You have it exactly backwards.

All other things being equal, the larger the trail measurement, the more stable the vehicle will be at speed and the more steering effort will be needed to make the vehicle deviate from a strait line. This is easily proven. Look at a shopping cart. The front wheels are offset from thier pivot axis. When you push the cart, the wheels swivel and 'trail' behind the pivot axis. If the front wheels were not offset from the pivot axis, that is, if the front wheels were mounted directly under the pivot axis, you could not push the cart as the front wheels would stay pointed in whatever random direction they happend to be pointed when you grabbed the cart. If the two front wheels of the cart where connected with tierods and had no offset, you could not steer the cart as the front wheels would steer themselves based on bumps in the floor.

Okay, you've got my interest now with the mention of front end push. It's the "backwardness" of tandem handling traits that derailed me in the past. I'm an ex motorcycle road racer (not engineer) and what you call "racey" handling is not what I have always thought of as "racey" handling, but you have mentioned the area of deficiency in our 05 Trek T2000 and correctly attributed it to the manufacturer. The front end is the first to start scrubbing when having fun in 25-30mph corners (coasting, weight on the outside pedal, not on the brakes). I don't push it hard enough to get the same results at higher speeds mostly because my stoker wouldn't appreciate it.

The bummer about front end push on the tandem is that I can't use the throttle to bring things back in balance.

Is there a fork that you believe would bring the bike in balance, or do they just give less feedback and provide a false sense of security?

I think we might be test-riding Co-Motions this weekend...

There are three forks that will improve the handling of your Trek:

1. The Burley-True Temper Alpha Q with canti bosses is the correct length and has 47mm of offset which would, in effect, give you Co-Motion like steering geometry... not cheap but a great fork for tandems with Cantilever brake requirements.

2. The Wound-Up carbon fork that Co-Motion uses on it's tandems would also give you a significant change in steering but, at the same time, it would also lower the front end of your tandem a bit.... it takes a few rides to sort out your revised pedal clearance relative to cornering and your saddles would most likely need to be tilted back a little to off-set the change. Your choice of Canti-bosses or caliper.

3. Co-Motion's chromoly fork. It's a pig, but it's also quite stiff. It has 50mm rake and would also lower the front end of your Trek a bit but still yield Co-Motion like steering geometry.

The True Temper Alpha Q X2 would also work, but the drop in the front end height on a Trek would be pretty dramatic.... a full inch. Given the other options, this would not be as high on my list of recommendations as it was in the past when the pickin's were pretty slim.

As for the change in performance, it's all real... not smoke and mirrors. Most teams who have a hankering for bombing through corners will end up with a gleeful smile once they acclimate to the Co-Motion's somewhat unique handling and lively feel. It's quite different from the Trek and it's peers.

K&M you are spot on: the word "trail" did confuse me as I had a tendency to think of it the other way around. Thanks for clarifying. TandemGeek's drawing and diagram helped, too.

So, I can see that it won't tell me much but I am interested nevertheless: I will get out a 2x4 and have a go at measurements this weekend. Thanks.

JayB: I bought teh Reynolds based on my experiences with their line and the similar geomtery of the Reynolds to teh C'dale it first replaced. As TandemGekk says, they're almost identical. So, since I had a near-new Reynolds when I got the Co Motion, I just swapped it. It's a lot lighter than the WOund Up, and quite simply I hate the way the Wound Up looks (pretty stupid, eh?). The ride may be slightly more stable than the original Co Motion fork in theory, but that is not really noticeable while the clear advantages in ride quality are. I ride on aerobars in a timetrial position much of the time, so the extra bit of rake is advantageous: aerobars on a quirky bike don't mix well when wind and potholes are added to the mix. There are lots of disagreements about this topic. My suggestion, and one I learned by asking this sort of stuff years ago, is do a websearch and read what the premeir designers say. I did a quick search on Goggle: trail, rake, steering geometry. I got a great article where Erickson, Dwan from CO MOtion, Zinn, and a bunch of premeir designers weigh in on the topic. They do talk as if the frameset is a single piece, not a frame and fork in concert: they're asuming you're going to stay with the fork they sell you which doesn't happen as often as it used to. They also don't agree technically any more than we do!!! So, the best thing is to ride all the variables. Unfortunately that doesn't work when you're buying a new fork for an existing frame. Then I'd suggest asking others what their experieinces with that change have been.

Here's where that article is: http://www.thetandemlink.com/articles/headtube.html

ElRey: Thanks for the link you provided in a different message. Interesting what you say about the Woundup vs the Reynolds forks. The newest Woundup fork, as supplied by Co-Motion is pretty much all carbon, like the Reynolds Ouzo, isn't it?

