38 am |
Art: Fair enough. I agree that the bike fit and handling issues are of a more organic nature and not so much related to hard numbers. It is also interesting to note that in the road bike arena, at least, a big deal is being made by the bigger manufacturers in regards to bike fitting. This is translating over to competitive mountain biking as well.
January 7, 2008 at 11:57 am |
It seems like it’d be most beneficial for bike fit optimization to be most prevalent in the competitive realm, however I don’t think pedaling efficiency and a good, or “correct” handling bicycle are mutually exclusive pursuits. I prefer the way my bike handles when it’s set up for the way my body prefers to pedal it, which is to say on most bikes, it means the saddle is set almost all the way forward on a zero-offset thomson seatpost. for many riders, that would seem to be far from optimal from a handling standpoint, but for me it’s perfect.
While I like the overall playful nature of 26er handling, I’ll gladly take the more sedate, stable handling of a larger wheel as a tradeoff for the decreased frequency of wipeouts that I incur today. If it means I’m going to start wiping out more to have a faster handling bike, I’m not sure it’s a tradeoff I’m willing to make. That said, if a happy medium exists, and you can make my bike handle a little quicker without making it more nervous or less stable, or making me crash more, then I suppose it’s not a bad deal. I need to spend more time with this getting first-hand experience though, because a lot of my time has been spent on forks with 38-41mm of offset.
I am planning on trying both the Manitou and Fox forks in ’08. I’m definitely buying a Manitou for my new El Mariachi, and I’m hoping to find the funds for a Fox for the race bike I’m building up in a few months (fingers are crossed). But those two forks will both have more than 41mm of offset, and will give me a little greater perspective. I don’t expect the difference to be startling, however. They’ll still be good handling bikes — just a little quicker.
January 7, 2008 at 12:29 pm |
To further aid in bike fit, I like this chart to record my position on the bike. 26″ or 29″, your basic contact points – bar, pedals, seat – should remain the same. I believe the only fair way to judge how a bike rides relative to another is to make sure you are in a familiar riding position.
http://www.parktool.com/repair/readhowto.asp?id=73
Click to access mtbpositionchart.pdf
January 7, 2008 at 1:38 pm |
Mike: Thanks! 🙂
January 7, 2008 at 3:32 pm |
I designed my most recent custom bike around a more relaxed head angle & greater offset fork. 71* HA & 56mm rake equate to a trail of ~68mm. The most striking thing I noticed was that the 29er wheel felt more intuitive in its steering…not necessarily twitchier (as is commonly implied), just much more natural feeling with NO floppy wheel syndrome.
I think that the larger diameter wheel tends to give a wheel flop sensation when coupled with standard 26″ xc geometry….the greater offset & relaxed HA may achieve what the steeper HA & lesser offset could not.
January 7, 2008 at 4:03 pm |
This may be off topic, but here goes…Recently, I’ve been checking out some of the porteur style bikes that are designed to carry heavy-ish front loads. Most are designed around what seems like short trail dimensions (between 26-38mm (that’s trail, not fork offset – I had to double check too at first). At first glance, that just seems so wrong, but with a heavy load on a front rack, that seems to work very well. The rule of thumb seems to be more weight over the front, less trail; more weight over the rear, more trail.
Throws a whole new dimension into designing a frame around a specific duty. At one time in the past, when I was reading some articles by Lennard Zinn on bike handling, I asked him what he thought the ideal trail was, he threw out 65mm. This was for a road bike but…
Keep up these good topics, G-T.
January 7, 2008 at 5:31 pm |
Excellent stuff GT, I don’t have any kind of patience for reading, but I’m digging this. You make it all read very exciting what we’ve been throught he past couple of years.
Offset vs weight load. I think larger offset means that the front end needs to be lifted further per degree of handlebar movement. So, much offset will handle heavily from the ligting perspective. It turns quick per degree of handlebar, but it takes a lot of effort. Interesting variable to throw in the mix. Perhaps not an issue if you’re just weighing the front with your own weight in a general riding position. For touring with front racks, something to think about.
