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Thread: Pirelli CN36 turnover vs tubeless-- original fit

  1. #1
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    Pirelli CN36. Was tube or tubeless-- original fit

    Pirelli had a presence yesterday at the NEC Autosport International which is the major trade (and public show) for motorsport in UK / Europe. It is good to see the Pirelli support classic car owners including cinturato CN36 in 185 70 15 and 215 60 15 sizes*. Latest releases of these tyres receive good reviews in the German press comparison test on an early 911 also read positives from CN36 buyers here. A strong contender for folks seeking replacements it seems.

    They are tubeless versions today, but that wasn't the case originally. I've read question about whether the CN36 (as the only tyre fitted originaly by the factory on 73 Carrera RS until Dunlops arrived) were originally tube or tubeless.

    It is my understanding based on some evidence that the original version fitted on the Carrera RS was actually with a tube.

    Redpctd references on RS and later Carrera 2.7 state factory change use of tubeless only happened during December of 1974 which would have been for impact bumper Carrera 2.7 (well after the limited edition RS had finished production). The change from Pirelli tube type tyres to the replacements with steel belt tubeless for the 215/60 15 (also the smaller from 185/70 15) is documented in sources that have access to factory production records. The use of the small valve support attached to rim on the 7/8inch wheel were introduced the very same day in December 1974 according to these sources -- not a coincidence, specifically introduced to support tubeless stems I suppose.

    Original examples of the tube type CN36 are obviously well past sell by date and not for use beyond static display where every detail of originality is important, such as concours or museum. Neverthelss there are some folks here interested in finer points of originality so these photos is an early German made tube type Pirelli Cinturato CN 36 215 60 15 one of a pair taken off an original genuine RS with tube type markings. German made tyres, they are vintage items and only for Carrera RS or Carrera 2.7 at that date:
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    I have them in storage. Pirelli inner tubes too. Not saying these these examples were the actual ones factory fitted on my 1972 production date / model year 73 RS as part of the RS conversion order post homologation, of course.

    However with the change from tube type to tubeless documented in respected RS reference sources as December of 1974 these examples were almost certainly made before that date because they are the tube type that were made by Pirelli for only a short time. Someting borne out by their DOT date markings being consistent with 1974. These tyres probably originate from Pirelli's Hoescht/Odenwald plant, in Germany. I think it is about 80 miles from Stuttgart?

    Also as discussed elsewhere such tyres were often fitted on the original correct spec for early RS 6 and 7 by 15 inch Fuchs (not the now often seen 7/8 that only later became fashionable fit to last series RS or sometimes got fitted afterwards).

    Wheel part numbers for 72/3 are discussed/well documented elsewhere so haven't duplicate part details of them in this post.

    Never looked in detail at the internal profile of the later Fuchs vs the earlier three prong Fuchs regarding the dimensions and design of any internal "tubeless hump" on these Wheels. My car has its original factory wheels based on date stamp and presence of original RS only blue paint -- pretty sure despite originally having tube type they have a rim hump.

    This generic information about tube hump shape is taken from a German Pirelli technical
    booklet published around 1972:
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    For those who were asking those questions on factory original being tube type or tubeless for pre impact bumper: I'd say spec was the German-made tube type Pirelli Cinturato CN36, no rear valve support yet and the distinctive profile shape balancing weights sometimes applied prominently to the external rim as needed.

    That in my opinion was as it was probaly done by the factory back in the day in late 72 and early 73. Don't believe the Model year 73 TES got Pirelli CN 36 when new from factory, particularly not the unique to RS 215/60 size?

    The tube type version being original spec to Pirelli MY 73 is somewhat substantiated by photographs taken when the cars were new by absence of the stem supports. Also this particular datapoint in a road test report about the RS printed in May 1973 is very clear -- they were tube type :
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    Conventional wisdom can result in what we think was the original spec of the car obscured or lost over time! It takes research to find the in period proof as memory and opinion are often misleading and restorations destroy history or necessary later replacements of things can mislead.

    The Carrera RS is to my knowledge the first road-car car to have been produced with a factory spec mismatched size front and rear wheel/ tyre axle pair so there is a small automotive historical footnote among such a small tyre specification details.
    Not all the anorakish finer points that get looked into on this forum can claim to be about an automotive historical first.

