More info on YZ450FX

Suspension and and engine function matter more than weight.

 

This coming from the guy who shaves down brackets on his WR to save ounces...

This coming from the guy who shaves down brackets on his WR to save ounces...

 

Sorry, I didn't shave any brackets.   I got one hell of a lot of performance out of the WR platform.  Interesting to see that the 450FX has some of the mods I did, like the 22mm offset TCs.

It is designed especially to be like a FWW.  Some bikes don't have room to add weight to the FW, so they add it to the clutch basket instead.

Actually a good find.

Sorry, I didn't shave any brackets.   I got one hell of a lot of performance out of the WR platform.  Interesting to see that the 450FX has some of the mods I did, like the 22mm offset TCs.

Hum I believe they are 24 or 25mm offset.

Sorry, I didn't shave any brackets.   I got one hell of a lot of performance out of the WR platform.  Interesting to see that the 450FX has some of the mods I did, like the 22mm offset TCs.

 

I started to read your thread in the WR forum a long time ago and I was pretty sure it said in there somewhere you had cut down or shaved parts of off brackets to get the weight down.  I'm not interested in starting an argument on how you got the weight off, but I still find it odd that someone who spent countless hours and many dollars to make his WR lighter and constantly brings up the issue of weight is now down-playing it and trying to say that engine and suspension performance matter more than weight.  If you actually think that's true, why didn't you invest your energy into that on your WR?

Hum I believe they are 24 or 25mm offset.

 

The YZ is 24mm for 2016 but the FX is 22mm, which is what the YZ was in 2014-15.

I wonder if that would work like a heavy flywheel, there was a lot of chatter about the Rekluse z-start and zsp clutches doubling as a flywheel weight but in the end dispelled because it counter rotates in relation to the motor as well as not being directly connected to the crank. I guess it can't hurt as its all rotating mass.

 

It adds very little to the inertia mass of the crank for two very simple reasons:

 

1) Inertia mass is a function of weight (and weight placement) and speed. The clutch basket rotates at 2.6 time slower speeds than the crank, which reduces the inertia mass of the rotating clutch exponentially, giving it as much as 7 or 8 times less effect than if it were turning crank speed. 

 

2) Flywheels have two functions: storing energy from the power stroke, and returning it on the other three cycles.  The energy that a clutch would return to the crank, which is already reduced from what you might expect, has to be delivered back to the crank through the same 2.6:1 ratio that it's geared to the crank by, and it's a 2.6:1 mechanical disadvantage going that direction, so whatever it does return is reduced by that amount. 

 

A weighted flywheel gives far more bang for the buck, especially at half the price.

I started to read your thread in the WR forum a long time ago and I was pretty sure it said in there somewhere you had cut down or shaved parts of off brackets to get the weight down.  I'm not interested in starting an argument on how you got the weight off, but I still find it odd that someone who spent countless hours and many dollars to make his WR lighter and constantly brings up the issue of weight is now down-playing it and trying to say that engine and suspension performance matter more than weight.  If you actually think that's true, why didn't you invest your energy into that on your WR?

 

If you read the thread closely, I didn't spend any money making it lighter.  I just removed things.  I put a PC4 muffler on it, but I did that for performance reasons.  I didn't even buy the lightest muffler and I didn't touch the header pipe either.

 

Light weight + good engine + good suspension + reliability = win.  My WR has a good mix of these things.  It was the best platform (for me) to start with at that time.  I suspect the FX is going to take this a step further, thus the WR is probably going to get replaced.

 

If there was an FX when I started, I probably would have bought that.  I certainly have no regrets about my WR project.

Edited by MidlifeCrisisGuy

It adds very little to the inertia mass of the crank for two very simple reasons:

 

1) Inertia mass is a function of weight (and weight placement) and speed. The clutch basket rotates at 2.6 time slower speeds than the crank, which reduces the inertia mass of the rotating clutch exponentially, giving it as much as 7 or 8 times less effect than if it were turning crank speed. 

