Recently in the comments section from the post, “A Historical Perspective: An Editorial“, I was asked to comment on the following statement: “……please talk about how “standard” 29?r geometry has changed in the last 4 years and the effect 29?r specific forks have had.”
This is an important point to understand concerning 29″ers. I felt it was a serious enough subject that I conducted my own fork offset/axle to crown tests in 2008. It is a subject which has far reaching impact and still confuses riders up to the present day. (Editor’s Note: Due to a technical problem with Twenty Nine Inches picture host that we used in 2008, the images for the ” An Experiment In Front End Geometry” posts were all lost, but the text and data are still there for reference.)
This will be a brief look at where 29″ers were in 2006 and what the changes since then have wrought in terms of geometry, forks, and what we know about 29″ers handling in 2010. First off, we need to draw a baseline, circa 2006, so we can see what was being done then to accomplish the goals of big wheeled bike designers.
The first generation Reba used the old 26″er offset standard which limited what designers could do with 29″er handling.
Humans are a paradoxical species. We are at once extremely adaptable creatures, yet we often fall into distinct patterns which we like to maintain. Creatures of habit that can get used to changes. Weird isn’t it? Well, the 29″er front end geometry story has elements of both these human traits running through it, oddly enough.
When the 29″er came about it was understood from the start that a bigger diameter wheel was going to change the “trail figure” for the bicycle, which is of paramount importance in terms of handling. (See this page for a brief explanation of the term “trail” for bicycles as it applies to front end handling.) Because a larger diameter wheel causes the trail figure to grow, if all else remains the same, designers knew that a 29″er would automatically handle in a more stable/slow manner. Some designers embraced this while others felt it was a hindrance to big wheels and wanted the 29″er to handle like their old 26 inch wheeled bikes. Here was where the rub came for the latter group. Suspension fork crowns were “locked in” at about 38mm of offset.
While it is true that a rigid fork can be made to any specification desired rather easily, the suspension fork crown requires very expensive tooling to manufacture, so making offset changes isn’t something that is done easily or cheaply. Gary Fisher Bikes managed to have the early Marzocchi forks made with a 43mm offset, but even with head angles set at 72 degrees, (a full degree steeper than most 26 inch XC rigs), there was still criticism of the handling for its “sluggishness” and the Marzocchi fork wasn’t well received besides. In lieu of this, designers started playing with head angles instead, to achieve similar results to what a longer offset would achieve.
Salsa Cycles first generation Mamasita rigs had a steeper head angle to quicken up the handling using a 38mm offset fork.
A great example of this would be the first edition of Salsa Cycles Mamasita which used a very steep head angle to realize a lower trail figure but still could use the first generation Reba fork with its 38mm offset. Intense Cycles also did something similar with their Spyder 29″er which featured a 73mm head angle! While these bikes and others had a quick, nimble handling feel, the steeper head angle wasn’t optimal for a couple of reasons. First,it placed the suspension fork legs at an angle that made bump forces want to bend the fork backwards more rather than compress the telescoping parts together. Secondly, it made making anything under a size medium a huge compromise due to potential for toe overlap. The head angle trick worked, but at a cost that many designers were unwilling to make.
This was at a time when detractors of the 29 inch wheel were saying that 29″ers were not good for riders under 5’7″, (many still say this), that 29″ers were slow and ponderous, and that 29″ers would never be able to handle like a 26 inch bike. And you know what? They were all right about that back then. However; something happened that blew the doors off of conventional wisdom regarding 29″ers.
Back in 2006, I was invited by then Twenty Nine Inches head honch, Tim Grahl, to come out to Interbike and help with the 29″er coverage. That is a completely different tale, but I bring it up because of a chance meeting I had the first day in Las Vegas I was there. Tim spotted Gary Fisher in a local Vegas mall we were in and he tracked him down. We soon were chatting over a cuppa joe when Gary said the following: “Soon we will all be able to tune our rides.” What he then revealed to us was that there were plans afoot to change the offset of suspension crowns. To where exactly the offset would end up at wasn’t revealed then, but now the whole story can be told.
