650 SS tyre size

There is adequate room between tyre and chainguard on my 1964 cycle.

As per Avon, the 4.10 is equivalent, it appears you may be OK.

Yes Bob - that'll be fine on a WM2 rim.  I'm using Avon Roadrunner rear on my Mercury. Cheers,  Howard

My 1963 had 100/90 AM18.  It measures 109mm wide.  It is just post card thickness from the mudguard inside the swing arm.  But most rear gears are trimmed off just above the swing arm.  So if inflates not more than 110 wide, it should fit. Just.  Depending on rim offset. And wheel alignment.

When I raced my 99 (don't laugh, it went pretty well) I had a 4.10 x19 TT100 on the back. I managed to scrub the tread off the sidewalls and still had plenty on the crown - a never to be repeated feat. 

Heyup Bob - The swinging arm had plenty of room even on my Atlas, as supplied by the factory, with an Avon SM 4.00 X 18 rear tyre.  Are you sure  that you don't have a WM3 rim ?  4.00 X 18 in old money equates to 4.25 / 85 X 18 in more modern terms.  A 3.50 X 19 will be 4.10 X 19 and a 3.25 X 19 equates to 3.60 X 19.  So shorten your rear chaincase screws or get a factory fit rear chainguard.  Is your chaincase a fully-enclosed type, perhaps ?     Cheers HR

Not quite correct Bob - the 4.10 measurement is made in a different place to the 3.50 measurement.  I have an old 3.50 X 19 K81 Dunlop and it is identical in all measurements to a 4.10 X 19 K81 (TT100).  Check your alignment again,  regards, Howard

Just a couple of years ago, my local VMCC had a run out to visit the Fekked Exhaust and Silencer makers. In their accessories shop was no less than 3 Dunlop K81 tyres for sale. All of which were suitable for the back end of a Dominator.

The choice being 3.50 x 19"........4.10 x 19" ........100/90 x 19".......Pay your money and take your pick the assistant said.   

25 years ago, I put a 110/90 x 18" Roadrunner on the back wheel of my Atlas and rode down to Rome and back. The clearance inside the swinging arm was tight but a worn rear chain meant that the wheel axle was further back than usual just leaving few threads on the end of each adjuster. This was interesting as a 4.25 x 18" TT100 needed the side tread blocks thinning down to run in the same position.

At roughly the same time, I had a small collection of partly used TT100s in my shed. These being manufactured in the the UK, Fance, USA, Italy and Japan. The last had a strange grey colour appearance which apparently was due to being made from synthetic rubber.