Inner tubes with AVon tubeless tyres

[911MRP]

Thanks Andy. I ought to set up some capability to post pictures. Will do if I ever plan to post more frequently on DDK.

The smallest picture above is from my copy of a Roadtest of the U.K. Carrera RS press car from early in 73 -- a 72 production date example-- clearly road tester states tube type. It appears the factory used tube type on the early RS maybe even all the RS fitted with Pirelli until the introduction of tubeless along with valve stem support. This change as I've stated on other forum was December so in the 74 Carrera 2.7 impact car after RS model was completed apparently. My original 72 dated Carrera RS blue wheels do have the hump. Fortunately that design is suitable for today's tubeless. I do read that tubes are considered not suitable for 60 profile tyres these days and certainly wouldn't challenge experts on that, but apparently not always the case. At least on the basis of this in period road test info and my 74 dot code 215 60 15 cn36 examples in storage, which clearly state tube type made in Germany. The rears are from a genuine RS. I suppose what was previously acceptable use of tube in 215 60 15 tyres in 72/3 is no longer accepted.

I've just this morning posted more pictures on Early S registry forum of the insides of my original 1974 CN36 that compare the interior of a Pirelli CN 36 tube type to a tubeless of that era. This is posted on Darren's different thread over the pond about cutting tyre valve seats:
http://www.early911sregistry.org/forums ... dification

Being in the position of owning what might be now quite a rare surviving vintage set of circa 74 cn36 thought some photos might provide some historical context to the point I've read about use of tubes and interior tyre smoothness. Both tube type and tubeless have mounded diagonal ribs with a raised curved profile. The pictures show that the area between those interior ribs is slightly rougher texture on the tubeless than the contemporary tube type. Wouldn't say either is exceptionally rough but they do differ. Not qualified to say if that is material to safety if using tube in one marked tubeless if they are similar interior surface today to my vintage one.

Wouldn't say my old photos answers today's dilemma but these pictures shows (on a small sample size of one old tyre car-set) how it was probaly done back in the day by factory for that RS model.

Many things have moved on in tyre and rim design since these classic cars were new around half a century ago so as stated previously treat with great caution these old historical interest data points when deciding what to do today!

More generally the various thread discussions on tube vs tubeless made me curious:
If some vintage Porsche rims were not designed tubeless so have questions on suitability what options are available with tubes available these days beyond Avons or Pirelli for those wanting to use such rims?
Do the various risks being discussed here and on Early S affect the ability to use the earlier humpless rims for those who want to use them with or without tubes for the street free of concerns on safety...
...or possibly in worst case is thre a risk of insurance comebacks from use?
What is the position with FIA or other scrutineers on using these old rims in race or track day applications with or without tubes?
What is the position on road insurance of such old wheels with tube tyres when several manufacturers having previously made these "conditions" clear?

[Dougal Cawley]

Hi

Good stuff. I have the 1972 version of that Michelin book.

There were definitely cars made with wheels that did not have the hump on them, that were sold without tubes.

There were also definitely 60% profile tube type tyres made when 60% profile tyres were first invented.

But this when it was all new. Now no on makes a 60% profile tube type tyre & everybody puts humps on their rims.

there is a clue in that.

in an ideal world, have rims with humps and no tubes.

If you are fitting 215/60R15 tyres onto a rim with no hump, then er towards a higher pressure and keep a regular eye on the pressure (swerve round nails). but it is not an ideal scenario.

[Nick Moss]

The smallest picture above is from my copy of a Roadtest of the U.K. Carrera RS press car from early in 73 -- a 72 production date example-- clearly road tester states tube type. It appears the factory used tube type on the early RS maybe even all the RS fitted with Pirelli until the introduction of tubeless along with valve stem support.

I am not aware of any Fuchs flat sixes (the original front rim for the 2.7RS) designed for tubed tyres. These tubeless rims were fitted on 911s from March 1971, so no 2.4 or 2.7 911 should have tubed rims. I certainly would not trust a road test for technical details!

