As soon at you touch the brakes, use engine braking, or regen, you become less efficient. Or if the downhill exceeds the target speed, that burns energy as well since speed increases are not proportional when it comes to energy lost.
So for gentle rises, not a big deal. For steep grades, you take a big hit.
Another item is cross wind. People assume that if you a roundtrip with a crosswind, you don't lose anything. But, it effectively increases the frontal area and increases the CD too.
Head winds and tail winds also hurt a roundtrip. Say your target is 65mph and the wind is 5 mph. Going with the wind gives you a drag equal to 60mph. Going into the wind gives you 70mph. The difference in drag from 65 to 60 is less than the drag difference from 65 to 70. The higher the windspeed, the more the effect.
So for gentle rises, not a big deal. For steep grades, you take a big hit.
Another item is cross wind. People assume that if you a roundtrip with a crosswind, you don't lose anything. But, it effectively increases the frontal area and increases the CD too.
Head winds and tail winds also hurt a roundtrip. Say your target is 65mph and the wind is 5 mph. Going with the wind gives you a drag equal to 60mph. Going into the wind gives you 70mph. The difference in drag from 65 to 60 is less than the drag difference from 65 to 70. The higher the windspeed, the more the effect.