Gary Fisher obviously understood the criticisms of 29″ers and that is certainly shown by his early experiment with Marzocchi. This time there was a whole lot more research going on into the front end geometry of a 29″er. After all the numbers had been crunched by engineers, Fisher had several forks made as test mules and sent them out all across the United States to different test riders that worked for Trek. Six different offsets were tried by each rider. Word is that the decision on which was best was nearly unanimous. Travis Brown, the Mountain Bike Hall of Fame member and long time Trek R&D rider told me that when he tested the forks and found out what the offset was on the one he liked best, it was a big surprise to him. 51mm of offset! Well, as we all know, this became Fisher Bikes G2 Geometry’s focal point on the 29″er side. (26″ers got their own increased offset G2 crowns)
Now Fisher had to convince someone to forge new crowns to match his new offsets. Fisher managed to partner with Fox, getting Trek to front all the money for the tooling for the fork crowns that Fox needed to make the longer offset. This brought Fox Shox into the 29″er game, and so made even more of an impact. Because Fox only made the crowns to 44mm offset, and gained the remaning 7mm by using different lowers, they could use the same crowns for other companies and aftermarket 29″er forks.
It should also be mentioned that the suspension fork offset changes made since 2006 have been influenced by a couple of rigid forks. The first was Brant Richards’ On One Superlight steel fork which came out with a 47mm offset. This was a full two years before the Fox fork. Redline’s Monocog 29″er also was important as it mimicked the same geometry and was a wildly popular bike in North America. Because these two bikes were well received and well liked for their snappier handling, it was becoming obvious to those who were paying attention then that suspension fork offsets needed a change for 29 inch wheels. Fortunately, the market got big enough to make the investment into new crown forgings something that made sense to the major fork manufacturers.
What works and doesn’t with 29″ers? Well, this bike has a 51mm offset/74 degree head angle. It rides quick, but not out of the range of most riders.
29 inch fork geometry has now evolved to the point that 29″er handling has overcome many of the early complaints about a 29″ers handling traits. It also has allowed for a way to make smaller sizes work to the point now where we see even smaller women racers aboard 29″ers and winning. These bikes handle as well or better than 26 inch wheeled bikes with no toe overlap. However; more challenges have arisen with 29 inch forks. They have a longer “lever” than a 26 inch fork, so designers have been making specific lowers for the 29 inch forks in some cases. Tapered steer tube forks have also been employed to strengthen the critical crown race area of 29 inch suspension forks. Through axles were also employed to stiffen the wheel/fork interface and to more effectively remove independent fork leg movement from the equation.
Finally, getting back to Gary Fishers “tune our rides” idea, we now can choose different offsets and different head angles to find what makes us as individuals happy. Will a 51mm offset G2 fork work on a “non-G2″ bike? How about a Fox 44mm offset fork on a G2 Fisher 29″er frame? The answer is: A definite maybe. If there was one thing I took away from my own experiences on messing around with several different forks on one bike, it was this: That the 29″er wheel has a much wider range of possibilities when it comes to geometry than what would be workable with 26 inch wheels. Added to that is our own innate adaptability. Put a rider on a G2 frame with a 44mm offset fork, and after a few rides that rider will be going as fast or faster than they were on the same bike with a 51mm fork offset. I am not saying that the rider in question will prefer that, but I am saying that rider could adapt to it, and quickly.
The Opposite End Of The Spectrum: Even with a trail figure well over a 100mm, this Lenz handles quite nicely.
Of course, that begs the question: “Does any of this really matter?” The answer, I feel, is definitely yes. For everyone of us, that answer will be a different combination that sparks our feelings when we are riding our favorite trails. The beauty of all of this is not only does it matter for each one of us, but also that we actually can tune our rides. A thing that wasn’t really possible not too long ago with any front suspended mountain bike of any wheel size.