The '06 Wound-Up forks coming available in late December will feature a carbon crown that replaces the aluminum CNC'd crown presently in use, making it essentially an all-carbon fork. However, the construction method for the Wound-Up is very different from the Reynolds and most others in that the carbon fork legs are produced individually and then bonded to the crown as is the steerer. The Reynolds Ouzo & True Temper's forks are layed up such that the legs and crown are a single carbon structure that is integrated with the steerer during the autoclave (cooking) process to produce a one-piece unit.

The best analogy I can think of is comparing lugged frame construction (Wound-Up) to a Trek OCLV frame (Reynolds / True Temper).

More on the True Temper process can be found here:
http://www.truetemper.com/performanc...ooting_big.jpg

Oh, I see. Interesting. I hadn't realised that there was this difference. Sounds as if the Reynolds / True Temper approach is superior. Is that what you are implying?

Absolutely not; they're simply different approaches to a common end. Lugged carbon construction is actually not all that unusual, noting that Calfee builds its carbon bikes and tandems using a carbon lug & tube approach, as do many other builders along with Ti & carbon, etc...

In fact, it could be argued that the use of the CNC crown with bonded legs and steerer results in a very robust fork. However, that robustness carried with it a weight penalty that made the Wound-Up fork (~800g) less attractive to gram shavers than the Reynolds Ouzo Pro Tandem (~535g) or the very svelte True Temper Alpha Q X2 (~445g). The new carbon crown will bring the Wound-Up fork's weight down to ~680g, quite respectable for a very robust fork. However, it's also worth noting that the Reynolds fork is also very robust, enough so that Santana offers it as an option on triplets. Notwithstanding the different rakes and axle to crown lengths -- the Reynolds @ 55mm & 395mm , the Wound-Up at 45mm & 387mm, and the Alpha Q at 41, 44 or 48mm & 374 -- the one thing that some folks don't find attractive about the Wound-Up fork is its looks: it's definitely one of those "love it" or "hate it" things.

http://www.advancedcomposites.com/im...ndem_fork1.jpghttp://www.precisiontandems.com/cat_pics/fkalphaq.jpghttp://www.awcycles.co.uk/smsimg/78/...tandemfork.jpg

Thanks for the advice, Mark.

An excellent thing to do when pondering component upgrades or otherwise curious to know how other tandems might compare to what you're currently riding. Often times teams will discover that they made the right choice the first time when they scratch that itch and go on to ride their trusty steed for many years without wondering if the grass was greener on the other side. Conversely, some teams experience an epiphany when they try out a different material or brand of tandem and opt to upgrade the entire machine vs. "tweaking" their old one. After all, the heart of a tandem is it's frame and the geometry that it was designed around and there's only one economical way to change that. Moreover, it's very easy to over-improve a tandem beyond a reasonable return at resale and many teams searching for that "killer upgrade" to their tandem will spend a fortune on wheels, forks, carbon bits, and other bolt-on happiness before realizing that they could have taken what they spent upgrading + the resale value of their tandem before they started upgrading and purchased an entirely new tandem. The latter, should you start down that path, is why it's usually a good idea to keep all your original parts since a used tandem -- regardless of how many upgrades it has -- is usually worth less than the sum of it's parts. Thus, if you've upgraded and then decide to sell, use your old parts to put the tandem back in original trim and sell it outright, and then sell off the upgraded components: you'll usually come out ahead and won't find yourself with a bunch of spare parts that you'll never use or be able to sell for a decent return.

You're welcome :)

I would never have figured this stuff out myself if it hadn't been for TandemGeek (although he went by some other name back then).

Galen: Not sure what you think I have backwards. You are right that long trail tandems tend to be more stable "at speed." That's why I got one. The reason most tandems are made with shorter trail, though, is that they feel more stable at the recreational speeds that most users prefer.

Here is the qhote from your other post: "The more trail there is (i.e. the closer the wheel is tucked up under the frame) the quicker it will tend to steer"

The fact is that the longer the trail measurement, the slower the bike will steer.

Short trail = quick steering

Long trail = slow steering

Long trail = slow steering = stable at speed

I like long trail on my single bike for the same reason.

Galen: My quote is exactly correct. A tandem with longer trail will tend to have steering that feels much quicker under normal (i.e. slower) riding conditions. That's why people with CoMo's (with long trail) rave about how they steer more like single bikes and why average tandems (with shorter trail) tend to steer more like the Queen Mary at normal speeds (yet feel comfortingly stable and not apt to wobble across the road whenever the stoker shifts weight).

