Need more room for Stoker

[cfblue]

We have a Co-Motion Speedster, large size, bought second hand. We are both tall people, the lovely Rear Admiral is 6' tall with 36" inseam. The MTB she rides has 28 inches between the center of the bars and the center of the seat post mount. The same measurement is 22". Now i know there is no way any frame stretcher will yield 6", but I need to do something.

A set back seat post will eliminate the shock absorber post, but would yield an inch or so.

I've also look into a riser so she can sit more upright, but as I write, I havent a combination of bars/stem that fit at all.

Am I on the right track?

thanks...

PS, while I am a vertan tandem captain, she is new to it.

[dbohemian]

A really tough delima. The setback post is probably a good idea but you want to make sure that it does not set her too far out of her standard bike position, lest she end up with a temporary or more serious knee issue.

sitting her more upright will decrease her reach and is about the best you can do under the circumstances.

One of my biggest pet peeves is stoker compartments that are too short! Not all stokers need long rear compartments but it really opens up the possibility of a variety of stokers and allows all stokers to obtain there optimum positions with an adjustable stem.

Dave Bohm
Bohemian Bicycles

[TandemGeek]

You might want to give the folks at Co-Motion a call and see what they suggest as a fast-track through the trial and error process. They may even be able to sell you all the right bits and pieces.

Obvisouly, if you and your stoker are in this for the long-haul, a tandem with a longer stoker compartment would defnitely get you closer to the finish line on that right track. If you can resist adding all the chi-chi components, couplers, custom paint, and signature level finish work (fillets & 7-step paint) you might be surprised at how affordable a custom frame can be. Just something to think about.

FWIW, I believe the pecking order for tandem models with the longest "stock" production stoker compartments are Rodriguez (30"), Cannondale's L/M & X/M models with 29.1", Trek's large size tandem (28.8"), Trek's small size tandem (28.7"), and then Trek's medium & all Co-Motion models are tied (28.5"). Most other "stock" size tandems have stoker compartments that are under 28.5". I would have included Bushnell but I think most of his tandems are built-to-order and I'm not exactly sure what Dennis is using for a "default" stoker compartment but it's likely in the 29" - 30" range.

BTW, our Erickson tandems (as well as most all others) have 31" stoker compartments. However, my lovely wife is 5'2" and uses only 42.3cm (saddle nose to center of her handlebars) of the generous reach that is available. This translates into a 9.5" long stoker stem that puts her handlebar behind my saddle instead of under it.

[SDS]

It has occurred to me that one way to add length to a stoker compartment on a tandem that is too short in back, is to send it back to have couplers installed, and at that point add longer lengths of tubing. It seems to me that the direct/internal lateral would then have to have a serpentine shape, but that doesn't sound too difficult for accomplished framebuilders.

Good tandem fit consists of the proper road bike fits of the two riders, and the space in between. This space is needed so that the stoker can naturally move forward when standing up, and to put the head down when that is desired without interference from the captain's body.

Given a known refined road bike fit (in particular, the horizontal center-to-center seatpost to handlebar spacing), this can be transferred to a tandem, and subtracted from the horizontal bottom bracket spacing to get the horizontal stoker stem dimension. This is about the best way to define the space in between for discussion. The question is, how much is enough for any given size of stoker, certainly a matter of interest for anybody considering a larger stoker compartment?

5'2" stokers who have a choice between single road bike fit with six inches of remaining horizontal stoker stem dimension and eight inches prefer eight inches. I have tested this a number of times with my older Cannondale J/L with its 30" BB spacing. I've had a lot of 5'10" and 6' stokers too (I had a 6'4", 240 pound stoker once), and 5 to 6 inches of stoker stem was not enough for them. I solved nearly all possible fit problems for taller stokers by getting a tandem with 37" bottom bracket spacing. 5'10" and taller stokers reported that that was better than 30" spacing, most notably in that they now had room to stand up and to naturally move forward, which meant that the bike went straight, because they could get the needed bend in the elbow, so that they could properly counter leg motions by pulling with the arms. I would guess that the least you need is something around 34-35" of BB spacing, with more possibly being better.

I would have guessed that the road bike fit for a 6' woman would have about 26-27" of horizontal space between the seatpost and the handlebars.

[zonatandem]

No matter what, it will be a make-do fit.
Setback seatpost, more upright/higher stoker position and putting stoker adjustable stoker stem at its shortest setting or using a very short non-adjustable stoker stem, while moving captains saddle as far forward as what he can tolerate and maybe then need a bit longer stem for captain.
Retrofitting couplers and getting longer tubing would probably be impractical/expensive; better off waiting 'til you have the bucks for a full custom machine.
A custom sized tandem would be best; however, seeing that you bought a previously owned 2-seater, it implies that finances have dictated this purchase.
In the meantime, a make-do fit is the best you can accomplish.
We have the opposite problem . . . stoker under 4'11, and yes, that also dictates a custom machine for proper fit. All our custom tandems have logged 50,000+ miles each. Current Zona tandem is 'just broken in' with 14,000 on the odo. Well worth the inve$tment!
Good luck!
Pedal on TWOgether!
Rudy and Kay/zonatandem