Thursday, March 22, 2012

Installment #6 – Brakes and Wheels

Porsche was fairly late getting into the disc brake game.  There were several reasons for this; among them were the car’s light weight that put less strain on Porsche passenger car conventional “drum/shoe” brakes.

Another factor was that Porsche conventional brakes were an excellent design, made from highest quality materials.  They were, unlike brakes on many other “high performance” passenger cars in the 1950s and ‘60s, large enough to be “more brake” than the car really needed.  

But time and technology moved on and the first street legal Porsche with four-wheel disc brakes was the 1964 356C.

Early (1964 to 1968) Porsche passenger car disc brakes were race car proven and, not surprisingly, excellent.  

But, compared to the 356C, even the early 911/912 models were bigger and heavier.  The 911 models were also more powerful and much faster.  

It soon became clear that merely having excellent disc brakes wasn’t enough.  So Porsche enlarged the size of the front and rear brake pads on all 1969 models.  

Porsche wheels and tires also received additional attention in the 1969 model year.  Stock 911S and E models had 6” X 15” light steel rims with 185/70X15 tires.  

My 912 was delivered with the standard (for a 912) 5.5” X 15” light steel wheel painted a soft silver-gray.  While there were other factory wheel/tire combinations, my stock 912 5.5” x 15” light steel wheels sported 165 X 15 tires in a setup that, while not exactly exciting, was perfectly adequate for street and highway driving. 

In the early 1970s I found and purchased a matched set of the larger OEM 6” X 15” light steel wheels that had come from a 1971 911.  I put a set of new 185/70 X 15 tires on them.  All of a sudden, the adequate but wimpy looking 912 wheels and tires had been replaced by the much more substantial 911 wheels and ever so slightly “taller” tires.  I liked the change.    

About 25 years later I tried to find another set of high performance 185/70 X 15 tires but what I wanted were no longer available.  (I didn’t know it at the time, but that was my introduction to the term “NLA” that would become very familiar to me.)  

So now I’m running very similar 195/65 X 15 tires on my 912.  See photo below.

My OEM 911 wheels fitted with these slightly “taller” tires give me about 4% fewer wheel/tire revs per mile than the smaller stock 912 tire setup.  

This also means about 4% less engine revs at any given speed in top (4th for my 912 Porsche) gear.  

4% isn’t much but, on a 2,500 mile trip I enjoy slightly better fuel economy and slightly less power train wear and tear because the engine and transmission are turning about 4% “slower” than the car moving over the highway.  

Finally, on Porsche 912 wheels, the OEM light steel wheels are becoming increasingly rare.  If you are looking for a set, and find one, look closely at the oval holes in the wheel surface between the rim and the lug nut holes.  

If you see the die mark parallel to the oval hole in the wheel, as you can clearly see in my wheel above, it’s the real thing.

If you don’t see those clear die marks in the wheel stamping, it may be a perfectly satisfactory wheel, but it’s not a Porsche OEM wheel.