Introducing. . . Helga III

I am planning on doing a couple of posts on winter riding. Over the last few years, a lot more information about winter riding has been shared. A few short years ago, it was difficult to find advice on riding through the winter. These posts are based mostly on learning through experience and reflect what I do to get ready to ride through the chilly season. This first post is on the all important steed! All my winter bikes have been named Helga. She was tougher than Hagar, and a bike has to be pretty tough to make it through … Continue reading Introducing. . . Helga III

My New Sekine!

This is my new commuting bike. It is a Canadian made Sekine from the mid to late 1970s. I have been looking for a vintage road bike to use as a commuter. I thought I had one back in the spring. I found a great Peugeot at Recycle Cycle in June. I rushed home and talked my wife into getting it for me, for Father’s Day. Unfortunately, when she got down to Recycle Cycle, it had been sold. I kept checking Recycle Cycle and Kijiji over the summer, but didn’t find anything that interested me. I have many reasons for … Continue reading My New Sekine!

The “Stella” by Light & Motion – Gear Review

I got this light at the Adventure Guide members’ sale last week. It was regularly priced at $150 and marked down by 40%. I checked the price on MEC’s website. It was also listed at $150. The 40% discount means I paid about $89 for it. However, I had a gift card that my son gave me for Christmas and also had some Adventure Guide bucks saved up. The out of pocket cost to me was about $25. I’m not a fan of spending a lot of money on gear! The light straps to the handlebars and the battery easily … Continue reading The “Stella” by Light & Motion – Gear Review

Building with Bikes in Mind

We all get very excited when our city or region builds something with bikes in mind.  It might be something as elaborate as the “complete street” Waterloo turned Davenport Road into, or it might be something simple like Kitchener painting bike lanes on Margaret Avenue.  Heck, some days, I even get excited if I can find a nice place to lock my bike! What about us, though?  Have you ever done any building with bikes in mind?  A few years ago, my wife and I built a sizeable addition on our house.  Outside of the foundation and the gas work, … Continue reading Building with Bikes in Mind

Bicycle Transmission Physics

Bikes are pretty simple machines. Completely enjoyable without special mathematical treatment. But if you’re an obsessive engineering-type geek like me, you’ll feel better when you have a little math to go with all that exercise.

This is a real simplified run through power transmission in a bicycle as I understand it. The numbers check out as do the units of measure. Somebody call bullshit if you see it.

Definitions

First, some definitions. These are just to clarify the physics meaning of these words.

Power – The rate at which work is done. If you bike on a flat road at constant speed, then your power output was constant for the whole trip.

Work – Power integrated over time. Power multiplied by time if power was constant

Force – A force acts on a body to produce an acceleration.

Torque – A measure of a force’s tendency to produce rotation. Think about a wrench. If you used a wrench that was 1 foot long and applied 25 lbs of force on it, then the torque on the nut is 25 ft*lbs. Double the distance, double the torque.

Assumptions

Let’s assume that a random dude is driving a bike down the road. The dude weighs 200 lbs and he is driving an old-school ten speed. Let’s also assume that the losses of the bicycle mechanics are small and ignorable (called negligible in the business).

We’ll ignore the wind. Suffice to say that wind resistance increases the power required to move the bike. Quantifying this value is difficult because it depends on a lot of factors. We’ll also ignore rolling resistance. Just know that narrower, higher PSI tires give less rolling resistance.

Pedals and Crank

Force is applied to pedals. If random dude is standing on the pedal and the pedal is parallel to the flat road, then he’s exerting 200 lbs of force downward on the pedal. Really, you cannot apply your full load into the pedals at all times and the average force will be less, but we’re simplifying. Also, if the pedal is not parallel, then only a trig ratio of the force on the pedal is producing rotation.

The crank is fastened to the bike chainring. The cranks job is to transform the force into a torque. The torque is then applied to the chainring which pulls the chain (no duh).

The torque on the crank is 111.5 ft-lbs if the crank is 170mm or 6.7 inches

200lbs * (6.67 inches/12 inches/ft) = 111.5 ft*lbs

Chain

To calculate the force and torque delivered by the chain, you have to know these three things.

  1. That power is equal everywhere in the system and it is calculated by rotational velocity multiplied by torque.
  2. By using the same chain on the front and back gear, we know that the ratio of front and rear gear rotational velocity is the same as the ratio of teeth on the gears.
  3. The ratio of torque is inversely proportional to the gear ratio. It has to be to make the power equal in the front and back even though the speed of the front and back gears is different.

Continue reading “Bicycle Transmission Physics”

Bell

I just installed a bell on my bicycle. After 4 years of commuting by bike, I’m slowly dropping my cyclish habits.  I also have to credit the friendly writers at WaterlooBikes.ca for raising my awareness of the harm caused by agressive cycling habits. I bought the Incredibell BrassSolo at Ziggy’s Cycle & Sport for $15.99. No longer will I silently wizz pass pedestrians scaring them. Now I can make them jump with the angelic ding of a bell.     The pedestrian traffic on my route home has increased dramatically with the opening of the Engineering 5 at the University of Waterloo. … Continue reading Bell