The Official 356Talk Forum

Hi All -
I have read in a few different sources that the two piece riveted RSK/Carrera wheels were simply painted the same color as the standard steel wheels. However, I have seen more examples/restorations where the outer rims were either left raw or semi-polished, with the centers appearing to be painted a bit darker than standard. A set I recently come across is done this way (raw/darker center). If I move forward with the purchase, I want to have them refinished correctly. What is original?

Thanks very much -
Scott S

Having owned and restored a 1959 Works RSK and a competition 1959 Carrera GS-GT that won People's choice and Judge's choice at the Parade in Monterey in 1990, I can say with some certainty that you were right the first time. The wheels are all fully painted silver as the standard wheels. The other looks are a visually enticing direction (that I tried out myself on the RSK at one point), but they are not correct. I have also seen the odd period photo with a race car wheel with the darker center you referred to, but there's no documentation to support the notion that was anything more than an individual situation, and in no way a factory spec.
Good luck with those very rare wheels.

Hi Dick
i agree with the silver paint but a race car might have had the wheels before they were painted if they were in a hurry. What is your take about fan shrouds and surrounding sheet metal were some race cars not painted but just zinc plated?
j

Jacques Lefriant wrote:Hi Dick
i agree with the silver paint but a race car might have had the wheels before they were painted if they were in a hurry. What is your take about fan shrouds and surrounding sheet metal were some race cars not painted but just zinc plated?
j

In my 80 some years I've not seen unpainted sheet metal as original but could have been done later.
Some thought that chrome was quicker, me thinks not!

My Carrera GT wheels were completely painted, at least the last one that split.

Norm, The alloy/steel wheels were never meant to last for 50+ years in a high stress race application. Like as not they went away with a worn race tire. Racing the RSK, especially with the Dunlop CR-65's with the stickier rubber, put enormous demands on the wheels and they started to show stress cracks around the stud openings. We retired them in favor of all steel wheels with a full spacer behind them, not pucks. Safety and confidence over unsprung weight!...Today of course they are worth their (light) weight in gold...especially the 5 1/2's. Great to have if you're not going on the track.

Photo: 718-009 and 718-005, out from East Hampton to give our West Coast friends a run for their money...

Jacques, The only engines I'm familiar with with unpainted shrouds and other sheet metal were all works motors, but not all works motors were unpainted. I have never seen any informed commentary on exactly why. Were they in such a hurry they had no time to paint them?? Seems unlikely to me. Personally I don't think they were plated at all. I would love to hear reflections on this obscure issue...

Dick: I have always thought that zink plated shrouding and sheet metal would radiate heat into the cooling air better than painted. I have not dared to try it.

Hi Dick
I have the remains of a Miles Gupton engine (no engine no.) that had unpainted sheet metal. The pieces have been scattered but they are still shinny. On the wheels you would have to remove the paint to do a proper dye penetrant inspection?
j

Jacques, I am no expert but I think you may be correct. In my case, the cracks were small, but they were visible to the naked eye. That was enough for me...
After I sold the RSK to Ralph Lauren I purchased, restored, and raced the ex-John Mecom Lotus 19 Buick for 15 years or so. After every season I had all the suspension components including the upright castings crack tested. Anyone who plans to race a 50+ year old car without confirming that it's safe for the task is literally taking their life in their hands.

Here is a are some example's of un-restored steel/alloy's. Considering you can see the blue primer, I think it's safe to say they were painted, or there would be lots of blue wheels in old pictures.

Erik Thomas wrote:Dick: I have always thought that zink plated shrouding and sheet metal would radiate heat into the cooling air better than painted. I have not dared to try it.

Actually the opposite. The ability for wheels (or shrouding) to cool off is in part, a complex mix of wheel material thermal conductivity, wheel mass and tire mass and a combination of factors like surface emissivity (ability to radiate energy), absorptivity (of incident radiation) and physical geometry/directional orientation. But simply speaking and only considering surface emissivity, the highest value of 1.0 is for the perfect surface of flat black. Compare that to zinc plate at 0.25 (tarnished) or 0.045 (polished) and painted surfaces (no color in particular) of 0.96. So a painted wheel is much more effective in emitting energy and staying cooler: 4x better than tarnished zinc and 21x better than polished zinc. Polished chrome comes in at an emissivity of 0.06, only slightly better than polished zinc. And those cool looking, highly polished aluminum outlaw wheels? They come in at about 0.04, similar to polished zinc and equally as ineffective for cooling considering only surface emissivity.

Who could take issue with that erudite comment?

Once in awhile the mechanical engineer cells resurface amidst the larger body of gray cells and that's what comes out.

Hi Mark could you ballpark the % amount of cooling by the various methods in the most critical conditions for wheels and engine shrouds?
TIA
j

Jacques Lefriant wrote:Hi Mark could you ballpark the % amount of cooling by the various methods in the most critical conditions for wheels and engine shrouds?
TIA
j

Jacques,
The short answer is no, sorry but I can’t. I don’t have enough specific experience to address it and it’s not a simple challenge.

Getting at what you are asking for and coming back with realistic numbers would require some fairly complex analysis, part of which would have to include some empirical evaluation of a specific wheel/ brake/ shroud /tire/road assembly (WBSTRA) in a‘typical’ i.e. street or racing situation. Then you would have to figure out the physics of the rotating mass, define the heat transfer relationship between all of the components, define the boundary layer effect at the interface between the air and all the surface areas on the rotating mass and evaluate the fluid (air) effect beyond the boundary layer, all in real time, in motion, to come up with an overall heat transfer coefficient of the whole WBSTRA.

Heat transfer is a very geometrically driven science so part of the empirical evaluation would have to address the shape and surface orientation of the whole WBSTRA. Heat transfer coefficients for materials are readily available but getting the modeling correct to plug those numbers into, is the challenge. The simplified account I gave in my previous post is due to that complexity and only touches on the bigger picture.

I did some research to find similar information – don’t want to reinvent the wheel…groan. This is a link to just the Abstract portion of a technical paper written in an attempt to analyze the heat transfer of a rotating turbine blade: http://turbomachinery.asmedigitalcollec ... ltClick=24 In a very broad sense, this project and a spinning 356 wheel are very similar. Both have cantilevered, complex shape rotating masses immersed in a fluid medium. The turbine guys want to know how much heat their blades take on to determine stresses etc. Because air on a turbine blade ADDS heat to the blade due to the high speed and air friction involved. In the case of a 356 wheel, we want to know about the road heat the tire picks up, the heat added from braking and how much gets to the rim and how much of that the air takes away. So somewhere in the paper, there are probably calculations that would at least give someone a start on evaluating a 356 wheel. You can get a feel for the complexity just from the abstract.