Been playing with the shocks and their oils on my 04 RK. Being short, I've also been playing with 12" shocks as well. Finally got it about as right as I'm likely to get it, and it's pretty darn good, if I say so myself.

15 weight Maxima fork oil.

In the 13" stock air assist shocks, the ride is heavenly. There is no crashing in potholes, the bike rides like it's on a cloud, and stays planted superbly in the turns. Solo, with my ~165-170 lbs, I need no air pressure in the shocks.

In the 12" shocks, I'm still not crashing into the suspension stops when I go crashing through potholes. Yay! The ride isn't as plush with these shocks, because they clearly are more stiffly sprung than the 13" shocks are. That wasn't so clear with thinner oils. It's comfortable, just not as Cadillac like. Oddly and inexplicably, the bike doesn't feel quite as planted in the turns either. Again, zero air pressure.

As a short legged smurf, I want to use the 12" shocks. But I'd say the gain in lowering is outweighed by the wonderfullness of the 13" shocks in ride comparison. Since it's easy to swap shocks, I'll do this a few more times to decide.

Can't say I'm detecting much if any difference from varying the quantity of oil in the shocks. 8 oz in the 13" shocks at the moment. I've varied it from 8-14 oz.

I had gotten semi-good results with the 10w Amsoil shock therapy. But in the 12" shocks that required something like 30 psi to keep from crashing into the stops when hitting potholes, and make the bike prone to flipping me off the seat going over bumps.

Warranty neither expressed nor implied, your results may vary. I will say I am very happy running a heavier oil than typically tried in these shocks.

 

I put the amsoil 10w in my 12 shocks being 400# with 10 lbs of air it is a huge difference. love the ride now still going to play with the air pressure some only have 1 ride on it so far but I am hugely impressed

 

I been running 10wt. Bel Ray HVI in my 12" shocks and it worked out well. Today I'm putting 10wt. Bel Ray HVI in my 13" shocks. Also putting in Mono tubes standard height in the front end. Going back to original stock height.

 

I recently put ATF in my shocks with about 25 PSI of air. The ride is greatly improved and I think I have too much air pressure in them. Great improvement for only about 7 bucks.

 

Same here, synthetic atf and it rides nice. 2 up with TP and even with 10 lbs no bottoming on mild stuff and at 20 it is smooth on the back bumpy stuff. I am 275lbs, wife might be 125.

 

Currently I have the Bel Ray 10w fork oil in my shocks. But now I am also going to try the HV1 BelRay. It is actually a rear suspension fluid rather than a fork oil. I have been scratching my head on whether to start with the 5wt, or the 10. Now I get to consider their 15. At least the oil is easy to change to experiment with.

 

The 10 worked. It was quite an improvement. But it still jarred on potholes and bumps. Without air could still crash into the stops, especially the 12" shocks. That's pretty indicative of being over sprung and under dampened.

The 15 worked better. No more jarring and no need for added air to keep it from crashing into the stops. The heavier oil increased the damping rate, and let me run a softer spring rate.

I was planning to continue testing with thicker oils, like a 20 and 25. But with the 15 being so sweet, particularly with the 13" shocks, I decided to stop here. I've a jug of 20 that isn't going anywhere, so I may try it anyhow. I'm kinda curious to see how it works in the seemingly stronger sprung 12" shocks.

 

Great info Foxtrapper!! That is my next project!!

How many ounces did you put in the 12's? That's the shock I'm running right now in the rear.

 

Last time, 10 oz. I've varied from 8 to 14, and darned if I can say I've really detected a difference.

 

Regular fork oil is Okay but no comparison to actual shock oil which is hard to find and also costly compare to fork oil. I was able to find KYB shock oil made in Japan and made a big difference how rear wheel sticks to the road IMO.