Frame geometry and handling

galen_52657

I will try to help you then Mark can clear up what I mess up.

On any two-wheeled single-track vehicle (bike or motorcyle):

For any given head angle (say, 73 degrees), the more rake in the fork (the higher the offset measurement) the less trail the bike will have. Bikes with less trail will initiate turns quicker and with less resistance. Longer trail (less fork rake) will result in a bike that is slower to turn. Think Harley (lots of trail, wants to go strait) or Kawasaki Ninja (less trail, wants to turn).

Some folks rave about the Co-Motion 'racy' handling which in fact has more trail than other tandems which would result in slower steering. I have never experienced this first-hand. But, I would guess that on high-speed descents, the slower steering imparts a greater sense of control and stability to the pilot and thus the pilot pushes the speed of the descent.

Tandems are very stable at speed anyway because of the long wheelbase, so I can't quantify how much difference it would make.

JayB

Useful info on angles. How is seat tube angle measured? And how does it equate to the millimeter figures TandemGeek throws around? Thanks.

galen_52657

Seat tube angle on almost all production tandems is 73 degrees front and back. I think large Burley's might be 72.5. Seat tube angle on tandems has almost no effect on the steering. The bike is too long and changes in how much weight is on the front wheel vs the back wheel will be negligable. Most folks adjust the seat fore-aft to the KOPS of their single bikes anyway.

ElRey is talking about single bikes.

ElRey

Frame geometry is not the same as fork rake, trail etc.... Best to keep the two separate. Your riding demands should determine what type of frame (touring vs. racing) you lean towards. The fork will probably come with the frame, so you don't have to know anything about it: no good Mfg. will put an inappropriate fork on their product. If you're replacing just a fork then you need some more data. If that's the case, this sort of forum is not the best place to decide: contact your frame Mfg. and get recommendations from them. A racing fork on a touring frame won't make a racing frame.

galen_52657

ElRey.....

Frame Geometry IS the same as fork rake, head angle and trail. They are the DETERMINING FACTORS of the frame geometry and how the bike will handle. The combination of head angle and fork rake have more effect on the bike's steering than any other factors. Fore-aft weight distribution, center of gravity and wheelbase will also determine how a bike handles, but to a lesser extent than the front end geometry. After all, it is the fork that does the steering.

We are talking about tandems here, not racing singles or TT singles. If you look at any tandem manufacturer's website and look at the frame specs, you will find that with few exceptions, the frame geometry is identical within the models/price ranges for each give frame size. The seat tube angles are the same, the wheelbase is the same, the fork rake (offset) is the same. Burley offers an upgrade to a carbon fork with less rake but otherwise, everything is the same across the line.

ElRey

You can change your fork rake and trail by buying another fork. You can't change frame geometry. And frame geometry is not determined by fork rake, trail or anything else related to teh fork. Once the use of a frame is established and an appropriate geometry layed out for that use, then the fork is designed around that. The frame is not designed around the fork. Call a frame builder and ask them.

ElRey

galen_52657

ElRey,

Changing the fork on a given frame will completely change how it handles, even to the point of making the bike unstable.

Of course all other factors are considered but the frame's steering angle and fork offset are primary considerations.

And again I will state that with tandems, with very few exceptions, the frame geometry is the same regardles of it's intended use.

And here are some long-establisthed general guidelines for single bike geometry:

Racing frames:

Crit racing bike - moderate to steep head and seat angles, short trail, high bottom bracket for quick steering and pedaling through corners.

Road racing bike - moderate to slack seat angle, moderate head angle, moderate to long trail, lower bottom bracket for comfort, more control descending, powerfull climbing position.

Road racing TT/Tri bike - extremely steep seat angle, moderate to slack head angle, moderate to long trail, low bottom bracket for aero riding possition and stability.

Through the size range:

Smaller frames have steeper seat angles and slacker head angles and more fork rake. Larger frames are the reverse.

Small changes in rake/trail - 3 mm - can make a big difference in the way the bike steers.

Due to the advent of brake/shift levers, racing bikes in general have less trail than they did 10 years ago IMHO.

ElRey

Let me attempt to restate since I don't sem to have made myself clear: you can't determine trail and rake from teh frame's geometry. They relate to the fork. Of course rake and trail impact handling, but where did I say they didn't. BUt they are changeable, not frame geometry. Our friend here semed to think that they were all one: he lumped head angle, rake and trail into one grouping and they aren't in the same grouping. Rake and trail can be alterd by buying a new fork. You're stuck with frame geometry so that's where you look closely. Hence, I initially bought a frame set with 73 degree frame geometry (Cdale) and changed out the fork with something a little bit quicker. Changed the handling characteristics completely. Frame geometry didn't change.

