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Author Topic: Vibration Problems  (Read 5707 times)

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march2011

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Vibration Problems
« on: April 18, 2011, 07:31:50 PM »
After not driving my 73 B-GT for several years, I had a local Alfa shop bring it back to life. They did a great job. Among the things they did was to replace the original 165x14 radials with 185/70 Dunlops. When I bought the car in 2003, the only thing that bothered me was that at about 60 mph there was a vibration that made my mirrors useless. Above or below that speed, I had little problem, and it was clearly not a matter of RPM. I thought the problem might have been caused by improperly balanced wheels, but I have the same problem with the new rubber, so that seems unlikely.

I like the look of the Rostyle wheels, but I wonder if the wheels are where the problem lies. I had the same problem many years ago when I put Corvair wheels on a Datsun 510 to accommodate more rubber. They did the trick at lower speeds, but it seems they were not perfectly round. I have heard the same about Rostyle wheels.

Any opinions?

James
« Last Edit: December 31, 1969, 07:00:00 PM by amgba »

amgba

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Re: Vibration Problems
« Reply #1 on: April 18, 2011, 07:33:20 PM »
Balancing Rostyles can be a bit of a dark art.  And frankly while I prefer them to wires for simplicity they are fairly cheap wheels and have a couple of problems.  For one balancing is very difficult.
 
Most balancing relies on the wheels being held on the balancing device (meaning a rotating, off car unit) with two cones, inner (brake side) and outer (tiny hubcap side).
 
The hole for the hubcap side is not necessarily coaxial with the center of the wheel's mass and so when balancing the device is actually compensating for the wheel not being held properly.  But when on the car the balance weights work against you once the wheel now mounted on the qualified lugnuts is turning coaxially with its mass center.
 
With modern tires, themselves usually quite well balanced as opposed to 40 years ago radials, a simpler 'bubble balancer' which uses the inner part of the wheel but not the outer hub cap hole can actually do an OK job.  Only an older shop will even have one.

But since you mention one particular speed as being the cause, items such as wheel and tire run out and even proper dampening (shocks) are all factors.
 
One easy thing to do is switch the front and rear tires ONE ONE SIDE ONLY at a time and observe any change.  One slightly off wheel/tire might be less annoying on the heavier rear axle.
 
Also while the car is in on a jack and observing proper safety (jackstand) turn the wheels and look at the lateral runout and radial runout.  Even the best tires can be a bit off.

Paul Resch
American MGB Association
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Art

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Re: Vibration Problems
« Reply #2 on: April 21, 2011, 01:09:01 PM »
As Paul describes, the Rostyle is not the most accurate wheel to balance, second only to wires in the expertise required to do them right.

Dynamic balancing of Rostyle wheels requires an older type of machine that actually bolts the wheel to a flange, much as it is bolted to the axle of the car.  If someone has either the mount for a new machine or the older machine, it would make life easier. 

As for replacement wheels that might be more serviceable, Panasport alloys keep the vintage look, but are lighter, more easily balanced and properly suited for the 185-70 rubber (the Rostyles are a bit narrow for them). 

The MGB uses a 4-bolt, 4 1/2" bolt circle, so anything that would fit an early Datsun 240/260 Z series or 1960's era 4-bolt Ford Falcon or Mustang (from very early 6-cylinder cars) would work.  They were available in 13" and 14", up to 5" width stock (1/2" wider than the Rostyles).  Hard to find these days, but some can work with the old MG hub caps giving a unique vintage appearance.  American Racing and Enkei also make modern alloys that fit, but watch the width and off-set, or they will hit the bodywork.

I hope that helps you.

Art 
Art Isaacs
AMGBA Tech Staff
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