The rule of thumb is that there is a 20 to 30% reduction in power required when one drafts another bicycle. But what about a tandem? On occasion, I have drafted a tandem on my road bike and the benefit seemed really good. On a recent ride, I had the opportunity to draft a tandem while on my road bike and made some mental notations about power output (I have a power meter).
Climbing a 2% grade, I was at 150 watts (1.94 w/kg) and off their wheel by several bike lengths. For a 310 pound team (estimate) that puts them at 273 watts combined assuming the same power to weight ratio as me. Riding and chatting side by side, we were on a slight descent and I was 150 to 170 watts. From the side by side position I dropped behind and for the same speed by power dropped to 70 to 80 watts. So instead of the 20 to 30% reduction in power, I was seeing more like 40 to 50%.
We come to a downhill section 3 to 5% and my friends decide to ride me off their wheel. Tucked in behind required very little power. I backed off to create a gap and my power went up to 300 watts. I stayed off their wheel to confirm the number and then bridged back - 600 watts. We started another 2 to 3% climb and I was next to them at 150 to 170 watts. I said boy that was fun. I could have easily rode away as they were now working hard climbing.
To potentially put me in trouble on a climb, a 310 pound team would have to make 550 watts for at least 5 minutes. This assumes I am on their wheel getting some drafting benefit.
We really did not need a power meter to confirm what all tandem riders know by simple observation and experience that riding with others on road bikes puts the tandem at a significant tactical disadvantage but I thought some may find this interesting and it is a nice diversion from low spoke count wheel failures.
Any other drafting experience or observations?