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Old 08-14-2018, 07:58 AM   #11
Dwight Southerland
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Default Re: Axle weight?

The distance from the center of rotation is a factor in calculating the resistance the engine has to overcome, more than the total mass. Basic physics. A 12" 25lb. flywheel has less inertial resistance to overcome than a 14" 25 lb. flywheel as long as the mass is evenly distributed. Same with axles.

Unsprung weight reduction is the advantage of lightened axles, along with being able to distribute that weight more efficiently in the car.
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Old 08-14-2018, 11:07 AM   #12
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Default Re: Axle weight?

Not necessarily true. If the engine has to overcome a certain weight it takes torque to do it . If the weight is less then less torque will be needed to overcome the lighter weight if the torque produced remains the same all things considered to be the same then it should translate into a quicker ET because the torque is now available to move an object instead of trying to overcome the weight of the heavier part
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Old 08-14-2018, 01:03 PM   #13
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Default Re: Axle weight?

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Originally Posted by FED 387 View Post
Not necessarily true. If the engine has to overcome a certain weight it takes torque to do it . If the weight is less then less torque will be needed to overcome the lighter weight if the torque produced remains the same all things considered to be the same then it should translate into a quicker ET because the torque is now available to move an object instead of trying to overcome the weight of the heavier part
Not disagreeing with you, but the physical laws that describe the characteristics of this situation show that distance of the mass from the axis of rotation is more of a factor than the overall mass of the rotating object. While reducing the weight of the axles by rifle drilling has some positive gain, much more will be gained by looking at the rotating mass that is much further from the center of the axle. If I were only concerned with positive rotational inertial benefit and were considering cost, I would pay for lightened flanges before rifle drilling.
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Old 08-14-2018, 01:29 PM   #14
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Default Re: Axle weight?

A simple study of some Applied Physics will always win over intuition driven or "some guy said" approaches. The matter of rotational inertia or inertia in general certainly falls in the problematic area. What Dwight has suggested is absolutely correct. Not just the mass of the item but where the mass is concentrated is most important and that is referred to as the radius of gyration on rotating components. The rotational inertia of parts can be measured by using a homemade torsional pendulum. The measurement is often easier than more complex calculations and is certainly more accurate. So doing things in this manner quite often is a bubble burster, but finding the actual truth will not only help your racing program but also save you some money in the process.
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Old 08-14-2018, 01:41 PM   #15
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Default Re: Axle weight?

I was always told torque is what gets it moving horsepower is what keeps it moving. Look at a typical passenger car once its moving at 55 mph it takes very little HP to keep it moving especially when the engine is only running at 1600-2000 rpm maybe 12-17Hp
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Old 08-15-2018, 09:19 AM   #16
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Default Re: Axle weight?

Dwight is correct.
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Old 08-15-2018, 10:38 AM   #17
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Default Re: Axle weight?

Quote:
Originally Posted by Dwight Southerland View Post
Not disagreeing with you, but the physical laws that describe the characteristics of this situation show that distance of the mass from the axis of rotation is more of a factor than the overall mass of the rotating object. While reducing the weight of the axles by rifle drilling has some positive gain, much more will be gained by looking at the rotating mass that is much further from the center of the axle. If I were only concerned with positive rotational inertial benefit and were considering cost, I would pay for lightened flanges before rifle drilling.
Thank you for this, lots of info for me in the responses I appreciate it guys.
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Old 08-15-2018, 01:31 PM   #18
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Default Re: Axle weight?

I doubt very much that you will see any decrease in ET with a lighter axle........
Theory and real life sometimes differ.
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Old 08-15-2018, 02:10 PM   #19
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Default Re: Axle weight?

In the case of wanting (needing) to accelerate all the whirlygigs in a racecar, theory and practicum parallel as the issue is the classic application of F = ma. Force = mass x acceleration.



A rifle drilled axle doesn't help much (if at all) because the concentration of mass at the radius of gyration is not centered on the axle shaft itself. And tires are heavy and wheels might be light, but the concentration of mass is somewhat past the rim. Lots of money is spent on things that don't give a bang for the bucks spent.


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Old 08-15-2018, 03:45 PM   #20
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Default Re: Axle weight?

the only real benefit to the light weight axles is if you need to get some weight off of the car to get closer to the minimum weight for the class then this will help in that area and possibly show some improvement in performance from the overall weight reduction. If you have to buy some axles anyway and you need to reduce weight then get the gun drilled and light flange axles. If not then performance gains will be minute.
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