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From: Zen Cycle <funkmaster@hotmail.com>
Newsgroups: rec.bicycles.tech
Subject: Re: Suspension losses
Date: Fri, 3 Jan 2025 13:49:46 -0500
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On 1/3/2025 11:17 AM, AMuzi wrote:
> On 1/3/2025 9:41 AM, Zen Cycle wrote:
>> On 1/2/2025 11:06 AM, AMuzi wrote:
>>> On 1/2/2025 9:42 AM, bp@www.zefox.net wrote:
>>>> AMuzi <am@yellowjersey.org> wrote:
>>>>>
>>>>> I don't have a coherent argument either way but a rumble
>>>>> strip test introduces a repeatable experience so that
>>>>> various data may be compared.  Each rider on a dirt or
>>>>> gravel path, and each ride experience by any given rider, is
>>>>> an unique set of impedimenta such that data cannot be as
>>>>> readily compared.
>>>>
>>>> AMuzi <am@yellowjersey.org> wrote:
>>>>>
>>>>> I don't have a coherent argument either way but a rumble
>>>>> strip test introduces a repeatable experience so that
>>>>> various data may be compared.  Each rider on a dirt or
>>>>> gravel path, and each ride experience by any given rider, is
>>>>> an unique set of impedimenta such that data cannot be as
>>>>> readily compared.
>>>>
>>>> But one can observe that in the case of smooth pavement,
>>>> suspension losses vanish, while hysteresis losses persist.
>>>>
>>>> In the end a bike is an overdamped resonator excited by the
>>>> pavement and damped by hysteresis, separately in the tire and
>>>> suspenesion. In that limit, suspension would be faster if used
>>>> with very hard tires on very smooth surfaces. In the limit of
>>>> hard tires and no suspension, the dissipative element becomes
>>>> the rider whose elastic properties are apt to be poor, perhaps
>>>> accounting for the apparent slowness of solid tires.
>>>>
>>>> Use of a rumble strip for testing is equivalent to selecting
>>>> a particular excitation spectrum. Choice of spectrum will affect
>>>> dissipation depending on internal resonances of the bike/ rider
>>>> system. A real road likely corresponds to a 1/f spectrum, but
>>>> a rumble strip will likely be something else. How much difference
>>>> that makes isn't clear but it could be estimated using a mechanical
>>>> analogy equivalent circuit of the kind used to model loudspeakers.
>>
>> This is a great analysis and reveals a highly problematic aspect of 
>> the "rumble strip" test. As Bob notes, it's essentially limiting the 
>> noise input into the system to a somewhat narrow spectral component 
>> (though the 1/f assumption for real-world is way to broad)
>>
>> The idea of using the rumble strip test seems adequate at first, but 
>> is prone to misleading results. Since the rumble strip sets up a 
>> regular frequency component, there's a possibility that a resonance or 
>> cancellation effect can occur which can dramatically skew the results.
>>
>> In the world of environmental testing, physical vibration analysis is 
>> typically broken up into three different stimuli - swept frequency, 
>> noise*, and environmental specific (usually a combination of noise 
>> with higher energy components around certain frequencies).
>>
>> It's nearly impossible to simulate all the possible real- world 
>> conditions, which is why the testing regimen includes a sweep - the 
>> intent being to see any resonances. I've personally witnessed an 
>> electronic assembly quite nearly disintegrate with the right frequency 
>> and energy input. The task then was to redesign the piece such that 
>> the resonance was damped.
>>
>> It's easy to see how this can translate to the rumble strip test. 
>> Under the right conditions, one might actually see a speed _increase_ 
>> as a result of a sympathetic resonance.
>>
>>>>
>>>> A pair of series RLC circuits (one for the road-tire interface
>>>> and a second for the suspension-rider interface) would be a good
>>>> start. I'm not skilled enough to do the calculations, but others
>>>> on this group likely are. The hardest part is apt to be finding
>>>> an equivalent circuit for the rider, who isn't a rigid mass but
>>>> rather a dissipative blob....8-)
>>
>> In the old days, we had to do reiterative tests on massive vibration 
>> tables. These days, FEA software removes the vast amount of guesswork. 
>> The last few times I've had to conduct these tests I only had to do 
>> one test twice, and the problem turned out to be an assembly 
>> specification error rather than inherent design.
>>
>>
>>>> Thanks for reading,
>>>>
>>>> bob prohaska
>>>>
>>>
>>> Clever.
>>>
>>> I take from that, you think the actual impact/height change/velocity 
>>> change etc from various irregular surfaces can be quantified for any 
>>> given random gravel (or road) experience and used to compare 
>>> efficiency for other iterations.
>>
>> "Real-world" would simulate a more stochastic environment with larger 
>> "impact" events rather than a regular "sinusoidal" spectrum like a 
>> rumble strip. Currently, for example, we use this for our truck- 
>> mounted electronics:
>>
>> https://cvgstrategy.com/wp-content/uploads/2019/08/MIL- STD-810H- 
>> Method-514.8-Vibration.pdf
>>
>> Refer to page 514.8C-5 (Page 58 in the PDF).
>>
>>>
>>> I hadn't thought of that, but if that's true then the rumble strip 
>>> test isn't necessary for comparison. Which assumes sensors have 
>>> adequate sensitivity across whatever range and that software for that 
>>> data truly derives actual impedimenta values.
>>
>> Even low-cost accelerometers have incredible accuracy, sensitivity, 
>> and repeatability across spectrum they're designed to operate these 
>> days. We have two 3-axis units accurate to .01G that we paid like $25 
>> each for - coupled to a mid-range oscilloscope they give more than 
>> adequate results for our "warm fuzzy" testing before we send of to a 
>> testing lab for 3rd party analysis.
>>
>>
>> *"Noise" being a broad term meaning quasi-random frequency and 
>> amplitude components within limits.
>>
> 
> Thanks I knew nothing about this before our discussion.
> 

The lab we go to has a system similar to this:

https://www.youtube.com/watch?v=AI6svg4lTMo

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