73T tyres!

[911hillclimber]

Yep, this could be boring for sure, but I'm a bit lost and need some thoughts.
I have a 911T, 73 with 7" cookies.
Currently have Dunlop Blu Sports on and cannot get rid of a wheel 'balance' wobble at precisely 70 mph.
The car is in great running condition, and these tyres went on because they were cheap and the car is not thrashed any more.

I've swopped wheels round with the spare etc all to no avail, all 5 are from the same batch, fitted at the same time and balanced to 'Zero' on the machine.
Pressures are 28/32 psi and it runs smoothly just below 70 down to stop. You can quickly drive through the 70 wobble to smooth, but at times at a sustained '75' the wobble will come and go in a continuous predictable cycle of around 5 to 6 seconds.

The tyres are 185/65/15 and are now 3 years old and 2000 miles in.
The car runs hands-free arrow straight.

So, assuming the tyres are un true as opposed to un balanced, I am considering a total change to another tyre.

I will not pay the silly prices for 'real' period tyres, the car is not used enough to justify £1000+ a set (of 4)

I feel OK with 70/80 each.

Any thoughts please.

Kumho's come to mind.

[url=https://postimages.org/]

[Nine One One]

These get a good review and are a lot cheaper elsewhere

https://www.halfordsautocentres.com/tyr ... r15-92t-xl

Ian

[911hillclimber]

I looked at them last night, but discounted them as they seem winter tyre biased?
Good make though!
Thank you.

[Lightweight_911]

.
Out of interest, why did you opt for that odd size ?

I think you'd have more choice in 195/65 which is almost identical in overall diameter to the original size of 185/70 ...

[911hillclimber]

It was 3 years ago, and the Blu Response Sport was fresh to the market, but the rolling dia was close to the rears of a 3.2's rear.
I have a 3.2 engine and box from a 3.2 super sport in this car, and wanted the speedo to read reasonably correct.

Not wedded to this size, but nothing bigger due to body clearance.
Current tyres clear.

I like the thought of AVONs.
I hope to borrow a pair of Fuchs with blackly tyres before buying a set of something to rule out the tyres in the chase to sort the wobble.

The cookies once had Kumho V70 205x50 profile and ran perfectly, so I feel the wheels are true.

The Dulops were well rated for wet weather grip and noise level, wet grip was a key decision.

[fcd911]

I hope to borrow a pair of Fuchs with blackly tyres before buying a set of something to rule out the tyres in the chase to sort the wobble..

And they are still available - sat at the back of my garage waiting for that test!

John

[911hillclimber]

Will give a call John to pop round and test drive on the M54.
Got to get this fixed.
Car runs at its best at '70' mph.
G.

[jb]

Old info but my input still valid
I think I got continentals because I asked Gary71 what he used
viewtopic.php?f=1&t=59131&hilit=pirelli&start=0

[kitesurfer2]

Just a thought, I used to have a 1972 T with 7" Cookie cutters all round and it was transformed by fitting 6" wheels to the front.

[Berny]

I fitted Avon ZT7 195 x 65 x 15 to my targa before going to Classic le mans last year very happy with them, fitted and balanced myself and cost about £140.00 for the set cant be bad ! Berny.

[911hillclimber]

Went to Oulton Park today, 60+ miles, some at 70 ish.

Before this, and irritated by the last wheel change which, if anything, made it worse, I changed the NS front wheel having changed the OS front.
Today was the first time I've driven it and the wobble has GONE.

Before I rejoice, I'll do a few more runs to triple check but it did not wobble at all, just the usual 911 steering movements over the surface of the road.

I had thought of 6" on the front having a 6" cookie in the shed, needed another, refurbish them and 2 narrower tyres, so pushed that back onto the back burner a few months ago, BUT the car has driven wobble-free with these 7" wheels all round for about 6 years on 2 sets of Kumho V70 tyres (50 profile), so things should be good.

I will look at the tyre suggestions, but will try FCD's wheels first.

Was certainly nice to cruise back at various speeds including several miles roaming between 65 and '70ish' to see if sustained speed would induce the wobble, but not so.

Tomorrow I will put the wheel in the boot (that came off the NSF) and clock the rim and the tyre for truth.

[911hillclimber]

Checked the errant wheel for truth today.

The rim is 1mm out of true laterally, ok on concentricity, the tyre is 2mm out on lateral and concentricity both in the one 'area', about 70/90 degrees of the circumference.
This is obviously with wheel jacked up, 28 psi.
Hope you can see the yellow crayon marks in these pics.

The second pic shows the ton of balance weights used to true the wheel. The other 4 wheels are much the same!

These seem ok to me, but are they excessive?

[Dougal Cawley]

Why not fit a proper tyre?

It will handle better.

a modern 185/65R15 will give you too wide foot print. and a carcass shape that is suited to a totally different car.Fitting 195/65r15 will make it even worse.

Fit a proper high quality tyre. and fit a carcass that is designed to make your car handle well https://www.longstonetyres.co.uk/classi ... -r-15.html

In fact, now i come to think about it, a 911T from 1973 should fit 165R15 CN36 https://www.longstonetyres.co.uk/classi ... -r-15.html

why not fit a proper tyre that will make it handle well.

[hot66]

hes on 7" wide rims dougal so the standard 911t info doesnt stand. I also think a 1973 2.4T did come with 185/70 on a 6" wide rim

[Dougal Cawley]

OK so the 7" rim means a 165 would not really be right.

The point is that the steering is suited to a 165R15 tyre with a nice rounded shoulder so fitting a proper period 185/70R15, will make the steering heavier but still progressive.

However fitting a modern 185/65R15 with its wider foot print will make the steering quite a bit heavier. But more importantly the modern carcass willl iradicate the progressiveness of the handling and make the car have handling more like the handling that these early 911 cars earned their reputation for; where it grips, grips, grips then lets go violently, because the inside of the tyre has lifted off the road, because of its inappropriate carcass.

Of course 195/65R15 will be worse.

It is a fabb little car don't spoil it to save a few quid

next time you need an engine build, why not save a few quid and fit a Beetle engine?