changing fork springs for a oem new set how do you measure oil and air gap

[psyfi_1]

hi guys looking to change fork springs for a new set question is............. if you measure fork oil and air gap before you put the spring in how are you supposed to know if it is correct because you wont know.......... obviously air gap is 121mm and fork oil is 475ml but is the spring is going to displace more or less oil how do you get the correct amount apart from buying originals from say folwers or such???

[bandit]

Oil level is checked without the spring in, fork held vertically,add oil then slide fork inner tube up & down to distribute oil fully in fork leg don't go by quantity of oil add to near then measure from top of fork tube down inside to get correct level (fork fully compressed).

[Freck]

You want one of these. 
https://www.demon-tweeks.com/bikeservice...gwQAvD_BwE

[kebab19]

Please tell me I've read this wrong - you're replacing the OEM fork springs with another set of OEM fork springs?

[psyfi_1]

nah replacing old originals that are fucked after 50000 miles just wondering becuase if the new oem displace more oil how would you measure oil level.. so air gap is correct............... becuase obviously if they displace more or les oil you would have to add more oil or take some away....... how would you know if you measure the oil out before putting the springs in.....

[Jules-C]

The air gap measurement allows for the volume displaced by the standard springs.  Even if you fitted different springs the difference in the volume displaced would be minimal. 

[psyfi_1]

ah okay thank you i was worried that there would be a difference in oil displaced and wasnt sure if i had to work it out lol i am terrible at maths lol