Frame size question

[Richbiker]

Does tandem frame sizing "work" the same as for road and mountain bikes. For example, I ride a 54cm road bike. When ordering a tandem or tandem frame, would I make sure that the captain and stoker seat tubes have pretty much the same dimesions as our singles? (I'm talking about a road tandem here, not an MTB tandem?)

richbiker

[galen_52657]

I am assuming you are considering a stock sized road tandem frame. If that is so, check with the manufacture as most have fitting instructions. In most cases, the captain's portion will be close to his/her standard road bike sizing. The stoker can fit a frame larger than he/she would ride as a single as standover is not an issue (stoker stays in the pedals at stops).

In order to fit the most riders with the least amount of frame sizes, I would say that in general, tandem frame manufactures build - and you can fit - a frame a little smaller than your road single. Excepting the Cannondale jumbo/large, a 23" frame is often times the biggest stock size. But, with a bunch of spacers under the stem, it can be made to fit like a 24 +" frame. However, if you are riding a 54 cm road bike, that won't be an issue for you.

[TandemGeek]

Does tandem frame sizing "work" the same as for road and mountain bikes. For example, I ride a 54cm road bike. When ordering a tandem or tandem frame, would I make sure that the captain and stoker seat tubes have pretty much the same dimesions as our singles?

Yes and no.

Let's talk about the front end of the tandem first.

For the captain, their end of the tandem should provide a riding position that is very close to what they would normally find on their primary road bike, allowing for some fine tuning of fore-aft saddle position with different length/rise stems. Since tandems often times use different head and seat tube angles, buyers must be mindful of baselining their "fit" by starting with the saddle set-back. Once they have the proper relationship between their saddle and the crank axle (+/- a few mm for eccentric rotation), they can then evaluate how long the top tube "should" be to re-establish the desired reach. For production tandems, this often times results in picking "close enough" from the available stock sizes. Best case scenario is to make a trip to a tandem-speciality dealer who has a full range of different sized tandems in stock to use for size comparisons. You'll want to bring your primary road bike along so that you can transfer your riding position to the tandem with a tape measure & plumb bob (aka. plummet). Same goes if you're having a custom tandem built, as the builder should be asking you lots of questions about your current bike, fit, etc... along with information on your current riding set-up or physical dimensions that all factor into the design.

The captain's seat tube height is merely a by-product of the tandem design process and it will vary depending on how tall the head tube and stoker's seat tube need to be. For example, traditional upright tandem designs (http://64.23.127.197/images/noventa.jpg) tended to use top tubes that were horizontal or nearly horizontal, such that a 54cm CTC is 54cm. However, tandems from builders like Erickson (http://www.sandsmachine.com/bp_erick.htm)-- and more recently other performance tandem builders (http://www.co-motion.com/graphics/supremo04.gif) -- adopted what is now commonly referred to as a sloping top tube design where a virtual seat tube height needs to be used as longer than average seat posts are used to allow for a shorter & therefore stiffer frame. Photos of our two road tandems are here (Note how far the seat posts extend above the top tube even for a 5'2" stoker & 5'8" captain):

'98 Erickson "Signature" Tandem (http://www.bikeforums.net/attachment.php?attachmentid=22616)

'02 Erickson S&S Travel Tandem (http://www.bikeforums.net/attachment.php?attachmentid=22617)

Now, some caveats:

1. Bear in mind, the vast majority of tandems sold (95%?) are stock models that captains adapt to, much the way most 1/2 bike buyers adapt to their stock sized bikes. While that sounds good on the surface, it's worth noting that 1/2 bikes have traditionally been produced in 1cm or 2cm increments, from 48 - 62; tandems usually come in only 3 or four stock sizes.

2. Some tandem dealers, builders, and captains advocate a more upright riding position for tandems under the premise that tandems are "usually" ridden more for pleasure than competition and, therefore, don't need to fully replicate an aggressive road riding position. The best way to figure out if you buy-into this approach is to take a stock tandem out for an extended test ride to see how "stock sizing" works for you and your stoker (more on that in a minute).

3. The hazards associated with caveats 1 & 2 are that often times captains are sold tandems that really don't fit where the saddle has been shoved all the way back or forward in combination with some really odd stem lengths, e.g., 8.5cm - 15.0cm or super high-rise models to "fine tune" the riding position. Obviously, if the saddle is being used to adjust the top tube length, saddle set-back position is being compromised.

