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Wheel rim size confusion

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Hi. Before I bought my 1960 Dommie 99 I bought John Bacon’s book ‘Norton  Twins‘. I needed new wheels building so I looked in the data section at the back of the book, where it states that wheel rims are WM2 size. So I had my wheels rebuilt with WM2 rims. Some time later I bought John Bacon’s book ‘Restoring Norton Twins’. On flicking through it tonight I notice that he says wheel rims are WM1 size. Looking at the Avon Tyres web site, it would appear that the 3.25 and 3.5 inch versions of Speedmaster, Safety Mileage and Roadrider-2 tyres all require a rim size of between 1.85 inches and 2.5 inches (WM1 size). The size of a WM2 rim is 2.72 inches. Am I ‘stuffed’? It will be very annoying to find out that John Bacon sent me down the wrong path - how can one ‘expert’ quote two different sizes for the rims?

Opinions please.

Thanks

Regards

Tony

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I have WM2 replacement rims on my 60  99  for the last 25 years . With  300  x19 Avon ribbed front  and 350 Avon SM rear ,  Anything more modern  is wider and  may not clear on some bikes. .I have come across WM1 rims  and  while may work with  a 275 or 300 front  ,is no use for anything bigger. You need to check the rims are central in forks and rear  suspension units.That usually works well enough, although the wheels may be slightly out of line. Getting them perfectly in line and central is good but can be a bit of a faff. Due to weight distribution perfectly central does not always handle perfectly !. So if it feels good ,it is good.

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Just make sure you are checking Bacon's properly. 

The early Model 7's had Wm 1 rims fitted with 3.00 x 21" tyres. These changed to WM2 rims and changed to 19" tyres during1953.

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Not sure where you got your info from, but-

WM1 is 1.65 inches wide

WM2 is 1.85 inches wide

WM3 is 2.15 inches wide

I'm sure your bike would have had WM2 originally. WM1 is very narrow and usually only used on smaller bikes with skinny tyres. Relax, you will be fine with WM2.

Ian

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Thanks Robert. That’s reassuring. How does the bike handle on the ‘old style’ tyres? I’ve never ridden a bike on Speedmaster/Safety Mileage tyres - does the bike feel stable when leaned into corners? They just look a bit square compared to modern tyres. It looks like the rear wheel will be perched on the corner of the tread when leaned over - that concerns me as the contact Mitch must be very small. How have you found them overall?

Thanks

Regards

Tony

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The bike handles the best of all the bikes I have ridden.  The SM rear  has very deep sidewalls and runs at a lower pressure than  you would consider right. the sidewalls are designed to flex and allow the tread to stay on the road  ,quite different to the modern round profile tyres ,works well as long as you don't overpressure or try for knee down. When they do let go on slipery greasy roads you can feel it slide and correct it like Rossi !!, absolutely NO highside .I also get to  ride a VTR 1000 Firestorm ,an MT10 and a BMW 1200. I still prefer the 99. I would be happy to use modern rubber but no room on my bike . Interestingly the late Atlas on modern rubber feels like a tank in comparison ,not sure why, work in progress.

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John is not incorrect with his mention of a 1.60" inside well width. The WM 1 Rims when made in alloy often lost that 0.05". The Devon Wheel Company used to offer Flangeless WM1 Rims  with 1.65" and Flanged WM1 Rims with 1.60" wells.

The attachments may be of use to Tony Wood as the pages cover a range of points relating to Norton Wheels, Tyres and Rims.

 

I ran my 1959 '99' on Safety Mileage front and rear as it had previously been used with a sidecar and I couldn't afford to buy new tyres!  I spent money on new pistons, valve guides, and other such trivial stuff!

Now here's the REALLY scary part!  I rode the bike to its limits, which are only down to having the driver's footrests scraping the tarmac - that improved the ground clearance after a while by chamfering the big chrome dome nuts and slightly bending the footrest bar. On dry tarmac or concrete you couldn't lose it!  On oily or greasy and wet roads I came off twice at low speeds, but my Britax Double "D" crash bars saved the bike from any significant injury, although I did get a hole at the hip in my trousers!  Luckily one of our beautiful office typists was able to sew it up whilst I was still wearing them - thanks Val!

I can't believe that any other bike could handle as well as the Featherbed, which didn't care what tyres it wore.

 

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"I can't believe that any other bike could handle as well as the Featherbed, which didn't care what tyres it wore."

I take it that you haven't ridden anything made since around 1985 then (or earlier if Italian)

Featherbeds do indeed handle well and goes around corners pretty well, and considering that the design is 70 years old it is amazing, but any modern (2000 on) 600 would run rings around a Dommi nowadays. Evolution and all that...

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I have a 500cc single with a Featherbed frame made in 1955 which runs very well on TT 100s and they look right for the machine.  The rim size is 19 inch WM2 front and rear.  There is just enough clearance between the tyre and the swinging arm.  I could have fitted Avon Roadrider Mk.IIs but whilst they would have [probably] produced even better handling they would not have looked correct on the machine.  I am using the same size as a Commando, 3.60 / 19 front and 4.10 / 19 rear at 28 psi front and 30 psi rear.  I have Avons in the sizes 90/90 front and 100/90 rear on my 1978 Commando and both look slimmer and skinnier than the Dunlops.  Tyres and pressures are always very subjective issues; Phil Read's son, Graham, ran rings around me on his Suzuki GSX1100 but he ran his tyres at 12 psi front and not much more in the rear [usually on race tyres marked Not For Road Use].  He ran the bike on Jersey plates and whenever he was stopped for speeding [which wasn't very often because they couldn't catch him] he always got off by saying that he was flying back to Jersey the next day.  On the other hand, I was riding a 100,000 mile CX500...

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Thanks everyone.  Philip, thanks for those files - really useful.

Having read all of the above, I think I’ll go for a 3.25 Speedmaster on the front and a 3.5 Safety Mileage on the rear. Wheelhouse Tyres do pairs deals that look reasonably priced. Thanks again to you all

Regards

Tony

A rather pointless response George as my comment stands alone.  My point is about the tyres being both the square-section Safety Mileage, which shouldn't handle well. Of course a modern bike should "run rings" around a Dommie - that's what people would expect when they pay a King's Ransom for a bike - or any vehicle come to that.  Try them with Safety Mileage front and rear and I think you would get a shock!

At 74 I have absolutely no interest in trying any bike made since about 1975!  Ostrich head firmly in sand!

 

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