July 26th, Day 38: Mount Pleasant, MI to Birch Run, MI: 74 miles, 206 ft. ascent

Today’s ride was as flat as it gets, but the headwind was relentless. Fortunately we caught a ride on the Davey Train and with some great teamwork managed to average 18.8 mph.

James, Chris, Senator Dave, and Portland Dave stand in the hotel lobby. Chris looks tired!

James, Chris, and the Davey Train: Senator Dave (left) and Portland Dave (right)

To provide a bit of contrast with such a flat ride here are some thoughts on hills I prepared earlier.

I have now spent over 5 weeks doing very little except cycling, preparing for cycling, repairing after cycling, blogging about cycling, dreaming about cycling and (increasingly) fantasising about not cycling.

This has provided ample time and ample empirical evidence for formulating some unscientific theories about what makes hills cruel and what makes hills kind.

But before getting into the geeky stuff, here’s a novel piece of stoker abuse. The common refrain to the pilot is “Hey, the guy behind you isn’t pedalling”. If I had $1 for every time I have heard this banter then I would not have needed to solicit any donations for this ride. However, the park ranger at the Badlands National Park entrance far surpassed this when Alastair provided his name. She took one look at me and then simply asked “and your passenger’s name is?”.

Now the geeky stuff…

The received wisdom (a.k.a. innumerable post fact cycling blogs of dubious provenance) provides that hills slow you down by anywhere between 4mph and 10mph per 1,000ft of climbing. So, a century with 5,000ft of climbing seems to be viewed as equivalent to anywhere between 120 and 150 miles on the flat.

But most of the stuff I’ve read starts with some throw away comment like ‘ignoring the effects of the descents’. This seems to me an outrageously specious assumption. If we were 100% efficient at converting muscle energy to the Potential Energy associated with an ascent and if we did not lose any energy as heat converting that Potential Energy back to Kinetic Energy, then hills have zero effect on the effort required for any ride, assuming that the start and end points are at the same height (this height assumption is obviously true for circular rides).  

So the two real questions seem to be:

  1. How much energy do we waste climbing (i.e. energy expended heating up our muscles rather than lifting ourselves and Genevieve up the hill)
  2. How much energy do we lose as heat descending again (i.e. heat in our brakes and heat dissipated through air/road resistance above and beyond the rolling resistance we suffer under our own power).

Before contemplating both of these negative effects of hill climbing, it’s worth noting two very positive effects:

  1. Anyone who has ridden 74 miles on the flat into a headwind will attest that this is a pretty demoralising experience which makes continuing to deliver a good power output psychologically very challenging. So to that extent a bit of up and down variety is (albeit unquantifiably) A Good Thing
  2. Descents are a great opportunity to freewheel, which is in turn a great opportunity for muscles to recover, and return to their most efficient power generation state.

Going back to the first source of energy loss on hills, this seems to be most significant when the gradient is ‘too steep’ resulting in anaerobic energy burn. Simply put, if your heart rate goes too high in order to sustain the necessary power output to get up the hill, then the muscles don’t work as effectively – an obvious symptom is lactic acid build up and the consequent burning sensation. On a tandem this gradient problem happens on less steep hills than for solo riders. My own explanation for why this should be is that tandem riders do not quite deliver twice the power of a solo rider. On the flat and downhill this is outweighed by there being less than double the air/road resistance. However on steep hills, where the air/road resistance is not a significant factor, the failure to deliver twice the power output becomes crucial. Even strong pilots like Alastair and James struggle to keep Genevieve on the tail of otherwise similarly paced solo riders when the gradient is sustained at more than about 5%. (Aside: we can often more than recoup this on the flat/downhill but it does make paceline riding quite a challenge). 

The second source of energy loss on the descents again kicks in when the slope is too steep. And once again this is more pronounced for tandems than for solo bikes. This is because flat/downhill terrain is where tandems naturally benefit but on a really steep slope we cannot take full advantage without exceeding 40mph. This is about where I start worrying that one of the notorious potholes we have come to know and love will bounce me so far off the saddle that the temporary removal of pain from my rear end will be replaced by something substantially more serious. Consequently on steep descents we burn a great deal of energy heating our brakes. And even if we don't brake, the air/road resistance at greater than 40mph is so high that we are burning lots of energy heating the tyres, the road and the air.

My conclusion from this rather extended ramble is that hills start getting cruel if the ascent and/or descent gradient is sustained at much more than 5%. But conversely, if the ascent is not too steep, and the descent is relatively gradual with a smooth surface and good visibility, then hills become positively kind. The psychological and freewheeling benefits outweigh the energy losses and we can enjoy a varied but fast and satisfying ride.

And just to prove how much we love hills, here is a video of us powering up a long climb.