Tyre recommendations

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hot66
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Tyre recommendations

Post by hot66 »

Why 185/65 rather than correct 185/70 or equivalent diameter 195/65

I get your obsession with parking speed weight, but how much time do you spend parking your car ?

Btw, my steering is fine at parking speeds .Set up can effect this more than tyres

Also it’s a comfier ride than my 964
James

1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster

Its not how fast you go, but how you go fast ;)
IanM
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Re: Tyre recommendations

Post by IanM »

Lightweight_911 wrote: Mon Jan 02, 2023 11:59 am .

When you have different width wheels front & rear it's normal practice to reduce the aspect ratio of the rear tyres so that the overall diameter remains roughly the same - a 205/65 x 15 tyre will be approx 1in larger in diameter than a 185/65 x 15 tyre ...

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Andy,
205/65 is only 6mm (1/4") taller than the Michelin XWX 185/70, so this will not affect the speedo reading.

Yes 185/65 is an inch shorter in height than the 205, which might make the car look a little odd, but does the Porsche 934 pictured below look odd?

.
934-side.jpg
.
The only reason that all 4 tyres were of the same size was because of the German law prior to 1973. In later years, Porsche carried on with same rolling diameter front and rear purely for aesthetics reasons on production cars. This did not matter for works race cars.
Last edited by IanM on Mon Jan 02, 2023 5:38 pm, edited 1 time in total.
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Re: Tyre recommendations

Post by IanM »

hot66 wrote: Mon Jan 02, 2023 12:15 pm Why 185/65 rather than correct 185/70
There is no tyre manufacturer that makes both 185/70 and 205/65 of the same tread.

or equivalent diameter 195/65
Well, my thinking is why spend a fortune for 7R wheels if the difference in tyre width between front and rear is only 1cm? It doesn't make financial sense.
Might as well forget about 7R wheels and buy either 185/70 or 195/65 for all 4 corners.

Set up can effect this more than tyres
Yes, I suppose you're right.
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Re: Tyre recommendations

Post by IanM »

Lightweight_911 wrote: Wed Dec 28, 2022 9:28 am .

CN36 - overall width 196mm & overall weight 8 kg
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Andy,
I assume you got this info from the Longstone website? It's a typo. They have got the weight of the tyre wrong way round between 175/70R15 and 185/70R15.
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Re: Tyre recommendations

Post by IanM »

Lightweight_911 wrote: Mon Jan 02, 2023 11:59 am .

When you have different width wheels front & rear it's normal practice to reduce the aspect ratio of the rear tyres so that the overall diameter remains roughly the same - a 205/65 x 15 tyre will be approx 1in larger in diameter than a 185/65 x 15 tyre ...

.
Andy, Were you suggesting 205/60? The aspect ratio of 60 is too low for an inner tube.

More info:
https://www.longstonetyres.co.uk/classi ... tubes.html
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Re: Tyre recommendations

Post by Lightweight_911 »

.

I know it's a bone of contention but I ran 7R's without tubes on various early 911's (along with countless other owners) for 10+ years & thousands of miles without any problems ...

.
Andy

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- subtracting weight makes you faster everywhere”
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Re: Tyre recommendations

Post by 911hillclimber »

Sorry in advance!
Why do these early cars with these rims need tubes?
Is it because there is no bead lip inside the rim?
73T 911 Coupe, road/hillclimber 3.2L
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Re: Tyre recommendations

Post by IanM »

.

A couple of quotes from Roland Kunz:

Humpless

Hello

Early Fuchs rims are not designed to be used without tubes, Porsche does not allow them to be used without them. The tire sits very good but under hard cornering or if your car spinns off the tire can losse the pressure in a sudden.

If you use tubes then only the right size from the right companys ( Dunlop, Pirelli, Metzler, Conti ). X-brand tubes had some trouble reports, yet maybe the monting from the tube/tire was the bigger problem.

You can weld on the safety humps and rework the valve seat area to accept normal long rubber steems like also used from mercedes benz.

grüsse

Humps

Hello

The tube Fuchs rims are without hump but they hold the tire much better then steel rims. If you ask a local tire guy to mount tires on humpless Fuchs and he knows his job he will tell you that those are requiereing hard work to come over the edge and to be beaded correct.

When Porsche developed the Fuchs rims the saefty hump was in the development but Porsche allready knew from tests on the steel rims ( Mr. Bott was the responsible engeneer ) that under hard use the tire can slip from the bed. This was a problem only occuring with the then new steel radial tires ( Nyloncord was the normal tire ).

Just recal the first tire generations where 155/165mm wide

The Fuchs rims where designed to support the then new X radials to the best and they grip the tire toe much better then a steel rim yet they still have not the saefty hump wich does not allow to use them without tube on puplic roads. Porsche just didn´t liked to be responsible for the chance that the wrong type tire was mountet bad or wrong or mechanics did shortcuts to mount the tires. ( like said it needs more time & force then on humped rims.

