7R , no tube

[Dougieboy1]

I know this subject has been discussed many times but thought i would just check a few things:

1. Have two 68 dated 7R wheels and 2 avon CR6 215/60 tyres.

2. As i understand it, the valves to use are the TR415 which i have now ordered

3. I have read that
a) you cant use tubes with tubeless tyres - confirmed by the tyre shop yesterday - they rub on the rough inner surface of the tyre and will then be perforated over time. If you want to run tubes, you need to drive slowly although they did point our that the inside of the CR6 Avons is rnot too bad
b) Some people run a bead of weld around the rim to 'keep the tyre on'
c) the valve seats may or may not need machining.

4. My wheels are fully restored and i dont especially want to start welding a bead or machining a valve seat


So i have the following questions:
1. If i have to have the valve seat machined, i will. But it is unclear to me what machining refers to. Is it simply ensuring the valve seat is perfectly round or is it machining a lip so the 'pull in' valves have something to pop over and fit on

2. If it is the former, i.e. making sure the valve seat is perfectly round, do you bond the valve into the seat to ensure an airtight seal and to make sure you dont push the valve out of the seat when try to attach an airline.

3. If you dont bond the valve, do you simply rely on the interference fit of the valve and the seat

4. If you machine a lip for the pull in valve to pop over, is this easy to do for any machine shop?

The tyre shop i went to yesterday were trying to get me to put a tube in the tyres but given i intend to do exactly the sort of driving they said will cause failure of the tube (high speed and long distance), there doesnt seem much point. I would always be paranoid.

Thanks

Andrew

[210bhp]

I ran 7R’s on the back of my 73E without machining the valve hole nor a tube for several thousand road only miles. The key is to get the correct valve (and the correct spacers if it’s a narrow bodied car). There seems to be several ‘TR415’ valves on the market but only one type will work. It’s an interference fit and I believe (although willing to be corrected) any machining is more to provide a flat surface (rather than angled) for the valve base to seat better. If you machine the hole I’d imagine that it would need a different valve to the TR415 as the diameter would no longer be interference fit.

All this info I gleaned from Andy many years ago (including the fact that your Avon’s are unidirectional) and I’m sure he will be along soon to add his experience.

Regards
Mike

[Lightweight_911]

.
Mike's covered most of the relevant points but I'll add a couple of things ...

As you pointed out at the beginning of your post, this has been discussed 'ad infinitum' previously & you will get as many differing/conflicting suggestions as responses.

I can only give my personal opinion & only you can decide what the best solution is for you.

One of the first pieces of advice is to find yourself an 'old school' tyre fitter whom you feel happy/confident to work with - amending your avatar to give your actual location will help with this & any subsequent questions as someone familiar with your area can often offer suggestions for local 'specialists'.

I have run deep sixes & 7R's on various early cars (probably half a dozen) over the past 12 years & have never fitted a tube to any of them. Trips have included motorways/autoroutes (when unavoidable) including high speed runs to Spa & Classic Le Mans plus many 'spirited' miles & have never had any problems.

Most of the wheels did not have any valve hole modification & I've always used TR 415 'stubby' valves - which, as Mike stated, are just an interference fit - no additional 'bonding' of any sort.

I did run a couple of sets of wheels restored by Harvey W - which included his valve hole machining modification - but never noticed any difference once the tyres were fitted.

In virtually every case the tyres fitted were Avon Cr6ZZ's in 185/70 & 215/60 sizes - usually utilising 15mm spacers on the rear (typically combined with increased negative camber) - all were LWB models - but this can vary to a degree from car to car.

I also know many early 911 owners in the US who've driven without tubes in their deep sixes/7R's & covered many thousands of miles over many years - including on track - without any problems.

Darren has probably more experience of this in the UK than anyone else - & he drives his cars 'hard' - &, as far as I'm aware, he's not had any problems.

.

