Tell me all about gearing on tandem bikes

June 29, 2004 9:28 PM

BikeFilter: How does the gearing on tandem bikes work? (more inside)

I just got back from a great little family trip to Mackinac Island, where we rented bikes and went around the island on a beautiful day. Once we got back, though, this question started driving me crazy...can you have a tandem bike where both riders can contribute disproportionately to the work?

The tandems I saw--from a distance, we didn't get one--all seemed to have the front pedals chained to the main gear of the back pedals, and the back pedals were the only ones chained to the back gears/derailleur. So it's not to hard to envision a sort of ratchet gear on the middle gear (back pedals), where either the back pedals are driving the rear wheel, or if the front person's pedaling faster, then they're spinning the back wheel, but that's a "one or the other" scenario. From trying to research this question on the web, it seems that most tandems aren't even really that sophisticated--the two sets of pedals are basically "hard-wired" together, and are forced to spin at the same rate.

Is it possible to have a gear on the middle that could actually add the asynchronous efforts of two riders, rather than either requiring them both to pedal at the same RPM, or just take the faster spinning of the two? Mechanically, I don't know how this could work, without the second rider spinning in space behind the first one, but there are many, many mechanical things that seem almost impossible to me, but which are part of our everyday lives, so I figured, why not ask?

posted by LairBob to sports, hobbies, & recreation (7 comments total)

Look around a bit for IPS (Independent pedalling system) on tandems. That's sort of what you're talking about. It lets one person coast while the other pedals. For whatever reason, it seems to only be available on recumbent tandems, like this one.

These have the pedals connected with a ratcheting system like you have on your rear wheel. Trying to pedal slower than the faster rider would probably be like trying to augment your speed while going downhill by pedalling slowly - it just doesn't work. You have pedal as fast as the bike is travelling to push it along.

I can't think of a sensible way to accomplish what you're saying. Maybe if each rider had their own cog set and a derailleur, and then their chains went independently to the drive wheel, with a ratcheting system for each. Sounds pretty complicated. Also, there are real advantages to having each rider precisely 180° apart that this system would defeat.
posted by mragreeable at 10:02 PM on June 29, 2004

Up until about 5 years ago, tandems were always synchronyzed, so if the person in front was spinning, the person in back had to be hitting the same cadence and there was never time for one person to freewheel. But like mragreeable said, they now have independent systems so each person can do as much as they want.
posted by mathowie at 10:43 PM on June 29, 2004

Like mragreeable said, you *could* have a system where people pedal at different speeds while still both contributing. You'd just need to have two sets of gears on the drive wheel, each attached via its own independent ratchet mechanism. That way, each person would have their own gearing. They would still have to pedal fast enough to contribute, but "fast enough" could be defined independently by their different gearing ratios. I don't think it would be too complicated, really.

That said, the amount of effort involved isn't just related to the pedaling speed. They say you want to keep your pedals spinning at a constant speed (what is it, around 80 rpm?) anyway. So I think it's better to have the pedals linked. People can still contribute different amounts of effort when their pedals are spinning at the same rate. It's like pushing a big heavy thing. One person can push with ten times the force of the other. The object is moving at one speed, but the person pushing less is still contributing.
posted by whatnotever at 11:07 PM on June 29, 2004

Burley Samba rider here. What whatnotever said. It's not the speed of pedaling that's important but the force you put into it. My wife can sit behind me and and just let her legs spin (although, for the record, she's a dynamo). In the picture I linked our pedals are "in phase," which is good for beginners (think about how you set your pedals to lean into a turn), but for smoother power many people set the captain's pedals a quarter turn ahead of the stoker's. Go rent one next time. It's fun. There is a little handbook called The Tandem Scoop that gives the ins and outs of tandem riding and safety, etiquette, etc. For example, when you get on your "half-bike", you usually lean it side to side when mounting. As a tandem captain, you shouldn't do this when steadying the bike for the stoker to mount, because it is not intuitive motion if you aren't doing it yourself. If your stoker is the person who makes your dinner, this is double important. A good tandem is easy to ride after the initial weirdness, and so much fun.
posted by planetkyoto at 11:43 PM on June 29, 2004

With just a little practise, tandeming is easy and massive fun. There's been various mechanisms devised, since as long as there's been tandems, for allowing independent gearing and coasting for each rider, but none has ever been very widely adopted. The direct coupling between captain's and stoker's chainrings is the most efficient and least complex (and therefore most lightweight) mechanical solution and therefore remains the standard. Most experienced tandem partnerships don't want it any other way, anyhow. It's a teamwork, empathy, cooperation, connectedness and mutual understanding thing.
posted by normy at 3:32 AM on June 30, 2004

Thanks all. Those answers make sense, and I guess that especially in a two-adult setup, keeping the wheels synchronized does keep things rhythmically tuned, and is clearly far more straightforward mechanically, which is a huge advantage.

My curiosity was partly just driven from the context I saw it--Mackinac Island--which was clearly very family-heavy. You see a lot of parent-child pairs on tandems, and while my oldest rides a bike on his own quite well, I was just wondering if he and I ever shared a tandem while he's still a little kid, if there was a way for him to meaningfully contribute without having to keep up. (More just idle musing, where that's concerned, because as a little speed demon who just wants to race, race, race, I don't think there's any chance of him just sitting behind me and pedaling. Does seem like a very fun idea for my wife and I to look into, though...we really enjoy cruising around together on our bikes.)
posted by LairBob at 6:20 AM on June 30, 2004

a way for him to meaningfully contribute without having to keep up

The Trail-a-Bike is popular for this. Never used one myself, but know some folks who like them.
posted by normy at 11:28 AM on June 30, 2004