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I'm putting a 2000 ST4 back on the road that has had PMS for some years. Suspension oils need to be done. Standard suspension setup.

I weigh 80kg, partner weighs 65kg. When travelling 2 up, short trips only, no luggage. When on my own, say 30kg luggage.

I use Fuchs RSF. So what weights should I start with?

And measurements would be appreciated.

Regards, Greg
 

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i use 5 weight in the forks, helps to take the edge off the high speed compression. height depends on how much travel you're using - if it has std springs you'll probably need to go up around 100mm - spec is 94. if you put some heavier 0.90/0.95 springs in them i usually drop the oil to 135mm or so.

it could probably benefit from some more preload if it has std springs. they're 0.83 std.

if you're using too much travel raise the oil. if not, drop it.

dunno about shocks - don't do them.
 

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Pretty subjective. You first should identify what you like or don't like about how it came from the factory. Assuming it hasn't been replaced already, the OEM oil is Shell Advance 7.5W.

Now to really confuse things. 7.5W oil from one manufacturer is not the same as 7.5W from another. In fact the oil weight listed on the bottle is not the way to buy fork oil. You want to look at centiStokes and viscosity index... Also, you'll find that there isn't much in oil listed as 7.5 weight, even with Shell Advance. How to get that? Mix the 5 and 10W oil.

This is a great link that lays it all out. A good one to save if you're going to care about this.
Fork oil weights

My preference is Bel-Ray 5W fork oil. Note there is also a Bel-Ray 5W HVI. It has a higher viscosity index and is considered suspension fluid. You'd use it in a shock, not a fork.
 

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i use maxima 5 wt, which is around 16 cst. similar to the belray 5 and rsf 2.5. rsf 5 is around 26 cst, which is heavier than maxima 7. so it's a bit confusing.
 

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Yeah... Before I knew this was even a thing, I dumped in a 5W oil available locally, don't remember what, and it felt like I'd used cement. It does matter.

Also you mention oil height. Good point. I've adopted Race Techs method of measuring with the springs in, especially if you're changing springs. Harder of softer springs and different manufacturers may displace more of less oil than the OEM springs. If you filled to the OEM specified level with the springs out as you're supposed to and then put in different springs, there is no telling where you really are for oil height. RT says 110mm with springs in, works for me.
 

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IDK, maybe. I haven't measured with them in at the OEM level to compare. I've done the zip tie on the fork tube thing while riding in my most aggressive mode (which isn't very aggressive) on our crap NE US roads and it doesn't bottom. Uses most of the travel. I'm sure that is pretty situational. Even RT calls it a starting point and to add or subtract 5mm at a time from there. 110 just happens to work for me.
 
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