Dean V

Has anyone done any testing, or noticed how the old tandems compare to the new for speed on a flat road.
I am referring to the difference in the stoker top tube length. Some of the older tandems are much shorter here and I was wondering if they had better aero with the stoker closer to the captain. We have an old Bob Jackson racing tandem that we used for a long time (18yrs) but also got a C'dale RT3000 a couple of years ago. My wife likes the extra room back there and it is definitely stiffer in the bottom bracket, but I have a feeling the old BJ might be at least as fast or maybe faster. It is in parts at the moment but when it is back together I will do a bit of testing.

Ritterview

There are so many variables, knowing what to attribute any speed difference to would be difficult. Scrunching up the stoker might affect stoker contentment, which likely has a non-linear negative effect on stoker power output.

Charles Ramsey

Tandems are roughly 1.2 times faster than singles. For a simple calculation if you double the horsepower this means the effective frontal area is multiplied by a factor of 1.1574. Here is the simple equation 1.2^3=2/1.1574 If you scrunch up together the effective frontal area is multiplied by 1 and you will only be going 1.26 times faster than singles. For a small change in top tube lenght say one inch a linear model will not produce too much error. Say you are 15.74 inches apart and you move to 16.74 inches apart then the frontal area is multiplied by 1.1674 this will mean you are going 1.196566 times as fast as a single. This is about .03 mph at 10 mph. Tailwind used to advertize their panniers effectivly reduced the frontal area of a single. Then someone did a test and found a lot of pannier brands did the same thing.

Dean V

The stokers top tube on the Bob Jackson is 22.5" centre to centre. The C'dale is 28.25".

MB1

Depends on how old or new the riders are.

rdtompki

My perception riding with my 6' tall son as stoker is a loss of aero advantage versus my 5'6" tall wife. Of course his extra power output more than makes up for the difference. My wife can't see around me at all, my son can see over my shoulder. I'm sure when I'm in the drops into a headwind he's catching a lot of air. I would think getting the stoker in the shadow of the captain is really the issue, not the top tube length (although they do interact).

WebsterBikeMan

Exactly. And the interaction may, for some stokers, be that if the top tube is too short, they can't get as low without the Pauli Exlcusion principle getting in the way (meaning their head and some part of the captain's body need to occupy the same space). I suspect that the optimum top tube length from a speed/wind resistance point of view, be the one that allows the stoker to get in a low tucked position without the need for inter-penetration.

jnbrown

It depends what distance you are riding and the the terrain.
Short and flat maybe the Jackson is faster by a small amount.
As distance and hills increase fatigue maybe become a big factor and the bike that the least stoker fatigue would win. I remember the first tandem I ever wanted was a Mercian. I saw one and thought it looked awesome. So I ordered one through my LBS and waited over a year and then was told Mercian was not building any until they got more orders. Sadly I had to cancel the order. My first tandem was built by Andy Gilmour in Arizona. I did own a Mercian single bike for a time and it was one the nicest rding steel bikes I ever had.

merlinextraligh

If you look at purpose built TT tandems, there appears to be some support for that belief. There's a picture posted here before with a tandem with a very long stoker top tube, and aero bars mounted to the top tube.

Getting the stokers arms in and back flat in all likelyhood is going to be faster than a more up right position, even if that position is closer laterally to the captain.

Just anecdotally, when my stoker gets down in the Cane creek speed bars, which give her a pretty flat back, and hands in just wider than the stem, it's worth about .5mph with the same perceived effort.

rfutscher

My stoker has back problems and can't get down into the flat back position. She does report that she has less wind noise in her ears with our short tandem. Besides she likes to look around and enjoy the scenery.

Ritterview

I came across some interesting photo's on Flickr of purpose-built tandem track bikes, from the British Nationals. The top tubes don't look particularly long.







Also, a tandem track video here.

merlinextraligh

These were the ones I was alluding to:





I would think that a track tamdem, presumably used for different events, is going to have different design considerations, than a tandem built for the specific purpose of going fast over a 40k road tt.

Ritterview

Those do look aerodynamic. We can also look at what appears to be a standard sized new Calfee ridden by Canadian Paralympian (VI) Brian Cowie (at Kona IronMan with a blazing cycling time) although I think he uses this for road races as well.

TandemGeek

Just some food for thought in terms of what might influence tandem frame design...

1. You don't suppose that track tandem stoker compartments are short for some other reason such as frame stiffness?
2. You don't suppose the very nature of a track tandem event places LESS emphasis on having a stoker position that affords long-term comfort and more on a stoker position that affords better power transfer over short duration maximum efforts.
3. You don't suppose that sight or hearing impaired stokers might prefer to be closer to their captains so they can hear audible prompts or get a better feel for the captain's movement.

There's a completely different set of "you don't supposes" that can be applied to dedicated time trial tandems as well as to why so many tandems that show up at events like the Co-Motion classic are simply stock tandems.

merlinextraligh

Not the least of which is money. You'd have to be pretty seriously into tandem racing to have a road racing tandem, and also have a second tandem specifically built as a TT bike.

And having flown to the race, I could not imagine the logistical nightmare of getting 2 tandems there. and traveling from stage to stage with 2 tandems on a rental car.

I think even at Master's nationals, for the most part people of using regular road tandems, with some aero add ons, such as clip on bars.

