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my sag measuring setup

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I was inspired by the instruction manual for the digital sag measurement gauge:

https://cdn.shopify.com/s/files/1/1866/4961/files/Offroad_Full.pdf?3430719202814749508

My measurement probe is a piece of aluminum TIG welding wire

A screwdriver that slips nicely into the swingarm bolt and the axle bolt is required

A small loop is formed around the screw driver on one end of the wire

Then the screwdriver is slipped through that loop and into the swingarm bolt

Pivot around and pull the wire taut against the axle bolt

Make a mark with a sharpie on the wire where it intersects with the center of the axle bolt 

Now rotate the wire in an arc upward until it intersects a place on the fender where you can conveniently drill a downward facing hole

(optional: dont drill a hole, and put something else there to act as a hole..not as good IMO)

drill the hole

now move the screwdriver and wire to the axle bolt hole, slipping the wire through the hole in the fender

put the bike on a stand to take the weight off the wire

pull the wire taut through the hole and mark it where it comes out of the hole

this is the "zero" / "unloaded" measurement

now take the bike off the stand and hold it up gently vertically

pull the wire taut and again make a mark

the distance between this mark and the zero mark is the static/riderless sag

now you need an assistant or some way to hold the bike up vertically while you sit on it (without the method putting any weight on or lifting the bike up)

sit on the bike in the position of your choice (whatever you think represents what you want your zeroed suspension geometry to be)

pull the wire taut and make a mark

The distance between this mark and the zero mark is your loaded/race sag

On mine..

97 XR400R stock suspension spring at 212mm suspension unloaded (not free length)

me with gear: 215lbs?

static sag: 44mm

race sag: 119mm

So looks like I need to preload the spring a bit (or really I guess get a different spring..although I read conflicting things on that)

 

Since the stock spring rate is known, can I just tighten the spring nuts a certain number of turns to get to where I have 100mm sag or whatever and get it done in one shot?
 

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Edited by guy_with_motorcycle

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