Changing from Heavy Ruby Rear Tyres to Light

[Hugh Barnes]

Tread depth on my just fitted 4.00/4.25 x 17 Longstones is 7.5mm.

Thanks Colin....

[Robert Leigh]

On my last Ruby I used 4.50 tyres for nearly 30 years, but finally changed to 4.00 Armstrongs. The steering was transformed and I asked myself why I had not done it sooner.

[Nick Salmon]

Robert - I completely agree. For some 20 years I asked why the steering on the Ruby was SO heavy. The answer (found after about 19 years) was that 4.50 x 17 tyres are not what should be used. Using 4.00 x 17 made a world of positive difference.

[Peter Naulls]

Some very interesting feedback here.

Are Howard's tyres just for the benefit of A7OC members or does he make them more widely available? Perhaps I should contact him to see if he has a mailing list for when they crop up.

[Mike Costigan]

It would be interesting to know the actual dimensions of the Michelins that Howard sells. Back in the 1960s I ran a pair of Michelin 4.00x17s on my Opal, but they were desperately under-sized, I wouldn't have liked to run them on the back of the car.

Not a very good shot, but compare the overall diameter (from memory the width was less than the 3.50x19s I had on my RK) with the period shot of a new Ruby:


  1966 Mallory.crop (2).jpg (Size: 80.62 KB / Downloads: 247)


  1934Mk1 Ruby.jpg (Size: 189.9 KB / Downloads: 246)

[Colin Morgan]

The various tyres I have here are of quite different profiles.  Obviously the 4.50 x 17" Firestone is going to be larger, but a 4.00 x 17 Waymaster is also very different from the Longstone tyre.  The Waymaster tyre's profile is tall and thin compared with the Longstone.

Firestone 4.50 x 17                 95mm Tread Width x 100mm Depth to Wheel Rim (tread worn down - was perhaps 105mm originally?)

Waymaster 4.00 x 17              75mm Tread Width x 90mm Depth to Rim

Longstone 4.00/4.25 x 17        90mm Tread Width x 80mm Depth to Rim

[andrew34ruby]

By chance I seem to have the right tyres. I am running my Ruby on some second-hand Armstrongs, 4.00 x 17 measuring 80mm tread width and about 87mm depth to rim (would have been 90mm to rim when new I guess).

Having not driven a seven before I find it drives very well, steering is light and precise and all seems good. Speed on sweeping bends is restricted by fear. It feels as if the back end might break away.

[Colin Morgan]

Have some worn Excelsior and Armstrong tyres in the garage used on the front in the past - they have profiles somewhere between the tall and thin Waymaster and
lower and broader Longstone.

With Longstones on the rear, it is noticeable that the engine is revving a bit higher to achieve a given speed than with the old 4.50 x 17s.

The rolling resistance when cold seems a bit higher - can't push the car along as easy as when the old Firestones were on the rear. Running the Longstones at 25psi, against the Firestones at 22psi.