    Afaik tube variant CN36 are not available new from Pirelli these days, so this particular historical detail maybe moot however. The current reissue are the closest to original and by all accounts a worthy choice. Many folks might not care about correct to original spec details, but this forum is the place of countless such small early 911 originality and authenticity details matter for some --- folks who sweat such finer points.

    The original old 215/60 15 (German made tube type version) were at one time very rare, sought out expensive items before the Pirelli reissue. I at one time had silly money offers to buy my examples from knowledgable folks. Being tube type they are not for sale even with the reissue

    There maybe folks who have documented sources that know more/can prove it was different? Always open to learn from folks regarded as RS experts.

    (*I've no affiliation to Pirelli or folks like Longstone who do much to support tyre supply classics from their base here in the UK.)


    Steve
    Last edited by 911MRP; 06-09-2018 at 02:52 PM. Reason: Correct thread title and typos

  2. #2
    Registry member# 206 fourteenten's Avatar
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    RS tires

    Great info as ever Steve! My RS came with Dunlops, do you know if that were SP57's? Also interesting fact that in the Italian brochure Porsche had 165 (front) and 185 (rear) tires fitted. Probably cheaper option but wonder if any of the Italian delivered RS's were equipped like that.

    Cheers, Cees
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    Hi Cees

    Hope all is well with you.

    On April 24 1973 model year Dunlop SP Sport of the correct ie different size pairing for the groundbreaking mismatched wheel on RS became available and were fitted by the factory interchangeably with the Pirelli CN 36 that up until then were the only supplier of the 185 70 VR 15 and the unusual size rear 215 60 VR 15.

    Afaik the Dunlops fitted to the Carrera RS and the later 911 Carrera 2,7 through to early 75 were steel belted Sport Super SP57 with tubes. These were superseded by the tubeless Sport Super SP60 sometime in 1975. The latter were not only tubeless but had a different tread pattern. Presumably as Carrera RS original SP57 tyres wore out the SP60 got fitted as replacement when cars were a couple of years old. I have some old Dunlops of correct RS size in my storage but wouldn't fit them (even for show) events as no evidence of my car having had Dunlops. I've read comments from knowledgable people old enough to remember that Dunlop Sport quality wasn't well regarded vs Pirelli CN36 quality -- Dunlop failures in period apparently , but I'm to young to know that first hand.

    Regarding the 165 185/70 Italian literature. I can envisage two explainations:

    1) some of the early RS material I have and have seen refers to the spec used for homologation the first 500 cars before any conversion order. Examples of that writ up are the Paris salon brochure from launch which also refers to that 165 spec. Not uncommon to see early publicity material use 165 when doubt anyone their right mind would use 165 in anger top of the range 150 mph car to save a fraction. As the RS were announced in early October 72 -- launch was out of step with the normal model year cycle -- I suspect many publications and information were done "on the hoof" just for the limited edition RS model which at the time was initially planned to be a run of only 500 examples. The sticker on the blue supplement book overwriting specs.. The famous last minute decal change on the erratum of brochure; drilled discs being shown but dropped ...plus other examples.
    2) being Italy it might have simply been to do with being "creative" about the vehicle tax laws that incentivised buying car cheap devoid of options then fitting options and extras at dealer to be more "tax efficient".

    If written that way in early Italian literature but not later literature I suspect 1) . If that spec persists for later Italian RS literature it suggests Porsche and importer helping bend the tax rules i.e. 2).

    This is the illustration in a neat unused French Dunlop page per day desk diary from 73. Probably diary deserves to be with a French market 911:
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    Incidentally I was interested to see Robert had gone to great lengths some years ago to get the correct, rare rear 215 60 VR15 Pirelli CN36 for his RS. I have stored my old set as pictured above very carefully over many years too. Respect for a man who clearly appreciates such finer points of RS originality and a free bump for his sale thread:
    http://www.early911sregistry.org/for...chs-CN36-3-0RS

    Give me a shout if you are ever in central London and fancy a beer at the Royal Automobile Club in Pall Mall.

    HtH

    Steve


    Ps I don't speak Italian but seems to be referring to tubeless front and tube the rear? It like most early referred to 6/7 inch.
    Last edited by 911MRP; 02-11-2018 at 06:00 AM. Reason: Add date of the introduction of Dunlops

  4. #4
    Registry member# 206 fourteenten's Avatar
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    Dear Steve,

    Thanks again for the lengthy explanation; you always have a wealth of info to share with us. Appreciated and hope to meet in person some day in London or elsewhere. I hope there will be a 45 yearRS celebration/happening some time next year.

