Guide

To fit an upside down (USD) front suspension system one must consider trail, travel, fork length, and in the event that the original front wheel is retained, the disc diameter. This database of fork dimensions might be useful. We have chosen the fork legs from a Yamaha R1 2002-2003 (5PW) model. These forks are designed to use with 298mm disc rotors, the same size as the 400, and they also have the same 120mm of travel. The length is 7mm longer than the 400 forks but the 400 top triple clamp has a drop of 10mm. In order not to change the trail it is necessary to use the same offset, so a lower triple clamp from the earlier 1998-2001 R1 was chosen. The top clamp will be custom milled from magnesium alloy. The 400 fork legs weigh 3379 grams each including oil. The R1 replacements weigh 3616 and 3643 grams. A gain of 501 grams. However the new triple clamps assembly is much lighter that the 400 version.

Before removing the original forks it is important to take a measurement from the axle centre to a fixed point on the frame. This is because the triple clamps from the new forks may be of different design and thickness compared to the original forks. In the case of the 3TJ1 the axle was 520mm from the base of the steering head.