Ditto, took me half an hour to drain and fill both rear shocks with a couple 2x4s and some hardware

 

What kind of bike is your brothers. On my 09 Ultra with 11.8 Oz of 10wt Maxima Fork oil in each they still feel a shade soft, even solo, and im only a buck eighty (at 20-25 psi). I do 90% of my riding two up loaded with luggage. It is a BIG improvement over the stock shock oil.

 

SG 12" shocks, we went with the Amsoil cause I already had it from when I worked on mine. started with 10wt and it was way to fim even for my 225 lb *** then started diluting it down, after about three fluid change cycles of him dinking beer and me working on his shocks, I settled for 50/50 of 5w/10w which felt pretty good to me.He's still assessing the the 7.5wt mixture, I think he's around 180. I got a viscosity chart somewhere, I'll take a look at where the Maxima falls in relation to the Amsoil. Thanks for the feedback on your experience.

 

Agree with 10Wt being to heavy. Initially I thought it was OK, but it's such a slow responding shock that it does what I call bump hopping. Tried 7.5Wt, 5WT, and wound up with Mobil 1 Syn ATF which is 0W20. I have 2 pairs of shocks and over the last two years been trying different fills.

 

fabrik8r, you ever get a chance to look at where that 10wt Maxima falls on the viscosity chart. just finished a 3000 mile loop through Yellowstone and South Dakota and that 10wt Maxima still feels pretty light in both the shocks and forks

 

Sorry for the delay, I lost my old chart but I found a couple new ones. Unfortunately they are PDF, eventually I'll try to put them in excel. Hope these help.
http://www.peterverdonedesigns.com/lowspeed.htm scroll to the bottom
http://www.peterverdonedesigns.com/f...ion%20oils.pdf
http://www.hrpworld.com/client_image...pdf_3119_1.pdf
You say the Maxima 10wt is a little soft, what is your weight, it might work for my Bro, or at least give me an idea where to head with it.

 

Buck eighty... the forks seem like they dive a little more under heavy front braking than they did with the stock oil. In the rear shocks I can run 25 PSI two up with a mountain of luggage with no bottoming. Thanks for the charts!

 

fabrik8r,
great info on those charts. too bad they don't show the HD factory type E and type B actual cSt viscosity. I see the Maxima 10wt fork oil is on the low end of the viscosity index of the various manufacturers 10 weight fork oils

 

It is a pretty extensive chart, but still some gaps, no Amsoil either. I started last night transfering it to excel. Slow and painful, but I'll get there eventually, then I can go back to resaerch individual brands and add info that latter. Navigate around that Peter Verndon site, there is a lot more suspension related info too.

 

Nice chart. I have also done a bit of experimenting with shock oils.
The amount of oil in the rear air shocks makes a lot of difference. On one of my earlier attempts, my homemade shock compressor was not fully depressing the shock and I had them ever so slightly overfilled. Man, was that a jolting ride. I recommend making sure not to go beyond full of oil at full compression. The volume left after the oil fill for an air cushion is small and explains the wide variation of preferred air pressures. I am currently at about 1/2 ounce less than full, this level makes a 5 psi difference very noticable, at least to me. When it comes to oil choices, I will try pretty much any ISO 32 hydraulic oil. The chart shows ranges from ISO 5 to ISO 68, with 15 being on the lighter side, 32 in the middle, and 46 or 68 being heavy. I am aware that suspension oils can and will get hotter than ambient temp, but we are not talking supercross here, and I pay more attention to the 40C specs. At present I am using Mobil SHC 524, a synthetic hydraulic oil that specs at 32@40C and 6.4@100C, it seems good for the rear and maybe a bit light for the forks.
Captsluggo