Biomechanical efficiency

Biomechanical efficiency is very important term in the cycling world. The term describes the energy moving your bike, related to all the energy you put in the bike at all. The main rule which applies to biomechanical efficiency is the rule that the force follows the path of least resistance. It all starts with this rule and ends with it. The whole biking world revolves over it. The bigger the amount of energy moving your bike, related to the overall energy you put in your bike, means your bike is efficient, and vice versa, if you put a lot of energy into the bike but small amount of it moving the bike, your bike is inefficient.

Different bike designs give different level of biomechanical efficiency, exactly because of the rule the force follows the path of least resistance.

Bikes with rigid frames and rigid forks are the most efficient. This is why this type of bikes is chosen for speedy races or long races. These bikes are good for acceleration, long-term climbing, long distance racing, long distance travel, and basically rigid frames are the simplest constructions. The point of least resistance there is the crank set. All the force goes there. Once went there, almost all the force moves the bike. Some force is lost due to gearing and tires rolling resistance which will also be reviewed here in a later section.This type of bike are usually bikes designed to be ridden in a hall or road, or light country road with small bumps.

Front suspension bikes
These bikes are known for their efficiency, while riding cross country and long travel trekking. The bikes can be as efficient as rigid bikes or loose some efficiency, because of front suspension. Some bikes offer advanced feature called suspension lock.

Bikes without suspension lock, are not as efficient, as bikes with, because the point of least resistance is the front suspension and it’s movement actually eats some of the force you apply, so you need to apply more force to compensate losses.

Bikes with the suspension lock feature, offer more, they can be as efficient and rigid bikes. Activating the suspension lock, means that the fork is fixed and it does not move, acting like rigid fork. In this mode, all the force follows the path of least resistance – it goes to the crank set. This is useful feature when you have steep climb, long climb, you demand acceleration when you pump the cranks, and you want predictable behavior of fast turns in the city.

These bikes can cover a wide range of terrain off-road terrain, mountain terrain, but they have their limits – they are not as strong as their full suspension brothers. They are generally lighter, faster, and accelerate better than full suspension bikes, but slower, heavier and accelerate worse that fully rigid bikes. While suspension lock is activated, they handle as good on tight fast turns in the city as their fully rigid brothers, because you can feel the feedback from both tires and adjust your speed or cornering angle immediately after you detect something. When suspension lock is inactive, front suspension acts as shock absorber, to a certain degree it absorbs the shocks, but some of the feedback is absorbed and you never get it, until is to late. This creates the illusion that the bike is more stable than in actually is, and the bike is actually less stable, compared to rigid fork or a fork with activated suspension lock.

Full suspension bikes are tough, heavy, the least efficient type of bikes in terms of biomechanical efficiency. This type of bike usually means that you have other goals in mind, and biomechanical efficiency is one of your LAST concerns. Usually Concerns fall with thin priorities like  strong frame, able to handle abuse from rough terrain, tough jumps. The least efficient part of biomechanical efficiency, comes because of the full suspension setup. These bikes do not offer suspension lock, and the suspension is very long travel suspension, eating a lot of force. Following the path of least resistance, the crank set is the third element in the chain. First element is rear suspension, second is front suspension and last is the crank set. Keep in mind, these are the slowest bikes, the heaviest and riding them is physically demanding.

Tires: width, tread, pressure.

Treads
Tires play crucial role in biomechanical efficiency, because of their rolling resistance. Rolling resistance is formed by adding tire deformation due to the pressure it is pumped and the treads. Long aggressive treads, offer superior traction in sand and mud, but the least biomechanical efficiency. Tires with lot of finer more shallower treads, offer better biomechanical efficiency, and good grip and traction for Cross country or a joyride, as a balance. Tires slicks with few channels to channel water away, are the most efficient tires. They offer the least rolling resistance, thus most biomechanical efficiency. These tires are only good in the city to ride them on asphalt, dry or wet, and that’s all they are good for.

Pressure and width
I decided to combine both in one because pressure and width are related to each other, and they form a part of the rolling resistance.

The relation is simple the wider the tire, the lower the pressure. As general rule on 29-er MTB tires for cross-country ride maximum pressure varies trough different width as follows:

29x2,35 maximum pressure is approx. 3.0 bars
29x3.0 maximum pressure is approx. 3.1 bars
29x2.25 maximum pressure is approx. 3.2 bars
29x2.2 maximum pressure is approx. 3.5 bars
29x2.1 maximum pressure is approx. 4.0 bars

As general rule the wider tire has more rolling resistance thus least biomechanical efficiency, than narrower, assuming tires are pumped to equal pressure.