My conclusion is that although you can see this as a Pandora’s Box, which has caused no small amount of confusion in the mountain biking circles, it also has been a boon to mountain bikers. Especially those who ride big wheeled mountain bikes where the choices are many for dialing in a specific ride quality and handling feel by simply swapping out forks. (Something road cyclists have been doing for years, by the way.) My feeling is that “now” is the pinnacle of this “tunability”, as I am sure certain market forces will ferret out the fringes and choices will become fewer in a move to “standardize” 29″er geometry. The times will change, but for now “tuning your ride” is definitely a possibility. My opinion is that it is a good thing.
Hi everyone i also like playing with forks . It really changes the personailty of your bike ! I’m referring to hardtails. the bike i kept as my favorite is a raleigh 29er. I have used reba ,zokes and G2 fox. My favorite for suspension forks goes to the fox G2 . On the flip side rigid forks have a precise feel and great feedback. i’ved used alm. steel and carbon. And last but an oddity are the softride stems , the give you a hybrid ride combinding rigid fork presision and lightweight shock absorbtion. Yes i can can hear you guys snickering. bottom line you can tune 1 bike to different styles of riding. I run 1 type of headset so it’s easy to swap forks without removing race from forks. Sure is fun to to be part of GROWING group of great riders sharing ideas and concepts. Happy trails from Abq nm.
Thanks GT. Another great post. I see why reducing the trail has sort of become the Holy Grail of 29er geometry over the years. I think I read somewhere (probably from you) that 29ers can work with geometry that would be too twichy for 26ers because of the gyroscopic stability provided by the big wheels.
Could you explain the Lenz? Shouldn’t a 100mm of trail make it handle like a pig with all kinds of wheel flop? The wheelbase doesn’t look particularly short. What other factors make the bike handle well with 100mm of trail? Does it have anything to do with the full suspension? I suspect that rear suspension design opens up a whole different geometry can of worms.
Thanks for the post. Trying to self-educate before purchasing my first 29′er, which will be a big, rigid SS. I do not have the luxury of being able to test ride virtually any of these options here at home. My question, based on the information above, is whether the 6’3″ plus rider need look out for certain forks that may have gone overboard with concessions to making the 29′er ride friendlier for a broader height distribution? Can one assume that when frames are over 20″ in size too much fork offset may detract from ride quality?
@dan,
Hey. I’m holding back my snickering. Can you explain in more detail what you meant about softride stems offering advantages on offroad riding? I’m of the opinion, through lots of personal experience, that softride stems change the geometry more than any other device ever put on a bicycle and should be left to a dimly lit corner of a bicycle museum somewhere. Get on a set of whoopdies, or on a flow track, or any downhilling with drops, or any drop with a turn in it, and it will leave you wondering why someone would use such a device.
They look cool and feel great for about 20% of what gets thrown at them, but that’s about it. There; that’s my piece. Have yours, please.
regards,
kurt
Interesting note on Mechanical Trail vs. Ground Trail:
http://www.pvdwiki.com/index.php?title=Mechanical_Trail
@John B: The Lenz doesn’t make sense on paper, but on the trail it rides very nicely. The wheels allow a wider range of possibilities due to their inherent characteristics, as I point out in the article. This is why numbers don’t really work for 29″ers as far as telling you much about how the bike will actually behave on a trail. You’ve got to ride it to see for yourself.
A Jack H: Really, height has little to do with this, as long as the bicycle fits you. Most rigs out there will handle fine. There really isn’t a bad bike, just some that lean towards stability and some that lean towards being quicker. Something in the 71-72 degree head angle area and 44-46mm offset should be a great starting point. Fisher G2 is great as well, but the numbers freak out some folks. I would strongly encourage a test ride/demo if at all possible so you can find out for yourself what you like.
@JT: I don’t really see any substantive reason why mechanical or ground trail would call out going with one way or the other in terms of choosing a fork. Semantics it seems. If one really wants to be persnickety, trail is constantly changing due to the dynamics of trail surface and how it interacts with a low pressure mountain bike tire. Just ask Keith Bontrager sometime.
Finally, I would point back to that Lenz and tell you that however you want to measure the trail figure, it handles waaaay better than that number would indicate. So, we can get lost in the minutae, or we can ride. This post is just a way to show that 29″ers have changed and for the better, in my opinion. You can influence your handling with different forks, and that’s cool. That’s all really.