[PeterK]

When I rallied (non-Porsche) as a yoof, I always fitted tubes inside my tubeless tyres and never had a failure. The general logic was that if you hit a rock, the tyre might momentarily move from the bead, but wouldn't deflate. If I was really worried about abrasion of the inner tube from the tyre carcus, then today I would consider cutting & fitting an old inner tube as a sacrificial lining.
Just my 2p worth
Peter

[BILLY BEAN]

It was fairly common to fit tubes in tubeless tires many years ago when a small hole in a tubeless tire could not be satisfactorily repaired. Frowned upon now.
I have run a set of Michelin tires on deep sixes for the past six years. These are tubeless tires but fitted with an inner tube. I have covered a little over 6000 miles with speeds in excess of three figures on occasions. My reasoning is that the rims were designed for tubeless and do not have a safety hump to prevent a tire from coming off the rim in a rapid deflation event. My anecdotal experience, in the past, is that a tube can slow down deflation rate and hence provides something of an early indication that there is a puncture. I have experience in the past of a rapid deflation of a tubeless tire on a wide steel wheel with no "safety hump" which probably tempers my attitude to this topic.
As for the notion that a tubeless tire is rough inside and will chafe the tube: I have a Michelin tire from the early 1970s (original to my 911) which states that it is a "Tube Type only" and is also extremely rough on the inside particularly where the tire " plies" butt up to each other.
As has been said before you have to decide for yourself the best approach.

As regards the hole for the tubeless valve? A 1972 9x 15 Fuchs designed for a tubeless tire, has the inner and outer surfaces around the hole parallel to each other and a wall thickness of about 4mm. A current Fuchs 9 x 15 designed for tubeless also has two parallel surfaces but also a counter sink on the outer face of the valve hole which effectively reduces wall thickness to around 2.5mm. Obviously this does not answer your question and I do not have an earlier Fuchs wheel at hand for comparative purposes. However it does illustrate a change in thinking regarding the valve hole.
In the various threads on this topic no one, as far as I recall, has mentioned the possible use of " bolt in vales" which are available in various sizes. This may be a solution to ensuring the valve seats properly but I don't really know.

[inaglasshouse]

My 69 car has 7Rs on the back. It came with modern track day tyres, legal for the race series in which it used to run - Yokohama AO48s I think. Those had been raced on tubes, and I ran them on the road with tubes, with no issues.
Now using deep 6s front and rear, Pirelli CN36s, also with tubes, again without problems. These are 185/70s. Some say that 70 is the minimum profile for which a tube is appropriate.
I use Michelin tubes - bit spendy but this is probably not a good place to economise.

With that said I'm pretty convinced that tubeless is also fine. Orange car will have 7Rs on the back and I'm going to try tubeless with TR415s.

[Dougieboy1]

thanks everyone, incredibly useful.

Am going to explore the bolt in valve route which sounds like an interesting idea. will report back.

Andrew

[stuby]

thanks everyone, incredibly useful.

Am going to explore the bolt in valve route which sounds like an interesting idea. will report back.

Andrew

My advice - speak to Dougal Cawley @ Longstone Tyres.....

Stuart

[Dougieboy1]

fell at the first hurdle on the bolt in - haven been able to find any large enough to cover the hole and create air tight seal. Am now having the hole in the wheel machined to provide better fit to TR415 valve and use it with none tubed avons 215....

[Darren65]

I've read all the scaremongering on this subject but I now choose to go without any valve stem modification and without tubes.

I've driven many thousands of hard miles and had no issues which includes track days where I have literally melted the tread on my tyres and never had a problem.

The only thing I would be careful about is the TR415 valves as some seem to be narrower than others and a batch I recently purchased were a tad slim, others have been fine. Ultimately you'll know this before the tyre is fitted so you just have to make sure it's tight. As Andy said find a good experienced tyre fitter.

Incidentally the only issue I've ever had is a slight leak from a valve on a wheel with the valve stem modification! A dab of sealant solved that for a few thousand miles and all was fine at the next tyre change.

I'll obviously tell the world if I ever have a tyre come off its rim or instantly deflate but then I guess people have been running these wheels and tyres this way since the 70's so that could be some time!

Cheers,