Wednesday, April 04, 2007

Road Bike Gearings : Getting Technical

This is an extension of my posting here.

Since road bikes are mostly technical rides, i think it's worth while to start looking at it from a technical point of view.

As we all know, most newer bikes come with 9 speed, at least. With sprockets from 11 teeth till 27 teeth for some 10 speed variant. But first, an introduction to what is a chain ring and what is a sprocket...

Chainring - item 22, Sprocket - item 26

Closer view...

Chainrings - 39-52 combo

Sprockets - 9 speed

My steel bike comes with a combo of 14-17-19-21-24 behind and a 42-52 chainring. (The chainring comes with sizes of 39,42, 52 and 53). Meaning my gearing are limited to a certain extend.

Take someone with a 39 front for example, even if his largest sprocket is 24, he still have a gear ratio of 1:1.625, which is still lower than my 1:1.75. What this meant is that the latter will climb easier...and most of these newer bikes has the larger 27 teeth sprockets...which ultimately gives them a good 1:1.44 ratio. The lower the ratio, the easier the climb.

The higher it is, the heavier it would be. If you are a strong cyclist, a combo of 53x11 (ie the heaviest/highest gear) would give you a 1:4.82 ratio...meaning, for every one turn he does, i'm constantly 0.82 turns behind...and that means with every one turn, he pulls away almost 1.751meter(3.142 x 680mm(wheel diameter) x 0.82) away from me...imagine how far he would be away from me pedaling at 90rpm on a flat ground.

I chance upon this website, wich offers great insight into all things cycling. According to these gurus, the old method of calculating the ratios are outdated. They introduced something called Gain Ratio and Inch Ratio and even Meter Development.

The easiest to understand is the Meter Development. In their own words:

Development (also known as rollout), is one of the three comprehensive systems for numbering the gear values for bicycle gears. Development is the distance the bicycle travels for one crank revolution, and is usually measured in meters. Development can be calculated by dividing the chainwheel size by the rear sprocket size, multiplying the result by the wheel diameter and by pi (3.1416). See also gear inches and gain ratios.

So, now lets look at what my 5 speed could do, compared to a 9 speed. Assuming the same tyre size of 700cx20, same rider, same ability ie me.

My combo

Newer bike combo

Above results thanks to Sheldon Brown. Thank you sir!

Now, what does all these gibberish meant above?

On the heaviest/highest gear, it simply meant that with the newer combo of 53x12, i could go 9.2meters in distance on one crank revolution compared to my older 52x14 combo which will cover 7.8meters.

On the lightest/lowest gear, the combo of 39x25, it will go 3.3meters and my 42x24 combo will go 3.7meters. This also indirectly meant my lightest is heavier to crank and will take more effort to cycle up hill. But if we both were to spin on our lightest on a flat, i'll be 0.4meters ahead every revolution, but translate it on an uphill climb, i will struggle more.

Hence, it's most important to build the engine first (as what Azmar would tell you). I'm trying very hard to make this 5 speed works for me.

So much red meat, need red wine

While sourcing for the above picture, i chance upon this blog here. I couldn't help by smile when i read what Team MWC, FTJ, NGT is...

It stands for Team Married With Children, Full Time Job, No Genetic Talent. Sounded like me! So, here's to you bro, greetings from Fellow MWC,FTJ, NGT all the way from Malaysia!

How we looked like

Proud to be Malaysian!

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