January 7, 2008 at 8:04 pm |
GT, excellent post. Undoubtedtly, my recent fork upgrade really improved the handling of my bike. I researched this exact topic for months before settling on the Fox F29, which I think was the best upgrade for my 2007 Fisher Geometry.
I for one am glad to have “options.” Being new to the 29er game this year, I realize that a few years ago, these options didn’t exist. More to the point, I can’t wait to see what other options emerge over the next two years. I think it’s an exciting time for the 29er platform.
I wanted to start my own 29er blog, but man, you would make hard competition. 🙂
January 7, 2008 at 8:53 pm |
jncarpenter: Suh-weet Wolfhound! Those are very interesting rigs. I’d love to ride one someday. Interesting geometry too, by the way. I think I know what you mean about the steering. If I’m right, I would totally be into your set up there.
Mike: That is very interesting. Wow, that is a short trail figure! You know, it may be done that way in aneffort to overcome inertia created by having such a heavy load on the front wheel. I sure wouldn’t think riding it unloaded would be a whole lotta fun!
By the way…..congrats on the new signage! 😉
Anonymous, Jared: Thanks for the compliments. It means a lot to me. Seems that once you take a close look at one aspect of the bicycle five more things jump out at you! It’s an indication that one small change can really affect the whole bike. It is a system, no? 🙂
January 7, 2008 at 9:06 pm |
G-T – yes, it’s due to a very front biased load distribution. And thanks. Whew, another thing to check off the list.
January 7, 2008 at 9:52 pm |
I actually was thinking the other day that “geometry” isn’t really the best name for a bike’s design. In math, geometry is quite simple. Bike design (especially when factoring a squishy rear end) is much more complicated than adding up the numbers and figuring angles. Of course, I don’t really have any other suggestions.
I agree w/ GT that a bike’s design is systemic. I would say almost ecosystemic as nearly everything is intertwined.
January 7, 2008 at 10:13 pm |
OOOPS! I mistyped. My HA is 70*…so that equates to a trail of 76mm ( I knew the other looked horribly wrong)….:)
GT, I thought for sure you had seen my thread already….grab the popcorn!
http://forums.mtbr.com/showthread.php?t=321081
January 8, 2008 at 12:05 am |
Marc, try your 29er theory here:
http://www.dirtragmag.com/print/article.php?ID=894&category=features
January 8, 2008 at 12:34 am |
Jared, thanks. My main question is what are the trails in Crested Butte like? I’ve never ridden there, which kind of makes my credibility on Colorado trails pretty flimsy.
January 8, 2008 at 2:59 am |
Oops, forgot to sign in there.
January 8, 2008 at 6:36 am |
Jared: I vote we switch geometry to dynamics. Just to underscore the fact that all of this stuff only matters when the bike is moving.
January 8, 2008 at 12:14 pm |
I forgot to mention that I do research, if it looks good on paper I try it, but as you say, you have to ride it, ponying up for research is one reason, just yesterday I ordered an Origin8 fork and not a more pricey one.
January 8, 2008 at 1:11 pm |
This is just a great forum and it makes me happy to hear/read/see peeps chiming in. My 29er stable just got a little bigger thanks to Craig’s list: A 2007 Monocog. I am going to keep it fully rigid and single speed but plan to mess around a bit. I have an XXIX that switches between SS and 1×8 and I mix up an MX Comp at times too (44mm offset?) This coupled with the 71 degree HA seems pretty good. I might experiment based on any suggestions and have pretty much designated XXIX or Senor Rollie McGrippenstein (offend no one or everyone!) as my experimental platform. Finally I bought a close out SuperCal last year (just before the G2 HIFI – UGH but a grand cheaper…) It is stock and I have been working up to racing old man style this year.
So “test and contemplate, cause its 2008” seems to be the mantra of twentynineinches this year.
Get Some
January 8, 2008 at 5:01 pm |
Marc, having never ridden crested butte, I can’t say, but regardless, that article was a great peek into the history of this much-loved wheel size.
Art: I think dynamic isn’t a bad way to go. It emphasizes “interaction” between components. Good call.