You mention that you haven't ridden a CoMo. If you tried one I think you'd see what I mean. The difference is quite striking.

I have enjoyed the reading of this thread. It is very knowlegeable. Does anyone know the range of trail measurements? For instance, I am interested in the Gunnar Rock Tour frame. It has a rake of 39 and a trail of 70. Does someone know where the numbers relate when it comes to steering geometry?

In a conversation I had with Marc Muller,Gunnar head of design,the finest silver brazer consuming oxygen,and all-around good guy, he told me that trail works in a range from about 53mm-70mm on road bikes.53 being twitchy quick and 70 being stable.

This thread has been generally worthless and misleading,since some are saying that more trail leads to quicker handling and slower handling,and less trail leads to slower handling and quicker handling....

Since all geometry charts I've seen lately suggest all road tandems are 73* everywhere,the only difference is in fork rake.I saw an old CoMotion chart that stated a 74* HA back in the triple lateral days,but no more.

A>Either some really aren't at 73* intentionally or not
B>They can all be made to handle the same with a maximum 1cm change in rake
C>Stem length must be considered.A long stem on a short rake fork would put more captains weight on the front wheel,creating a quicker steering bike.

dan

This is a true statement, at least for road bikes with 3' wheelbases. However, it's not true for bicycles that have 6' wheelbases designed to carry two adult riders. I have no idea if Marc has ever designed and built a tandem so you might want to make a point of having a follow-up conversation with him and asking him specifically about steering geometry and trail for tandems: at present, even your Cannondale tandem with 51mm of steering trail falls under the range specified by Marc. Moreover, you'll find that Bilenky is using 42mm - 46mm and the "norm" used by Santana, Burley, and Trek is 47mm - 51mm . If you think all of these builders are uniformly misrepresenting only the specifications for their tandems you could also call up someone like Mark La Plante at Cannondale, Dwan Shepard at Co-Motion, Todd Shusterman at daVinci, Steve Bilenky at Bilenky, or any one of the other road tandem builders to discuss tandem geometry. Or, you can accept the fact that different types of bicycles require different types of geometry and aside from unicycles, tandems are perhaps the most divergent from the steering geometry you'll find on road bicycles built for a single rider.


The subjective nature of handling descriptions has been addressed in this thread and, Yes, it is very easy to get confused given how the same words are used to describe very different types of handling characteristics. This is why some of us go to the trouble to quantify the differences by using more lucid descriptions, the impact of speed, and even pointing out which builder's tandems will demonstrate the different characteristics that are being described.


With regard to head tube angles and tandems, this is true... the exception being for certain builders who adjust the geometry of their very small size frames and the very large size frames. As for fork rake and trail, although the changes in numbers seem small the impact of the changes are tangible and often times quite dramatic depending on the size and riding style of each team.


As previously stated, I'm not sure why they'd mis-represent their geometries so give a few builders a call and challenge them on it. As for making them all handle the same, it would be more accurate to say that you could duplicate any of the builder's steering geometry on any of these tandems by changing forks. As to how they would handle, you would have to assume that the frame construction and other aspects of their respective designs all the way down to the wheel and tire selection were the same to have the "same" handling. And, yes, the position of the captain's weight over the steering axis will affect the steering on a bicycle; however, it is not as dramatic on a tandem as it is on a solo bicycle since the total weight of the tandem is distributed over a much longer wheelbase. Moreover, when accelerating or decelerating, there is also a more significant total shift of mass from front-to-back and back-to-front which must also be factored into the equation, never mind how differences in the captain & stoker weights can play into how a tandem handles, e.g., a child or very lightweight adult stoker.

Georgia boy asked about a Gunnar Rock Tour and those trail figures were for a single bike.I have no need to ask Marc Muller about tandems,but I suspect he designed a few at Paramount as well as Waterford.

Reading these posts again,there is no pattern or logic to the descriptions given as to steering characteristics compared to steering geometry numbers,and the numbers from manufacterers are very close to the same.

Anybody notice the new Calfee tandem prices?Down over a G for the new frame design.

dan

I can only speak for my own writings and, in this regard, short of posting the entire text, technical sidebar, and tables from a column of mine that was published in RTR a few months back, I would argue that the information I have provided has been consistent and quantified. That you disagree is your prerogative and perhaps indicative of my second quasi postscript reply on this entire subject, to wit: "... and if you haven't figured it out yet, steering geometry and frame design are the most controversial subjects in the bicycle sciences.". Moreover, if you read my compilation of postings from a few years back by Glenn Erickson, Dwan Shepard, Andy Dyson, and Todd Shusterman to which ElRey made reference and subsequently linked to, you would have seen that even the well-respected folks who design the tandems and bicycles we ride often times get wrapped around semantics while trying to describe the very same characteristics.


