SAXTRAK FORKS

If you have already read our potted history, you will know that the Saxtrak front suspension was initially designed to dramatically improve the front-end performance of the Saxon Laverdas we had been producing for a few years.

Nigel first conceived the Saxon front suspension system in 1983 and was so convinced of it's potential that a Patent was applied for with a view to selling the idea to a major manufacturer once the system had proven itself.

Having designed the new front-end, Nigel set about producing two prototypes, which were fitted to two Saxon Laverda chassis designed and manufactured specially to accept them. In the winter of 83-84, special fork slider castings were manufactured along with associated parts to produce the very first Saxtrak front suspension system.

In early 1984 first trials were carried out at the Goodwood race circuit with very encouraging results. The two test riders, (Mottod bosses Phil & Martin), felt very happy with their new toys setting the two fastest times of the day but as Nigel watched from trackside he became aware of the front-ends jerky response to bumps and depressions in the tracks surface. Upon listening to Nigel's observations the riders were unable to report handling consistent with his views. Convinced he was correct, Nigel set about finding the cause of this jerky behaviour, now known as fork stiction.

After a great deal of thought Nigel was convinced that the Saxtrak system actually increased stiction compared with conventional forks due to the proximity of the top slider plain bearing to the steering ball joint situated just above the front wheel, this caused a tremendous leverage fore and aft of the top slider bearing resulting in pressure between slider and stanchion high enough to squeeze out the oil that should be lubricating the forks.

Only two solutions occurred to us, one was to produce much longer sliders which resulted in the top bearing moving up and away from the steering pivot point dramatically reducing the leverage and therefore the pressure, (BMW have used this approach). Nigel soon dismissed this solution because of the increased unsprung weight, the increased overall length of the forks, and reduced rigidity due to a combination of the need to restrict the depth of the top yoke and the overall length of the whole system. (Saxon top yokes are 80mm deep which when allied to a pair of short 40mm diam. stanchions results in a very torsionally stiff front-end essential for good handling.)

Saxon's solution was to increase the length of the slider casting approx. 50mm and fit a recirculating linear ball bearing in place of the plain bearing previously fitted, although this did require the fitting of hardened stanchions to prevent indenting caused by the ball bearings. This solution worked perfectly for some years until Nigel decided to employ a pumped oil system to lubricate the now plain bearings much as a crankshaft is. This idea cured stiction and corrosion problems at a stroke and is still used today.

Much has been made of the fact that this type of front-end has the advantage of anti dive but Saxon's race experience has shown that anti dive is a disadvantage for two main reasons. Firstly, when the brakes are applied the bikes centre of gravity needs to be as low as possible to reduce the tendency for the bike to lift it's back wheel, obviously with anti dive the centre of gravity remains high reducing the braking effectiveness. Secondly, with a reduced dive set up, trail actually increases when brakes are applied making the bike more difficult to get into a turn.

Saxon motorcycles are actually set up to take advantage of dive, which can be adjusted to suit individual riders. This ability to easily change set up is one of the main advantages or the Saxtrak front-end as is it's torsional rigidity, it can even be set up to exaggerate the reduction in trail experienced when brakes are applied to assist entry into turns.