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Noisy Cobras
filed on: 17.02.2009 (17th Feb 2009)
Today's Tages Anzeiger newspaper reports about the continuing problems with noise and vibrations on Cobra trams. These are caused by unequal wear and tear on wheels which leads to wheelflats/polygon formation (with 15 to 19 corners). The noise and vibrations are especially marked in the interior. Such trams must then be taken to Oerlikon depot where the wheels are reprofiled on a lathe, a process that removes up to 3mm of the wheel tyre and takes two hours (for two wheels). In some cases this treatment is necessary after as little as 6000km, whereas in others it is much slower in manifesting itself. Normally wheels are turned after 25,000km and tyres changed after 360,000km. On Cobras the latter figure is 150,000 to 200,000. About three Cobras are currently receiving this unscheduled reprofiling every week. Typically only two of the 12 wheels are affected (usually adjacent on the same side).
This news item is from the 2009 newslog.
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http://www.proaktiva.ch/tram/zurich/newslog/newsitem.php?year=2009&item=170209