http://www.baileycar.com/oil_additives_html.htm

Maybe ZDDP is really just for race cars.

But then again, I do not know the date of this article.

The Zinc Question
The latest "miracle ingredient" in oil additives, attempting to usurp
PTFE's cure-all throne, is zinc dialkyldithiophosphate, which we will
refer to here after as simply "zinc."

Purveyors of the new zinc-related products claim they can prove
absolute superiority over the PTFE-related products. Naturally, the
PTFE crowd claim exactly the same, in reverse.

Zinc is contained as part of the standard additive package in
virtually every major brand of engine oil sold today, varying from a
low volume of 0.10 per cent in brands such as Valvoline All Climate
and Chevron l5W-50, to a high volume of 0.20 percent in brands such as
Valvoline Race and Pennzoil GT Performance.
Organic zinc compounds are used as extreme pressure, anti-wear
additives, and are therefore found in larger amounts in oils
specifically blended for high-revving, turbocharged or racing
applications.

The zinc in your oil comes into play only when there is actual metal-
to-metal
con tact within your engine, which should never occur under normal
operating conditions.

However, if you race your bike, or occasionally play
tag with the redline on the tach, the zinc is your last line of
defense. Under extreme conditions, the zinc compounds react with the
metal to
prevent scuffing, particularly between cylinder bores and piston
rings.

However - and this is the important part to remember - available
research shows that more zinc does not give you more protection, it
merely prolongs the protection if the rate of metal-to-metal contact
is abnormally high or extended. So unless you plan on spending a
couple of hours dragging your knee at Laguna Seca, adding extra zinc
compounds to your oil is usually a waste. Also, keep in mind that high
zinc content can lead to deposit formation on your valves, and spark
plug fouling.

Among the products we found containing zinc dialkyldithiophosphate
were Mechanics Brand Engine Tune Up, K Mart Super Oil Treatment,
and STP Engine Treatment With XEP2. The only reason we can easily
identify the additives with the new zinc compounds is that they are
required to carry a Federally mandated warning label indicating they
contain a hazardous substance. The zinc phosphate they contain is a
known eye irritant, capable of inflicting severe harm if it comes in
contact with your eyes. If you insist on using one of these products,
please
wear protective goggles and exercise extreme caution.
As we mentioned, organic zinc compounds are already found in virtually
every major brand of oil, both automotive and motorcycle. However, in
recent years the oil companies voluntarily reduced the amount of zinc
content in most of their products after research indicated the zinc
was responsible for premature deterioration and damage to catalytic
converters. Obviously this situation would not affect 99 percent of
all the motorcycles on the road - however, it could have been a factor
with the newer BMW converter - equipped bikes.
Since the reduction in zinc content was implemented solely for the
protection of catalytic converters, it is possible that some
motorcycles
might benefit from a slight increase in zinc content in their oils.
This has been taken into account by at least one oil company, Spectro,
which offers 0.02 to 0.03 percent more zinc compounds in its
motorcycle oils than in its automotive oils.
Since Spectro (Golden 4 brand, in this case) is a synthetic blend
lubricant designed for extended drain intervals, this increase seems
to be
wholly justified. Also, available research indicates that Spectro has,
in this case, achieved a sensible balance for extended application
without increasing the zinc content to the point that it is likely to
cause spark plug fouling or present a threat to converter- equipped
BMW models.
It would appear that someone at Spectro did their homework.