Making suspension measurements

[bumpy]

I have been trying, on my 1200GS, to set up my suspension from first principles by first measuring static and rider sag.

Most advisers talk about putting a plastic tie on the suspension tube so that movement of the suspension pushes the tie gently up the tube allowing measurements to be made.

But this all assumes conventional suspension and here we are dealing with the paralever system. Visible, is a nice shiny suspension tube which fully extended measures about 185mm and is close to the maximum travel of the front suspension stated by BMW to be 190mm.

So is it OK to measure the sag by attaching the plastic tie to this tube?

 

[Pukmeister]

You should use up about 1/3rd of suspension travel as sag, altering the preload accordingly. Its just a ratio and not an exact size so you should be able to calculate it with a cable tie on the fork leg.

The stepped preload adjuster on the front is pants. With mine it was a case of trying adjustments and seeing what happened, hardly scientific and not much control.

I went for Wilbers aftermarket units with infinitely adjustable preload collars front and hydraulic preload rear and found that 15mm of exposed thread was best at front as supplied (and trial and error after measurement at rear), any more or less adjustment affected the handling. Nice to have a damping adjuster on the front which makes a huge difference to front end feel and compliance over bumps unlike the standard non-adjustable shock.

 

[bumpy]

You should use up about 1/3rd of suspension travel as sag, altering the preload accordingly. Its just a ratio and not an exact size so you should be able to calculate it with a cable tie on the fork leg.

Front suspension set on lowest pre load:

The static sag (bike alone) 18.5%
Rider sag 10.5%
Dynamic sag (bike plus rider) 29%

In addition maximum travel over a variety of bumpy surfaces is 45% of total travel.

Is this telling me the front damper spring is too powerful for my weight

 

[Pukmeister]

I dunno, but I've always believed via my patented arse-o-matic dyno that the stock 'progressive rate' front spring is way too hard. Your measurements would seem to back that up.

 

[Slowdown]

Ohlins have really nice sheets covering GS suspension settings etc

They work for WP shocks too....

YMMV


http://www.ohlins.com/Product-search/?query=BMW+R+1200+GS+2004-2009