Bandit front suspension diving

[Commuter_Tim]

The Bandit front suspension is bouncing back and forth like a rocking horse.
Every poorly contructed patch of road my front end just launches downward.

I don't believe the seals have blown, the seals on my CB500 were fucked from the moment I bought the bike, so I rode for a while before realising that wasn't normal.
They're not empty of oil, and they're certainly not leaking.

I'm 6 foot 3 and about 14 stone, I also have a terrible tendancy to lean on the bars (lanky and bad back).
So some diving i expect, but compared to my previous bikes it just doesn't seem right.

Even with blown seals and it pissing out oil, the CB500 forks would dive less than the Bandit does.

What's the best way to stiffen them up?
Is it a case of harder springs, or thicker oil or both?
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The above post is most likely nonsensical.

I ride a Bandit 600... badly.

[Beehive Bedlam]

15W oil will firm the front end up.

[mudcow007]

might be old knackered springs?

[Kawasaki Jimbo]

I'd think about what the rear end is doing as well since any lack of rebound damping there will allow weight to pitch forward,

[Qyburn]

[Robby]

On basic forks like the bandit has, you have a few options to alter how they behave. It is worth knowing what these things do, and to avoid going too far or doing everything at once.

Springs. If your forks are diving all the time, your springs are too soft. You can either replace them with stiffer or progressive springs, or you can add preload, in the form of spacers. These can be a bit of pipe, old sockets, pennies - it doesn't really matter, as long it's the same length on both sides. Try adding an inch of preload - it's a good use for the old imperial sockets in your toolbox.

Oil weight. Oil weight governs damping, it slows down the fork moving both up and down. You generally want thicker oil when the fork is moving too much or jittering on rough roads. You should not use thick oil to mask diving forks, it slows them down in both directions, meaning your tyre can spend less time in contact with the road on rough surfaces.

Oil level/air gap. The air gap acts like a spring. Air is compressible, fluid is not. A smaller air gap can make forks firmer. Small changes here - I would usually add 5ml of oil per side, then ride it and see.

So in this case, I would go with an inch of preload on the springs and an extra 5ml of oil in each fork leg. Don't get too precious about the oil used - it's a tiny amount, so 10W40 engine oil will do.

[Qyburn]

Assuming you still have some sag left after winding in the preload it won't reduce the distance the forks dive when braking, that's controlled by spring rate and compression damping. If you think about it all that preload is doing is setting the ride height, it's still the same amount of weight transfer when braking, same spring rate and same damping. Possibly if you're bottoming out at the moment it might help, by diving from a higher starting point. Still the same affect on balance and tyre contact.

Actually it might even make it worse - higher centre of gravity means more weight transfer.
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Lord Qyburn

[Kickstart]

Hi

First thing I would suggest is draining the oil and replacing it with fresh oil of the stock grade and quantity. See if that improves it as no idea what anyone has done to it over the years

All the best

Katy
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