STM Street Wet Slipper Clutch- YAMAHA FYA-S090Fits YAMAHA R1 1998 to 2003 models.Please provide us with riders weight, power and torque of bike. We will have you slipper clutch supplied with the correct primary and secondary spring to match your setup at no extra cost.Please note: Clutch is not in stock, lead time is 2-3 weeks.You are buying off an Australian company we offer local support, technical advice, warranty and spare parts.WHY STM - FOR STREET AND TRACK:To help prevent rear wheel lock up and engine over running, to enable clutchless down shifting, to allow controlled sliding of rear wheel, to allow better take of and starts due to diaphram spring. STM becomes essential when improving Motor performance, as power increases you simply change the Drive Spring to cope.SPRING FUNCTIONING:Primary spring:• It applies pressure on the disc pack through the pressure plate;• It replaces the many helicoidal springs.• Allows adjustment when Motor performance is increasing.Secondary spring:• it applies pressure on the drum;• it regulates the opening of the slipper clutch and regulates the engine braking to the wheel.• It allows adjustment to rider preference - The lighter the spring, the less engine brake; the heavier, the more engine brake.Spring adjustment:• STM 125mm diaphragm primary springs are offered in 10Kg increments and are changed as Horsepower increases. There are 13 different weights to choose from (sold individually).• The 85mm diaphragm secondary springs are offered in 10Kg increments and are changed to rider preference and surface conditions. There are 6 different weights to choose from (sold individually). ARE STM SUPPLIED WITH A SUITABLE SPRING SET UP?All STM Diaphragm Slipper Clutches come with Primary & Secondary springs that have been calibrated for the specific application the clutch is intended for. The standard weight of both springs chosen by the STM Factory Technicians to be suitable for 90% of riders. One of the outstanding features of STM Slipper Clutches is that they offer a wide range of adjustment to suit any rider's needs. Both Primary & Secondary springs (weighted in Kilograms) are offered in 10kg increments and sold individually. Riders & engine builders can purchase additional springs to find the perfect combination to suit the rider preference and Horsepower output.