I guess this subject has been up earlier, but is interested in your recent opinions. What rider sag rear and front have you found to work best on a Bird having a 6 mm shim rear?

I'm planning to use 30 mm's rider sag rear and 35 mm's rider sag front, any opinions for better values?

The guy who reworked my forks (Dan Kyle) recommended 25-30mm rear, 35-40mm front. Of course, whether the static sag (without rider) is correct will make a big difference (the combination will determine whether you have the correct spring rate). IIRC - rear should be 0-5mm without rider. I didn't ask about static sag on the forks since I was having him respring them for my weight anyway. FWIW - the fact that you have it shimmed will make no difference in what the sag should be.

Thanks for the reply !

Then I go for 30 rear and 40 front to stay within Kyle's recommendation. That will give an even sharper steering response compared to 35 mm's front, even if is a small difference. The front springs are extra long and progressive so there is no risk for bottoming anyway. Yes, I know (or believe) that the rider sag value is there to keep the front and rear suspension in their right working positions and not to tilt the bike, and the static sag is more or less just a reference to confirm spring rate vs rider weight.

What is the best way to measure sag? I have heard that this is importnt but have honestly never done it because I dont really understand

Great explaination and procedure here:

Suspension Setup Guidelines

That said, I've found I can do it fairly closely myself without additional hands.

For rear sag, tie a string to the swing arm at the axle and place a piece of tape on the rear cowl directly above where you tied the string.

With the bike on the center stand, mark the string where it meets the tape on the cowl.

Take the bike off the center stand and, while sitting on the bike (only lightly touch toes to maintain balance), pull the string tight and hold with your fingers where it meets the tape. Get off the bike and mark where you are holding, then measure between the original mark and the new one to get rider sag. Admittedly, this is less accurate than having someone hold the bike while you sit on it and someone else measures the distance but, hey, if you're by yourself ya gotta improvise.

For the front, measure the distance from the top of the lower fork leg to the lower triple clamp while the bike is on the center stand. Take the bike off the centerstand and lightly tie a zip tie around the fork above the lower leg. Sit on the bike and allow the suspension to compress. Once off the bike, measure the distance from the lower leg to where the zip tie ended up with the fork compressed to get front sag. Again, not nearly as accurate as using multiple people but, it has worked to get me very close.

Checking sag