There are two big reasons why anyone would want to lower a motorcycle. The first is for drag racing, and if that is why you're doing it, you probably should have it done professionally. The other reason is because the bike is just a bit too tall for you. The Triumph Bonneville T100 has a seat height of 30.5 inches. Generally speaking, you should be able to place both feet on the ground comfortably if you have an inseam of about 30 inches, as the seat will compress a bit under your weight. If you need an inch or so, you may be able to simply adjust the preload settings on the rear shocks. Otherwise, you will have to modify the entire suspension.
Place the bike onto a bike lift and raise it until the back tire has completely cleared the ground.
Push up on the rear shock preload adjuster until you can turn it. Choose a different setting. Generally, higher preload will result in lower seat height, and lower in a higher seat height.
Repeat the process for the opposite side shock.
Lower the bike off of the lift and sit on it to test it.
If it is still too tall, try again. Once you've reached the highest preload setting, and if you still can't place both feet flat on the ground, you will have to modify the suspension.
Place the bike on a lift and raise it off the ground so that both wheels no longer touch the ground.
Place a block underneath the rear wheel.
Remove both the top and bottom bolt from each shock and gently pull on both ends of the shock simultaneously. Do not yank it, as this may cause the bike to fall off the stand.
Install the new, shorter shocks. To align them, lift the rear wheel until both the top and bottom mounting holes are aligned at once.
Bolt the new shocks to the frame with the mounting bolts that should have come with the kit. Do not use the old bolts.
