The ups and downs of owning a classic motorcycle
Reader Alan Cotterell's 850cc Seeley Norton Commando, now wearing TZ350 fork yokes.
Just writing to say how much I appreciate the attention to detail in your magazine, and its usefulness. The articles on the BMW RS255 and the MV Evoluzione 500cc in the September/October 2012 issue were superb and extremely useful. I own an 850cc Seeley Norton Commando, and I was able to compare the specifications on Agostini’s bike with it. One of the reasons that I found your story on the MV so interesting was that Ago made comments in another magazine about braking into corners, then accelerating around them. To be able to do that the bike must oversteer under power when laid over or it ends up running wide. In your article it mentions that Ago had a prescribed offset for his fork yokes on the MV3 to suit his riding style.
My Commando runs on methanol with a close-ratio gearbox behind a motor turning out about 70hp. When I first raced it, it was fitted with Ducati 450 Cerianis, which had a lot of yoke offset. Under braking it stood up and turned and almost decked me. I survived by turning it on again while trying to crash it on the grass. It turned out that the Seeley frames all have 27-degree head angles. I purloined the fork yokes from a TZ350 frame I had lying around (which have 26-degree head angle with 18-inch wheels). The bike now steers under power in the direction in which it is laid over. It means that I can get the power on extremely early in corners, and the bike is so much faster. Using TZ350 fork yokes with the Seeley frame gives 137mm forward offset, 65mm yoke offset, 72mm trail, a 27-degree head angle and a wheelbase of 1,496mm (58.5 inches). I hope this might help somebody go faster! Thanks for all your good work in producing a quality product.
— Alan Cotterell/Benalla, Victoria, Australia