Early Fuchs - Valve Stem Modification

[210bhp]

Just because it hasn't happened yet doesn't mean it won't....

Best,

Philip[/QUOTE]


Very very true.

Regards
Kike

[911MRP]

I have read opinion that one consideration of using a tube is the smoothness of the interior of the tyre for use with tubeless

Since I have a full set of what appear to be circa 1974 Cinturato CN36 in storage, I have taken pictures of the inside of the tube type 215 60 15 rear and a comparison to the 185 70 15 tubeless front.


Both my vintage examples have similar diagonal ribs that while slightly raised are rounded in profile. So the vintage tube type is not totally smooth on interior on the evidence of ribs on this small old sample. However it does appear the area between these diagonal moulded ribs is a bit smoother on the tube type (lower pic Vs) the tubeless (top)




I am not qualified to say if this interior difference is a material factor in what is a safe combination of tube and tubeless but share it as a point of historical reference generally and for those who might be professionaly qualified to pronounce on such things.

For me it is moot because my old tyres pictured are in storage and while visually great nick being 40 plus years old would only ever be used for static display where finer points of Early RS authenticity to factory spec mattered. Fortunately my original rims have humps and are suitable for the tubeless Cn 36 reissue which are afiak the correct spec, Porsche approved and available in right size -- visually close with exception of tube type writing and valve area. Tyres are a consumable after all. For some like me mercifully there is no dilemma due to wheels and thanks to Pirelli and their agents support of classics. I can see it might be a concern for others however hence sharing what I can from my old parts and old papers.

I don't have access to the interior surface of their current CN36 tubeless reissue to compare to the old ones pictured above nor do I know details of how their modern ones vary in constructio, sidewall stiffness, compound and so forth.

Since I have these old references to hand they might give some context to how it was back in 70s even if not conclusive on the modern dilemma on Avon's/humpless rims/valve seat etc

More generally the discussion made me curious:
If some vintage Porsche rims were not designed tubeless so have questions on sutability these days 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 DDK affect the use of the earlier humpless rims for those who want to use them for the street without concerns on safety ...
Or possibly in worst case scenario could there be insurance implications - what is the position re road risk insurance if a tubeless tyre is used on a non-hump old rim when several major tyre companies clearly have in past printed these "conditions"?
What is the position with FIA or other scrutineers on using these old rims in race or track day applications with or without tubes?

Steve

[911MRP]

UPDATE

Continental are a large tyre manufacturer. Fourth largest in world I believe "Continental's revenue from its tire division amounted to around 12.6 billion U.S. dollars in the 2017 fiscal year."

They have a publication from '13/14 on wheel and tyre basics. In it they are clear particularly in the final sentence :
"There are several rim contours:
1. Drop centre rim (normal)
2. Hump rim = safety contour
3. Ledge rim = safety contour
Thanks to slight curvatures, rims 2. and 3. guarantee the tubeless tyre sits firmly on the rim.
Such rims are absolutely essential for tubeless radial tyres."

To get the full context see page 29 in link
https://blobs.continental-tires.com/...asics-data.pdf

There's even more recent and further detail published for '17/18 from Continental:
"*) Safety shoulders (e. g. hump) are prescribed for tubeless radial car tyres."
In addition to being recent, it seems to be more technical beyond the basics and also claims to have looked into the standards: "The technical data and other details on tyres and accessories have been compiled to reflect as exactly and completely as possible the current state of development and are based on ETRTO, ISO, WdK and DIN. " See page 101 for comments rims:
https://blobs.continental-tires.com/...abook-data.pdf

As previously stated I'm not a tyre or rim expert so just sharing this from a large tyre company as input to the thread as the date of it is more recent than the publications shared for historic interest. Whether what continental published five years' or even more recently ago is still current, I don't know so viewpoints in link ought to be double checked with a current professionally qualified expert in the relevant geography.

I don't have the old style Fuchs rim that predate the later version rim with humps and frankly don't know what I'd do if I faced the dilemma.

