Track Tac

Discussion on rotating weight and its benefits

R

rlslmshdy

Member
Ok you have 2 karts running stock lite. Kart A weighs 330 lbs. with 12 lbs. rotating weight and Kart B also weighs 330 lbs. It has alot of lightweight components on the axle and hubs. So kart B only has 6 lbs. rotating weight. Everything else (tires,hp,gearing, etc.) is the same on both karts. Since both karts have the same overall total weight should they run similiar lap times?
 
If they never accellerate or decellerate, their laptimes will be equal.... the low polar moment of inertia kart will accellerate more quickly, but also decellerate more quickly, while the high polar moment of inertia kart will respond more slowly. Theoretically, the low MOI kart should take off better from the start, then the high MOI will lose less when they let off for the turn. Which is faster?? Kinda' depends on the track type and how much time is spent off / on throttle. It also bears mentioning that the "flywheel effect" is negated if the clutch disengages while coasting, so the low MOI kart can keep the accelleration advantage with an appropriate clutch setting.

Similar to how a heavy driver can win a mid weight class if it's a wide-open track with no cautions, high MOI karts have to have the right conditions to excel. The difference in analogy is that rotational weight is magnified in effect compared to static weight. Rotational MOI also has more to do with mass than its' derived component of weight, but since they're related, most go by "weight". (it's easier to stop a kart tire from spinning in outer space than a car tire, though both are "weightless" -- it's the mass you're acting against, and therefore whatever you can do to reduce mass = good.)

I'm kinda' surprised that nobody's using carbon fiber, titanium, or magnesium rims in LTO racing... ditto for sprocket hubs, brakes, brake hubs....etc. etc.

Since FORCE = MASS x ACCELLERATION, get the most HP to boost ACCEL you can reliably stand , then working on reducing MASS, first rotationally, then overall. Add weight back on as needed to balance kart.
 
Ted Hamilton;525074 I'm kinda' surprised that nobody's using carbon fiber said:
per volume, titanium actualy weighs more than aluminum. magnesium is lighter but more brittle. carbon fiber is lighter and stronger but considerably more to manufacture. titanium costs more to manufacture also. aluminum = best bang for the buck. im sure if you wanted a titanium sprocket hub with considerable material reduction, someone would make it for you haha.
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The lighter rotating weight will accelerate faster and also allow you to drive further into the corner as it also decelerates faster. You need to take advantage on both ends and adjust your driving style or the result is a net zero .
 
We run new 3D printed wheels, unobtainium axle, and fill the tires with helium. The kart actually weighs less than it does without the running gear.
 
I HAVE seen a carbon fiber axle with metal inserts for the keyways... Not sure how the flex characteristics compared.
 
... and the only reason lights can be faster then heavies is because of rotating weight.

All the reasons given for rotating weight for engines, clutches, chains, axles and wheel assemblies, are the same for rotating around an oval track. The equalizer with on board rotating weight is maintaining momentum of rotating parts when not accelerating, it's the same with what your racing in total, rotating around the track.

Maintain Thy Momentum, Lest The Slow Come Up And Smite Thee.

Weather it's on what you race or the whole of what you race, fast is about maintaining momentum and accelerating. How you slow down and if you slow down is also about maintaining momentum.

"Brake, Insert Arc, Turn, Accelerate"
 
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Ted wrote: "It also bears mentioning that the "flywheel effect" is negated if the clutch disengages while coasting, so the low MOI kart can keep the acceleration advantage with an appropriate clutch setting."

I disagree with what you wrote. The "flywheel effect" is not maintained better if the engine is disengaged. I assume your thinking if it's not disengaged, rotating parts are forced to loose momentum by the engine.

I think if engagement is maintained momentum can be maintained by slight input from the drivers go pedal. Also because when slowing down you will be in a turn, normally with lateral grip available and being used, a skilled driver can slightly enhance rather then loose momentum with the go pedal. Maintained engagement of the engine and the possibility to reduce loss of momentum, even slightly raising speed, is the reason for the "Insert Arc" wording at the end of my last post.