[911MRP]

I've somehow tripped over old tyre and wheel information snippets as a byproduct of detailed research into my own car's original factory spec and the finer points of RS originality --not looked into topic for own sake but happy to share them if they shed any historical light in the tyre and wheel dilemma at hand.

Agree magazine road tests not always reliable on details. Wouldn't use that as a sole source for my assertions. As folks who knows me appreciate, I don't operate that way.

Pretty sure that the 73 Carrera RS tyres were tubeless originally but got fitted by factory on the model year 6 and 7 Fuchs which had rim humps. There is evidence for this:

1) Snodgrass in Carrera 2.7 who had access to factory archives says: December 12 1974 Pirelli tube tyres replaced with Pirelli steel belted tubeless version for size 185 70 VR 15 and 215/60 VR 15.
2) On same day same source says: Rubber valve stem and valve support added...
3) My "for show not go" 74 ( 04 dot code) vintage 215 60 15 Germany made Pirelli CN 36 on shelf that definitely came off a known genuine original RS -- presumably its second ever set, are clearly marked "tube type". For those interested they're pictured on early S. While dot O4 could in theory be 84 the fact they are the tube type that Snodgrass says were superseded December 74 suggests not. No triangle on code so certainly not 94 and I've owned the car since car before that anyway!
4) the roadtest comment in AutoCar in early 73 of a 1973 production RHD RS. Iirc Gordon Bruce was the tester and soon became long term second owner owner RHD that he kept until a few yeas ago This is probably the most reliable road test written in period -- as shown above it state that the RS had tube type.

The above, taken together, would seem to corroborate the early (and indeed all RS) had tube type and that it continued until December 74 with the change to tubeless Pirelli and Dunlop during the 74> impact 2.7 Carrera model. Seems the factory fitted tubes to the 6 and 7 with the hump, suggesting it was unavailability of tubeless tyre that dictated the initial tubed tyre choice.

Pretty sure the correct original early RS spec was 6 and 7 Fuchs with tubed Pirelli CN 36 and no stem support. Maybe not the best and safest combo with benefit of hindsight and later developments of tyres but as far as I can deduce from the references it what the factory did at the time. Not saying that's what folks should do now!

At first Dunlops in larger unique to RS rear size weren't available. Then Dunlops tube type SP 57 came avsilsble and were used. These too switched to tubeless -- supercession was Super Sport 60 formula 60 December 18 74. Again this change was after whole RS production run completed so suggests later Dunlop or original Pirelli factory fit of the unique in MY 73 to RS 215 60 15 were all tubeless. I've a pair of vintage ones of those 215 60 15 Dunlops too but my car's factory production order that I have is clear it was Pirelli. Unusually ( msybe uniquely for RHD Carrera RS ?) I've got a copy of from 1972 Pirelli for my chassis when it left the factory. Inter tingly Pirelli is a handwritten change on the original factory production order that was once attached to the car. Hand written showing the change from the 165 15 285 70 15 it wore for FIA homologation weighing prior to conversion. Quite neat to see the chronology of what happened in the facility on a day by day basis from the different assembly operation date stamp plus hand annotations as the RS was assembled with its engine, transmission and and then reassembled with conversion plus options customer wanted. Goes beyond CoA or Kardex in many regards.

Incidentally no option code for ordering 7 and 8 Fuchs existed on the Carrera RS. It became fashionable to fit 7 and 8 to the model but I've found no hard evidence of any of them leaving factory with that larger size before third productionized RS series. Found couple of examples brand new or neatly new after homologation was completed for first 1000. Suspect 7 and 8 was done locally as an upgrade even for majority of those considered these days to have had 7 and 8 from new.

In addition to a copy of my car's old factory production order paperwork I am fortunate to have the original dealer RS order procedure in my cars file dating from when the car was picked brand new. This is a factory document to dealer. It lists all the options and permitted combinations for RS model (along with RS spec) including detailed instructions to a dealer on how to fill in the customer order specifically for a the base homologation RS. As well as it requiring a separate letter for conversion order. Like the production order paperwork not intended for end customer but I assume the original purchasor must've picked it up.