TandemGeek

Over the years I have heard lots of references to frame geometry which cite "angles" such as 73 degrees (apparently that's what Co-Motion design to). Also references to millimeters of rake eg, 55 for Santana and 45 for a Co-Motion with Woundup carbon forks. But . . . what do these figures mean? Can anyone explain in layman's terms how this affects handling and stability of tandems? Perhaps I'm not the only one who would be grateful for an explanation.

Here's something I wrote in Aug '04 during a thread discussing the differences between a Santana Sovereign and a Co-Motion Speedster. I think it's perhaps closer to what you're looking for...

Co-Motion Speedster/Roadster - Total road bike feel. Pretty unstable @ lower speeds, but handles like it's on rails @ higher speeds.

It's probably an overstatement to say the Co-Motion geometry is "unstable" at slower speeds in much the same way it is to say that the Burley, Santana, or Trek tandems are "unstable" at high speeds.

Not to put words into other folks mouths, but having read how various folks have attempted to put riding impressions into words over the years -- myself included -- I think a more accurate way to characterize it is....

A Co-Motion demands more attention and steering control by the captain at speeds under 10 mph and is very sensitive to weight shifts or movement by the stoker. This is sometimes disconcerting to new teams during initial test rides or even experienced tandem teams who have ridden tandems with less steering trail when they first ride a Co-Motion. However, it's also something that almost any but the largest teams or teams with stokers who move around a lot will assimilate into their normal riding experience in short order (like a couple of rides). The other, shorter trail models (Santana, Burley, Trek, Bilenky, and most others) have a more refined feeling at slow speeds and are less sensitive to weight shifts or minor movements by the stoker. The Bilenky is perhaps the most refined in this regard as it has very short steering trail. At the opposite end of the performance spectrum, the Co-Motion comes into it's own as it is very responsive to leaning inputs for directional control and does not exhibit any oversteer throughout the speed range. The tandems with less steering trail will begin to exhibit understeer at higher speeds and do not inspire aggressive cornering as much as the Co-Motion. In the mid-range, the Co-Motion is a livelier ride than any other the others, whereas the Santana and Bilenky are perhaps the most refined. In short, comparing tandems is like comparing fine wines (or coffees and cigars, noting that is what Co-Motion names its tandems after). Some are more sweet, some have more body, and some are just plain awful. Everyone's tastes vary, so you try to find a good match.

If you can find it, my column from Issue #16 (August/September) of Recumbent & Tandem Rider Magazine also addressed tandem steering geometry without getting too tied up in the numbers. However, as others have noted, unless you are having a custom tandem built or changing the fork, a given tandem's steering and frame geometry are factored into the tube selection (material, diameter, thickness, internal or external butting, and shaping), and even the wheel and tire selection to create the steering, handling, and comfort that the designer or marketing department believes are what its customers are looking for and/or what they believe exemplifies how their products should perform. The latter is why test riding is so important, both when shopping for your first tandem and more importantly after you've been riding for a year or so and start considering the things that you'd like to change about your next tandem.

TandemGeek

... and if you haven't figured it out yet, steering geometry and frame design are the most controversial subjects in the bicycle sciences.

galen_52657

Hence, I initially bought a frame set with 73 degree frame geometry (Cdale) and changed out the fork with something a little bit quicker. Changed the handling characteristics completely. Frame geometry didn't change.

And I went the other way on my old Gitane with 74 degree head angle. I had the steel fork straitened by about 3 mm thus increasing the trail.

Both of us, by our fork modifications changed the frame geometry: We changed the rake, we changed the wheel base and I changed the steering angle slightly by raising the head tube a smidge.

My Gitane was much less twitchy on rough descents after the change.

ElRey

You didn't change frame geometry, you changed steering geometry! They're not the same, which is my point. You can only really change "effective" frame geometry through the offset of your seat post; head angle can't be changed. If you straightened your curved blade fork, not only did you change the rake, you changed the blade length, so the frame may not ride plumb anymore. I don't mean to be combative here, but I think the guy really wanted to figure out what some of this stuff means. My intent was to point out that fork variables like rake and trail are true variables within a frameset (frameset: frame and fork in concert) since the fork can be changed. Headtube angles and seatube angles are fixed (until you begin to offset your dsaddle one way or the other with a rear or forward ofset seatpost). Good thing JayB didn'st ask about how all this relates to stem length.....

