Coming back from the Rallyman Rally on the trusty Comm-n-go pretty well completely wore off all the tread on the rear Dunlop TT100/K81. I’ve had this bike for 38 years and have done all the tyre changes myself. I have the original 19” front rim and many years ago I changed to an 18” rim on the rear as the choice of good 19” rear tyres dried up. I’d settled on and was very happy with the original fitment K81 410 X 19 front and similar K81 4-10 X 18 rear. Needing new hoops I dropped into Graeme Morris Motorcycles in Newcastle where I’ve been buying them for years for another pair. I started with the rear. Off with the old hoop. The new was a bit tight to get the first bead onto the rim, but I just discarded that as being new and tight. Next, fit the tube. Trying to poke my fingers under the bead to stick the tyre valve through the hole in the rim proved impossible. I was really doing some damage to the skin on the back of my fingers. The tyre walls were as stiff as. It wasn’t working! Tore the tyre back off the rim and put it side by side with the tyre I’d taken off. Despite them being both marked as Dunlop TT100 K81 4-10 X 18, they were different. The new tyre is smaller in cross section. The tyre I took off was made in Japan. The tyre I’d just bought was made in Indonesia. Now, as long time buyers of these tyres, I’ve bought them Made in England, France, Spain or Portugal (I think) as well as Japan, several different countries over the years, why should Indonesia be any different. I looked at the front tyres, also different. I took some sidewall measurements and the Indonesian tyre is smaller in cross section. The sidewalls on the Indonesian tyres are shorter, making the overall diameter of the tyre less. The shorter sidewall dimension on the Indonesian tyre making it impossible to be able to stretch the beads apart enough to get the valve stem into the hole in the rim while doing bad things to the backs of my fingers. Not to mention the appearance of the tyre when under the mudguard looks like it should be fitted to a 125, not a 750. The next day I got onto the blower to Dunlop. I was told that Dunlop had been making tyres in
Indonesia for about the past eight years. The person I spoke to knew there had been a change in the design specifications/dimensions for the 18” tyre. This had come from JATMA; Japanese Automotive Tyre Manufacturers Association. The guy I spoke to said that JATMA had decided the design size of the 4-10 series tyres were always ‘oversized’ and so they re-designed them and re-did the specs so they were now, in fact, smaller in cross section. So, am I hearing this right; the tyre size was always oversize? Always oversize, even ever since 1969 when Mal Uphill rode his works Thruxton Bonneville to victory with a fastest lap of 100.37 mph during the 750 cc class of the TT Production race? Remember my 1972 Norton Commando was fitted standard with K81 4.10-19 tyres both ends. So now with a re-design of tyre specs making a smaller cross section and smaller sidewalls I was having all sorts of problems trying to fit them to my rim. I called the Australian Tyre & Rim Association and talked to a lady there who knew that JATMA was the Japanese version of the Australian Tyre & Rim Association and that’s the sort of thing they did. I have no other technical details or political information other than this, however I do know for a fact that the two K81’s I bought were dramatically different to the tyres I’d been buying and fitting for the past 38 years. I took the K81’s back to Graeme Morris Motorcycles and Graeme himself and his staff were very helpful in helping me go through his large selection of stock to find a pair of suitable tyres. I’ve fitted a Bridgestone Battleaxe BT-45 100/90-19 M/C 57V to the front and a Pirelli Sport Demon 110/90-18 M/C 61H to the rear. It was more about the actual size of the tyre and the way the appearance is as fitted under the guard etc. Nothing worse than looking at a bike that looks like the tyres are too small for it, just looks weird. I’d be very interested to know if anyone else has experienced these issues with the current K81’s.
Bob Davis Warners Bay, NSW Email: bob[email protected]pond.com