You'll excuse me for previously sharing only the tandem builder trail numbers that were shorter than the range provided by Marc Muller in your post to illustrate (or as evidence, if you will) that the information pertaining to solo road bikes is a bit different from tandems. Therefore, to round out the full range of popular contemporary tandem designs let me add that Co-Motion's standard tandems & Burley's "Race Package" use approximately 54.5mm of trail, with Co-Motion's carbon fork-equipped models being closer to 57mm, and some of the Ericksons including our two having somewhere around 60mm of steering trail. Interestingly enough and perhaps purely coincidental, this provides a useful range of steering trail for 700c wheeled tandems of 42mm to 60mm which closely approximates the same ~1.7cm span provided by Marc Muller for road bikes. As for Marc's comments on the shorter numbers being "twitchy" and the longer numbers being stable, we're back into semantics and parsing the differences in how steering geometry acts on a 3' wheelbase vs. a 6' wheelbase or longer.

In closing, while I don't totally disagree with your assessment that in some respect the various "different" tandem designs are perhaps more similar than they are different, the vast majority of tandem enthusiasts who have ridden the full range of tandem offerings usually pick-up on the differences and find a preference for one or the other. Therefore, when someone asks "what are the differences" the discussion will invariably go down this dirt road. Does any of this matter? So long as anyone in the market for a tandem finds one that meets their expectations for quality, cost, comfort, and performance, probably not. Thus, it remains an academic exercise for tandems as well as solo bikes where the differences are even harder to detect... since they usually don't have a passenger who is just as likely to wiggle around as they are to sit and spin as nicely as can be.

How does tire size affect all of this? I made a crude drawing and it looks like a taller tire would increase the trail, but probably not by much.

Example:

700x28mm tire on frame with 73° headtube & 55mm fork rake = 46mm (1.81")
700x37mm tire on frame with 73° headtube & 55mm fork rake = 49mm (1.93")
700x47mm tire on frame with 73° headtube & 55mm fork rake = 51mm (2.00")

Thanks for your response. With trail of 70 on the Rock Tour frame making it stable is what I am looking for.

To Georgia Boy, yes... if what you're looking for is that effortless, down the road performance that century riders and folks who do brevets or loading touring favor, 70mm will certainly deliver on that. However, just be aware that this thread has been addressing steering geometry in the context of how it affects tandems which you've probably picked up on.



Actually, I tend to side with Galen on this latest round....

I know what you're trying to say; however, Dan's (dfcas) observations regarding the confusion factor are in full swing here.

You had it "right" when you posted, "Galen: Not sure what you think I have backwards. You are right that long trail tandems tend to be more stable "at speed." That's why I got one. The reason most tandems are made with shorter trail, though, is that they feel more stable at the recreational speeds that most users prefer. Your follow-up post just didn't track well...

Again, the problem is using words like "twitchy" and "quick" to describe different things. A racing bike with short trail does have "twitchy quick" steering which is good and which might be better restated as being "light, quick and very responsive to steering inputs". Tandems with longer than average trail like Co-Motion and Ericksons are often referred to as "twitchy" but in a bad way since at slow speed long steering trail causes front wheel flop (which does make the wheel turn quickly, even when you don't want it to), making the steering heavy, slow and shakey since a heavy hand is required to keep the wheel headed in the desired direction. As speeds increase, the negatives associated with long trail on a tandem tend to diminish IF the stoker is a smooth rider. If the stoker tends to move their upper body a lot or rocks their hips while riding, life on a Co-Motion or an Erickson can be quite fatiguing to the captain since every time the stoker shifts their center of gravity to the left or the right, the captain must counter each shift with a steering input.

The upside of long trail on a tandem is having a bike that is very responsive to the leaning inputs that most folks who ride racing bikes intuitively learn to use when steering, which is why a lot of folks who ride Co-Motion's tandems find that they are very responsive to the same leaning inputs.

Santanas, Burley, Trek and others with their "light, quick, and very responsive steering" do, in fact, behave quite nicely when starting, stopping, and riding a slower speeds (e.g., climbing steep grades) and don't tend to turn left or right as much as the tandems with longer trail in response to weight shifts by the stoker. They are also quite stable at high speed, e.g., cruising down the road. However, when it comes to cornering at high speed they are less responsive to turns initiated with leaning/countersteering inputs than the long trail tandems and can exhibit some understeer when pushed hard enough.

Despite Co-Motion characterizing their tandem handling as "neutral", Cannondale actually owns that spot. Co-Motion only becomes neutral when you throw something like an Erickson into the mix...