Alloy rims worth it?

kommando said:

Not sure why you are saying my post is BS, Avon GP tyres were racing tyres, the link I posted confirms they were racing tyres and Bob Currie when riding the first Commando production model for a road test in 1968 says they were fitted with Avon Ribbed front 3.00x19 and Avon GP rear 3.50 x 19 which confirms the info in the link I provided is correct ie they were used on Commandos. If you believe that UK 18 inch rear tyres of the day were capable of coping with the power of the Commando and Trident then you need to explain why both Norton and Triumph independently fitted 19 rims to both models at the same time with both claiming 60 BHP, all other lower HP 650's and 750's were using 18" rears. I also have a very fuzzy Earls Court info sheet for the show bikes showing in 67 they were using 18 WM3 rim, so something caused the change changed between 67 and 68 to make them go 19 on the rear.

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Your original post was Quote;” If you research the tyres of the time the only tyres capable of the high speeds and loading of the Commando and the Trident were 19 inch, 18 inch could not handle it. This is the reason for the 19 rims front and rear, the tyre technology has now moved on and the restriction forgotten.”

Yes they were originally race tyres that powered the MV and Gilera 500racing bike, these bikes were capable of 150MPH + . . . are you saying I have taken your post out of context?

The 19” rears in 1969 Nortons appears to be mostly hype. As I already posted, the faster, heavier 1969 Honda CB 750 came with a 18” rear tire.

I’ve noticed, over the years, certain myths about Nortons die hard. Some refuse to accept the laws of physics and hard empirical evidence. Example: for years Norton owners were busy changing crankshaft seals to stop oil from the crankcase entering the primary. They seemed to be convinced there was a magic seal made of unobtainium that would stop the leak. All the while ignoring the fact that the crankcase was pressurized. No way in hell they were going to hang a sissy reed valve on their manly Nortons. Another myth I see still being perpetuated is a Brembo master cylinder, regardless of size, will out perform any other brand master. It’s the size that matters, not the brand.

The same company that marketed a motorcycle with a grossly mismatched master cylinder/caliper combination marketed that same motorcycle with the claim it was so fast it needed a special 19” rear tire. That was marketing BS.

I wouldn’t call it marketing BS...

If you’re hypothesis is correct in that they created a myth that’s survived 50 years, that’s marketing GENIUS !

The theory that they fitted the same tyre front and rear to get a lower price only fits from 71 onwards when front and back were 4.10x19, it does not explain 68 to 70 as the tyres fitted front and rear were different widths so different moulds even though both 19 inch diameter, so why did they fit 19 inch rims from 68 to 70 on the rear. You can put forward that from 71 onwards they kept the 19 rear and fitted the same tyre for lower cost but why was the 19 there to allow that to happen, so it explains why they retained the 19 but not why it was there in the first place and does not explain why the 67 show bike had the WM3 18 and the 68 production had the WM2 19. They certainly did not fit a 19 inch rim in 68 on the expectation they could use the same tyre front and back in 71.

I still have the orginal sales brouchers from when I brought my 850 new the brouchers were from the factor whether or not they were sales BS but one book was just about tyre and another book was from Avon tyres, the Commando came stock with 4.10 x 19 front and back Dumlop K81 the tyre book also said the Commando was designed for 19" wheels and K81 tyres.
I found the British made K81s were the best tyres in the days as they were a sotfter compound but wore quicker, after a few years of riding the British K81s were hard to get and Dunlop K81 were made from different countries like Spain and Japan, these tyres where not as soft as the British made Dunlops they handled ok and lasted a lot longer, but after a year or so after owning my Norton from new I started to run a K81 3.50 on the front and a 4.10 on the back it made the bike turn in quicker in the corners and to this day I run the same sizes but on Avon RR, moden tyres are so much better that 40 years ago and they run higher air pressure than the old K81s and after converting my Commando to Featherbed I am still running the same size wheels and tyres and moden tyres are lower in profile as well.

Ashley

kommando said:

You can put forward that from 71 onwards they kept the 19 rear and fitted the same tyre for lower cost but why was the 19 there to allow that to happen, so it explains why they retained the 19 but not why it was there in the first place and does not explain why the 67 show bike had the WM3 18 and the 68 production had the WM2 19. They certainly did not fit a 19 inch rim in 68 on the expectation they could use the same tyre front and back in 71.

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True, and this is even odder as all Matchless roadsters went for 18" rims F/R in 1964. That includes the racey G15CSR which was heralded fastest british production bike for 1965 with a claimed top speed of 115 mph. It was shod with Avon Speedmaster tyres on a WM3x18 rim at the rear. At the front N-V changed the rim size to WM2x19 for the 1967 G15CSR model, claiming a stability gain, but I suspect it was rather an act of rationalization, as all the "genuine" Matchless roadsters had been discontunued by then and the remaining Norton roadsters (Atlas, 650SS) had 19" front wheels from the outset.
So, I think the decision to go for WM2x19 for the Commando was a result of cost cutting wrt. purchasing and stock-keeping.

-Knut