Easier to pedal with physics

[Dark85]

TL;DR Summary

Does pulling up on the handle bars of a bicycle make it easier to pedal?

Hey everyone,
I have a question. Does pulling up on the handle bars make it easier to pedal. I believe it is true as by pulling up on the handle bars,
the normal reaction force reduced which reduces friction(friction = coefficient of friction*normal force) which hence, makes it easier to pedal.

 

[.Scott]

Having pumped up many hills, pulling up on the handlebars is an enormous help.
It allows you to get a lot more of your muscles involved in propelling the bike.

 

[DaveC426913]

Not sure if it makes it "easier", but you can certainly get more power out of it.

You can greatly increase your apparent weight on the pedals.

 

[Dark85]

I was also thinking even if one lifts the handlebars up, won't the decrease in the normal reaction force on the front wheel be compensated by an increase of the normal force on the back wheel. So it would just result in more friction on the back tire wouldn't it? It would just increase the wear and tear since back tire experiences more friction now. I dont think lifting up the handle bars would reduce friction then.

 

[PeroK]

TL;DR Summary: Does pulling up on the handle bars of a bicycle make it easier to pedal?

Hey everyone,
I have a question. Does pulling up on the handle bars make it easier to pedal. I believe it is true as by pulling up on the handle bars,
the normal reaction force reduced which reduces friction(friction = coefficient of friction*normal force) which hence, makes it easier to pedal.

There's no kinetic friction for a wheel. That's the point of a wheel. It rolls without slipping rather than sliding along the road surface.

 

[Dark85]

There's no kinetic friction for a wheel. That's the point of a wheel. It rolls without slipping rather than sliding along the road surface.

But it would be static friction since it rolls without slipping right?

 

[PeroK]

But it would be static friction since it rolls without slipping right?

Static friction is the external force needed to accelerate the bike. By accelerate I mean speed up, slow down or change direction. It's not needed to roll without slipping. It's also needed when going uphill to overcome gravity.

There is an element of "rolling resistance" that slows down a wheeled vehicle. This is more complicated than kinetic friction.

Note that tires are made of high-friction rubber in order to improve acceleration and turning capability. If friction were involved in rolling, them having high friction tires would be absurd.

 

[Baluncore]

If you have cleats attaching your feet to the pedals, then you will be generating a rotating force with both pedals over the full cycle. That crank torque must be countered by leaning your body mass forwards, with your hands on the handle bars. Since there is a left-right alternating pedal force, you should counter that with a lift of one hand while pressing down with the other. Do not sit on the seat, hold the front of the seat between your thighs, to keep your body in the same plane as the bicycle frame.

 

[Dark85]

Static friction is the external force needed to accelerate the bike. By accelerate I mean speed up, slow down or change direction. It's not needed to roll without slipping. It's also needed when going uphill to overcome gravity.

There is an element of "rolling resistance" that slows down a wheeled vehicle. This is more complicated than kinetic friction.

Note that tires are made of high-friction rubber in order to improve acceleration and turning capability. If friction were involved in rolling, them having high friction tires would be absurd.

What is rolling resistance exactly? Why is it more complicated than kinetic friction?

 

[PeroK]

What is rolling resistance exactly? Why is it more complicated than kinetic friction?

Look it up.

 

[Dark85]

Look it up.

Hey i appreciate that but the reason I post my questions and doubts here is because i don't want to look it up. I want to hear it from experts like you and others on this platform. Rather, could you please suggest any book on the topic, I will go refer to it. Thank you.

 

[PeroK]

Hey i appreciate that but the reason I post my questions and doubts here is because i don't want to look it up. I want to hear it from experts like you and others on this platform. Rather, could you please suggest any book on the topic, I will go refer to it. Thank you.

The Wikipedia page on rolling resistance says way more than I can reproduce on my phone.

The important point is that no energy is lost to kinetic friction or static friction on a wheel rolling without slipping. Try pushing your bike with the brakes locked to see how much friction there is between the tires and the road surface.