As General Rule Lower pressure means more rolling resistance, and least efficiency, than higher pressure, assuming tires are the same size.

If we take both into account, turns out wider tire offers much more rolling resistance, because it is pumped to a lower maximum pressure, and offers greater level of friction, which might be your best bet in mud or sand, but for city ride and cross country ride, narrower tire will offer much more efficiency and much less rolling resistance. This is your best bet if you ride long distances in the city, cross-country or climb a lot.

Nitrogen Pump
Nitrogen pump of the tire, actually offer better behavior of the tire, better overall control over it, and this is how you might increase your biomechanical efficiency indirectly, by making your bike behave better. With better behavior, you will struggle less to keep the bike under control, so this saves you energy – you put less energy because you struggle less, therefore better biomechanical efficiency. Nitrogen pump also offer other advantages such as less pressure variation because of temperature, less tire deflation over time, homorganic contents in the tube, which offer the better behavior of the tire – you have only one gas inside, instead of mixture of gasses – the air, the worst of air pump behavior comes from the fact the air is mixture of gasses, where each gas has slightly different behavior, under pressure. This problem is also eliminated with the nitrogen pump.

26-er VS 29-er
This topic is full f controversy, some say 29-er is more efficient, than 26-er, because of larger diameter, makes a bigger circle means longer circumference, therefore longer distance covered by one full rotation. Other say that larger radius usually means that the leverage effect counteracts the force so you need more force, while on rough terrain, 29-er handles the rough terrain more smoothly, actually increasing biomechanical efficiency, by reducing resistance when negotiating an obstacle or rolling over roots or other obstacles.

Gears and shifting gears
This is the largest source of biomechanical efficiency or inefficiency, it depends on how you pedal and on how you shift gears. Let set the terms first.

Front shift means you are shifting the chain on the front gears
Rear shift means you are shifting the chain on the rear gears
Up shift means you are shifting to a faster gear
Down shift means you are shifting to a slower gear
Front gears means the gears or cogs on the crank set
Rear gears means the gears or cogs on the rear wheel

Our body’s biomechanical efficiency, is at it’s greatest, when you pedal at certain range of rpm between 60 and 90 rpm, which basically means that at 60 rpm, you make one complete pedal rotation for one second. At 90 rpm, you are making one and a half rotations of the pedals for one second. To give you a perspective this means 44 kph speed of the bike with 26 inch wheels, when the fastest gear of a bike usually 42x11 is selected. This means the largest gear at the crank set and the smallest at the rear wheel.

The large number of gears usually are there to help you pacing, because while you pedal within the range 60 – 90 rpm, you are biomechanically efficient. If you go below 60, or above 90, you become inefficient. The more gears you have, this means more options to keep pacing at steady rate over various terrain. Pacing means to shift gears in order to maintain the current rpm at the crank set, which is the main idea of the whole deal with gears. When you are about to overrev you rear shift up, until you can pace. When you are about to underrev, then rear shift down to allow yourself to pace. Front shifting is usually done, when a terrain or surface changes in general, or when angle changes – climbs with various steepness, or, going downhill to keep you pacing. Use all of your gears wisely, maintain steady pace, and you will be able to ride further with less effort.

While shifting gears, there are few thing you need to know. First, when preparing for a climb, front shift down in advance, overrev for a moment, then while gently rotating pedals front shift down once, then pick up the pace, now rear shift up twice to return to nearest gear to the original one, now crank with steady pace, if you are about to go under 60 – rear shift down one gear, still going under 60 rear shift down another, and another until either you run out of gears of you find your pace. If you run out of gears, overrev the crank, then go gentle on it, front shift down, rear shift up two gears, and continue rear shifting down.

Going downhill? Your pace is above 90? Start rear up shifting, until you find your pace, not enough front upshift one gear, and rear down shift two gears, then keep rear up shifting, until you find your pace.

Obstacles prevent you from pacing? Rear shift down two gears and rev up the crank. While negotiating obstacles, it is always a good idea to rev at 90 rpm, selecting the slowest gear which will allow you to both rev up to 90 rpm and keep the current speed. Once your reached this gear keep it, until you leave the obstacles.

Misc. tips:
If you want easy leisured ride, go calm, enjoy the joyride and scenery, maintain a pace at 60 rpm. If you want dynamic ride, fast speed, acceleration, pace at 90 rpm.

If you want more fun when you ride dynamically, make sure to visit the nitrogen pump. Ask the employee, to let all the air out of your tires, then pump them up to maximum pressure, with pure nitrogen. Your tire will have better behavior, and the whole bike will behave better.

Enjoy your ride.