BunE: I was talking with my riding partner a month or so ago. We’d LOVE to get out East and see what the terrain is out there. Here in Utah, SS rigs don’t go over to well (at least in the mountains) so we’d love to see about Wisconsin or some place more “hilly” where a single speed might work nicely. I’d love to start expanding my stable with wire donkeys tuned for more specific riding types. I’d love to try a ridig single speed with some funny handlebars on some smooth single track.
Mirroring GT’s comments, I love that I have tuning options for big wheels now. IMHO, the future looks bright for the 29er platform.
January 8, 2008 at 7:18 pm |
Marc,
Crested Butte is pretty tough to lump into one sort of riding. You can bet you will climb a lot and if you are from the midwest, you might want to put that small ring back on your bike, you will be using it.
Various rides there have different characteristics. 401 offers climbing to the top of Schofield pass at nearly 11000 feet just to get to the bottom of the trailhead. After a few more miles of climbing the trail, you will ride down some very smooth and very exposed single track.
Other rides there are very rough and rooty with a lot of seriously technical sections. Your can test your skills on some of the short rides right outside of town. You will find babyheads and exposed aspen roots in many spots and rhythm is sometimes hard to find.
The descent out of the epic Reno Flag Bear Deadman has thirty two switchbacks in less than three miles. It is rutted, steep in spots and shredded by dirt bikes. I am able to navigate it on my Mamasita with a Reba, but I will get dropped by riders on 26ers who would not drop me on any other part of the trail. The long wheel base on my 29er is a bit of a penalty, but everything can be ridden without a lot of drama.
The only real constant in CB is that the soil is great and there is a lot of traction.
Everything can be done on a hardtail, and most trails should be done on a hardtail. Some trails make you wish you brought a double squishy.
The most important thing to do when in that part of Colorado is Monarch Crest Trail. It is the most beautiful trail I have seen. It starts near the top of Monarch Pass and goes ends near Salida, The high point is well above timberline at 13xxx feet. You will ride a ton of different terrain. I can not emphasize enough that if you are near it you have to ride it. There is no place I would rather be and if somebody wants to drop my ashes there after I die, that would be fine with me.
Sorry to get so far off track for those of you that were looking to tune their ride.
January 8, 2008 at 10:41 pm |
Jared,Marc: Take that Rag story with a HUGE grain-o-salt. The story teller is a bit over the top and the truth of it all is a bit different than he implies. That said, some bits are great in that story and it does show some of what had to go into getting THE TIRE into production.
January 8, 2008 at 10:48 pm |
GT: I think the story is quite well-written, but probably a bit biased to his experience. I’d like to see some other points of view regarding the issue. I see little compiled information elsewhere. Just tidbits of this and that. Any other good reads on the subject?
January 8, 2008 at 11:02 pm |
Jared: There was a thread on mtbr.com at one time that was an investigation into the history behind the Nanoraptors developement and the first 29″ers. A fellow that posted by the name of “Bigwheel”, a Crested Butte resident and a very knowledgeable and influential 29″er pioneer himself had a bunch of gems posted on that thread until he butted heads with another poster and pulled all his info out of the thread. This fairly gutted the thread of any really good information and that was that.
Well, some of us read it and some smarter than I downloaded all the info and pics before the stuff got pulled. Let’s just say that the true information is a different tale than Mr.Cook’s and I have it on good authority that the first “modern 29″er” built with “THE TIRE” actually came out of Wes Williams Willits Brand shop in Crested Butte.
So, that’s the first 29″er and everything afterwards is really just anecdotal. The meat of the story is that Mark Slate was convinced and designed the tire and had it authorized to be manufactured. Others took that first batch and did more convincing, and on down the line to today. Without that first tire, we’re still riding 26″ers today. So, to all those who played a part, and especially to Mark Slate and WTB, I say THANK YOU! 🙂
Whatever way you want to read the history, the facts are that it comes down to getting that first tire, and to me that is all that really matters today.
January 8, 2008 at 11:08 pm |
GT: well put. Bringing this back into line, the fact that I have many tires to choose from to help change the performance of my bike makes me very happy. I would agree with you, thanks definitely go to those you mentioned.