Where did I screw up?

Ernest Montague afm199 at earthlink.net
Tue Mar 10 08:52:44 PDT 2009

Don't calculate sag, measure it.  Unless you love doing math.

You sure about that 360 pounds? My race bike with alu subframe and 
light bodywork is 380.

On Mar 10, 2009, at 8:46 AM, Steve Robertson wrote:

> Can someone point out where I made a mistake? The answer of 60mm
> of sag doesn't match up with the reality of 35mm of sag on the bike. 
> There
> is currently no internal or external preload on the springs. What did 
> I miss?
> bike weight 360lbs
> rider weight 200lbs = 560lbs
> unsprung weight ~25lbs x 2 = ~50lbs
> total sprung weight 510lbs = ~230kg
> weight distribution 50/50, so sprung weight on front 115kg
> fork springs 2 x 0.95 kg/mm = 1.9kg/mm
> 115kg divided by1.9kg/mm should equal ~60mm of sag

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