OK, now that I know that increasing your average wattage from 150 watts to 175 watts is actually quite a bit of work. So what are some other ways to be more efficient.
Why this matters? Being dropped
Some wonder, why any of this matters for the average rider who is going in a group (as opposed to a Tour de France competitor). Well, the reason is simple, if you are in a group, you don’t want to get dropped and fall behind. Why? Well, once you are dropped, you now have to fight the wind by yourself. And that is the major use of energy. Even being 10 watts behind means that on a hill you can fall behind. So the smart rider who wants to have a good time, does need to care about this.
As I’ve been cycling more, I’ve discovered that I can go faster and faster with less and less energy. Of course it also makes sense to increase your power output and lose weight, but even then changing some equipment or even how you sit on the bike is additive.
What power do you need? Resistances explained
In the end, you are your power curve. That is how much wattage you can put out for how long. So what are the kind of resistances that affect riding? Ridefar.info has a good overview, but they are, for the average rider on a long distance
- Air resistance. This dominates at higher speeds, but 43-57% of the total wattage. The key things here are your position on the bike and also how aerodynamic the components of the bike and your clothes are.
- Gravitational resistance or Weight. This is carrying your weight up the hill, you theoretically get it back on the downhill, but there’s a loss due to air resistance and braking on the way down. This is 38% of the total wattage used (which is why it is important to lose all your fat since a typically rider at 165 pounds far exceeds the weight of the bike at say 17 pounds).
- Rolling Resistance. Energy lost because the tires deform as you ride. 11% of the total. Picking the right tire and tube makes difference.
- Mechanical Resistance. The losses due to the wheel hub at 1% and drive train at 4%. As an aside, this is why biking is so fun, it is very efficient to pedal a bike 🙂
- Braking. When you use your brakes, you lose power of course. 2%
Air Resistance: Make yourself small
Well the big ones are to get a faster wheelset and better bearings and a more aerodynamic bike, but here are the easiest ways to get more power. Much thanks to bikerollingresistance.com for much of this data and ridefar.info has a great overview:
Aerodynamics If you keep your elbows parallel to the ground and then are on the top of the bars, then you have a much lower aerodynamic drag coefficient (Cd) and then you multiple by your aerodynamic size (A) will give you the total CdA which is the aerodynamic drag, Now if you know your velocity, then you can see the amount of power that is required to keep you at that speed. This is just to
F = CdA * p/2 * v^2 where p is the air density in kb/m^3 which is 1.225 and velocity in m/s (23mph is 10.28 m/s). Assuming a CdA of .32, then this is
0.32 * 1.225 * 10.28^2 * ½ is 20.71 Newtons of force. Then finally
P = F * v, so this is 20.71N * 10.28 m/s is 213 watts. It also turns out that you have to take some of average depending on how the wind hits you, this is called the yaw.
You can measure this yourself, but broadly, you can estimate the area of a person by a regression against their height and weight and then assume a Cd for a road bike (on the drops this is 0.88). So for say a person 5′ 11” (180 cm) and a weight say of 168 pounds (76.5 kg) which would yield an estimate area of 0.431 meters, so a CdA of 0.431. Depending on the model, you can get 0.38 Cd
Air Resistance: Equipment
The next areas are to change the equipment that you have. Here are some simple examples. Red Bull points out some other areas where you can save by changing equipment and Shop for Watts did a nice chart of cost per watts saved
- Giro Empire SLX Shoes. These are laces ups and can lower wind resistance by another 5-12 watts
- Velotoze Shoe Covers. If you don’t want to spring for $200 shoes, then a $22 shoe cover will save you 1.4 watts (assuming 75kg rider, 8kg bike, 40kph and 300 watt output).
- Castelli San Remo 3.0 Speedsuit. This is a skin tight suit that can gain 15 watts at speed. Yes, it is $400, but that is very significant.
- Specialized Evade helmet. These helmets are hotter, but at speed, an aero helmet can save 9.5 watts for $300
- Cabron fibre aero drop handle bars. Rather than a round shape, use one that is aerodynamic saves 4 watts at speed for $300.
So after that what can you do to reduce wattage
Rolling Resistance: Tubes and Tires
There is actually quite a substantial difference in the type of tire and tube that you use. When you realize that the difference between an average rider (150 watts FTP) and good rider (200 watts FTP), then you can see that saving 10 watts with the right tubes is a big deal.
Tire rolling resistance. The Continental GP4000 II can reduce 12 watts, but you need to make sure they are inflated to at least 80 psi.
Latex tubes. The same Continental latex tubes reduce by another 5 watts. The Victoria Latex is nearly identical. The main disadvantage is that they lose pressure quickly and if you have aero wheels, then they need long enough stems.
Weight or Gravity Resistance: 2Kg is 1% on hills
Well, it is not an accident that the main place people get dropped is on hills. When you are on the flats or downhill, then aerodynamics dominate, but the farther back in the back the less power you need. So, it is really hard to breakaway unless you are climbing.
When climbing, air resistance falls away and it is just weight that slows you down. The actual measurements from Ridefar.info for transcontinental riding shows that on a 1-4% grade, the difference in 5Kg in total (rider plus everything) results:
- At 1-4% grade, in a 3% increase in speed from 18 km/h to 18.5 km/h that’s 3:20 minutes vs 3:14 so about six seconds
- But at 4-7%, that increases to 5.2% (11.4 km/h to 12 km/h) or 5.2 minutes vs 5 minutes or a 12 second lead
- For >7% to 5.9% that is going from 8km/h to 8.5 km/h. On a 1 kilometer hill that’s the difference between finishing in 7.5 minutes vs 7 minutes so a nearly 30 second lead.
The effect of weight is quite linear to the power required, basically, 1Kg of saved weight means you go 1% faster or about 2 seconds on a medium hill and 6 seconds on a big one. This doesn’t sound like much, but on a 1km hill, it’s enough to breakaway, so that’s why you need to focus on:
- Yourself. You are the heaviest thing on the bike. So going say 170 pounds to 168 pounds is going to make you 1% faster on hills., on a medium grade that means about 2-3 seconds faster which is enough to break away. Obviously, the whole point of cycling is to get in shape, but this is even more incentive. If you are say 15% body fat at 170 points, then just getting to 10% is 8 pounds (3.5Kg) and that makes a huge difference.
- Wallet. It sounds silly, but even this weights a pound and the same with toolkits and everything else
- Your backpack. This is one reason why road bikers don’t use hydration packs while mountain bikers do. A typical lightweight pack weights 2 pounds and has a reservoir, if you replace it with a water bottle cages and two water bottles, you are probably saving 1.5 pounds.
- Electronics and lights. There is a tradeoff here, but not carry a cellphone isn’t really an option, but there is a difference between lights that weight 1.5 pounds and 0.5 pounds.
- The bike itself. Well, a 19 pounds vs 15 pound bicycle is way more expensive,
Net, net, it all adds up
Even though this is the smallest factor, there are still simple gains to be made here:
- Wattshop DirtyFast Chain. 5 watts by reducing mechanical resistance for a $80 chain
- CeramicSpeed oversized pulley wheels. This is crazy expensive way to save 2.4 watts for $600.