My 72 production RS still has its original 6 and 7 wheels. Confident of that based in stamp dates, presence of original Mexico blue paint on inner surface and conversations with all the (few) previous owners. Unlike countless replicas this is one of a handful of genuine original RS in GPW with blue RHD factory cars in that colour. Despite the popularity of the colour in homages replicas etc just over 200 or of all RS are orginal in that colour combo. These wheels have humps on all four corners fortunately given the present. Fortunatly this means I can fit the latest Porsche approved tubeless CN 36 reissues without worries on safety or fear of comebacks on insurance for not following wheelrim and tyre configuration "conditions". Same as for folks with that flat 6 I assume? I probaly wouldn't fit cn36 tube type to my car now even if they existed.

Tube type tyre with rim hump on RS -- one of those quirky details of originality that can get lost or presumed otherwise. Always open to be corrected on RS the specific viewpoint if hard evidence exists from RS "experts"

Regarding the more general point: On evidence of these publications it appears getting the rim and tyre combo right was certainly was a safety consideration back in the day even when inflated to correct pressure judging from the Michelin " conditions" and Pirelli comments back in the day. Might a diligent insurance company claim assessor look at humpless tubeless combo if there was an accident? Think the tubeless need for a hump wheel dilemma is fairly well known based on a quick general www search. That would trouble me personally if I had humpless old wheels and modern tyres. Not sure what the tyre company and insurers position would be on putting tubes in tubeless these days -- do the old books seem to suggest it was once acceptable?

As I repeatedly to point out I'm no expert on tyres and rims and these tyre company books etc are nearly 50 years old so best to take qualified current advice if owning old humpless wheels when considering current tyre options.

HtH

Steve

[Nick Moss]

Very odd. Porsche changed from the deep 6 (tubed) to the flat 6 (tubeless) with humps in May 1971. You can't fit tubed valves into the smaller valve hole on the tubeless rim.

[911MRP]

Hi Nick,

As stated I'm open to be corrected as I'm certainly no expert on old wheels tyres but sharing what I have found as byproduct of more some general research on various spec things.

The Snodgrass running change comments were taken direct from Carrera 2,7 source as I typed previous post. Assume his data-points are from factory archive information available to author and TAG as in the extensively documented production changes section of that book -- each with precise comments each with date details?
The AutoCar comment is a photo of what they wrote in early 73 about the AFN PCGB demo car that was built in calendar 72... albeit accept caveat about not relying on Road test it neverthess it is contemporary with brand new car and it quite specific on stating tube type so does correlate to Snodgrass.
Never tried to fit a tube to 7 inch rear rim of an RS personally so can't comment on that.
The CN 215 60 15 CN 36 I have on shelf are definitely Germany made tube type as have checked sidewall writing and have pictured them elsewhere. Matching rear pair with dot date code 404 which I take to be week 40 of 1974 which www says was September 30 1974. If so made in the period Snodgrass says factory were still fitting CN 36 tube type, shortly before before the tubeless change he notes. Unlikely to be 84 if Snodgrass says tube type were superceded by tubeless in 12 December 74. Certainly no triangle in dot date code so not 94. Also the sidewalls on these examples are two plies rayon -- are not steel belted type that Snodgrass says were construction of the tubeless replacement. I doubt many types of cars used this CN 36 215 60 15 size at time -- RS was famously the first, earlier Carrera 2.7 until change according to Snodgrass and I've a vague recollection of some Lambo?
The old front tyres I have are not tube type.

I'm too young to remember it firsthand but do recall the Chopper bike I was pedalling about that time also had had fairly groundbreaking different size front and rear tire / rims and was a tube type rear iirc -- may even have had a car valve fitting rather than puny old-school hand pump

Hope this isn't straying too far of on a tangent from original question -- some of the old reference info I posted seemed relevant?


