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Discussion Starter · #1 ·
So I've installed a set of FOGs shorter dogbones in the rear, and a set of 0.90 kg/mm sonic springs in the front. Now I want to set the sag. I tried measuring it myself, because I was unsuccessful in bribing my friends to come over and help on a nice Sunday afternoon. I even tried offering beer!

Anyway, what I ended up doing is taking a vernier caliper, and taping it to the end of a yard stick. I then extended the caliper to a even number like 6" and held the yardstick to the rear foot peg with the tip of the caliper rod just barely touching the ground. Then as I weighted the bike the rod in the caliper was pushed in and would give me a reading.


I'm getting very low numbers though. Like 0.5" in both the front and rear. Granted it's hard to measure this by myself, but still I'm sure I'm not up to 1", and from what I understand it should be 1.25". I've adjusted the rear shock preload collar quite a bit, but I haven’t' see any major improvements. Maybe I just haven't taking it out far enough yet?

Is there a "proper" measurement of sag? Is it really just the amount the frame moves down when you sit on the bike? Where is the best to measure it from?
 

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I didn't set the sag in the rear, but here's the method I used on the front.

Inspect the spacer length, record this length as S

Get the bike on the center stand, and lift the front wheel totally off the ground. measure from the fork dust seal to the lower triple tree clamp. This is measurement A

This is the hard part. You must find some friends more easily lured by beer. Find two. A brother/father/uncle will work. You can also substitute a girlfriend/wife/mother/sister/daughter for one of those guys, to do the measuring.

OK, sit on your bike, with the big guy behind you, keeping the bike upright but applying no other forces to the vehicle that would upset the front suspension. Sit in riding position (the bike is back on the floor). For full effect, get into the full tuck (this position place your CM (center o' mass) as far forward as possible. Think, 80 mph in a school zone. Have your weaker buddy make that same measurement from dust seal to lower triple tree. This is measurement B.

Okay, take measurement A, and subtract measurement B. This is the difference in fork extension between 100% unloaded and regular load. Add that to your spacer length, and you get the spacer length for zero sag. subtract length to increase sag. I am highly entertained by my combo of 10w oil, .9 kg springs, and 30mm of sag.

Recommendations: 20-30mm for track, 30-40mm for street. If you don't know, cut the spacers a bit long. It's easy to cut, hard to weld. 8)

I'm unsure of the exact procedure for sag-setting in the rear, but you'll need to take the same measurements, and adjust the preload adjustment of the rear shock to compensate.
 

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In the FYI section there's a full write up on setting your Sag.

FOG
 

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Discussion Starter · #4 ·
I’m been reading through Dad's very in depth post on suspensions. For the front he recommended just wrapping a zip tie around one of the forks and sliding it down to the fork seal. Then when you sit on the bike the zip tie will get pushed up and stay at the highest point, and you can measure it at your convenience. I haven't tried this yet, but it definitely seemed like the best way to do it.

For the rear I was trying to measure between the ground and a point on the bike, but I can see why it would be better to measure from the axle as then you don't have to worry about keeping the bike *perfectly* vertical.





1.25" of sag still seems huge. I have set of 0.90 kg/mm springs from sonic springs, which is what they recommended on their website, and I've seen other people with a similar body weight say they use. Here I try to calculate the amount of force needed to be put on one of the springs to get it to compress 1.25" the recommended amount of sag

[1.25" (of sag)] * [25.4 mm/1"] * [0.90 kg/1mm] * [2.205 lb/ 1 kg] = 63.008 lb

[Desired sag] * [convert inches to mm] * [spring rate] * [convert lb to kg]

But there are two springs. So my body weight must put 126 lb on the front to compress the springs 1.25". This is assuming that the weight of the bike itself overcomes any preload that has been put on the spring, and there is at least a little bit of free sag (or just barely zero).

0.90 kg/mm was the recommended spring weight on the website for my weight of 175 lb. But how should I be expected to put 67% of my weight up front when the seat on the EX is actually a little back from the center of the bike? It seems that either the spring rate is way off, or 1.25" of sag is no realistic.

From what I've read in other posts (specifically Dad's super long post on suspensions) it sounds like you always want the bike to have *some* free sag. This makes sense because you don't want the suspension topping out as the wheel drops into a dip in the road. The static sag you measure should therefore occur after the weight of the bike has overcome any preload you've put on the springs. If this is case then how can you adjust the sag by adjusting the preload? Whether your bike weighs 300lb or 500lbs as long as the preload has been overcome by the weight of the bike then any sag cause by the weight of a rider will only depend on their weight and the rate of the spring. This is of course assuming that the spring rate is truly linear.


Eric
 

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aireq said:
So I've installed a set of FOGs shorter dogbones in the rear, and a set of 0.90 kg/mm sonic springs in the front. Now I want to set the sag. I tried measuring it myself, because I was unsuccessful in bribing my friends to come over and help on a nice Sunday afternoon. I even tried offering beer!

Anyway, what I ended up doing is taking a vernier caliper, and taping it to the end of a yard stick. I then extended the caliper to a even number like 6" and held the yardstick to the rear foot peg with the tip of the caliper rod just barely touching the ground. Then as I weighted the bike the rod in the caliper was pushed in and would give me a reading.


I'm getting very low numbers though. Like 0.5" in both the front and rear. Granted it's hard to measure this by myself, but still I'm sure I'm not up to 1", and from what I understand it should be 1.25". I've adjusted the rear shock preload collar quite a bit, but I haven’t' see any major improvements. Maybe I just haven't taking it out far enough yet?

Is there a "proper" measurement of sag? Is it really just the amount the frame moves down when you sit on the bike? Where is the best to measure it from?
easy way is use the keyhole for the seat to the swingarm with a tape measure :)
 
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