4. If you're contemplating a big outlay of cash for a custom-sized tandem, the best way to blast through the B.S. is to know what your optimal "fit" is based on a past or current bike fitting by a qualified bike fitting specialist. At ~$75 a pop, it's money well spent and it will also confirm if your current riding set-up is optimal as well. Often times we begin riding in our teens or 20's and hold onto that same riding position into our 40's... unfortunately, our bodies don't usually hold onto their same form during the aging process: heck, even Lance seems to raise his bars a little each season. Anyway, it's just a recommendation.


Now for the stoker:

Let's talk about top tube length first: Production tandems seem to use 27.5" - 28.5" stoker compartments, which are actually quite a bit longer than they were in the 80's and early 90's when 25" - 27" was more common. However, once you allow a minimal 6" - 7" for a stoker stem that's long enough to move their hands out from under the captain's saddle (and their nose back a bit from the captain's back side), there's a nominal 52cm - 54.5cm top tube left over. For some stokers this is enough. However, for taller stokers, they are often time forced to live with their hands nestled under the captain's saddle(forget about ever seeing that computer on the bars), shoving their saddle well back of the optimal set-back, or adopting a more upright riding position when fresh air is a higher priority. So, as with the captain's riding postion, the best way to evaluate how standard sizing might work is to take an extended test ride. Again, if your stoker is already a cyclist who has a bike that "fits properly" (see caveat #4, above, on bike fitting), it should be brought along so that you can transfer their riding position to the tandem with a tape measure & plumb bob. If the stock sizing provides an adequate fit, then you may be fine adopting that for your tandem. Again, as noted in caveat #1, above, the vast majority of tandems sold fall into this category and most stokers are able to adjust to the available spacing.

Now, it's also worth noting that there are a few champions of extended stoker compartments who advocate the premise that a stoker should be able to replicate their exact riding position on a tandem. We and many of our friends fall into this category; however, were the exception and not the rule. That said, all of our stoker's are quite happy with the extra room in their stoker compartments, noting that even though my 5'2" wife only "needs" a 49" top tube, she appreciates having the ability to see her bar-mounted Polar S720i HRM.

You'll find a protracted discussion on stoker comfort / bike frame design here in the archives:
http://www.bikeforums.net/showthread.php?t=45049&highlight=erickson+stoker

Glenn's tandem building philosophy, circa 1996 (some things change while others remain the same):


Erickson Tandem Frames: My tandems are designed to fit both riders, but I pay particular attention to fitting the stoker so that a position similar to their single bike is possible. This positioning enables both riders to cycle with the same rhythm, stand on hills and in sprints, and experience much less perceived flexing of the frame.

The front end steering geometry handles much more responsively than traditional tandems, allowing the captain to steer more by leaning than by turning the handlebars. My tandems can easily be ridden with no hands if you are so inclined.

The tubing is my own special mix of thin gauge oversize tubing from a variety of suppliers. Some tubes are custom ovalized to achieve maximum efficiency and comfort. I like to use short seat tubes with long seat posts. The low-slung frame combined with the thin gauge of tubing creates a tandem that absorbs more road shock, and hence is more stoker-comfortable than any other tandem. (This is not just my opinion but feedback from many stokers.) The frames typically weigh 10 - 10.5 lb with forks less than 2 lb.

Most of my tandems are road bikes using 700c wheels and sidepull brakes. The dual pivot brakes from Shimano or Campagnolo are incredibly strong and positive, better than most all sidepulls. However, these are custom tandems so nothing is written in "stone" except high quality.

Climbing, sprinting, corner, descending, time-trialing, or touring, Erickson tandems perform like single bikes, only faster. In comfort, lightness, performance, and, of course beauty, Erickson tandems are the best.

You can read a little bit more about our Glenn's philosophy on tandems in this 1998 review by David Morgan: http://www.tandemmag.com/roadtest/erickson97/

One by Russell W. Howe appears here:
http://www.bicycletrader.com/archives/18articles.html#03

Mind you, I'm not trying to sell you on Erickson in that, for one thing, he's not actually looking to build lots of bikes and tandems these days. His primary occupation is www.Ecycletours.com. As already noted, there are a few other builders out there who have adopted similar designs and the more conventional frame designs also work equally well for many teams. Ultimately, it will be up to you and your builder to work out the details of what will be the right design for you.