Is there anyone reading that is a master physisist/engineer who can explain why a tandem is slow going up hill. I know why it goes extra fast at high speeds (aerodynamics) but am baffled why 2 equal riders can not go uphill as fast as one on a single bike.
Monty says Jack Mott or Tom A may have some answers.
Thank you!
PT
Slower than what? Slower than the weaker/slower member of the tandem or slower than the stronger/faster?
Slower than a single rider is what he is looking for. Say you have two equal pro guys on a tandem and another equal guy on a single, climbing a 10% grade for 10 miles. The single guy will crush the two guys every time, but on the flats the tables are turned. I told Pauly that it is a power to weight loss on the tandem, but he cannot fathom why two guys putting out 400 watts does not equal 800 watts. I just know it is, he just wants to know exactly why…
I think there are 3 parts to this answer:
machines don’t scale up linearly. A tandem bike will generally weigh more than twice as much as two single road bikes. This is compounded by the fact that few people try to build super light tandems. A nice tandem will usually weight 35 to 50lbs, though there are a few super expensive ones in the uppper 20lbs range
They do not climb slow as much as they just SEEM to climb slow because they are so fast as shit when it is flat or downhill
Probably a little power is lost when the riders have to struggle to stay coordinated grinding up a real steep hill
Has anyone tried putting the cranks for the 2 riders on a tandem 90 degrees out of phase with eachother? It would help even out power distribution around the cycle which is better for maintaining inertia, especially when climbing.
I had a friend try that on a tandem. He said it became too difficult to pedal efficiently. Everything was fine when both riders were seated and pedaling smoothly but when anyone was standing, or when cornering, it was utter chaos. I remember he said the first and only ride with it that was very short and utter chaos.
It has been done:
http://sheldonbrown.com/tandem2.html
Makes it hard to stand, and dangerous to corner
Has anyone tried putting the cranks for the 2 riders on a tandem 90 degrees out of phase with eachother? It would help even out power distribution around the cycle which is better for maintaining inertia, especially when climbing.
I’m not certain, but I would guess:
No clue, but when I rode a tandem with my wife we would fly in the flats (same frontal area as me alone, but with her power added), but suck climbing (I felt like I was carrying up the hill more than my normal share of the of the load… she felt like she was flying).
Everything seemed harder on a tandem- communication to coast, stand, bumps etc. If were were equal weight and equal power, and well coordinated, would it have been different, I’m not certain.
Is there anyone reading that is a master physisist/engineer who can explain why a tandem is slow going up hill. I know why it goes extra fast at high speeds (aerodynamics) but am baffled why 2 equal riders can not go uphill as fast as one on a single bike.
If a tandem goes uphill slower than the captain and stoker would individually, either the drag is higher (because of either total weight or rolling/bearing/drivetrain losses) or else the power is lower.
I suspect there is some increase in Crr for a tandem, and possibly some small increase in bearing/drivetrain losses. Taking differences in mass into account is actually pretty simple. The big unknown, and the one I’ve wondered about for years, is whether tandem power output is lower than when the individuals are riding alone. Part of this is because the data are pretty hard to get.
…the data are pretty hard to get.
Might be a good application for Garmin Vectors.
Is there anyone reading that is a master physisist/engineer who can explain why a tandem is slow going up hill. I know why it goes extra fast at high speeds (aerodynamics) but am baffled why 2 equal riders can not go uphill as fast as one on a single bike.
Monty says Jack Mott or Tom A may have some answers.
Thank you!
Well…my opinion, and it’s based on having a MTB tandem for the last 20 years or so, is that appropriately geared, the tandem SHOULD be able to climb as fast or faster than an a single rider of equivalent W/kg of the tandem riders. The whole point is that it’s not worth it to try to climb standing on a tandem due to the coordination issues. Instead, you need to make sure you’re geared low enough that you don’t need to stand to climb effectively.
Despite what Jack states above, it’s my experience that a tandem will weigh less than the equivalent of 2 equally kitted single bikes of similar frame construction.
For example, my MTB tandem ('93 Yokota Twin Peaks) weighs approximately 40 lbs, whereas 2 single MTBs of the same construction (rigid Cro-Mo) weigh ~24-25lbs per.
I know that when my wife and I ride the tandem that we climb at a faster rate than the average of our 2 solo speeds (hence a big part of the motivation for getting a tandem…I got tired of waiting 
I also recall climbing (off-road double-track) at rates basically equal to friends on their single bikes.
It really is all about W/kg (for climbing) and W/CdA (why tandems are so hella-fast on flats). Put 2 “strong” dudes on a tandem and gear it so they don’t need to stand climbing and they’ll have no issue keeping up with equivalently “strong” single riders.
It’s my suspicion that much like recumbents, tandems tend to get a “bad rep” about climbing more due to the “engines” that are typically on board rather than for any true physics reasons :-/
Is there anyone reading that is a master physisist/engineer who can explain why a tandem is slow going up hill. I know why it goes extra fast at high speeds (aerodynamics) but am baffled why 2 equal riders can not go uphill as fast as one on a single bike.