    Kind regards,

    Cees

  5. #5
    To be frank when you guys showed me the tube type 60 profile tyres i was suprised.

    I think what is interesting is that they didn't make tube type 60% profile tyres for long. And they didn't make tubeless wheels without the safety rib for long too.

    i think this was a brief learning period

  6. #6
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    On the factory production order I have for my first series RS, the typed Dunlop 185 70 VR 15 is crossed out and handwritten with Pirelli 215 x 15. Referring to rear pair.

    There are probably not too many factory production order sheets for RS dating from late calendar 1972 with their respective cars. These sheets were attached to rear lid during assembly as shown in a photo of a yellow example in process from 73 model year that was posted elsewhere
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    The one pictured on car can not be read from the distance but has yet to receive its distinctive coloured gearbox, motor or VIN stickers (top right), nevertheless the layout of the sheet's content with shading and boxes of text is evidently that production order document when compared to my examples.

    I am fortunate to have my car's original production order dating from back in calendar 1972. There were only 300 RS examples made that 72 calendar year. Let alone paper for an EG C16 RL (RHD) of which there are a little over 100 were made in total. Roughly a dozen or so of those RS from calendar 1972 were RHD.

    Not seen (m)any other production order papers for RS beyond the couple that illustrated in the Carrera RS books. The RS Book shows a few as examples: from an early RS series and one from a late series papers, as examples only. These versions are different reflecting how the third series cars became much more productionized process like TES. Paperwork for third series was no longer needed in the two parts and so forth.

    The first series example shown in that RS book isn't quite as early. It has a similar handwritten amendment to the tyre section on first page iirc.

    It is well documented that at the time in late calendar 72 early 73 Pirelli were the only manufacturer and factory supplier of the 215 60 VR 15 Cinturato CN 36 tubed tyre uniquely fitted to the 7inch rears of Carrera RS. The information being hand corrected on the original production order paperwork from the time of the car's build I suppose was due to homologation example being assembled at first with 165 15 and 185 70 VR Dunlop brand for FIA weight checking purposes, then got swapped to the correct Pirelli cn 36 185/70 VR 15 and 215 /60 VR 15 as part of the second step "conversion order". 165 15 front and 185/70 15 of those 500 RS base cars when in homologation configuration was hardly appropriate for real use. Or maybe Dunlop dropped the ball and didn't have supplies of the larger rear tyre available in time to meet the limited edition RS homologation programme timescales?

    To Dougal's point: Could it be the tubed 215 60 VR 15 German made CN 36 like I have in storage were unique to the RS model (and maybe a few of the 74 Carrera) of if tubeless replaced them very soon?
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    As below these have 404 date code. Week 40 of 1974. Could be 84 but evidently the early soon supeceded tube-type (not the tubeless) maybe suggests not? Not original factory fit tyres from 72 but maybe the correct Pirelli RS spec as fitted new replacements in 74? Wheels are original. Who knows?
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    This RS production order handwritten correction on tyres unique to model by the folks who built car is one of those original first homologation series ( and maybe second/ third series) RS small details. Neat data point that is hand annotated on rare original factory papers from 1972. Someting from contemporary papers refering to the related chassis that establishes useful provenance in context of the highly unusual, convoluted order/ assembly process required to achieve original RS homologation for those 500 (or 1000?) FIA homologation certified chassis.

    Later RS examples got Dunlops or Pirelli brand interchangeably once the former was able to manufacture that unique 215 60 VR 15 rear size.

    Things these days are becoming very controlled on data privacy in Europe with new stronger legislation effective in just a matter of days, this making all companies (not just Porsche) very concerned about what data they can share.

    Steve
    Last edited by 911MRP; 05-22-2018 at 09:43 AM. Reason: Typo more photos

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    Duplicated my photos from another thread as it fits the thread here....

    The humped rim shape picture from Pirelli made me curious so I dug out a second tyre manufacturer reference from 1974 which is also very clear on the wheel rim shape for tubeless radials and tubed radials.