___________________________ Please read in between the lines. ... :)

edit: Thinking about this some more, I feel it would do every oval racer good to get seat time in a direct drive sprint Yamaha. It would afford them training in how to maintain momentum. Writing and reading in this thread has given me an appreciation for the love of direct drive Yamaha racing, a couple of racers I've know in the past had.

___________________________
 
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negated = not maintained better. Slow down a little there, Paul. ;)

Also, Formula Y (DD KT-100) is nice, but 100cc Direct Drive ICA is even better.
 
Ted Hamilton said:
negated = not maintained better. Slow down a little there, Paul. ;)

Also, Formula Y (DD KT-100) is nice, but 100cc Direct Drive ICA is even better.
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Thank you, the thoughts while writing were the "loss of" momentum can be negated, but I did it Your Way fixing it, which was an easier fix. ... :)

I assume other then prose I get no argument on the logic. ... :) and ???
 
paulkish said:
... and the only reason lights can be faster then heavies is because of rotating weight.

All the reasons given for rotating weight for engines, clutches, chains, axles and wheel assemblies, are the same for rotating around an oval track.
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I don't agree with this, the physics doesn't support it, and the budgets of pro race teams spent on lighter rotating assemblies (ie: clutches, flywheels, etc.) disagrees too. :) I'm not trying to be unfriendly, just pointing out the lighter rotating mass makes more difference than overall weight, assuming we're comparing 2 cars that are relatively close. Mass centralization helps too, both in rotating assemblies related to the drivetrain, and kart (changing directions more quickly...)
 
What is different between weight rotating around the center of an axle connected physically to the center of the axle by metal and a race vehicle rotating around a track/turn connected physically to the center of the tracks/turns arc by the ground?

I see all variables being the same which mainly consist of weight, speed, the arc traveled and friction. Aren't the physics of weight, speed and friction on an curved path the same no matter how the connection to the center is defined? Weight is weight, speed is speed and friction is friction. Is there any difference between friction created in a bearing and friction created by tires interacting with the track? I think not. ... :)

But then again I'm no engineer, just a back yard and professional mechanic for around 50 years, winging it on my reply. ... :)
 
The one variable that pertains to handling and not rotating weight is steering input from the driver, which cannot be repeatably quantified like the physical attributes of rotating masses.
 
ONEHARDHEAD said:
The one variable that pertains to handling and not rotating weight is steering input from the driver, which cannot be repeatably quantified like the physical attributes of rotating masses.
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I think I see what your presenting and I agree with it. While writing I had what I think was the same thing being presented to me, when I took into consideration track configurations not being perfectly round.

I wrote in and then deleted when writing about the comparison I was making, about involving a point in time at a specific place on the track. I deleted it because I felt any calculation for a 'revolving' rotating, would have to be compared to the same inputs taken from any point of travel around a track.

I did not think of or consider steering input. I think your offering on steering input relates to having to take inputs for calculation from a point in time at a point on the track. I see now because of your input and because of constantly changing inputs to the calculations, on track answers because of track configuration and steering input would need to be shown as a graph. While a rotating mass calculation can be shown as a definitive single answer.

edit: Steering input and your insight means the driver not only has some control over maintaining momentum with the go pedal, they also have some control over maintaining momentum with the steering wheel. I have no problem at all adding steering into it and it fits with: "Brake, Insert Arc, Turn, Accelerate" ... :)

... how'd I do with my reply?

ps ain't this stuff fun to think about?
 
rlslmshdy, I hope I didn't hyjack your thread and your question. I hope the discussion I offered helped.

Is my input helping answer your question? If not I'll stay out of it and you won't hurt my feeling telling me to go.
 
No keep on discussing. When I posted the question. I figured you would have some thoughts on the subject lol. You make me think thats a good thing. Ive had to re-read several of the replys to try in get a better grasp on what was being discussed. Im just trying to decide if its worth the time, effort, money to try and lighten up all my rotatating parts.
 
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