I know it is hard to size via email but if we currently ride a 60 cm
bike for captain (6"4" tall) and a 51 cm bike for stoker (5'6" tall) for
our road bikes. What would you recommend in the tandem. We are looking
at either the X/M or J/L Cannondale. Looks to me like the X/M = 56/48
and the J/L = 61/53 and so I am leaning towards the J/L.
Justin from Kentucky
Generally, the bike needs to fit the captain as the stoker cockpit is highly adjustable. To be sure, you can request a fitting at a LBS to get their recommendation prior to ordering. The X/M sounds like it's too small for the captain, so I'd also lean towards the J/L. We are Captain 6'0, Stoker 5'4" and our tandem is a Trek T2000, size Large, 58/46. You are both taller then we are. Hope this info is helpful.
I am just over 6' and I can go Medium or Large, prefer Large, my stoker is 5'2" and can generaly go S or M, (even L without a suspension seat post). My road bike is a Medium, with a longer stem. I looked over the Cannondale size chart for the J/L and the X/M. Looks to me like you can go either way. J/L has two drawbacks: more weight and more difficult to resell if you might sell it some day, rule of thumb if you can go either way is to go for the smaller one. I have been lurking around in the used tandem market and have seen how the very large and very small bikes have a much harder time finding a customer. But more important than height for the stoker can be the inseam, turns out my stoker has longer legs in proportion to her height than average (she appreciated the compliment).
The J/L is the way to go if the front end can be made to fit satisfactorily, because according to the 2006 Cannondale catalog you get an extra inch of horizontal stoker rear top tube with the J/L over the X/M (29.1" v. 28.1"). The horizontal front top tube on the J/L is 24.6", about .8" or 2cm longer than the X/M (which would be the stem length difference--you would go 2cm shorter on the J/L) and even if that is slightly longer than you are accustomed to, my inclination would be to use a shorter front stem and get the J/L.
I have different views on the relative fit flexibility of the front and rear ends of a tandem. For riders that are at least large enough to fit the tandem vertically, the problem can be one of lack of sufficient horizontal space, and in that case the space on the front end is only limited by the length of the handlebar stem that can be obtained, with any additional captain size only cantilevered farther forward.
On the back the space that is available has hard endpoints. Given that a particular saddle setback is best, that end is set, and of course at the other end there is the captain, blocking farther forward movement. This is definitely different from the open-ended captain position.
What you are after on the back of the tandem is the ability to use it as much as possible like the stoker's single bike, and one of the most length-dependent requirements is the ability to stand up and naturally move forward as a stoker would on a single bike. I can guess that if you measure horizontally between the center of your stoker's seatpost and the center of the handlebars, you will get about 23", leaving 5" of horizontal stoker stem with the X/M and 6" with the J/L. Your stoker will be happier with 6".
I went with the J/L...had to get a slightly shorter stem but it now fits great (or seems to). I haven't had the weather to take it out and really test it but it is now set up very similarly to my most comfortable road single bike. This size was definitely the way to go for us. My wife is pleased with her fit and still has enough room for a suspension post. When I walked in the door at Tandems Ltd in Birmingham he immediately said my only two standard options were the J/L and the XL Santana. We are Cannondale fans and so went that direction. Thanks for the help!