A car can go from 0-7000 RPM. you can go from 0-100. So the usable speed within each gear for a rider is much lower.

https://en.wikipedia.org/...ariable_transmission

A car engine has a much broader torque/rpm range. Nevertheless, it would be more efficient if they could design a transmission that would keep the engine rpm at it's more efficient point regardless of vehicle speed. Maybe some day this will be a reality. Some of the CV transmissions are trying to approach this. But they have losses, and lots of moving parts, etc.

Depends on whether you mean system efficiency of engine efficiency. For example if an engine is most efficient at 3000RPM, but you only need to go 10MPH, then it may result in lower overall energy consumption to run at the engine at a less-efficient 1000RPM. I don't think there's any type of gasoline engine that can vary torque at the same RPM?

Yes, what I meant is to maintain engine rpm at the point delivering maximum torque, regardless of commanded vehicle speed. So this refers to "system" efficiency for lack of a better word.

Oh geez.. I'm tempted to write a lot here! But yes, all engines can vary their torque at a given rpm. It has to do with how much fuel you're​ putting in to the engine at that rpm. You can't go above the max torque, which is what the torque curves you see in marketing materials represent, but you can go below it.

Most engines' point of peak efficiency is at a relatively low rpm, but at high load - i.e. close to peak torque for the speed. But normal driving conditions rarely are conducive to that condition. But if you design a series hybrid electric drivetrain you can operate the engine at that point all the time.

Also blueapplepaste is right. Most cyclists want to stay in a +/- 7 rpm range under normal conditions. Say 80 to 94. Maybe up to 115 on hard efforts. A car is happy to stay between 1500 and 3000 under normal conditions and up to 6000-7000 on hard efforts.

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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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I clicked on the web site in your signature line. Looks like a interesting engine design. Going to watch the video when I get some time to do so.

You could ride a fixie with just one gear. You'd get where you're going, but not nearly as fast or as efficient as using 15 gears.

15 gears allows you to stay in the sweet spot of power. The sweet spot of power production for a human is a very narrow range. Cars have much wider power ranges, so they can get away with less gears. Note tho, that cars are being designed with peakier engine again, and going with more gears than 5 to optimise the amount of time they're in the new narrower sweet spot.

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TriDork

"Happiness is a myth. All you can hope for is to get laid once in a while, drunk once in a while and to eat chocolate every day"

Because transmissions are 10000x more complex than bikes so it's harder to make. Also they are moving towards it my Jeep has an 8 speed I think there may be some 10 speeds now too.

I think you mean sweet spot of torque or cadence?

But at a fixed load and fixed gearing wouldn't adding more fuel just increase the RPM?


Depends on how you define "normal driving conditions," but freeway driving is a very common condition that seems very conducive to that condition. I think that's the whole point of the "overdrive" gear?

Only 15 ratios!?...

You need a new bike, chap ;)

A standard crankset paired with an 11-speed 11-25T cassette offers 15 discrete ratios
A compact cranks paired with the same cassette afford 16 discrete ratios .

A semi truck has 18 speeds. A diesel engine has a much narrower power and RPM range... kind of like a biker's legs.

How are they 'discrete'?... Does no one see them change!?...

The new ecoboost F150 offers a 10 speed transmition.

Damn, you get there first.

Got to love a crash box!

I can't believe no one's given the obvious answer yet. Because bike manufacturers want you to buy a new bike.

My first racing bike had 5 rear cogs. My next racing bike (steel) had 6cogs. When the industry went to 8cogs, I took it to LBS to have the chainstays spread.

My current bike has 9cogs, which apparently makes it suitable for dinosaurs.

All 3 bikes worked perfectly well. The main performance variable was my fitness.

And on the other end of the spectrum, electric cars typically have just one forward gear-- they single speed.

I was trying to think if our human body has a limited Torque "band" or a limited "power band" or a limited "RPM Band"

Our Power band is limited only by aerobic output if we can stay in a reasonable "RPM range" I can't generate 300W at 3 RPM or 6 RPM or even at 24 RPM and it is tough for me at 48 RPM (although I have been forced on occaission to do that when my front derailleur cable broke and I had a few 15% grades to deal with). But the toque = F x distance even at 24 RPM is low enough that my body should be able to apply it in one direction it's just that it is not good at keeping that force going in a small circle that well. I would guess that I can apply much more force just walking really slowly up a 25% grade hill!

So that leaves me to think that my "cadence" band is the limiter assuming I am inside my aerobic power envelope for a given duration. I am great at generating 300W anywhere from 70-105 RPM or so if I have to. Outside that, I want to get back into the range, ideally right around 70 RPM standing and 83 RPM sitting. If I need to accelerate quickly and pop the power way up, it's much easier to do that going up to 110 RPM momentarily (than applying more crank torque) before I settle back down in the 90's and then down to the 80's.

One more thing I have found. I have noticed that riding at the same intensity pack riding in a draft, I am more comfortable at higher RPM because I have to be 'ready' to react to jumps. I can't be "bogged down" in a higher gear like when I am TTing. But just drafting higher RPM seems easier than when I am solo. I can only chalk this up to higher wind resistance of the leg against the wind at higher RPM than at lower RPM (the foot/leg is moving faster as it move forward at higher RPM, generating more relative air speed, thus more work even before any power goes into the pedals). This is different on the rollers indoors when there is no airflow against the legs. Drafting is a less extreme case of being on the rollers.