Steve

[Dougal Cawley]

I suppose what is a reference now is that the current 215/60WR15 CN36 tyres are tubeless https://www.longstonetyres.co.uk/catalo ... gory/9110/

current thinking is that you should not drive 60 profile tyres with a tube.

As a result nobody that i know of makes an inner tube for a 60% profile tyre. (Certainly not Michelin, and we tend to sell their tubes where possible)

[911MRP]

Delete duplicate post

[911MRP]

I defer to folks like Dougal who sell and therefore are probably expert on vintage tyres etc but it seems a pity that those who have earlier design wheels on 911 these days do seem to be facing quite a dilemma. From what I gather from the threads (if there are no suitable tube type tyres or tubes of correct aspect ratio ) there might be:
- safety risks due to the insecure location of tubeless valve -- without finding someone who can do the rim machining and accept the liability?
- safety risks due to lack of rim humps if going to tubeless -- doesn't meet conditions at leat according to manufacturer's in period information apparently?
- safety risks if fitting an tube to lower profile 60 tyres -- especially those with rough or damaged interior tyre surface where it is said they can fail due to chafing and friction?

If no suitable tube type / inner tube is currently available, I hope this doesn't consign the older type wheel to "show not go use" for those owners who are concerned about these risks and/or the possibility of invalidating road insurance? While cars of certain vintage may be exempt MOT they still need to be roadworthy -- curious what the official view would be particularly in event of an accident?

Since my earlier post, a few more observations/clarifications ...

One manufacturer using tube type up to December 74 might be an typo in his book but Snodgrass notes these production running changes to both Pirelli and Dunlop tyre manufacturer changes happening in short order around the middle of December 1974. Separate entries, three in fact (see Michelin comment below) in his list of factory production running changes discuss tube to tubeless tyre change during the 74 onward Carrera 2.7 MFI impact bumper era. This seems to suggest it was actually the case dor the factory to use tubes with flat 6s and the related 7s on RS and early carrera 2.7 according whatever material he used as source references in that book.

What size are the holes in flat 6 Fuchs and the associated 7s from 73? Never measured a Fuchs stem hole diameter as used in the flat 6 (and 7 Fuchs uniquely for MY 73 on RS) but If I'm not mistaken the fairly commonly available straight rubber SAE TR13 tube valve stem is designed to fit as standard standard 0.453 (circa 11.5mm) inch diameter rim stem hole?

If so, does it mean the factory could at that time have fitted a tube with TR13 spec stem to these 6 (and 7) Fuchs that had the safety hump? Would seem from the various datapoints they did fit in fact somehow fit tubeless for a time back then -- assuming the AutoCar road-testers of 73 were correct about their specific comment of it having original factory fit tube type Pirellis on the importers then brand new RS press car. Snodgrass clearly concurs with use of tube type for a time at least when he comprehensively lists the various production tyre switch from tube type to tubeless starting around middle of December 74

Curious if this was the case at the time which overall tube 15 inch size the factory deemed acceptable for the 215 60 15 which at time was a quite a low profile tyre. Today I understand from Dougal and others who presumably know about such things that fitting tubes in low 60 aspect ratio covers is no longer considered advisable and tubes for 60 aspect ratio aren't available?

It is well known that 6 as well as 7 three prong Fuchs wheel on RS changed to later version. This happened once the remaining stock of them were used up in MY 74. The few hundred larger width 7s from surplus RS inventory being quickly consumed by impact bumper Carrera 2.7 production. The bigger surplus inventory of three prong 6s by that model and others that use this size.

Might somehow this be related to the tube to tubeless switch which presumably was around a similar time. Maybe, but seems unlikely since those RS three prong Fuchs used in MY 73 and the later replacement Fuchs that followed both have tubeless rim safety humps I assume? A conclusion further supported when Snodgrass goes on to list that Michelin 185 70 15 switched from tube to tubeless in 1975. Three different tyre manufacturers all switching from tube type to tubeless on 911 during a year or so. The latter was long after that three prong Fuchs wheel was changed to later type . It would seem that from the well regarded Snodgrass book tube type tres were in use by factory on 911 by not just two, but by three different OEM tyre suppliers -- long after the old humpless early style rims were superseded by evolving flat 6s!

