Exhaust springs

[Billing]

Hi all, hoping someone can help me figure this out.

I bought an s/h aftermarket half system for my NC30, today it arrived, exactly as described, with no exhaust springs. It's a TSR system, which just uses springs to hold it together. I would like to know how I figure out what size springs I need for it, I can measure the distances between the spring hooks to get a rough idea.

Is it something like 20mm less than the hook distance (i.e 75mm spaced hooks need a 55mm spring?

As ever, any answers much appreciated
____________________
'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
BCF Eastern members map here ---> g.co/maps/2tm8b PM me to be added to it!

[0ddball]

Got an Arrow system in the attic and that is 94mm between hooks with 84mm springs.

[Billing]

cool cheers, I managed to find one spring, it was hiding in a packet which had the rear manifold in.

How do I know what size spring I need? I have measured it and got these figures;

overall length: 85mm
coil legth: 55mm

I'm guessing it's the overall legth I need to be paying attention to then?
____________________
'84 TS50X, '91 TZR125, '89 CBR400RR, '91 VFR400R NC30, '98 R1
"Hey copernicus! Why don't you navigate yourself to the back of the line with your feet and stand there with your shit."
BCF Eastern members map here ---> g.co/maps/2tm8b PM me to be added to it!