Main thing is folks are safe and classics comply with road regulations when it comes to safety critical things such tyres and wheel rims etc.

Steve

[endo911rs]

I just had a deep 6 suddenly deflate. Luckily the car was parked but it went flat, flat, flat! There was no way I could air it back up. The tire store said it was because of the valve stem not seating correctly on the contour of the wheel. They installed tubes and said everything should be fine. Note...this was with a set of recently restored deep sixes and the Avon 185's.

If there is a specification on the "valve seat modification", I'd like to know how to do that.

[Darren65]

I've had one wheel slowly lose air pressure even with a wheel with the valve stem modification where one valve didn't sit quite right. I initially thought it was a puncture but once I found the cause you could hear air escaping when moving the valve slightly to one side.....have to admit I just used a bit of sealer at the base of the valve which solved the issue and carried on until the next tire change.

I've also used early wheels on track without the valve stem modification and had no issues, tires are still fine and inflated now. Obviously the main thing is to make sure the valve is seated correctly in the rim.....in the UK I used stubby TR415 valves which I believe are wider than newer valves and these have worked perfectly.

Cheers,

[911MRP]

By coincidence when discussing plans and preparations for heading for for CLM today in a small classic group it was mentioned by a friend who sometimes posts here that he was once told it was illegal for a tyre repairer to use a tube in France. Something he had learned the hard way with his classic, apparently.

If so does this mean that French owners doesn't have the option of considering a tube when trying to decide what to do. Seem to recall Dougal saying french company Michelin the inventors of radials are good quality tubes in his experience -- seems ironic if France don't permit tube. Rules might vary by country.

Is a tube better than trusting a dab of sealant on a known leaking valve - I'm not qualified to know?

[Arne]

I suspect it is illegal in France to repair a leaking tubeless tire/tyre by fitting a tube. If the tire or rim in question is in fact not tubeless approved, the tubes are probably fine.

[Harvey Weidman]

I have looked at this issue carefully since Porsche went to tubeless tires. The early 6s had tubes and we at the dealership put them back in when changing tires. As soon as the Michelin XWX were available in tubeless, we installed them without tubes. We found that the 415 valve stem worked and I used them for decades at my shop. About 10 years ago, the 415 started to be made thinner above the groove. That is the area that held the old 415 in the tube type hole. After a couple of iterations, the 415 was so thin it fell out when inflating or pulled all the way through the hole.
About that time I received all sorts of different attempts at solving the issue. From custom made metal stems to long truck version of the 415. Then, a set of wheels came in that had the wheel stem hole machined to actually fit the 415.
The inside of the hole was machined to 90 degrees and bored to 5/8 round. The original tube hole is not very round and not 5/8 but the early 415 made up for that with all the extra rubber.
Then the hole was machined from the face a little larger to make a step so the 415 would snap in. I called the owner to ask if he was willing to do that modification to my wheels and he wasn't interested. So I had the tooling made and we machine all the early wheels for the snap in 415.

[Harvey Weidman]

About the "safety bead" or hump. I was interested in it also. I looked at many modern wheels that had no bead and measured them. The early Fuchs was the same. The very early wheel that has the different angle was on an old steel wheel as far as I could find. I searched the history of the beads and the article that I found was well before tubeless tires were in use. The bead was an early attempt at a runflat. The early tires seemed to blow out frequently and this was designed to help with the control of the car. Auto manufacturers and some aftermarket wheel manufacturers didn't use the safety bead. I always point to the 80s XJ6. They didn't have the bead as well as others. The conclusion that I came up with is, the safety bead is not necessary nor does it help keep a fully inflated tire on the wheel.
H

[fourteenten]

I just pulled a 5/73 dated Fuchs 6J x 15 out of storage and clean it up a but. The tire is Michelin XWX with tube, probably 1972 dated (?). Funny thing is that the inter tube must be deflated, I can push the valve inside but the tire itself is still inflated! Or it is just hard and dry but feels like there is a air inside.

Cees