Just to clarify, that +/- 5% is at the extreme end across very different alloys. In family (like 43xx) it is less than +/- 0.3%
Ok that is back in the realm of what I always understood based on the values we used at work.
There are alloys with radically different hardnesses and yields, i just donāt get how either of those relates to kart performance.
I think that was the point of Larry Hās experiment, the same weight applied to different stiffness axle resulted in same amount of deflection.
In otherwords, the spring rate (atleast in the load range he tested at) , is the same.
Yet the N and H OTK axle clearly handles very differently.
So his theory is axle affect the handling due to the damping properties.
And i ask these questions:
If axle is indeed acting like a damper, then itās basically controlling how fast the load transfers to the outside rear tire? Then it is similar to the compression valving on a damper?
A stiffer axle would transfer load faster than a softer axle? (to the outside rear)
And what is the axle dampening? the chassis flex?
I think another important question to test this theory is, why does OTK rear axle affect handling in opposite manner to other chassis makes?
The damping present in steel is considered extremely minimal, and vibrations are transmitted freely for the most part.
Hard to imagine how that could be having an effect one could feel or see on the stopwatch.
Especially when you consider the magnitudes of external damping factors - just look at the energy that could be lost through internal damping compared to the energy lost through the contact patch. I canāt imagine how many orders of magnitude that is. The human blob also acts as a very strong damper for the same modes the axle would be trying to damp out. One constant in all of these related threads is the engineers saying it canāt be damping. We could all be wrong thoughā¦
@alpine911 There are a couple questions I have about his test. You can see that the gauge was not in the same position each time, and I am sure he zeroed it out, but it could be reading different relative displacements. Even the angle of the bar to the ground could matter when talking such small displacements.
Going back in the thread, it was shown that, for a given alloy like 11xx steel, hardness and damping are inversely related so a truly hard axle would be less stiff dynamically.
Any interest in trying this test again but with some repeatability improvements? It looks like the H measurement is closer to the end which would mean the Q test is reading low. If the Q measurement was moved closer to the edge, it would read higher which would be expected for a softer axle. Not by much, but the change from alloy/treatment isnāt going to be much anyways.
Also, did you measure the wall thickness? I know they are claimed to be the same, but technically 2.1mm and 1.9mm both are 2mm
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Thousandths of an inch will matter with loads that small. Repeatability and accurate measurement are critical for any meaningful data with that bending test.
Caleb, sorry all my kart stuff is gone.
I do remember that the OTK axle thickness were the same, less than .001 variance. Also the outside dia has more impact on bending stiffness than inside dia.
This is all way to complicated Iām leaving my standard axle In
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Dang, that sucks. I think that was a very good test. If the Q measurement was more inboard, then that would imply the modulus did change, and Iām much more comfortable with that.
Yes, ID is less sensitivity, but hardly when your wall thickness is so low. They are both very sensitive.
Seems like a hydraulic press with a pressure gauge, a V block type arrangment and a few dial indicators in spots along the axle would be the hot ticket here. As long as everything is always in the same place too, I canāt see a reason why you couldnāt support the axle in V blocks at each end and just press the center of the axle with the ram for ease and repeatability; should all be relative. Measure the load from the ram at a couple points and delfections on the indicators, average a few runs and youād have enough data to plot curves for the different axles.
Understanding why the hell axles make a difference is an age old problem in karting 
At end of the day, you have to do what works, even if thereās 6 different theories on why it works (or doesnāt)
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This is where I ended up about 5 years ago. I stopped trying to figure out āwhyā things work and spent my time focused on āwhatā changes do work.
As an engineer, I very much like the āwhyā, but it wasnāt making me any faster.
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The less understanding, the more āvoodooā. Plenty of yāall older guys are good at understanding the voodoo and have a whole catalogue of experience to draw from. Stuff like āan OTK will do this but an IPK will do thatā comes from that experience. My greatest weapon as a new guy is that I understand the physics well enough to make up for some of that trial-and-error. The more I can fill in the physics gaps, the less trial-and-error Iāll need.
Absolutely. This is definitely true. But donāt let your understanding of the physics lie to you. Practice and changing things is the only whole truth. Donāt be afraid to go the āwrong directionā when trying things.
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I totally agree, I never approach this as an āeither/orā. Physics/theory and practice should never, ever go counter to each other. That means something is wrong in the understanding. One common understanding is āthe stopwatch never liesā. It absolutely does. Outside of a laboratory-clean setting, the other variables are huge, and the human element is annoyingly huge. It takes a deeper understanding than just āfasterā to understand where it was faster, why, and where it was not faster.
Iāve also never once said to myself āIām going to skip practice today and work on some math insteadā.
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Always remember that even F1 teams need to physically test parts and cars to figure out how they are going to work. They have literally every resource available and THEY make the parts and cars and they donāt understand fully why or how some things work or donāt work. They can sit and do CFD and wind tunnel work until they are blue in the face but until they get onto the track they donāt notice things like excessive porpoising for example, or if the suspension arms are going to snap off at load a la Toro Rosso in China.
Which is why I always suggest to drivers who donāt know how to tune a kart to go to the track on practice day and make as many adjustments as they can, one at a time, and see what happens and record that. Then do that for several weeks across different weather etc. and see what happens. Not a luxury everyone has, but if you focus and make an effort to practice and test in a mindful way of exploring the kart and all the tuning options, you can certainly gather enough data to get a picture of how everything is working over time.
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I agree with the only addition being to not focus on the laptimes. There are a lot of factors throughout the day and its more important to just understand the effect of the change. Raising the rear ride height did XYZ, narrowing front width did ABC, etcā¦
@dodo Iām an engineer also and honestly I think the best way to understand it is to just listen to exactly what the manufacturer says. An OTK soft axle will flex more than the hard axle - simple as that. There are plenty of other topics that you can apply your engineering skillset to - youād be interested in the post I wrote about Ackermann. @tjkoyen Iāve seen AMVās axle chart and even as an engineer its not really that helpful lol interesting, but sometimes voodoo is better left just untouched - just tell me which one is soft and hard and Iām good 
@KeslerDesignWorks I fully agree with you that the axle length change matters because youre changing how much axle is in the hub, not because youāre changing the length of the axle. For that reason I never run hub spacers, it just messes with my mind. @gxbry with this in mind I never think of using a shorter/longer axle as stiffer/softer, I think of it as more or less ābiteā, with a shorter axle providing more ābiteā but less stability.
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I am also an engineer. I get the practical nature of just doing what works, but I know that figuring out why things work like they do gives me an advantage. This isnāt rocket scienceā¦ itās harder. Itās kart science.
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