Bobbing seems to make my bike go faster

[ichitan]

When riding most bikes with rear suspension, some of the energy you use for peddling, results in the bike bobbing up and down. As a result, with equal effort put into peddling, the bike goes slower than a hard tail. You can minimize this by increasing the tension in the spring to minimize movement. But while there is suspension movement, it still requires more effort to pedal.

I have one bike where bobbing seems to make the bike go faster. It has a stiffer spring, which results in it springing back much quicker than many other bikes. When peddling hard, like riding up a hill, the rate of return of the suspension is such that, each time I push down on a pedal, the pedal is coming up towards me.

It would be interesting for someone to do a study on the optimum rate of return for bike rear suspension, and whether having suspension which returns at that optimum rate does make the bike go faster.

[ReapThaWhirlwind]

Bobbing in the suspension (and/or in the tires from lower PSI), produces buoyancy against the ground (and the force of gravity), which in turn creates eccentric resistance. This slows you down. And thus, some front suspensions have lock-outs for traveling on road to take this effect out from your ride and help you go faster.

[Jesper]

@ichitan , you are experiencing the extra ease and extra effort of pedalling due to your pedal stroke being in or out of sync with the movement of the bike (specifically the bottom bracket).
I used to lift weights when on a ship and during rather heavy seas (something I don't recommend!). When lifting during the ship's rise on a wave it added to the perceived weight being lifted just as when the ship was descending the wave the weight seemed less. Of course the actual physical weight never changed, it was only due to a change in the force vector during a specific point of the lift. If you check your speed you really won't find it changing, but you can make it easier (or harder) depending on where your pedal stroke is in relation to the up and down movement of the bottom bracket. This is not taking into consideration that the suspension helps keep the wheel(s) in better and more consistent contact with the ground. If the rear wheel is in the air while pedalling you are losing speed (uphill at least), and is similar to the wheel spinning in the dirt from loss of traction resulting in a loss of speed. I probably don't notice this on a road bike with high pressure tires, plus the fact that I am trying to pedal with both legs during up and down strokes even during climbing (trying to not "pedal squares"). If you tend to only be pushing down on your pedals and not utilizing your legs as much on the upstroke the difference in pedal effort might be more obvious when bobbing up and down.

[ichitan]

A bicycle manufacturer could do a study on this, work out the optimum suspension, see how much difference it really makes, then manufacture bikes like this. If their bikes win races, it will be a big money maker.

I know with some bikes there are various ways to adjust the suspension. Maybe setting up some existing suspensions well, my be as good or better.

I have never heard of anyone talking about setting up a suspension, so the bobbing is in sync with the peddling. Maybe someone has looked into this, but I just haven't seen it.

[Jesper]

(05-15-2022, 06:35 AM)ichitan Wrote:  A bicycle manufacturer could do a study on this, work out the optimum suspension, see how much difference it really makes, then manufacture bikes like this. If their bikes win races, it will be a big money maker.

I know with some bikes there are various ways to adjust the suspension. Maybe setting up some existing suspensions well, my be as good or better.

I have never heard of anyone talking about setting up a suspension, so the bobbing is in sync with the peddling. Maybe someone has looked into this, but I just haven't seen it.

I'm sure that you are correct about being able to take advantage off the inertial gain, but in doing so on a standard bike it may end up being a situation where the power to weight ratio would not be feasible. Maybe on a battery powered bike where weight is already compromised.

My thought would be for suspension equipped e-bikes to use the movement within the suspension to create electricity in order to provide charging to the battery. Same thing could be utilized with any moving parts in order to create electricity, but again you are adding weight to achieve that power gain. Of course cost would also be an issue. If carbon frames and parts start to become the prime material for future bikes and it reduces the manufacturing costs then it may be more feasible to add systems and keep a bike's weight within reason while being able to provide additional power advantages be they mechanical and/or electrical without significantly increasing the weight.

[ichitan]

(05-15-2022, 02:19 PM)Jesper Wrote:  I'm sure that you are correct about being able to take advantage off the inertial gain, but in doing so on a standard bike it may end up being a situation where the power to weight ratio would not be feasible. Maybe on a battery powered bike where weight is already compromised.

To get the bike to bob in sync with peddling, the suspension needs to return quicker than the suspension on most bikes. This is not possible with suspension with a long range of travel. So you need a suspension with a shorter range of travel. A suspension with a shorter range of travel, should weight less than a suspension with a longer range of travel.

Some people may not want a suspension with a shorter range of travel.

The issue might become, riders want that shorter range of travel for riding up hill, and a longer range of travel for riding down hill. Then can somebody come up with a way to switch from one to the other while riding.

[Jesper]

(05-15-2022, 04:12 PM)ichitan Wrote:  

(05-15-2022, 02:19 PM)Jesper Wrote:  I'm sure that you are correct about being able to take advantage off the inertial gain, but in doing so on a standard bike it may end up being a situation where the power to weight ratio would not be feasible. Maybe on a battery powered bike where weight is already compromised.

To get the bike to bob in sync with peddling, the suspension needs to return quicker than the suspension on most bikes. This is not possible with suspension with a long range of travel. So you need a suspension with a shorter range of travel. A suspension with a shorter range of travel, should weight less than a suspension with a longer range of travel.

Some people may not want a suspension with a shorter range of travel.

The issue might become, riders want that shorter range of travel for riding up hill, and a longer range of travel for riding down hill. Then can somebody come up with a way to switch from one to the other while riding.

Not being a mechanical design engineer, but realizing that you would still need to add something the bike to convert up and down motion into forward motion, whether as a mechanical or electrical gain, and regardless of the actual suspension travel range; you would still have added weight to the bike. I have a general engineering background, but I would have to fully research the motion dynamics and power loss/gain. It's mostly math which even for my background I am woefully lacking in talent and would need assistance in doing. The main issue is if you are actually receiving a net gain from the bike traveling in and up and down manner when your goal is to go forward. Good luck on determining that since as I said I'm no mathematician. Transfer of energy from one plane of motion to another is not my area of expertise.
You mentioned having a "switch" for the suspension to reduce or increase suspension travel. Possibly something already exists in that area; I do not ride any bikes with suspension (my mtb is old school; fully rigid) so I have no idea.

[ichitan]

(05-15-2022, 09:26 PM)Jesper Wrote:  Not being a mechanical design engineer, but realizing that you would still need to add something the bike to convert up and down motion into forward motion.

If you take into consideration this point.

(05-14-2022, 10:58 PM)Jesper Wrote:  I used to lift weights when on a ship and during rather heavy seas (something I don't recommend!). When lifting during the ship's rise on a wave it added to the perceived weight being lifted just as when the ship was descending the wave the weight seemed less. Of course the actual physical weight never changed, it was only due to a change in the force vector during a specific point of the lift.

If you timed your lifts to be in sync with the rise and fall of the boat, lifting would be easier.

The theory is, if the suspension is in sync with peddling, peddling is easier. You could ride in a higher gear, and the bike will go faster. Even if you don't ride in a higher gear, and peddling is easier, you conserve energy, and could ride faster on another part of your journey. So the overall journey is faster.

For sure, a bike where the suspension is in sync with peddling, is faster than a bike where the suspension is out of sync with peddling.

The important question is, is it faster than a rigid bike? It seems to be, but I have no way of testing this scientifically.

An idea for a test would be to ride up a hill with this suspension, then switch out the spring for a solid pipe, making the bike a rigid, and repeat. It would need to be done multiple times, and by multiple riders, to see if the average is really faster.