tag:blogger.com,1999:blog-1564958057737541664.post5237402596769773511..comments2015-01-18T17:11:02.699-08:00Comments on On Bicycles, and.... what else is there?: transmission of road vibration through bike tires (2)djconnelhttp://www.blogger.com/profile/01484858820878605035noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-1564958057737541664.post-28357304469881353302014-11-25T14:40:03.111-08:002014-11-25T14:40:03.111-08:00Thanks for that reference! Indeed, it had been a ...Thanks for that reference! Indeed, it had been a long time since I did this post, and it was nice to look back on the results I'd gotten at the time.<br /><br />It is interesting that the difference in the numerical model between the primary and secondary modes is 69%, where my stick model (modeling the bike as a stick connecting the hubs) yielded 73%. It goes to show the utility of simple models.<br /><br />djconnelhttp://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-58096117594824230632014-11-25T13:02:30.178-08:002014-11-25T13:02:30.178-08:00Hi Dan,
I am also a cyclist who tries to understan...Hi Dan,<br />I am also a cyclist who tries to understand the transmission of road vibrations to saddle and handlebar. I agree that it is complex subject, so joint brain power may do some good.<br />You seem to be unaware of two studies that contain interesting data.<br />One is from 1993, in German: http://www.forschungsbuero.de/PV38_S6_8.pdf . It confirms that the resonance frequency of wheels is in the range of 7-10 Hz, at 5 bar inflation pressure and a load of about 60 kg (not mentioned in this article, but in the original study by Kai Moennich). There are also some estimates of the damping coefficient.<br /><br />The second is a recent master thesis from the University of Ghent. It is one of a series of investigations around the Museeuw bike: http://buck.ugent.be/fulltxt/RUG01/001/805/380/RUG01-001805380_2012_0001_AC.pdf . I haven't yet found a clear result that delineates the effect of the flax-composite frame, but it describes a lot of effects from the tires and the wheels. A pity that the author didn't truncate his data to a few significant digits, but the report is a treasure trove for serious study. Mathieu van Rijswickhttp://www.blogger.com/profile/07918887659342199131noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-28915727485835235502010-01-05T12:04:17.570-08:002010-01-05T12:04:17.570-08:00Ron:
Nice work! I'm going to be looking you...Ron:<br /><br />Nice work! I'm going to be looking your posts over carefully. I think my calculation for the even mode is good (hard to believe I made a factor of four error in the spring constant of tires). Clearly the odd mode is more relevant to single-wheel events, and the odd mode frequency comes out a bit right. Maybe I'll take a stab at estimating my moment of inertia, which will allow me to estimate the odd mode frequency more precisely than assuming I'm a sphere of sea water.djconnelhttp://www.blogger.com/profile/01484858820878605035noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-74773129108625712132010-01-05T01:33:17.418-08:002010-01-05T01:33:17.418-08:00Aah shoot, forgot to pass this along as well in my...Aah shoot, forgot to pass this along as well in my previous comment. <br /><a href="http://cozybeehive.blogspot.com/2009/08/dynamic-ride-comfort-measuring.html" rel="nofollow">Measurement of vibration in Museeuw's flax bike. <br /></a>Ronhttp://www.blogger.com/profile/18394865788996482667noreply@blogger.comtag:blogger.com,1999:blog-1564958057737541664.post-44278530075901556752010-01-05T01:17:09.040-08:002010-01-05T01:17:09.040-08:00Dan,
Tires are unsprung masses that filter high f...Dan,<br /><br />Tires are unsprung masses that filter high frequency, low amplitude vibrations. I have read the study you quoted before and even made a <a href="http://cozybeehive.blogspot.com/2008/10/bicycle-structural-dynamics-by-vlus.html" rel="nofollow">mention of Velus' research work on my blog</a> in the past, including some bits on EMA. <br /><br />Some personal observations :<br /><br />1) Difference in EMA between no cyclist vs occupied cyclist, as the latter introduces vibration at the handlebars. Still, the numbers behind the modes in EMA (SIMO) are sort of close to what would be seen in a modern sporting motorcycle, you know..for example, with a mass of 190 kg, 1st through 4th modes are 23, 28, 32 and 36 Hz respectively although structural elements and their planes of vibration differ. Your calculation of 10 Hz sounds a little low-ish to me.<br /><br />2) OMA results in fewer modes than that seen in the EMA in the lab but perhaps this is from the fact that they exaggerated the treadmill bump and hence the excitation made available. I have written about the dynamic behavior of the bicycle, and in <a href="http://cozybeehive.blogspot.com/2009/09/dynamic-stability-of-bicycle-design_14.html" rel="nofollow">Part II of my series,</a> I noted that the state-of-the-art mathematical model designed for the bicycle at Delft has about 24 degrees of freedom (DOF=independant co-ordinates). It is ridiculously complex than previously imagined. This may mean that the bicycle actually shows 20+ different modes of vibration as # of vibration modes should equal the DOF. I don't think it is practical to study all these little tiny modes, there's more sense in concentrating on the dominant ones that affect dynamic comfort.<br /><br />3) In the past I have rummaged through available literature to find an objective set of absolute limits for vibration. I have found zero for the bicycle but some for the passenger car. SAE's Janeway Report for amplitude vs frequency is a good resource to have and is often quoted in vibration literature but I find that you cannot fix the limits for human comfort objectively. The problem is complicated by variations in individual sensitivity and diversity of test method and by the fact that such "limits" are based on just single sinusoidal frequencies.<br /><br />4) I have thought a lot about vibration dampening of tires and it is almost a forbidding topic, specifically due to the math involved in handling the degrees of freedom and the modeling parameters. Computer programming and analysis is apt. Experimental measurements are even better.Ronhttp://www.blogger.com/profile/18394865788996482667noreply@blogger.com