+2 rear sprocket?


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UselessPickles

New Member
Could you point out what part of that article is relevant to the discussion of whether lower RPMs, more throttle, and taller gearing yields better fuel economy? All I see is a discussion of optimizing air intake and then determining whether you have a fuel system that can supply fuel at a high enough rate to maximize acceleration.


BTW - I was wrong about the most efficient way of accelerating being full throttle and short shifting. It would actually be full throttle and shifting at optimal points for max acceleration, then shifting into a higher gear as soon as you reach your cruising speed.


I'm now exiting this discussion. If I get around to researching this idea more and can work out a decent model of all the dominant factors involved, I'll enhance my full-throttle acceleration simulation code (read about it here; also featured here) to model fuel consumption and also partial throttle acceleration and start a new thread to discuss the results. Since I doubt I'll be able to obtain an efficiency curve for the FZ6R's engine, I'll probably have to end up using a "typical" efficiency curve and call it good enough for the purpose of showing general trends.
 
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Chevyfazer

New Member
The first 2 sections are all about improving efficiency, the first thing it talks about is cold air, in no way will warm air help improve fuel mileage, the cold air being more dense allows for a more efficient fuel burn, creating more power by wasting less fuel, and burning more of whats already there. If you can make better use of the fuel already going into the engine you get better mileage, going full throttle is the opposite of being efficient, it that still doesn't make sense then it probably never will...
 
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UselessPickles

New Member
Chevyfazer said:
If you can make better use of the fuel already going into the engine you get better mileage, going full throttle is the opposite of being efficient, it that still doesn't make sense then it probably never will...
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You're getting different types of efficiencies mixed up. Cold air is more efficient at producing torque/power output from the engine, but not more efficient at minimizing fuel consumption over distance at a given speed.

It takes a fixed amount of power to maintain speed in a vehicle - the power necessary to match the power of drag at that speed (plus some friction, but drag is most dominant at freeway speeds). Take that same vehicle and put a cold air intake, and now it produces more power at any given throttle position. To maintain the same freeway speed, you'll need to use less throttle. Less throttle means that a larger percentage of the engine's power is being wasted on sucking air through a smaller throttle opening.


Full throttle is less efficient at minimizing fuel consumption over time, but what we care about is fuel consumption over distance. I'm not saying that on a given vehicle it is more fuel efficient to go full throttle full speed down the freeway than it is to cruise at 55mph. I'm saying it's more fuel efficient (over distance; not time) to accelerate at full throttle UP TO 55mph than it is to accelerate gently up to 55mph.
 
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Chevyfazer

New Member
UselessPickles said:
I'm saying it's more fuel efficient (over distance; not time) to accelerate at full throttle UP TO 55mph than it is to accelerate gently up to 55mph.
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If you ever have the chance to, or already own one, get on a carb'd bike start it up with the fuel cutoff on, once it's running turn it off, go full throttle running through as many gears as you can for as long as you can before the bike runs out of gas, then start in the same spot turn the gas off and go about 1/2 throttle for as long as you can, see which gets you further...
 
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UselessPickles

New Member
Again... not a valid comparison. At continuous full throttle, you accelerate to and cruise at a higher speed (top speed) where the force of drag is much higher. Of course cruising at 125mph is much less fuel efficient than cruising at 80mph (because force due to drag increases relative to the square of speed, so as you increase speed, it requires more and more fuel per unit of distance to maintain that speed).

You have to compare fuel consumption over distance between full throttle acceleration up to a given speed (let's say 55mph) versus half throttle acceleration up to that same speed. There's lots of different rates involved that will cause confusion. Fuel consumption as you think of it relative to throttle position/rpm is a rate over TIME. Acceleration is a rate over TIME. What we care about is fuel consumption over DISTANCE. With full throttle, you will consume more fuel over TIME, but you'll also gain speed more quickly over TIME, causing you to cover less DISTANCE in less TIME and reach your target cruising speed in less DISTANCE and TIME. Everything mostly balances each other out, except that full throttle will more efficiently accelerate per unit of fuel consumed due to reduced pumping losses, such that you will use less fuel per distance traveled leading up to your target cruising speed.

