Help - What Shock After Swingarm Conversion.

[Little Pink Steve]

When swapping the swing arm on the FJ,  how do you work out what shock to use?  Obviously springs would be changed for the heft of the FJ and lump that sits on it. But do you account for the different pivot points and linkage?

[Pat Conlon]

3 methods:

1) Find someone who has already done it, and use that they've learned.
2)  Trial and error.
3)  Math. There are software programs that can calculate your needed spring rate. Once you get the correct spring rate you then design the shock valves needed to control the spring.

Folks go to school for this stuff.


What are you trying to do?

[nlovie]

thats a very good question - and i'd add to the mix - your probably fitting modern larger width wheels = radial tyres + all these mod's and more effecting overall weight and unsprung to sprung weight ratio. Add all these variables to ( swing arm pivot length / 3 point link ratio changes / fwd / rear weight bias change )

good luck trying to analyse all this - or indeed copy other folks solutions whilst maybe not copying their total set up package

for me-  it really only leaves one route, other than a lot of trial and error: you just got to get the cheque book out - lift the phone and talk to some of the well respected suspension guru's - i.e. Maxton  / Nitron etc.. who custom build - forsure it hurts the wallet, but the pain might not be as sore versus trial and error. Noting - the guru's don't always supply what you want 1st time out but most are more than happy to take the shock back and re calibrate it - once you have some feed back ( atleast this is what i've found with previous projects ) and for me - this is where the value is - and TBH, its not until you get this right do you realise that what you thought was good before -well it wasn't

[Millietant]

What swinging arm are you putting on Steve (is it a 3CV alloy one, a Thunderace, or a Fazer/FZ1) ?

Personally, I wouldn't faff about trying to get a shock from another bike to fit, I'd just go to Hagon (or YSS, or Nitron). With the common swinging arm conversions mentioned, the geometry and linkages seem to work OK with aftermarket shocks for FJ's, but the shock manufacturers might be able to give you some guidance (and I'd guess it won't be totally free).

There are plenty of people out there who have done swinging arm swaps and they're likely the best people to talk to, but remember, most of us are distinctly average riders and no experts on suspension set-up - so it's likely we wouldn't be able to tell great from just good, or poor from terrible - and everyone's view is based on their personal circumstances.

If you're just going with the 3CV swinging arm, then personally I'd opt for the Hagon (cheapest but still good quality) to fit the 3CV. Anything else and I can't really help.

The last time I worked out a shock requirement/spec was back in 1982 when I designed and built a monoshock frame for a CB 500 and back then I gave Spax all of my design figures and they supplied me with the appropriate shock - and it was brilliant.