Lightweight_911 wrote:It would still look like a tractor ...
Well, I don't think there is an alternative tyre size that can be run with an inner tube for the 7R rim. This rim was originally intended for the Dunlop racing tyres (5.50 M - 15), which unfortunately are not road legal.
The road legal 205/70/15 is the nearest size to that.
Lightweight_911 wrote:Yes, for road use, the original 911R's were fitted with 185 x 15 HR-rated Dunlops ...
I didn't know that. I learn something new everyday. Anyway, I think those were without the 70, which is not the same as 185/70 because the overall diameter is different.
Overall diameter
185/70 x 15 = 640mm
185 x 15 = 675mm
205/70 x 15 = 669mm
I don't post here often but havea thread on early S which might have some things of historical interest on tubed / tubeless, humped vs old rims etc...
The topic in the link was about the original fit tyres for Carrera RS so might be broader than the topic under discussion here However it does address tube vs tubeless as well as old vs hump rim shape using some of my original technical source documents from Pirelli and Michelin published in early 70s ( but not from Avon).
I am certainly not a tyre or wheel rim expert. These historical documents used in the post may be out of date or regulations might vary by country.
Do not rely on this historical stuff for your current wheel and tyre choices. I strongly recommend taking expert advice from a current suitably qualified expert on safety critical items including wheel and tyre choices. Since both these OEM tyre manufacturers both gave strict conditions in their 70s technical data about such things choosing the appropriate wheel rim design and radial tyre configuration is evidently a matter of physics -- not fashion.
Steve
PS if someone who knows how to post pictures here also has access to early S registry feel free to put my old Michelin and Pirelli tech document excerpt pictures here directly. That is the most relevant historical content from a longish thread about the original RS wheel and tyres. If I was here enough to post pictures that is what I'd have done rather than linking a tangentially relevant thread.
The rim shape profiles that these two early 70s tyre company documents illustrate along with their "conditions" for retro fitting tubeless radials might be interesting for folks to compare with various early Porsche rim profiles. Neither publication discusses the valve seating point specifically as far as I can see although valves and tube neck are shown in cross section in the various line-drawings by Michelin.
Last edited by 911MRP on Sun Jun 10, 2018 7:11 pm, edited 1 time in total.