A corrected version of your test would be to accelerate up to 55mph with the fuel cutoff, then shift into top gear and continue cruising at 55mph and see how far you get before it sputters. Try this with both full-throttle acceleration up to 55 and half-throttle acceleration up to 55.
 
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Chevyfazer

New Member
Point being if you were to try that on most bikes going full throttle you won't even make it to 55mph if the fuel is cut off, I know I've done it on my klr vs going about a mile to 2 miles riding like I normally do, but anyways you keep contradicting yourself so I'm done now, I've made my point 5 ways till Sunday take it or leave it...
 
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UselessPickles

New Member
Looks like I was right the first time about accelerating full throttle with early shifts:

InsightCentral.net - Honda Insight Fuel Efficiency Tips

I forgot to consider increasing losses due to internal friction at higher engine speeds. There's still the question of at what RPM does the friction loss get high enough that it's worth shifting up to reduce friction losses, but at the loss of acceleration (lower acceleration means consuming high rates of fuel for a longer time before reaching cruising speed). Lots of moving [figurative] parts to consider and balance, and I don't think I want to try to figure out the specifics.
 
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UselessPickles

New Member
KeysRider3 said:
I think the answer to the original question is "Yes".
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Oh yeah... that question.

The answer to the "more oomph on takeoff" is actually "kinda". Depends on other factors, as well as what you define as "takeoff" and "oomph". The +2 on the rear doesn't actually give you overall better acceleration like most people assume.

It can even depend on the weight of the rider. A heavier rider has a higher center of gravity on the total bike+rider system and the bike is more likely to wheelie under full throttle in 1st gear. If your bike already tends to wheelie in first gear with stock sprockets, then you won't actually get any acceleration benefits at all out of the +2 on the rear. You'll just wheelie more easily in 1st gear (not good for acceleration), cruise at higher RPMs, make your speedo and odometer more inaccurate, and use more fuel.

Lots of more details discussed here, as well as some performance comparisons of different sprocket sizes: http://www.600cc.org/forum/f89/effects-changing-sprockets-23986/
 
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MiltonDorkenhoff

Search, THEN post.
Elite Member
UselessPickles said:
If your bike already tends to wheelie in first gear with stock sprockets, then you won't actually get any acceleration benefits at all out of the +2 on the rear. You'll just wheelie more easily in 1st gear (not good for acceleration), cruise at higher RPMs, make your speedo and odometer more inaccurate, and use more fuel.
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But if I'm wheelieing in 1st gear, won't I get better acceleration because there is no loss of energy due to friction between the front tire and the road, the front wheel bearings, the brake pads rubbing ever so slightly on the rotors, etc?

Or would the answer to that depend on how much of a wheelie I do - too high up and the flatter, less aerodynamic part of my bike is heading right into the wind which would kill any gains I got from the lack of friction?

Maybe a tiny wheelie is the answer, so I can still take advantage of the bike's aerodynamics somewhat, but at the same time can eliminate a bunch of friction.
 
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UselessPickles

New Member
lol

It's possible that a micro wheelie might give the best acceleration.

The problem with a wheelie isn't so much the aerodynamics. The accelerating force at the point where your tire touches the ground is always being split up into a linear force (pushes you forward) and a rotational force (tries to do a wheelie) with the tire/road contact point as the axis of rotation. The position of the center of gravity of you and the bike relative to the that point where the rear tire touches the ground is what determines how much of that force goes where.

The lower the center of gravity, the larger the linear portion and the smaller the rotational portion. As you begin to wheelie, the center of gravity rotates up around that point where the tire touches the road (which moves in relation to the chassis of the bike as the wheelie continues; tricky stuff). Now more of the wheel's force is trying to continue the wheelie and less is pushing you forward. Even though you're at full throttle, you are now accelerating forward slower than you would at a lower throttle position that keeps the front wheel down. At that point, you must reduce the force at the wheel (tap the rear brake to bring the front down), or else the wheelie is likely to continue lifting, rapidly increasing the problem (unless your goal is to wheelie, then it is rapidly increasing your success).