Ride On!
I am expertimenting with my spare frame in order to get a long travel 29er, to that purpose I have converted my Marin Wolf Ridge 2004 (100-150 mm rear travel) into a 29er full sus. I managed to squeeze 29er wheel with Bontrager XDX tyre in the rear, but only 29 x 1,75. I have set it to 120mm of travel (rear) and 100mm (front – RS Reba). Due to very high BB position (390mm!!) and the centre of gravity It felt a little bit weird but not bad at all
.
. Just wish me good luck, the experiment is on its way 
In order to get the full potential in the rear (a “true” MTB tire, at least 2,1)and to lower a bit the BB I am planning to put a 650 wheel (rear) and either keep the 29er in the front or put there a 650 wheel as well. The travel in front would in both cases be kept at 100 mm (no spaer forks with longer travel
Michal, Slovakia, Europe
I really think articles like this can serve to confuse people more than anything else. These numbers don’t mean anything to the majority of everyday riders, and it says in the article “our own innate adaptability” allows us to deal with all these changes in angle and trail anyhow. By making a deal about numbers, people will concentrate on those instead of the overall ride. The overall combination of angles and tube lengths do make a frame, but whats hanging off that frame can make an even bigger impact on the way it handles and rides. Stem length can not only effect handling, but fit as well, making an ill fitting and ill handling bike.
Riding a bike is the only way to really tell how it will handle, the Lenz is a great example, but even then, bikes with similar numbers can ride differently as well. Having worked in bike shops for over a decade, I have had to try to talk people out of their preconceived notion that they can only ride a bike with angle/length/trail X. I have had thousands of customers tell me that they loved riding a specific bike and it fit them well and it had the parts they wanted, but they didn’t want to buy it because angle/length/trail X wasn’t the right number. This will never make sense to me.
Just my two cents.
ChiefRock – I see your point. But, frankly, I can read “laterally stiff, vertically compliant” anywhere. I like TNI and sites like it for this sort of “inside baseball” stuff that other media doesn’t touch. This article didn’t obsess about numbers or even state a conclusion on the “best” front end geometry. It just showed the industry’s progression over the years. I think its an interesting aspect of development of the 29 inch mountain bike. Maybe people do obsess about numbers too much. You can go out and have a fun time or even win races on quite nearly any bike (that fits well), after all. But isn’t crunching numbers and tweaking equipment part of any sport that people are passionate about?
Damn this makes me want to resurect Solitude Cycles and play about with geometry again!
The Blackbuck is a great handling bike despite what the “numbers” say…my only off-road ride now
Alex / SSP
Actually, the Redline Monocog 29er was a pretty basic build geometry wise. 72/73 angles, 39mm offset. The Monocog FLIGHT 29er got the 47mm offset (they didn’t dare venture further than On-One, but wanted the associated traits), un-29-orthodox short top tube (20mm less than the Monocog 29er), and unexciting 71deg HTA. Intentionally, wheelbase and trail were shared between both lines of models.
I think I first heard Eurobike 2006 that G2 would be 51mm. I was expecting that a new Fisher breed would be “right”, but so far out there. I was pretty awe struck. Especially learning that it would be Foxes. Not hat Reba’s were bad, at all, but realize how importatn Fisher has always been in getting new fork makers into 29″.
Those first Fisher 29″ers had, I think, 71.5deg HTA’s, with that 43mm offset. Rode just fine, apart from the V brake shattering flex in the Marzocchi forks. Look in today’s geometry sheets, and you’ll find some “innovative” bike brands still being where Fisher was in 2001.
Both On-One and Redline used only one prototype fork, that I’m aware of, to see if that suggested 47mm might possibly be a good idea. Makes you wonder, why it takes so long before someone actually went out and tested all options (Fisher). If one cares for making the best possible bikes for their customers, that’s what you do. Try things. Not publish your spec sheet before you’ve built your first prototypes, which seems to be common use.