Just in case you guys are not being facetious, a 2X11 has 22 different gear combinations but several of them overlap, most 2X11 setups will have 14-15 different gear ratios.

I agree that the much smaller RPM range is a big part of the need for more gears but does the lower power output play a roll too? Even the most under powered car can generate 100 horsepower where most cyclist can can barely break 1 HP for very short durations and sustained power is well under 1/2 hp for most cyclists. Even if you break it down to power/weight a low power car is 30lbs per hp where a cyclist is 300lbs per hp.

1hp = 750 watts

oh, you had me for a second when you said your Jeep has 8 speeds. Then I remembered my Tacoma has 12 (forward) gears - 6x in "Hi" and 6x in "Lo" (manual transmission w/4x4).

Some automatics (as I recall) have maybe a gear or two more.

But to the OP's question, we are most efficient around 75-95 RPM's. Gears help us stay in the ballpark given wind, hills, etc. This is why I focus my cassette choice on the size(s) that I'll use most of the time (of course so does everybody else).

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I saw this on a white board in a window box at my daughters middle school...
List of what life owes you:
1. __________
2. __________
3. __________

Geek note:

The gear ratios overlap, but a quick survey of three common cassettes (11-28, 11-32, and 12-25) with the three most common cranks (53/39, 52/36, 50/34) shows that the actual ratio duplicates at most once and that only on the even-numbered cranks (e.g. 50/25=34/17=2). It is conceivable to have two duplicates (2 and 4 or 4/3) on the 52/36 with a specific cassette, since both share two factors (2 and 2), but no one makes a cassette with all of 18, 26, 27, and 39 tooth sprockets and no one makes a 9-tooth sprocket. The vast majority of the ratios are irrational and there actually cannot be duplication on the one odd-numbered crank, since 53 is prime. Although, I will grant you that a typical human would not be able to tell the difference between 2.7894... and 2.7857...

Sorry yeah I meant gears, but most of the manufacturers are calling it speeds now.

My grand Cherokee is 8 gear auto. Without hi/lo

There is a new GM/Ford tranny that has 10.

With a 50/34 and 11-28 cassette most gears are 5-7 gear inches and around 9% apart. I consider gears within 1-2 gear inches (eg. 62.6/63.8 and 68.7/69.2) to be overlapping. Of course even if you did want to use all these you would need to be constantly jumping back and forth between chainrings and have a great memory. If electronic front derailleur shifting gets good enough perhaps with careful cassette sizing we could get sequential shifting that uses nearly all the gear combinations.

http://www.sheldonbrown.com/gear-calc.html

Why does a car have 100-300++ horsepower, and humans only have 1/4 - 1/2 horsepower?

A car typically lugs when below 1000 rpm, and likewise with a human grinding at say 70 or 80 rpm.

Conversely, cars redline at 5-7000 rpm, sometimes more -
most humans spin out at like 120 rpm or so.

We're underpowered, have a shitty torque band range, and limited RPM range.
So we need all the damn gears we can get.

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float , hammer , and jog

If you add fuel with no change in external load on the engine, then yes, rpm will go up because you have increased the torque. If you do not let up on the accelerator (reduce torque) or increase the load on the engine, the rpm will continue to accelerate indefinitely until inertial loads blow up your engine by throwing a piston through the head or some other catastrophic failure. If you are driving along on a flat road at a constant speed and you depress your accelerator, first torque will increase. This added torque will overcome the inertia of your car (i.e. external load will increase) and the car will accelerate (and the rpm will then increase) until drag forces equal propulsive forces or until the engine blows up as above.

Freeway driving is typically a very low-load situation and not conducive to meeting the max efficiency point of the engine. Can you cruise at 65 mph on a flat highway in your car with the pedal to the metal? Unless you're driving a go-cart on the freeway, probably not. Generally you only hit the point of best efficiency during acceleration or perhaps climbing very steep hills.

Here's what is called a brake specific fuel consumption map for a 1.9L Saturn engine.




The red curve at the top of the colored section is the max torque curve. The curved blue lines are lines of constant power (use right y-axis). The lines delineating the regions of different colors are lines of constant brake specific fuel consumption - i.e. how many grams of fuel are required per kW*hr of energy production. You can also think of them as lines of constant thermal efficiency. The engine can operate at any point underneath the torque curve, given the right conditions to make it happen. The point of best efficiency is going to be somewhere near the center of the darkest red region.

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Ed O'Malley
www.VeloVetta.com
Founder of VeloVetta Cycling Shoes
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Yup...my Acura MDX is a 9 speed automatic. Seems as though the auto industry is heading in this direction...so the original question may be in the process of being addressed...more gears is "better"!

Wait....and here are I thought that Murphy's Law was he 2 horsepower human. Did you get old and downgraded to 1/2 hp?

Oh come on Ed like you know anything about engines or something.

The old Macks I used to drive only had 5 speeds. Great engine with a wonderful torque range. Didn't have to shift all the time. One of my neighbors has a newer Western Star with only 8 gears in it. Doesn't sound like he was impressed with it though because the torque range is too narrow on the engine.

Cars are overmotorized, bacause they are an emotional product. To get from a to b, 15 or 20 hp would be sufficient. But then more gears would be very helpful indeed.

Look at trucks. They are not overmotorized, but rather economic, and have much less hp per kg compared to cars. Because of that they have more gears.

Modern autos are up to 8 speed now...