    Further to earlier post from Pirelli, below is a second opinion this time from Michelin as printed in their 1974 technical data book. It has specific recommendations on the acceptable wheel rim shape for tube and tubeless radials:
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    Reproduced directly above in photo of relevant pages from book -- obviously as before this period point of view may not be the current national regulation in each country or be the latest thinking of these tyre suppliers. Back in the day there was evident alignment between Pirelli and Michelin about the do's and don'ts on this tyre to rim shape compatibility point.

    Something the companies both deemed sufficiently important for safety to publish their hard and fast " conditions" with various go no- go illustrations in their technical documents of the early 70s. This old content might today still give food for thought about the wisdom of fitting tubeless on certain old rim shapes to get a "certain look".

    Not sure how all the old Porsche rim shape variants stack up vis a vis the profiles illustrated. Pretty sure the original Fuchs on my car have shape that can be used safely with cn36 tubeless or as they were originally, with cn36 tubed. Are such rim and tyre combo decisions these days made fully cognicant of the documented advice from several major OEM tyre suppliers from back in the day?

    Availability of tube type tyres generally is probably quite different these days compared to early 70s but that doesn't necessarily invalidate the viewpoint on what was being recommended by both pirelli and michelin back in the early 70s.

    Hope this post and vintage tyre company material from my literature informs wheel and tyre combinations.

    I recommend seeking current professional qualified opinion in each country regarding such safety critical items especially since these companies clearly considered it important.

    Steve
    Last edited by 911MRP; 06-08-2018 at 02:02 PM.

  8. #8
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    Sharing information from my personal literature collection for historical reference and interest only ...this shows a further page from the Michelin technical data booklet of March 1974.

    The extra page with footnotes is historical technical data information from Michelin in March 1974 that includes information about whether older Porsche wheels were suitable for tubeless tyres:
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    Pirelli publication from 1972 required humps with tubless tyres
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    Am I reading the annotation on Michelin table right that the wheel rims for 911 listed in table of the technical data booklet in March 1974 were not suitable for radial tubeless tyres by Michelin? I can only assume this refers to the earlier wheels without humps? Only 914 had ∆ in black it seems? See post #1 for introduction of tubes tyres which post dated the march 74 publication. Also the flat Fuchs with humps were comapartively recent being introduced just few years prior at that time of March 74 publication.

    The language used and annotation were at the time when radial and tubless were relatively new to the market but it seems the position of both major manufacturers regarding humpless with tubeless was very clear.

    Not only the rim shape but the valve hole position and mating surface is critical to getting a tubeless seal. Not clear how much this factor affects the published viewpoint.

    Pirelli and Michelin were (are?) OEM suppliers and the latter are regarded as the company who successfully commercialised radial tyres.

    More recently Pirelli issued this which comments on use of tubes in tubeless tyres; see point 15.

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    Pirelli's contacts are shown above. My understanding is they have a close relationship with Porsche AG today and also manufacture a range of tyres for classic cars so may be able to advise. https://www.pirelli.com/global/en-ww...is-for-porsche


    I'm not aware of any tube type tyres available in 60 aspect ratio 15 inch these days but they might exist?

    When taken together does this mean the fashion of running tubeless tyres of 60 profile on early style Fuchs rims without the later humps on rims / appropriate rim shape is against prior published tyre company advice? If so might unsuitable configurations under some circumstances invalidate motor insurance cover or worst case create liability in event of an accident? If so, who would be liable the car owner, the car driver the wheels /tyre fitter?

    If that remains the technical position todayis it likely if motor insurance companies were consuslted they wouldn't touch tubeless tyres / no humps with one of these of they knew at time of taking on the risk?
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    Probably better that than the insurance being invalidated at time of investigation of a significant claim? I don't know about other countries but I wouldn't want to have to explain it to police accident investigator or insurance claim assessor in the UK? Let alone my wife if in extremis there was a big uninsured liability because I liked the look of particular wheels and tyre combo!

    I'm not an expert so don't make recommendations; people should take professionally qualified up to date advice on potentially safety critical matters such as wheel and tyre combinations.

    Old information shown in this thread is for historical interest only. It might be out of date so do not rely on the historical content for making decisions today. Always check the latest wheel and tyre technical data and consult with currently qualified professional experts.

    Steve
    Last edited by 911MRP; 03-17-2020 at 07:47 AM.

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