The 2003 model is fitted with a showa rear shock, does anyone know what pressure the nitrogen cylinder should be? It has a bicycle type fitment for regassing it. Does 150Psi sound about right?
What I do know is to leave them alone, there is so little nitrogen in them that connecting a tyre type gauge removes about half the capacity due to the amount that the gauge holds, these need checking with specialist equipment. The nearest I have seen is a small bike pump affair for preloading with regular air, these do work but then you have air not nitrogen, abeit 80% nitrogen.
I actually took the rear shock to a bike shop so they could remove the spring for me as I can't seem to find my compression tool. I asked him whether there was a way of deteriming if the nitrogen pressure was still ok, after all its 10 years old and has done 17000 miles. He went around the back and pumped it with nitrogen to 150Psi and said that should do it. Lets hope thats OK then. Was just intrested to know whether there was a pressure setting for it.
I think the pressurized nitrogen is only there to stop the oil aerating.So perhaps the actual psi doesn't matter too much,as long as its reasonably high.?
150 is probably about right. Yes the pressure is there to stop the oil aerating, too little pressure and the oil will aerate but too much pressure and it will tighten the oil seal too much, which creates stiction on the seal/shaft and will wear the seal too fast.
Nitrogen is used purely because it is inert, and unlike air, it has no moisture content. 150psi is about right, but some dampers run higher @200psi. I don't know what the exact pressure for a Showa dampers should be. Dampers need a volume of gas which can compress, to allow for the extra displacement of the damper rod, as the damper shortens under compression. Engineers soon found that running higher gas pressures prevented the oil from cavitating as it was forced through the damper piston. The down side of the higher pressures is the spring rate of the gas becomes higher, and as has been mentioned greater stiction from the seals, both of which can cause poor ride and traction.
