Milano wheel shimmy & centering rings

[ALFAXTC@domain.elided]

Hi All,

I have a strange problem I'm trying to solve.  I have 16" 156 Sport wheels on my Milano which I had to machine the center hole so that it'll fit on the Milano hubs.  The wheels have been doing fine for about 1 year now and it's been fine, but lately I've gotten a shimmy at around 80mph.  I thought it was the balancing, but I've had all the wheels balanced twice and nothing.  I thought I bent a wheel, checked and they're round, not bent.  My mechanic checked and said that the Milano hubs are 58mm and the center hole in the wheels are 61mm and that centering rings will solve the problem.

My question is would 3mm (1.5mm on each end) make difference where the wheels would shimmy pretty bad?  And if so why did it just start now and not a year ago?  I was doing 120-140mph for long stretches on the way down to the TN convention and never had any shimmy.  Why now, is what I don't get.

Alan
88 Milano 3.0
87 Spider Quad FS
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