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Tripped1 said:
Traditionally I feel the amount of fuel more than the engine speed, my last true track bitch was a Daytona 675 though.
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I can feel a big difference between a full and a nearly empty tank on most of the bikes over owned. The only ones it wasn't noticable on were bikes that were top heavy no matter what.
 
Amos Malone said:
But not all chopped weight improves handling. Get your handlebars too light and they start to vibrate. Reduce rotating mass inside the engine too much and it'll become difficult to keep idling, and accelerate from stop.
Light parts also reduce strength. Put super light wheels on and increase odds of wheel failure.
As I said earlier in this thread light weight might be beneficial on a race track, but on the street where you're not racing against someone, or the clock, the advantage is not always noticeable. Placebo effect nonwithstanding.
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Reduced weight doesn't always make things weaker. Yeah, the general rule of thumb when making something strong is to add more beef, but sometimes that beef just adds stress to other areas. A light, short skirt piston puts way less stress on a rod/pin , which means you can make the rod/pin lighter...which puts less stress on the crank, so you can make that lighter, etc, etc. Smaller, lighter valvetrain components allows you to run smaller lighter cam drive components. Lighter valves need less spring pressure, which can allow slim rockers or slimmer cam lobes. Next thing you know you're able to reliably hollow out the camshaft which will allow for smaller cam chains and thinner gears.


It can be a snowball effect. A 800lb bike is gonna need burlier wheels, heavier rotors, bigger springs, bigger forks which hold more oil. If you start off heavy you'll keep needing to add beef to deal with the weight but, on the other side of the coin, if you build light and you can safely continue to remove weight.

Perfect example is modern 4t dirt bike engines. Look inside a 5 valve WR450 engine. The valvetrain is tiny , dead nuts reliable, happy to rev and makes twice the power of something like a XR400. All that big swinging mass inside XR400 engines keep it from ever making great power and it tears itself apart in the meantime. I've been down that road. I put a mild cam and exhaust on a XR400 to allow it to rev freer ( not higher) along with a slightly higher compression piston. Some revs and 11:1 compression and you cant keep the cylinder studs from pulling out of the cases. My KTM and Yamaha run much higher compression and you can wind em up and hammer on them day in and day out without issue.

Things were made lighter in order to make them stronger. Flywheel effect is not the same thing as heavy reciprocating assemblies. Heavy reciprocating things rob energy to change directions, and they impart that energy in to their surroundings while slamming back and forth.
 
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Boils down to an old "ism"

You can, light, cheap, strong, pick two.

You CAN have light and strong, the applications would be something like a KTM 450 RFR, 400lbs, 70hp, with a full damn near 9 gallons of fuel onboard.

Issue is they are also most of $50,000 dollars.....if you are one of the lucky 70 people they will sell one to.
 
Shinyribs said:
Reduced weight doesn't always make things weaker. Yeah, the general rule of thumb when making something strong is to add more beef, but sometimes that beef just adds stress to other areas. A light, short skirt piston puts way less stress on a rod/pin , which means you can make the rod/pin lighter...which puts less stress on the crank, so you can make that lighter, etc, etc. Smaller, lighter valvetrain components allows you to run smaller lighter cam drive components. Lighter valves need less spring pressure, which can allow slim rockers or slimmer cam lobes. Next thing you know you're able to reliably hollow out the camshaft which will allow for smaller cam chains and thinner gears.


It can be a snowball effect. A 800lb bike is gonna need burlier wheels, heavier rotors, bigger springs, bigger forks which hold more oil. If you start off heavy you'll keep needing to add beef to deal with the weight but, on the other side of the coin, if you build light and you can safely continue to remove weight.

Perfect example is modern 4t dirt bike engines. Look inside a 5 valve WR450 engine. The valvetrain is tiny , dead nuts reliable, happy to rev and makes twice the power of something like a XR400. All that big swinging mass inside XR400 engines keep it from ever making great power and it tears itself apart in the meantime. I've been down that road. I put a mild cam and exhaust on a XR400 to allow it to rev freer ( not higher) along with a slightly higher compression piston. Some revs and 11:1 compression and you cant keep the cylinder studs from pulling out of the cases. My KTM and Yamaha run much higher compression and you can wind em up and hammer on them day in and day out without issue.

Things were made lighter in order to make them stronger. Flywheel effect is not the same thing as heavy reciprocating assemblies. Heavy reciprocating things rob energy to change directions, and they impart that energy in to their surroundings while slamming back and forth.
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Exactly.
Point I'm also trying to make is that motorcycle designers are not dumb. Most modern motorcycles are a marvel of engineering. Your "perfect example" demonstrates the advances manufacturers have made over the years. 30 years ago you could cut a lot of weight from a piston and improve some bits. On most modern engines the manufacturer has done that for you. I'm not talking about 30 year old engine designs that are still being sold, but newly designed engines. On those trying to remove weight is likely to introduce some running issues.
 
Amos Malone said:
Exactly.
Point I'm also trying to make is that motorcycle designers are not dumb. Most modern motorcycles are a marvel of engineering. Your "perfect example" demonstrates the advances manufacturers have made over the years. 30 years ago you could cut a lot of weight from a piston and improve some bits. On most modern engines the manufacturer has done that for you. I'm not talking about 30 year old engine designs that are still being sold, but newly designed engines. On those trying to remove weight is likely to introduce some running issues.
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XR650Ls everywhere:



2tfsx4.jpg
 
Shinyribs said:
Interesting. With the tank that low I guess they were actually having to lift the weight of the tank like a pendulum. Makes perfect sense.
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In the four wheel world lowering the cg below the roll center does exactly that; it acts like a pendulum. This can be noticed by the tires chattering as they are sliding laterally. I have no idea if or how this translates to bikes but figured I’d throw it out there.
 
Tripped1 said:
Boils down to an old "ism"

You can, light, cheap, strong, pick two.

You CAN have light and strong, the applications would be something like a KTM 450 RFR, 400lbs, 70hp, with a full damn near 9 gallons of fuel onboard.

Issue is they are also most of $50,000 dollars.....if you are one of the lucky 70 people they will sell one to.
Click to expand...
Id be curious to see more how the manage the fuel, 9 gallons of fuel is 54ish pounds just sloshing around. The two front tanks look to be pretty reasonable compared to what we are used to on a normal dirt bike with oversized tanks but that under seat tank looks to have a large space that would benefit from baffling.
 
psykown said:
Id be curious to see more how the manage the fuel, 9 gallons of fuel is 54ish pounds just sloshing around. The two front tanks look to be pretty reasonable compared to what we are used to on a normal dirt bike with oversized tanks but that under seat tank looks to have a large space that would benefit from baffling.
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Maybe they're also packed full with fuel foam.
 
psykown said:
That makes a lot of sense, I keep for getting its a thing lol
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They still have issues with all of the weight back there. A full load rally bike and kickers have issues in that once you get all of that weight in the back moving vertical it KEEPS going vertical which tends to toss the rider.



or



Note the rear float in both cases.
 
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