Suspension Guru required!

Originally Posted by SV650Racer

If you have no static sag then your shock will top out as soon as it extends, ie under hard braking and will then lift the rear wheel off the floor hence causing chatter under braking.

Ask how many race teams measure rider sag!. Spring rate isnt 100% down to rider weight. Overall bike geometry, rider pace and style all are just as important.

I'd imagine race teels know exactly what rider sag their are running.. in wet dry and all other contitions for every track.

It won't top out if I'm running 80mm of rider sag instead of 40. It has 80mm to rise before topping out. My Bimota runs 50mm of rider sag and zero static sag because the bike only weighs 149kg and can't sag the rear with the rider sag set and that's with a spring thats too soft for me.

Some bikes run a very weight forward weight distribution compared to others. Take away the weight that the bike used to have in its tail end (tool kit, plate, indicators, all excess metal and bolts etc) when turning it into a race bike and the back end is then lighter and won't sag as much in stratic form. Therefore weight distribution, rear ride height, fork drop In stanchions) change in weight distribution etc have to be taken into account. Static sag is only a small part of the overall equasion.

I've now set up my 600 with 12mm static and 40mm rider sag so we'll see what that does to the chatter on the 28th. The 750 will be running 20mm and 75mm because I can't change the preload until stripdown.

C

[yorkie_chris]

Originally Posted by SV650Racer

If the preload canister has air in it then it needs bleeding and re-gassing.

Preload unit has gas in? Thought they were filled up under no pressure with just hydraulic fluid? Haven't had one apart, just curious.

Originally Posted by yorkie_chris

Preload unit has gas in? Thought they were filled up under no pressure with just hydraulic fluid? Haven't had one apart, just curious.

It does not, just fluid. Remote reservoir is gas charged.

Originally Posted by Berlin

It won't top out if I'm running 80mm of rider sag instead of 40. It has 80mm to rise before topping out. My Bimota runs 50mm of rider sag and zero static sag because the bike only weighs 149kg and can't sag the rear with the rider sag set and that's with a spring thats too soft for me.

Well, if spring is to soft for you it will have to be preloaded to get 50mm rider sag which would make you run out of static sag. Stiffer spring with less preload would give you better numbers.
Static sag is important, more than rider sag, simply because suspension works in two ways, compression and extension.

[Red Herring]

Forgive me for being a little bit ignorant here but under the circumstances originally given by the OP surely the rear suspension is going to top out regardless of how much preload/static sag it has. In my experience when braking hard into slow corners and hairpins how hard you can brake, at least in the dry, is governed simply by the need not to loop the bike over the handlebars, in other words the rear end is skipping off the tarmac and completely unloaded. The static sag/preload is important because it will effect how the suspension will react when some weight is returned to it (which is why we thought it could cause the chatter) and certainly if you start to turn in whilst still braking it will help you control the rear, but I don't see how it will stop it topping out under braking.

Originally Posted by Red Herring

Forgive me for being a little bit ignorant here but under the circumstances originally given by the OP surely the rear suspension is going to top out regardless of how much preload/static sag it has. In my experience when braking hard into slow corners and hairpins how hard you can brake, at least in the dry, is governed simply by the need not to loop the bike over the handlebars, in other words the rear end is skipping off the tarmac and completely unloaded. The static sag/preload is important because it will effect how the suspension will react when some weight is returned to it (which is why we thought it could cause the chatter) and certainly if you start to turn in whilst still braking it will help you control the rear, but I don't see how it will stop it topping out under braking.

Id say your right tbh Red.

Zadar; If you have a static sag of 8mm on a spring meant for a heavy person then surely rider sag will be stupid? I dont understand why people would set a bike for its own weight and not the riders as well...

you do set it up for both, static and rider but static is more important. rider can be +- more than static. ie. 5mm on rider sag will not make as big difference as 5mm on static.
if you have 5mm static and preload spring to get 0 mm static you will have no extension and top out.