TandemGeek

Let me attempt to restate since I don't sem to have made myself clear: you can't determine trail and rake from teh frame's geometry. ... Rake and trail can be alterd by buying a new fork. You're stuck with frame geometry so that's where you look closely. Hence, I initially bought a frame set with 73 degree frame geometry (Cdale) and changed out the fork with something a little bit quicker. Changed the handling characteristics completely. Frame geometry didn't change.

Actually, you need the head tube angle based on a given fork length + the fork's rake + wheel diameter to calculate the trail. You can unintentially alter the frame's geometry when you change fork to obtain a different amount of rake if the fork length is NOT essentially the same as the original. With regard to the change you made, replacing a steel Cannondale fork (53mm of rake) with a Reynolds Ouzo Pro tandem fork (55mm rake) would not have been much of a change as they most likely have nearly the same fork length @ 395mm (+/- 5mm): a small change in trail. However, given that most tandems use forks that are longer than solo racing bikes, a lot of folks who switched over to AME's (now True Temper's) Alpha Q forks lost nearly an 1" of fork leg length which had the net effect of change the head tube & seat tube geometry by a full degree, as well as lowering the front bottom bracket.

Thus, the suggestion to discuss fork changes with your frame's designers or builders is always an essential step as some changes -- if not fully understood -- can really alter how a tandem will handle, possibly making it better or in some cases making it worse. Moreover, when head tube angles are altered by fork leg length, the net head tube angle needs to be understood before you can decide on what amount of fork rake to use to achieve the desired amount of trail. Burley worked with True Temper on it's V-brake tandem fork (essentially an Alpha Q CX fork that was beefed up for tandems) to give it the same fork length (and a larger wheel opening) as their steel forks so that they would retain their 73 degree head tube angles and used something even more aggressive than Co-Motion's steel fork spec. of 50mm of rake to achieve what they call their "race handling" package.

Again, as a consumer, the only thing you need to understand is that some builders use different steering geometry. Ride different models for yourself and then ride them again before deciding which you prefer and, remember, you're buying to suit your preference, i.e., what's best for you.

stapfam

It is all very confusing, but the final test is in the ride. Steeper head angles will make the bike more responsive till it gets to the point where it is dangerous, slacker angles make the bike more relaxed on steering till the point comes where there is a time lag on what you do and what the bike does.

Then you change the fork and mess it all up, so providing the bike handles the way you want it to, Don't worry.

Then you worry about rake and what differences that will make, so why be confused. Leave the bike as standard, find out whats wrong with the handling and then talk to a frame builder.

Or just ride the damn thing.

ElRey

Yes, that was my meaning when I said trail related to the fork: it can be changed if the fork variables are changed. Changing effective headtube angle if you dropped the fork length an inch?? Yes, but you also change the balance point of the frame so much (more weight forward), and BB height (less ground clearance when cornering), that I would wonder if you're not better off buying another frame with a steeper headtube. (you noticed I got the exact same fork length to avoid this... I think the rake differential was actually more than the pulished numbers). Saw a guy riding a $9,000 carbon tandem yesteray from a custom builder... he had aerobars mounted up on an 80mm stem. Aerobars on an 80mm stem... try it sometime. You better not catch a crosswind when you're on them aerobars. I don't think he asked the right questions when he got his custom frame.

ElRey

We got JayB so confused now he's off buying a sled.

JayB

by the way, I'm not just guessing here: I just replaced the fork on my Co Mo with a Reynolds tandem fork (yesterday). Just went through all this. Done it a million times on racing bikes. Not my LBS, me... research, purchase, installation.

So you replaced a Co-Motion (steel?) fork with a Reynolds Carbon fork. Wondering why you went with Reynolds rather than Woundup? What differences have you noticed with the carbon replacement fork?

JayB

Well, have to admit some of this went over my head. Interesting though. TandemGeek says Santana etc are "most refined in this regard as it has very short steering trail". I was interested in his comparison about the way a Co-Motion and a Santana handle at various speeds. But on this "trail" business: let's say I want to measure the trail on my old 531 tandem. I've got a measuring tape in hand. What do I do now?

merlinextraligh

There's another way to get at this: Ride the bike, and see how you like it. How the bike rides is going to be determined by a lot of factors including the geometry of the frame, but also including the type of material, the weight of the team, the thickness and butting of the tubes, the type of wheels, the thickness of the tires, the length of the stem, whether it fits you, etc. etc.
You can go on ad infinitum about how head tube angle will, ceterus peribus, affect the handling of a bike. But in the real world, all other things aren't equal, and the only way to figure out wht works for you is ride the bike.

