Leonardo's gear sketch

[h.g.Whiz]

Suppose that it was possible to construct gears smaller than ones of modern ten speed bicycles(nano gears) and suppose your chain or belt could turn them and withstand the friction. First gear of course would be the same as a modern ten speed in order to get it moving. If the last gear's radius was 10,000 times smaller than the first gear how fast could this megaten speed bicycle travel

[Modified]

About as fast as a regular bike. Lack of higher gear ratios is not what limits your speed, unless you are biking down a mountain.

[kleinjahr]

What's the ratio between driver and driven? Do the math. Of course if, by the math, your gear is rotating at anywhere near 186000 mps, 'taint buildable.

[bruto]

Is the rider of this bike also only theoretical? If so, then you can just do the math for the gear ratios. All you need is the front ring size, and the wheel size, pick a pedal rpm and calculate.

Of course, if the rider is not simply theoretical, then you run up against biomechanical issues, and I don't think you need to bother with the math.

The horsepower of a human rider will limit the speed at which he can go. Gear up too far, and the torque requirements become so high that no human can turn the crank. Don't forget, too, that wind resistance increases dramatically with speed (a ^3 quadratic equation, I seem to recall). The most elite riders setting world speed records with vehicles to break the wind use very large front gears, but nothing even approaching the ratios you're talking about here. Realistically, if taller gearing were capable of achieving higher speeds, they would find a way to use it. If simply increasing gear ratios were the formula for higher speed, Honda Civics would be setting land speed records at Bonneville.

e.t.a don't forget, also, that you need not go to extreme lengths of gear cutting or sizing, since with very little added drag, you can accomplish much the same result with countershafts.

[h.g.Whiz]

Will someone take another look at my idea ?

[ben m]

Will someone take another look at my idea ?

Yes.

The answer is the same as before. The speed of a bike is determined by many, many factors, including (a) the rider's leg strength (peak force), (b) the rider's power output, (c) the gear ratio, and (d) the rider+bike's wind resistance, and (e) internal friction. A ridiculously-high-gear bike will not move at all because of (a) and (e). If the gear ratio is low enough that you can turn the crank, then the top speed is determined mostly by (b) and (d).

If you want to throw out the other factors and just calculate "how fast could the wheel theoretically spin", just multiply by a known gear ratio. If your hyper-gear is 10,000 times smaller than the next gear up, then at the same crank speed the bike will go 10,000 times faster---it's that simple. All of the other factors (a), (b), (d), (e), Special Relativity, etc., tell you whether or not you can achieve that crank speed.

[h.g.Whiz]

Couldn't materials at the nano scale escape some of those factors.

[casebro]

If your concept is that the smaller the component, the less the drag, I'll pee on your parade. The loss due to drag and friction, on a bicycle, is only a couple percent. So all those nanostuff will only improve speed by a couple percent.

I think you are falling for the Woo impact of the word 'nano'.

[ben m]

Couldn't materials at the nano scale escape some of those factors.

No. Bike speeds are mostly determined by air resistance taking power out and rider-cardiovascular-capacity putting power in. Gear ratios have no direct effect on power, except insofar as your legs work better at some speeds than at others. Your proposal for an ultra-high gear makes your the rider's legs much, much less effective.

It has nothing to do with whether the gear and chain is made of fancy materials or not, it's just mechanics.

[Bikewer]

To put it very simply, there are very few human beings that can "spin" a typical road bike's highest gear on a level road. That's a 52/53 X 11 cog, spinning a standard 700c road tire.

[bruto]

Couldn't materials at the nano scale escape some of those factors.Did you read my earlier response at all? Gearing is a very well understood subject. Torque requirements increase inversely with gearing. The same power going in goes out, simply at a different ration of torque to speed. We can choose gearing to optimize the ratio, but we cannot create power with gearing. The torque of a human rider limits the degree to which gearing-up will work.

If you actually care to learn something, rather than just spinning your own gears, you could do worse than to find a copy of Bicycling Science, by Frank Whitt and David Wilson, published by MIT Press. I think it's still in print. A fascinating book, it will answer some of your questions if you care for actual answers.

[TjW]

If you're interested in the current fastest bicycle ride, you could visit here. (http://www.fredrompelberg.com/en/html/algemeen/fredrompelberg/record.asp)
You should note that even with the higher gearing, this speed would not have been reached without the dragster in front of him.

[69dodge]

First gear of course would be the same as a modern ten speed in order to get it moving.

Why is it hard to get a bike moving in higher gears?

(Rhetorical question. I know the answer. Figuring it out will help you understand the other replies in this thread.)

[technoextreme]

Suppose that it was possible to construct gears smaller than ones of modern ten speed bicycles(nano gears) and suppose your chain or belt could turn them and withstand the friction. First gear of course would be the same as a modern ten speed in order to get it moving. If the last gear's radius was 10,000 times smaller than the first gear how fast could this megaten speed bicycle travel
0 Mph.

[Beerina]

About as fast as a regular bike. Lack of higher gear ratios is not what limits your speed, unless you are biking down a mountain.

IIRC, the fastest speed on a bike, according to Guinness, was a little over 70 mph. The guy's bike had a special giant gear on the pedals that almost hit the ground, and a tiny gear on the rear axle. He also had to slipstream behind a truck to get around the wind resistance.

So you won't get much faster than that without starting to mess with a chain of big-small gear multipliers.

[Molinaro]

To put it very simply, there are very few human beings that can "spin" a typical road bike's highest gear on a level road. That's a 52/53 X 11 cog, spinning a standard 700c road tire.

During my courier days, I rode a bike with 53 teeth up front and a microdrive cassette in the back that went down to 8 teeth.

And yes, turning that ratio on flat ground was not easy! However with just the right bit of tailwind I could spin out that gearing at around 55 kph.