Techtip19

SAVVA Technical Tip No 19

Wheel Rims

Like tyres, we tend to take our wheel rims for granted. Recently a club member came
across an amusing incident – for passers by that is. Evidentially a chap with a very
nice Mercedes 500 convertible was standing next to his pride and joy with the rear bumper
virtually on the ground. It appears the wheel rims he had replaced the originals with had
collapsed. The fancy spokes had disintegrated. When choosing the replacement wheel rims he
obviously didn’t take into consideration the power that his Mercedes 500 transmits to the ground
via the wheel rims. It had just turned the “spokes” off.

We often refer to “mag” wheels, however, as you are no doubt aware this terminology “mag” refers
to magnesium. Magnesium wheels were used in the early days when racing car wheels had a high content
of magnesium. Modern wheels are now manufactured from a cocktail of alloys, mainly aluminum with a bit
of magnesium. The motor trade refers to modern wheels as “alloy” wheels.

Today some of the world’s most powerful cars run on alloy wheels and they don’t break. It’s not only
the material that is a factor but also things like heat treatment and the composition of the alloys –
and of course, design also plays a major part. Wheels are often designed for aesthetics and/or for
specific lightweight vehicles if these are incorrectly used they are sure to fail. One must therefore
be selective and take the cars power into consideration. If the Mercedes owner had gone to a reputable
wheel dealer they would have advised him which rims he could use with his big V8 powered car.

By the same token we mustn’t take other types of wheels for granted. If you have an early
British sports car with spoke wheels – keep an eye on them. I recall a beautiful TR3 being
wrecked (rolled) after a front wheel had collapsed. Many of these vehicles are now over 50 year
old so it pays to have the spokes checked occasionally by an expert in that field. Ford Model A’s
are now 80 years old and their wheels have a tendency to crack between the bolt holes – check them
out occasionally.

Owners of early cars like Model T’s can have problem with wooden spokes. Many of these cars have
original wooden spokes that are now over 80 years old. Fortunately, one can replace these
with “look alikes” made from an alloy – a bit of black paint and you wouldn’t know the difference.
We have to keep in mind the wooden spokes relied on the occasional “spruit” to keep them wet and swollen.
The older codgers tell us that in the early days it was commonplace, when making a pit stop, to urinate on
the wheels to wet them – sis.

Thanks to Joe du Plooy – Tiger Wheel & Tyre for his input.