Im Germany there was much talk about banning tubes in HR/VR ratet tires and today the law is that you have to use tubes with old tiresystems despite there speed rating but you are not allowed to use tubes in newer tire systems ( Hump rims ).

However like mentoned before tubes are not equal and simple tubes used in VW´s do fit into the Porsche but are not as safe as the original used tubes from the correct brands.

If you compare them direct you well see and feel the difference.

Grüsse
Link:
https://www.early911sregistry.org/forum ... -six-wheel
911hillclimber
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Re: Tyre recommendations

Post by 911hillclimber »

Thought as much, thank you for those details.
Think today the safety head is called the J rim design
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Lola t 492 / 3.2 hillclimb racer
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Re: Tyre recommendations

Post by IanM »

.
Just saw this.
215tube.jpg
215tube2.jpg

Link
https://www.early911sregistry.org/forum ... tion/page3

Looks like 215/60 can be fitted with an inner tube, after all.

Even the interior of the new CN36 looks smooth.
IMG_20180610_130126.jpg
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Re: Tyre recommendations

Post by Dougal Cawley »

gridgway wrote: Wed Dec 21, 2022 3:57 pm So apart from how they look, what are the compromises? I think you need to do a better sales pitch for your CN36s than that!
the bit about the tread being too flat and the diameter being wrong are pretty strong elements.

It is alround the wrong shape, size and structure.

There are some pretty strong misconceptions about tyres.
  • the tread pattern is important - well it does count a little bit. but it is more about moving water, rolling resistance, noise and fashion.
  • the compound is what determins grip - the carcass and the way it presents that compound to the road is utterly critical
  • width of footprint determins grip - actually it is weather the chassis can keep that tread pattern on the road that determins that grip in the corners
  • modern tyres are better than old tyre designs - only on a modern car. on an old car the above doesn't come into play
Modern fangled tyres like the ones on your car are clever because the amount of foot print a tyre of that width presents to the road on a modern car. However they were designed to be fitted to a much more modern chassis with loads of adverse camber that increases relative to how much the suspension travels and heaps of caster on the steering that would make your cars steering dreadful, but on a modern car is overcome by clever power steering. there are some dramatic differences between your chassis and that of a modern car, and your car drives nicer on a tyre that is suited to it. not bought just because it is cheap. (oops sorry that was a little harsh).
Longstone tyres
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Re: Tyre recommendations

Post by Dougal Cawley »

Image
Longstone tyres
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Re: Tyre recommendations

Post by Dougal Cawley »

I dont think anyone is going to critisize the wet performance of the CN36 in the wet (let alone any other circumstance

Image

These are stounding scores for any tyre, but for an old tyre to perform that amazingly is fantastic. A bit of a kick in the nuts on rolling resistence, but i dont think they considered that when they designed this tyre.

So here is the full article translated into English.

https://scontent-lcy1-2.xx.fbcdn.net/v/ ... e=63E64959
Longstone tyres
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Re: Tyre recommendations

Post by IanM »

Dougal Cawley wrote: Wed Jan 11, 2023 4:27 pm
So here is the full article translated into English.

https://scontent-lcy1-2.xx.fbcdn.net/v/ ... e=63E64959
It's a pity that Dunlop Sport Classic was not able to take part in that contest as the tyre didn't exist in 2016.
dunlop-sport-classic-01_1440x655c.jpg
dunlop-classic-tyres.jpg
.
https://www.vintagetyres.com/dunlop-spo ... -70r15-89v
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Re: Tyre recommendations

Post by 911hillclimber »

And £319 plus fitting EACH.

This is all in my mind Horses for Courses.

I don't loon around on the road in any car I have, esp the 911, I just want a good tyre in the wet, so a Targa close to the limit is not relevant to me.

Thus the 'cheap' tyres are attractive as i do about 2000 miles / year of simple road driving.
My thoughts are toward the tyre I feel would be well made and under £80 each, easy to replace in case of a bad puncture etc, hence the Dunlop.
My local tyre place stocks them in modern sizes, my size for the 911 in a day, about 4 tyres for £319.

This all works for me.

I marshaled at the Greatworth Classics autojumble this year and set out in the 911 in pouring rain and pitch black with head lamps that seemed not to be on at all.
The conditions were the worst I have ever driven in.
Much of the motorway had lost its white line markings and I found myself heading right at the sharp end of the armco where a take-off slip road was. Quick avoidance was needed and the car simply swerved instantly back to the inside lane of the M40 and once my heart rate had settled, all continued.
The Dunlops were great, the car would/could have been speared by the armco and in flames and maybe I would not be here today.

This worked for me!
73T 911 Coupe, road/hillclimber 3.2L
Lola t 492 / 3.2 hillclimb racer
Boxster 987 Gen II 2.9
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