 

2) Flywheels have two functions: storing energy from the power stroke, and returning it on the other three cycles.  The energy that a clutch would return to the crank, which is already reduced from what you might expect, has to be delivered back to the crank through the same 2.6:1 ratio that it's geared to the crank by, and it's a 2.6:1 mechanical disadvantage going that direction, so whatever it does return is reduced by that amount. 

 

A weighted flywheel gives far more bang for the buck, especially at half the price.

 

 

You better go tell Steahly this.

 

 

 

Does where you put the flywheel weight matter? Yes, the amount of flywheel effect you feel is controlled by not only the amount of flywheel weight, but also the size (diameter) of that weight. In other words, a 12-ounce flywheel that is 4 inches in diameter will have more effect than a 12-ounce flywheel with a 3-inch diameter. That is why we always try to make our flywheels as large of diameter as possible, but still fit inside the stock ignition cover. Some newer 4-strokes do not have enough room in the ignition cover to add a flywheel weight to the ignition. For those bikes we offer steel clutch baskets, which are much heavier than the stock basket and have a much larger diameter than a standard flywheel weight, but rotate at a slower speed than a ignition flywheel. Therefore, a steel clutch basket usually gives you about the same amount of flywheel effect as adding 10 to 13 ounces on the ignition flywheel.

  Source: http://www.steahlyoffroad.com/flywheel-recommendations#answer6

 

But what would they know ?

Edited by MidlifeCrisisGuy

The YZ is 24mm for 2016 but the FX is 22mm, which is what the YZ was in 2014-15.

The 2016 YZ450F is 25mm. Both of these are from dirt bike magazine reviews.

The new triple clamps are now 25mm, up from 22mm. To boost braking power, the front brake rotor is now 270mm and the brake pad material is updated. The footpegs are also now 5mm lower.

450FX is also 25mm.

The FX chassis geometry is identical to the YZ’s, but Yamaha has tuned the chassis flex for off-road use by swapping to engine mounting brackets that are 2mm thinner than the 8mm units found on the YZ. They’re also shaped differently. Yamaha already tweaked the 2016 YZ450F’s chassis for better bump compliance by adjusting the fork offset to deliver more front-end feel and better turning stability and switching to frame spars that are 12mm wider at the swingarm pivot; the YZ450FX incorporates these changes as well!!

Edited by RMK800

You better go tell Steahly this.

 

 

 

  Source: http://www.steahlyoffroad.com/flywheel-recommendations#answer6

 

But what would they know ?

I could imagine what they are referring to is a certain + oz. flywheel may equal a certain + extra lb. clutch basket. Meaning the basket must be much heavier in relation.

"My 250FX has a 22mm offset triple clamp and after some research I found out the 450FX has the same 22mm offset."

 

http://www.mx43.com/about/2016/1/26/21j-looks-at-the-new-yz450fx.html

 

"The WR gets the new stiffened YZ chassis with thinner engine mounts like the FX, the new YZ linkage, spring rate and tripleclamp offset alterations."

 

http://dirtbiketest.com/fresh-dirt/2016-yamaha-wr450f-first-riding-impression/

 

I'm sure I read somewhere that the 450FX had 22mm TCs, but I can't find it now.

 

Edit: found it.

"A big difference from YZ motocross bike is the return of the 22mm off-set triple clamp and the use of a slightly longer shock length to raise up the rear of the bike. "

http://dirtbiketest.com/bike-tests/2016-yamaha-yz450fx/

Edited by MidlifeCrisisGuy

The YZ450F is 25MM

Multiple Sources:

http://www.cycleworld.com/2015/08/06/2016-yamaha-yz450f-first-ride-motocrosser-motorcycle-review-photos-specs-pricing

http://www.motorcycle.com/manufacturer/yamaha/2016-yamaha-yz450f-review.html

https://ultimatemotorcycling.com/2015/07/28/2016-yamaha-yz450f-review-incremental-improvements/

YZ450FX

Yamaha already tweaked the 2016 YZ450F’s chassis for better bump compliance by adjusting the fork offset to deliver more front-end feel and better turning stability and switching to frame spars that are 12mm wider at the swingarm pivot; the YZ450FX incorporates these changes as well.

http://www.motorcycle.com/manufacturer/yamaha/2016-yamaha-yz450fx-ride-review.html

Two different reviews that say different things. The post above was wrong about the 2016 YZ450F being 24. I don't understand why they would have a different offset then 25mm that the 2016 YZ450F has. 25mm should be more stable and 22mm would be better turning. Doesn't make since for it to have 22mm and two different parts compared to the F, but obviously it could be.