Dean V

There certainly are a lot of variables to consider. For both stoker and captain to be right down with their backs near horizontal like on the white TT tandem you do need a long bike. To my way of thinking this would be the most aero. But in saying that I have seen solo TT and pursuit riders at world class level that are not as low as this, say with their torso at about 15 deg from horizontal, and the position you are in most of the time for a road race is even higher again. On a tandem this would allow the stokers head to be above the captains backside/lower back, shortening the bike up somewhat.
I definitely want to ride a few TTs on both our bikes and maybe some coast down tests as well. At least then I may find out what works for us.

Ritterview

Even if this tandem was a dedicated time-trial /triathlon tandem , you'd need either the manufacturer (Calfee), or the purchaser, to push the idea of a long/aero stoker compartment, and so overcome the inertia of the stock frame design. This isn't usually likely to happen.

According to Brian, he likes the Calfee:

On the actual 112 mile Kona route, their time was 5:14, averaging 21.4 mph. The fastest bike time was 4:25:11 (25.5 mph).

TandemGeek

Would you like to try running that by us once more, but this time in plain speak.

I'm having a hard time connecting the dots from what you quoted in my earlier post, to the point you're trying to make which, on it's own merit, makes no sense, i.e., what the heck is 'the inertia of the stock frame design'?

Moreover, what does that have to do with what appears to be the somewhat longer than stock Calfee that Cowie and his pilot ride? I'm pretty sure that to a person, we all like our Calfee tandems and think they are the best tandems we've ever ridden. Just looking at the 'team' bike he was riding in Beijing, I can only imagine how much more comfortable he is on the plastic-fantastic.

Ritterview

Geez, it wasn't that cryptic. Since the long-stoker aero frame is out of the ordinary, if neither the manufacturer nor the customer initiates that the frame is to be different, the stock frame will likely be produced. There is inertia behind the stock frames.

So, we can't conclude from the use of stock frames by dedicated racers, be they track or triathlon, etc., that the stock frame is aerodynamically ideal. It might just be all that is likely to be produced.

I don't know if the Calfee that Cowie uses is any longer than usual. The obvious thing for a male stoker would be to order a large/large.

When I was visiting the Calfee factory in May, I took some pictures of the frame as it was being shipped out. Can we tell anything from the numbers?

zonatandem

jnbrown:
Have ridden a couple of Andy Gilmour's tandems; he's had one of his custom tandems used in the Paralympics with a very tall blind stoker a few years back.

Our first custom tandem in 1977 (60 and 1/4"" wheelbase, 34 lbs) was built for speed. Yes, we were faster on the flats then than we currently are, but heck that's over 3 decades ago! Our wheelbase is now a stretched out 63 1/2".
Longer stoker compartments might be needed for some stokers, but Kay is 4' 10 3/4" tall does not need that.
When we time-trialed she'd rest her head sideways against my backside and hammered.
We always had a 'do-it-all tandem'; used for daily rides, centuries, tours, time trials and track.
Specialization is nice but could not afford, or want, special tandems for each event.
After all the advantages in equipment is the two riders that count the most.
Pedal on TWOgether!
Rudy and Kay/zonatandem

TandemGeek

Good grief, that's even more cryptic. However, I believe what you're trying to say in some type of obscure techno-speak is:
Or, to be more succinct: Most tandems are built using stock sizing.

Yes, that's absolutely true and it appears as though Cowie's Calfee may or may not be a custom, per se. I say that noting even 'stock' Calfee tandems are 'built to order' and it's rare for any two to be alike. The same is true for nearly all boutique tandems that are built to order.

There's that pedagogical-sounding 'we' again... but, yes: It would appear to be a Large/Medium Tetra & the 305th tandem built by Calfee, just two frames ahead of osurxbiker's custom-sized coupled Tetra #307 which was delivered in early June.

Chris_W

While debating how long the top tube should be to maximize aerodynamics, I'm surprised that no-one has mentioned that the way to make the fastest tandem would be to make a recumbent tandem. Recumbent singles can easily go faster than upright bikes, so I assume that it would be the same for tandems.

wobblyoldgeezer

Just to chime in, because I'm reading Bikeforums and don't know any better than to do so

We started with a very short 'Orbit' which in its day was a good one. Discomfort and twiddly characteristics made our later 'Santana' seem much faster. In fact, though, on consecutive timed 60+ miles timed rides like London to Brighton or London to Oxford there was no discernable difference. Same legs, same routes, same speeds

We were much happier and much less beaten up on the newer and longer one, though

One consistent pattern though, which also presents with skiing

Good breakfast - fast
No beer halfway through - slow
A pint or (for stoker) a marguerita half way through - fast
More than the above - slow

OK, this isn't about absolutes or extreme performance, just about a couple of reasonably paced enthusiasts

To us, a bit more space equals a bit more comfort, and consequentially speed and distance

Homeyba

To give you a serious answer, there are engineering issues with recumbent tandems. First, DF tandems are actually pretty aerodynamic compared to upright recumbents, more so than single DF bikes. There isn't that big of an advantage. Look at the pics above of racing tandems and look at a racing recumbent tandem (if you can find one). To get some kind of significant aero advantage you'd need to make a lowracer type of tandem. Recumbent tandems are extremely long and very heavy to begin with, a recumbent lowracer would be the better part of 15ft long! That creates all sorts of strength and rigidity issues. Maybe someone has tried to overcome the difficulties and has already built one but I haven't seen it. If you have pics I'm sure w'd like to see one. Personally, I doubt that you will find a tandem recumbent that comes anywhere near the performance of a standard racing tandem.