Thank goodness for some owners, the later Fuchs have a safety hump and tyre companies like Pirelli and Avon support the classic market with tubeless offerings. For owners of the earlier type it also might give an option even if not period correct.

Just realised, I've I almost used my normal average annual DDK post count on a topic that doesn't particularly affect my car !

Cheers

Steve

[neilbardsley]

Cheers

Steve

Good to see you posting again!

[911MRP]

While searching for tyre info about the switch from tube to tubeless cn36, I tripped over this obscure link about CN36 in late 1960s-- which might be of general historical interest.

Post might belong in a new separate thread since it is not about the Avons with tubes referred to by o.p.

http://www.moderntiredealer.com/article ... oking-back

Article doesn't mention the size or Porsche.

My understanding is Porsche first fitted the Pirelli cinturato cn36 sometime during calendar 72 possibly 185/70 15 for model year 72 or possibly just for start of model 73?

I know for certain they were factory fitted on my 12/72 production RS new because as previously mentioned this fact is handwritten in the copy of the fahrzeug aftrag ie factory production order I've got for my chassis dating from late 72. Likely therefore amongst the earliest uses of the then new size Pirelli 215 60 VR 15 on a 911 in the UK. Among the first few handfuls seen in the U.K. Reportedly this RS homologation detail was the first ever use of different size front and rears tyre and rim on a road-car anywhere in world. From then forward, different front and rears rims and tyres became a famous 911 hallmark feature, along with a prominent rear spoiler (another 73 RS model historical first).

While I'll probably never fit the old tube type ones I have with 404 dot date even for Sunday Best static show purposes, I plan to keep them with the rest of the car's spares and original wheels for sake of this small car design historical footnote.
S

[Dougal Cawley]

I think the 911 is the first car i know of with 60% profile tyres.

i think they invented 60 profile tyres, and shortly afterwards found that inner tubes didn't work in conjunction with a 60 profile tyres, and stopped making them tube type, and also shortly afterwards the wheels all got the safety lump.

I think it is tricky for early owners that would like to keep original wheels, but they are in a tricky situation because this is part of a transitional stage of tyre production where they were finding things out as they went along.

[911MRP]

I've dug more into my various old RS sources. Another respected source Konradsheim and Gruber in book Carrera RS says that the 215/60 15 CN 36 was indeed tube type. It is mentioned as the spec for the conversion order of base RS car to M471 and 472.

To Dougal's point it seems likley RS was maybe the first car or 911 to use the back then low aspect ratio 60 profile. At least in recognised volume of approaching a 1000 car sets. The fact they were for a time tube type for that size and profile as factory fit seems to have been a bit of a surprise. Maybe it shouldn't have been as there is evidence of once been use by factory of tube type.

Curiously digging into the early original papers I have in my file for the RS majority of which are original with my own car (dealer order procedure, factory spec, English service information, sales brochure etc etc) refer to 165 tubeless Dunlop. This is because the earliest homologation examples went to the Stuttgart weight scales shod with 165 tubeless all round temporarily. Then a bit later homologation examples went to those scales with Dunlop tubeless front 165 and 185/70 rear for FIA homologation weighing purposes. Didn't keep them for use in anger just for the homologation proof of 500/1000. That is almost certainly why my car's original factory build sheet from 1972 has the typed wording Dunlops struck out and Pirelli 215 15 handwritten by the person on the build line who fitted them presumably at time of conversion order. It would've had Dunlops for the initial build, certification then conversion order went to final RS spec cn36 on 6 and 7s.