Edited by RMK800

You can, if you like, run the numbers for yourself.  Then maybe you would actually know something yourself. 

 

https://en.wikipedia.org/wiki/Angular_momentum#Angular_momentum_in_classical_mechanics

 

 

 

The energy that a clutch would return to the crank, which is already reduced from what you might expect, has to be delivered back to the crank through the same 2.6:1 ratio that it's geared to the crank by, and it's a 2.6:1 mechanical disadvantage going that direction, so whatever it does return is reduced by that amount.

 

How is this for starters... there is no energy lost between the clutch inertia and the flywheel.  There is a tiny amount lost in the gear train, but other than that, all the energy that gets stored in the clutch as rotational energy gets transferred back to the flywheel when it tries to slow down.  The gear ratio is irrelevant.  It is a lossless system, except for the gear friction.

Edited by MidlifeCrisisGuy

How is this for starters... there is no energy lost between the clutch inertia and the flywheel.  There is a tiny amount lost in the gear train, but other than that, all the energy that gets stored in the clutch as rotational energy gets transferred back to the flywheel when it tries to slow down.  The gear ratio is irrelevant.  It is a lossless system, except for the gear friction.

 

Rotating mass is a lossless system ??

 

...only in space...

Rotating mass is a lossless system ??

 

...only in space...

 

So where are the losses in this system ?   Where does the wasted energy go ?  If it doesn't go to the crankshaft/flywheel, where does it go ?

Edited by MidlifeCrisisGuy

There is a minor energy loss in gear friction as the inertia of the flywheel attempts to drive the crank, but the more obvious thing to most people is that the energy being transferred back to the crank is reduced by the 1:2.6 disadvantage it has through the gearing.  2.6 ft/lb of torque force applied by the clutch basket becomes 1 ft/lb at the crank. 

 

Also, again, at the engine's red line of 11,500 RPM, the clutch only turns about 4400 RPM.  At a more realistic speed at which flywheel weight might bear on engine stalling, say about 3000 RPM, the clutch only turns 1150, so there is really no significant inertia there in the first place. 

 

The only benefit to a steel basket is that the fingers won't notch.

 but the more obvious thing to most people is that the energy being transferred back to the crank is reduced by the 1:2.6 disadvantage it has through the gearing.  2.6 ft/lb of torque force applied by the clutch basket becomes 1 ft/lb at the crank. 

 

The speed and torque change through the gear ratio, but there is no loss of energy.  It is a coupled almost lossless system.  Doesn't matter if the weight is attached to the crank or the clutch as far as the energy transfer goes.

 

 

 

At a more realistic speed at which flywheel weight might bear on engine stalling, say about 3000 RPM, the clutch only turns 1150, so there is really no significant inertia there in the first place.

 

That is not what steahly says.  They say their heavy clutch baskets are equivalent to an 11 oz flywheel weight mounted on the flywheel.   Diameter plays into it as well.  I'll trust their engineering.

Edited by MidlifeCrisisGuy

 

 

  Diameter plays into it as well.  I'll trust their engineering.

 

You're free to do that.  It will be your $300 out the window, not mine.

 

Diameter does play into it.  Also weight placement within the mass.  The bulk of the weight of a clutch basket is in the disc section at the back, 2/3 of which is no larger than the engine flywheel rotor, then only the fingers, which are undercut and perforated, on the outer edge.  Changes up or down in rotational speed  have a greater effect than the same percentage changes in weight do, so we're back to that again.

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