 

[.Scott]

When I pump at my hardest, I pull the right handle bar while pushing with my right foot, then follow the same on the left side. I also use vertical motion of my body to allow me to set up for the next push when the pedals are at their lowest and highest. The bike itself will tilt away from the working foot on each thrust - by at least 10 degrees. So I may be compromising "rolling friction" but negligibly so.

Also, being an old-timer, I use a "standard" bike - that is, one without gears. When I was a youngster, I made several solo round trips to my grandparents house - about 20 miles each way. And was able to ride around my very hilly block with no hands. Those were the days before helicopter parenting.

 

[DaveC426913]

I was also thinking even if one lifts the handlebars up, won't the decrease in the normal reaction force on the front wheel be compensated by an increase of the normal force on the back wheel.

Hang on. You're not actually lifting the bike. You can't "pick yourself up by your own bootstraps".

What you're doing by pulling it the handlebars is increasing the force on the pedals, which are a moving part.

You can't change the aspect of the bike to the road; you can only change the aspect of yourself to the bike.



Equivocation: OK, if you were to grab the handlebars and lean back, you can move the centre of mass of the system backward, which would put more weight on the rear tire.

But I don't think that's what you were talking about in the opening post. If it is, please clarify.

 

[sophiecentaur]

What you're doing by pulling it the handlebars is increasing the force on the pedals, which are a moving part.

As you move about on the bike, you are raising and lowering your CM and altering the timing of the forces you apply. I'd defy anyone to analyse what goes on in any accurate way

 

[Ken Fabian]

Back in my early teens a friend found antique handlebars off an early motorcycle, that had the same 'expander' type fitting as bicycles used. The handlebars swept back - would only just allow the ends of the handle to pass in front of the saddle. Of course we tried them out.

re: the question, the hand hold position was almost directly above the pedals and we were surprised at how much force could be applied to the pedals by pulling upwards on the handles. Like the difference between picking up a heavy item with arms forward or picking it up standing over it. I remember thinking I might break something - the amount of force seeming so much greater.

Even now I remain convinced it worked better than the original forward placement for power to the pedals - with the downside of sitting upright (which would suit me better now, with age related hand and shoulder joint deterioration), so more wind resistance and a bit too easy to 'wheelstand' (which we thought was good at the time). I don't know how well that arrangement would work for endurance (my Dad ordered their removal, in his 'no arguments' voice - experiment ended) but seemed very good at acceleration and sprint. It seemed to use different muscles to normal, more use of my back?

I haven't ridden them but 'recumbent' cycles seem to have somewhat similar geometry - pushing against shoulder straps? - and I suspect that contributes to claims they work better.

 

[hutchphd]

My guess is that the best ergonomics for pedal power were very well studied by the Gossamer Condor group under Paul MacCready. As I recall these had upright posture and seat level handholds. My ~recumbant stationary bike also has handholds on either side of my butt.

 

[berkeman]

Hey i appreciate that but the reason I post my questions and doubts here is because i don't want to look it up. I want to hear it from experts like you and others on this platform.

This is not acceptable at PF. You are expected to do your best to answer your own questions here. We are happy to help you understand things that you don't understand in your reading, but we do not spoon feed you here. That is not PF's mission. In the future, please do your best to figure out your questions with your own research, and ask us questions about the parts of that reading that you don't understand.

Also, do you have access to a bicycle where you could experiment with this question?

 

[Ken Fabian]

My guess is that the best ergonomics for pedal power were very well studied by the Gossamer Condor group under Paul MacCready. As I recall these had upright posture and seat level handholds. My ~recumbant stationary bike also has handholds on either side of my butt.

I haven't used a recumbant cycle and my impression was users could push against the seating and what looked like shoulder straps. The position requires the 'handlebars' to be more in-line (butt level) just to reach them, but having that geometry also allows greater force to be applied.

I do note that serious cyclists will have strapover pedals that allow them to pull upwards on the opposite side, something I never got strong at or made much use of, tending to rely on body weight, so the advantage may not be as great as it seemed to me at the time. I also suspect that sustaining prolonged exertion has limits different from maximum force.