TandemGeek

let's say I want to measure the trail on my old 531 tandem. I've got a measuring tape in hand. What do I do now?

Some resources that you might find interesting relative to your last post:

http://www.phred.org/~josh/bike/trail.html
http://www.dclxvi.org/chunk/tech/trail/
http://www.slowtwitch.com/mainheadings/techctr/geometry.html#Anchor-BASICS-47857
http://www.kreuzotter.de/english/elenk.htm

There are many others, but these do a pretty good job and the last one will let you punch in some numbers to see how changing different fork rakes (or head tube angles) will affect trail. Off the top of my head, 28mm tires work out to something like 684mm in diameter for tire size.

To know how much trail your tandem has you could always call the builder and ask.

Otherwise, the easiest way is to get a helper. Lay a 2” X 4” X 8’ stud on the ground, flat side down next to a wall or some other object that you can rest your tandem against. Put the tandem on the 2x4 and slide the entire arrangement as close to the wall or object as you can so that the tandem’s handlebars can rest against the object sitting as close to upright as possible without falling away from the wall or object. Take the tandem off the 2x4 and use a carpenter’s level to make sure the 2x4 is level, shimming as necessary. Put the tandem back on level 2x4 and with the aid of a helper to hold the bike steady, drop a plub bob from the center of the axle nut and strike a mark on the 2x4 where the point comes to rest. Next, have your helper hold your plub bob's string tight against the stem's fixing nut and take the other end and run it down to the ground in a straight, taught line such that it splits the center of the head tube’s left side to represent the steering axis and mark where it contacts the 2x4. Measure the distance between the two marks; that’s your steering trail. The accuracy will be as good as your ability to eyeball the centerline of your head tube. It may even help to have a third person eyeball the fall of the line against the head tube or to use a set of Vernier calipers to find the center of the lower head set’s crown race to guide the fall of your line. It’s not fancy, but it will yield the answer to your question without having to resort to a protractor to measure the head tube angle and removing the fork to measure the off-set/rake.

Oh yeah, and if all of this wasn’t confusing enough, changes in tire diameter also alters steering trail.

K&M

Hey Jay: Last year I went through exactly what you are going through now trying to understand how "trail" effects handling. One problem, as you can see from reading this thread, is that people have a tendency to get things backwards and say the opposite of what they mean when discussing trail.

To put it as simply as possible, trail is the distance between the bottom point of your tire (where it sits on the ground) and the point where the steering axis meets the ground (an imaginary line down through the center of your head tube to the ground). It is called trail because (on almost any bike) the contact point of the tire trails the steering axis by a small distance.

The more trail there is (i.e. the closer the wheel is tucked up under the frame) the quicker it will tend to steer and the less stable it will tend to be. The less trail there is (i.e. the further out in front of the bike the wheel is placed) the more stable it will tend to be). People constantly get this backwards, though. Probably because it is counter-intuitive to think that the further a bike sits behind its front wheel the LESS trail it has.

As others have pointed out, though, trail is only one factor in how a bike handles and feels. If you are used to riding modern road bikes you will probably prefer the greater trail of the CoMos or Burley Race Package. If a more solid feel and less wobbling when the stoker shifts weight is more important, you'll probably prefer the shorter trail of the regular Burley's Treks, Santanas, etc. There is obviously no substitute for a test ride --- but finding the bike you want to test can sometimes be a challenge.

TandemGeek

One problem, as you can see from reading this thread, is that people have a tendency to get things backwards and say the opposite of what they mean when discussing trail.

Actually, I believe the problem is one of semantics surrounding the word stability and a failure to put that term into context when describing how bicycles handle, followed closely by the same ambiguity that exists around the expression "fast steering". Since I'm at home now I have access to some of the columns that I've written, to include one dealing with this topic and an illustration that also ties in with this discussion that summarizes my views on how sematics muddies the water.