This temporary use of Dunlops for the trip to weigh scales is not to be confused with the fitting of 185 70 and 215 60 Dunlops once that company finally got tyres of the relevant size for RS to market eventually on 24 April 73. Dunlops got fitted interchangeably with CN 36 from that date forward before cars left for customer. By end of March 1973 I estimate around 980 RS had already been built according to vin lists so in practice probably very few of the first 500/1000 homologation RS would have received the new final fit Dunlop 215 60 . All Pirelli I suppose unless maybe a handful or two of RS were not converted and kept 165s. Unlikely anyone would've used 165 on the then top of range 150mph 911.

Third series RS made using much more regular production process after homologation number achieved and the complex twin order and complex build convert process probaly got a share of the newly available 215/60 Dunlops alongside the similar size Pirellis. Also the later impact 2.7. Tube type on safety humped Fuchs rims for a while, evidently.

As stated earlier based on the prior evidence on posts above and the new further confirmed data point from the Carrera RS book it seems all the Carrera RS even third series ( plus 74 Carrera 2.7) would've had tube type through until around mid December 74 after which point tubeless came in for Pirelli and Dunlop sometime during impact 74 onwards Carrera 2.7, per Snodgrass. I don't know that first-hand as was too young but Snodgrass, Autocar testers and now Carrera RS book all combined seem to show this. As does my having 404 dated old CN 36 25 60 canvas belt tube type ( not later steel belt tubeless) old curiosity survivors.

Appreciate this further post is just getting to the bottom of a finer historical specification point while I'm on a roll looking into it. Interesting that even vintage tyre specialists seem to have learned that there was apparently a period of (60%) tube type for 911 a period of a couple of years or so from calendar 72 for MY 73 to late calendar 74 even after different hump type rims were introduced. Probably evidence presented surprising because of the way tube and tubeless particularly lower profile are viewed as not a good combination today according to people who know more than me.

I realise this doesn't resolve the dilemma of earliest humpless Fuchs and lack of current tubeless tyres, safe use of tubeless valves that is the central concern and hope the information of how it once probably done by factory doesn't detract too much from those current day concerns. It hopefully sheds some light on the interim period of fitting tube type with 60 percent to Fuchs humped safety rim based on various documented sources (rather than fallible memory and opinion) that might inform.

I genuinely don't know what I'd do if I had humpless wheels today and certainly not qualified to offer advise on safety issues of it but hopefully tyre specialists and tyre company experts help those with dilemma do the right thing.

Steve

[hot66]

Thanks for the info ... Love this kind of detail, and it is interesting to hear of how things developed


Sent from my iPad using Tapatalk

[Darren65]

When I recently delivered a set of wheels to Biagio for refurb I was surprised that he doesn't offer the valve stem modification as he's been restoring Fuchs for over twenty years and thought surely this would have come up previously from those intending to fit tubeless tyres to Deep 6's?.....

.....it prompted me to ask the question if this mod was strictly needed as I've tracked tubeless Avon's on 7R's without the VSM and never had an issue.

Incidentally when having them fitted I asked the tyre guys to use stubby TR415 valves as recommended by Andy. Not something they normally used although they found a few in an old spares case....like I said, no issues since.

I reached out to Harvey Weidman who's worked on one or two sets of Fuchs and this was his reply....

I have run tubeless tires on 901 style wheels since 73. Most are confused about the "safety" bead bump. The bead bump was invented as an early run flat and doesn't have anything to do with tubeless or tube tires.
Many manufacturers used wheels with no safety bead well into the 80s.... (You have to look no further than a XJ6-XJS alloy wheel to see what I mean!)

The valve stem mod was needed when the new thinner valve stem replaced the old thicker ones. The new stem wouldn't stay in. Just not enough interference.
If you have a stem that stays in then you don't need the VSM. There may be some of the old ones around or there may be a supplier in Europe that still makes the thicker ones.
I have even seen metal stems modified to work.
If you can't find some thicker valve stems, then I can send the info for a machinist to do the VSM. Some guys have done it themselves at home.
Good luck and let me know how you make out.

Works for me

Cheers,