If a tandem goes uphill slower than the captain and stoker would individually, either the drag is higher (because of either total weight or rolling/bearing/drivetrain losses) or else the power is lower.
I suspect there is some increase in Crr for a tandem…
Actually, tandems tend to run slightly wider tires than equivalent single bikes, so there should actually be a slight Crr decrease (all other things equal). The rolling resistance force merely scales with the mass supported by the tires, so “in tandem” that should be no higher than the total of the 2 individual bikes even if the Crr was the same.
…and possibly some small increase in bearing/drivetrain losses. Perhaps at the wheels only…but, the timing chain should have less losses than a derailleur chain setup, so I’m thinking it’s a wash.
The big unknown, and the one I’ve wondered about for years, is whether tandem power output is lower than when the individuals are riding alone. Part of this is because the data are pretty hard to get.
All you have to do is contact Coggan and JV. I’m pretty sure they had dual SRMs on the tandem they set the Masters National Record on
…the data are pretty hard to get.
Might be a good application for Garmin Vectors.
Only for the stoker.
All you have to do is contact Coggan and JV. I’m pretty sure they had dual SRMs on the tandem they set the Masters National Record on
Thanks to a friend/teammate of John’s, we had use of a Zipp/PowerTap disk.
Hunter, though, did get Quarq to make a special captain’s crank when he and a client took their shot at master nationals a few years ago (lost the TT, but won the RR).
good stuff I think another aspect is that there is very few people that spend enough time on a tandem to really work perfectly toghether. If you cycle 3 weeks everyday togheter you see quite an improvement in the coordianton when climbing. ( i guess this is why in tennis in the dobule combetiton usually the double specialists would beat the no 1 and 2 single player in the world becaue they know exactly what the other guy is going to do)
Well…my opinion, and it’s based on having a MTB tandem for the last 20 years or so, is that appropriately geared, the tandem SHOULD be able to climb as fast or faster than an a single rider of equivalent W/kg of the tandem riders. The whole point is that it’s not worth it to try to climb standing on a tandem due to the coordination issues. Instead, you need to make sure you’re geared low enough that you don’t need to stand to climb effectively.
Despite what Jack states above, it’s my experience that a tandem will weigh less than the equivalent of 2 equally kitted single bikes of similar frame construction.
For example, my MTB tandem ('93 Yokota Twin Peaks) weighs approximately 40 lbs, whereas 2 single MTBs of the same construction (rigid Cro-Mo) weigh ~24-25lbs per.
I know that when my wife and I ride the tandem that we climb at a faster rate than the average of our 2 solo speeds (hence a big part of the motivation for getting a tandem…I got tired of waiting I also recall climbing (off-road double-track) at rates basically equal to friends on their single bikes.
It really is all about W/kg (for climbing) and W/CdA (why tandems are so hella-fast on flats). Put 2 “strong” dudes on a tandem and gear it so they don’t need to stand climbing and they’ll have no issue keeping up with equivalently “strong” single riders.
It’s my suspicion that much like recumbents, tandems tend to get a “bad rep” about climbing more due to the “engines” that are typically on board rather than for any true physics reasons :-/
Not sure why they wouldn’t also work for the captain?
Not sure why they wouldn’t also work for the captain?
Sorry, was thinking of the cranks!
I suspect there is some increase in Crr for a tandem…
Actually, tandems tend to run slightly wider tires than equivalent single bikes, so there should actually be a slight Crr decrease (all other things equal).
All other things equal, yeah. However, I was thinking of the OP’s question, and I’ve often seen tandems with “sturdier” tires on them than the tires on the bikes of the individual riders.
…and possibly some small increase in bearing/drivetrain losses. Perhaps at the wheels only…but, the timing chain should have less losses than a derailleur chain setup, so I’m thinking it’s a wash.
But the total power still has to go through a rear derailleur. I guess it depends on whether drivetrain losses are proportional, additive, or some combo of the two.
Despite what Jack states above, it’s my experience that a tandem will weigh less than the equivalent of 2 equally kitted single bikes of similar frame construction.
My recollection is that, in full race mode (disc/808/etc), the tandem Andy and I set that record on in 2008 was under 30lbs. Everything on it was borrowed, except the saddles & pedals, but I made absolutely no effort to make it light. All my effort went into 1. re-creating our individual positions as best I could, 2. making sure we had adequate gearing (Andy still felt undergeared with 58x11), and 3. making sure it all held together for 46 minutes and 47 seconds.
JBV
From my tandem riding experience, the deficiencies of the weaker team member are really apparent on the climb. The stronger rider subconsciously tries to compensate and eventually pays the price! Maybe not early on in the ride, but as the miles add up the stronger rider works harder and harder!
Two “equal” riders I theory just doesn’t exist.