As for how short (conservative) or long (aggressive) fork trail feels, that's often times where the terminology and expectations can also create confusion. Based on my experience, the following is how I like to sum up how conservative and aggressive fork trail affect the steering and handling of tandems:

Conservative fork trail on a tandem (under 2") favors low speed maneuverability by providing lighter steering effort and faster steering responsiveness to handlebar inputs. Many teams will describe this as being "more stable" because, at least at slow speeds, it "feels" that way. Tandems with conservative fork trail take less effort and attention to steer in a straight line at slower speed and are resistant to inadvertent movements by the stoker, aka (stoker induced steering). However, conservative trail tandems also tend to understeer in aggressive or high speed cornering maneuvers which is not always desirable.

Aggressive fork trail on a tandem (more than 2") favors high speed cruising and aggressive cornering. This is because of their inherently greater straight line stability and smooth responsiveness to leaning inputs, noting that at speeds above 15 -20 mph all directional changes on two-wheeled cycles are accomplished through leaning the bike in the direction of the turn and countersteering with the handlebars. Many teams will describe tandems that handle well at speed as being "more stable" because, at least at higher speeds and for aggressive cornering, it "feels" that way. However, at slower speeds, steering tends to be heavier and less responsive which is often described as being twitchy. Moreover, for teams with stokers that are exceptionally tall, or who tend to move around along or "rock" when they ride, a tandem with long fork trail can make steering control a laborious task that can also be undesirable.

However, despite everything that's been written about steering trail and how well most people understand what they've read an studied in those writtings, tandems tend to defy logic since everything is backwards... instead of the "racing models" having shorter steering trail than the models favored for touring or less aggressive riding, they have longer steering trail. Again, from my column:

[after looking at steering geometry numbers for solo bikes]... you might logically conclude that high performance steering should be assigned to the tandems with shorter trail numbers instead of the longer ones since the racing bikes in Table 1 have the shortest trail numbers. Unfortunately, while tandems with short trail benefit from the more neutral handling in some performance areas, the long wheelbase and significantly higher gross weight of a tandem creates a point of diminishing returns for more aggressive riders. The long trail tandems, on the other hand, trade off that low speed maneuverability and neutral steering for better responsiveness in those more aggressive riding situations. So, in some respects, expectations about how changes in fork trail "should" effect the handling on solo bicycles can't be extrapolated into how fork trail actually affects the handling on a tandem.

Finally, I included the following illustration and summary of my perspective on tandems, steering geometry, and how they handle: feel free to disagree; after all, we are talking about steering geometry.

galen_52657

The more trail there is (i.e. the closer the wheel is tucked up under the frame) the quicker it will tend to steer and the less stable it will tend to be. The less trail there is (i.e. the further out in front of the bike the wheel is placed) the more stable it will tend to be). People constantly get this backwards, though. Probably because it is counter-intuitive to think that the further a bike sits behind its front wheel the LESS trail it has.

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.

turtlendog

However, despite everything that's been written about steering trail and how well most people understand what they've read an studied in those writtings, tandems tend to defy logic since everything is backwards... instead of the "racing models" having shorter steering trail than the models favored for touring or less aggressive riding, they have longer steering trail. Again, from my column:...

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...

TandemGeek

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.

JayB

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.

JayB

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.

ElRey

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.

ElRey

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

JayB

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?

TandemGeek

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/performance_tubing/images/carbon_rooting_big.jpg

JayB

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[/url]
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?

TandemGeek

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/images/WU_tandem_fork1.jpghttp://www.precisiontandems.com/cat_pics/fkalphaq.jpghttp://www.awcycles.co.uk/smsimg/78/2130ouzoprotandemfork.jpg

turtlendog

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

Thanks for the advice, Mark.

TandemGeek

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

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.

K&M

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.

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.

galen_52657

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.

K&M

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.

georgiaboy

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?

dfcas

TandemGeek

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 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 (http://www.cannondale.com/bikes/06/geo-30.html) falls under the range specified by Marc. Moreover, you'll find that Bilenky is using 42mm - 46mm (http://www.bilenky.com/tangeom.html) and the "norm" used by Santana, Burley, and Trek is 47mm - 51mm (http://www2.trekbikes.com/bikes/geometry.php?geomid=311). 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.

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....

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.

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.

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.

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.

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.

dfcas

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

TandemGeek

Reading these posts again,there is no pattern or logic to the descriptions given as to steering characteristics compared to steering geometry numbers,....

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 (http://www.bikeforums.net/showpost.php?p=1693666&postcount=13), 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 (http://www.thetandemlink.com/articles/headtube.html) 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.

...and the numbers from manufacterers are very close to the same.

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.

George Handy

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.

TandemGeek

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")

georgiaboy

TandemGeek

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.

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).

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...