If you could balance it perfectly with the front wheel just hovering over the road: 1) that would be quite impressive. 2) you might accelerate slightly faster.
 
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Chevyfazer

New Member
UselessPickles said:
Looks like I was right the first time about accelerating full throttle with early shifts:

InsightCentral.net - Honda Insight Fuel Efficiency Tips

I forgot to consider increasing losses due to internal friction at higher engine speeds. There's still the question of at what RPM does the friction loss get high enough that it's worth shifting up to reduce friction losses, but at the loss of acceleration (lower acceleration means consuming high rates of fuel for a longer time before reaching cruising speed). Lots of moving [figurative] parts to consider and balance, and I don't think I want to try to figure out the specifics.
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UselessPickles said:
Looks like I was right the first time about accelerating full throttle with early shifts:

InsightCentral.net - Honda Insight Fuel Efficiency Tips

I forgot to consider increasing losses due to internal friction at higher engine speeds. There's still the question of at what RPM does the friction loss get high enough that it's worth shifting up to reduce friction losses, but at the loss of acceleration (lower acceleration means consuming high rates of fuel for a longer time before reaching cruising speed). Lots of moving [figurative] parts to consider and balance, and I don't think I want to try to figure out the specifics.
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I'm sorry I can't help myself, are you really comparing a hybrid with a power to weight ratio close to a brick with a rubber band motor, not to mention a tip that was wrote by Joe Schmo who works at taco bell, to a sport touring bike that has close to the same amount of total power at a fraction on the weight.....

And my arguments are invalid?

I really am done now...I think...
 
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UselessPickles

New Member
Would you like another source? How about a report about a scientific study?

WHAT'S NEXT; Dashboard Miser Teaches Drivers How to Save Fuel - Page 2 - New York Times

Some of the gasoline savings came from changing the patterns of gear shifting. ''People were shifting too late from first to second, and from second to third,'' Dr. van der Voort said. People saved the most gasoline when they pushed down on the accelerator briskly and then shifted quickly, keeping the revolutions per minute low -- not by accelerating very gently.

''It's not commonly understood by people who drive,'' Dr. Dougherty said. ''They think that the way to get best fuel economy is to accelerate very gently, but that proves not to be the case. The best thing is to accelerate briskly and shift.
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U

UselessPickles

New Member
Ok, here's one that specifically mentions "WOT" (aka, "WFO"). It also mentions cruising at a low RPM with large throttle opening.

page 2 - Your Mileage May Differ - Tech News - RoadandTrack.com

Remember Coach Grimbly’s dictum about “driving with an egg under your foot”? Forget it. The most efficient way to reach cruising speed is wide-open-throttle (WOT) short-shifting. That is, not only do revs cost money, but so does prolonged motoring in lower gears, when throttling and pumping losses are their greatest.

WOT/short-shifting can save as much as 20 percent in city driving, worst to best case. In actual practice, rarely does traffic allow full WOT, but it’s certainly fun — and efficient as well — to accelerate briskly through the lower gears to whatever the ambient speed happens to be.

Once there, the appropriate choice of gear is the one that offers modest rpm with relatively large (and constant!) throttle.
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Chevyfazer

New Member
For every one that you can find to try to prove your point, I could find 2, and they ACTUALLY Pertain to MOTORCYCLES, but in the end it's just someone else's opinion, or what worked for them on a particular vehicle. I think we have both beat the dead horse until our bats broke, so for me....i really am done now
http://www.motorcyclenews.com/MCN/RidingEvents/ridingeventsresults/Riding-skills/2009/December/dec2209-how-to-get-best-mpg/


http://hallicino.hubpages.com/hub/Riding_Your_Bike_For_Maximum_MPG
 
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