Early Fuchs - Valve Stem Modification

[Darren65]

I've just sent a set of deep 6 and 7R's for refurbishment to Biagio Chrzanowski in the UK. When Harvey did my last set of deep 6 and his widened 7R's he suggested having the valve stem modification machined to run tubeless tyres.

I've since used 7R's on the track without the modification using regular tubeless Avon's without any issue.

Biagio doesn't normally modify the stem on early Fuchs and I imagine a number of people use these wheels without any modification and without inner tubes.

I'll be using tubeless Avons CR6ZZ and thinking I won't bother with the modification this time around but would appreciate your thoughts and experiences?.....



Cheers,

[RennTyp]

Darren, there's quite a bit on DDK about this dilemma. I run Avons on my 6s and 7s, including using them for the Modena Cento Ore (i.e. properly "in battle"). I opted to run them with inner tubes. Main reasons were that i) I couldn't find anyone in the UK who had experience of machining the valve holes on original Fuchs rims and didn't want them learning for the first time on mine and ii) the early wheels don't have a safety bead for tubeless tyres anyway so there would still be an element of risk. I consulted with the guys at BMTR who are the main distributor for Avon in the UK and they didn't think there would be an issue with putting an inner tube in a tubeless tyre of 70 profile or more. I run 185/70 front and back. One thing I discovered is that the stiff sidewall of the Avon makes them a devil to get onto a 7" wheel. I tried two different fitters who both failed. Went back to BMTR who as you might expect have more experience than anyone else and they managed to fit them - albeit with two goes at one of the 7s when the inner tube was holed at the first attempt. I hear that the 2.0L Cup has adopted the Avon as its control tyre so there may now be more people to ask about their experience of tube vs tubeless with these tyres. However a lot of racers use a modern cast Fuchs replica or an original flat 6 wheel precisely because they have the safety bead.

[Darren65]

Thanks for the reply. I'm obviously aware of the discussions on DDK regarding whether tubes should be used or not although I'm now on my third set of Avons which have all been tubeless and I've never had an issue and will continue using them this way. I'm running 185/70 fronts and 215/60 rears.

I'm more interested as to whether people feel the valve stem modification is truly needed?....

.....as I mentioned I've used 7R's on track without the mod and this has been fine so inclined not to bother with the set I'm refurbishing unless there are compelling reasons why I really should?

Cheers,

[911MRP]

Hi Darren

Hope all is well.

I am not qualified to comment on the valve stem modification question. Nor am I a tyre and wheel qualified expert.

I have previously posted this exerpt from an old Pirelli or Dunlop booklet which might be relevant to the broader question of tubeless or tubed tyres with old humped or plain rims mentioned in the discussion.



This snippet above is from an early 70s booklet when tubeless and radials were relatively new to the market so although of historical interest it may not reflect latest knowledge or current regulatory standards so I recommend getting qualified expert advice on the overall safety critical tyre, rim, tube( less) compatibility point particularly if it is something that might affect insurance too.

Having said that this was written by a leading tyre manufacturer / Porsche factory tyre supplier around the time the wheels found on early 911 would have been new. The author appears very clear on the point that tubeless radials do need a hump to be correctly located for cornering even when inflated at the correct pressure.

Having reread it I find interesting advice from an official albeit period OEM supplier source since hump and no hump with tubeless is not a topic I recall seeing discussed much. I don't know how much thought enthusiastic amateur owners of classics cars give to this matter of the normally available tubeless tyre and old humbles rim compatibility these days?

It is my understanding that Porsche introduced the self adhesive valve stem support to wider rear tyres around the time the 215 60 15 tubed switched from tube to tubeless on 74 Carrera 2.7. If this is a correct understanding then that might point to there being some valve seating or other valve considerations driving this innovation that are worth investigating with those who are qualified on the topic.

All the best


Steve

[210bhp]

FWIW Darren I have also never had any issues running deep sixes or 7R’s without a tube and without the valve stem modification.

I phoned Biagio two weeks ago to arrange a Refurb of four of my deep sixes and he said he was snowed under with work and had a weak wrist from a backlog he was trying to get through and couldn’t take my wheels at the moment. You must have crossed his palm with silver. I notice he is finishing the nut recesses like Harvey now.

Regards
Mike

[RennTyp]

I'm more interested as to whether people feel the valve stem modification is truly needed?....

.....as I mentioned I've used 7R's on track without the mod and this has been fine so inclined not to bother with the set I'm refurbishing unless there are compelling reasons why I really should?

Cheers,

Darren, I'd be worried about using tubeless tyres without the valve hole mod. The valves don't seat securely otherwise and it wouldn't take much of a knock to push them inside the tyre and cause a sudden deflation. Just because it hasn't happened yet doesn't mean it won't....

Best,

Philip

[911MRP]

Darren

The humped rim shape point made me curious so I dug out a second tyre manufacturer reference from 1974 which is also clear on this point.

It is not directly to the valve stem modifiication question so moved it to my earlier thread
http://www.early911sregistry.org/for...s-original-fit

It does however touch on things that might be more generally relevant if fitting tubeless tyres to some an old wheel rim shapes. Photos left here for information.

HtH

Steve

[Darren65]

FWIW Darren I have also never had any issues running deep sixes or 7R’s without a tube and without the valve stem modification.

I phoned Biagio two weeks ago to arrange a Refurb of four of my deep sixes and he said he was snowed under with work and had a weak wrist from a backlog he was trying to get through and couldn’t take my wheels at the moment. You must have crossed his palm with silver. I notice he is finishing the nut recesses like Harvey now.

Regards
Mike

Thanks Mike,

Yes he mentioned to me he's had a sudden influx of work although I luckily booked mine to be done some time ago. Worth the wait, his work is exceptional

[Darren65]

Steve, Philip, thank you for your input.....

.....I guess I'll be living life on the ragged edge but then I never drive fast anyway!

I did have a few photos Harvey sent me of the valve stem machining work but unable to locate them.....if anyone has those photos please can you post?

Cheers,

[fourteenten]

The old literature talks about soft side walls, Darren mentioned stiff side walls so that might be a big difference in risk.

Cees