Preload and Measurement Implications? (SOLVED)

[Iarn]

I've searched and searched and have been encountering difficulties finding consolidated information on the title point.

Does anyone have any good sources in relation to suspension? Specifically the numbers and their implications.

e.g. Fork sag is 18.5mm. Is that hard, or soft? Does that mean the spring is more compressed, or less?

My forks are currently 18.5mm and I am having a hard time finding out what that means. Is that a safe number? Is that stiff  or soft?

A source with a lot of information similar to that would be a big help, thank you.

[Janx101]

Rich Desmond on here is owner? Of sonic springs. . He knows many things of suspension setup! .. pop him a line maybe?

[RichDesmond]

I've searched and searched and have been encountering difficulties finding consolidated information on the title point.

Does anyone have any good sources in relation to suspension? Specifically the numbers and their implications.

e.g. Fork sag is 18.5mm. Is that hard, or soft? Does that mean the spring is more compressed, or less?

My forks are currently 18.5mm and I am having a hard time finding out what that means. Is that a safe number? Is that stiff  or soft?

A source with a lot of information similar to that would be a big help, thank you.

Sag, and it's immediate cousin, preload, have nothing to do with softness or stiffness. When the weight of the bike is on the suspension your spring is compressed the same amount if the bike has 18mm of sag or 38mm.

I kind of doubt that your total sag is 18mm, that would either be an extremely stiff spring or way too much preload. How are you measuring it? Total sag for a street bike is typically around 35mm.

Here's a page with some links:

http://www.sonicsprings.com/catalog/tech_articles.php?osCsid=b89a5e655d772bdef0fea934fb02e837

Give those articles a read and let me know if you have any questions.

[Iarn]

Just for for clarity's sake, I'll post my pertinent information...

This is the method I used to generate my sag number:

With the front wheel off the ground, measure the distance from the top of the lower fork leg (the big part of the fork) to the bottom of the bottom triple clamp. This is L1.

Push down on the forks and let them rise slowly. DON'T BOUNCE. Measure the distance from the same locations of where they stop. This is L2.

Pull up on the forks and let them sink slowly. DON'T BOUNCE. Measure the distance from the same locatins of where they stop. This is L3.

For L2 and L3 you need to balance yourself on a wall or have another friend balance the bike while you sit on it in your normal riding position. Feet should be off the ground.

Sag is:

S = L1 - (L2 + L3)/2

It is entirely possible I did this incorrectly, or that there are better methods.

I weight approx. 175lbs with gear on. and I have 0.85 sonic springs with 15w spring oil. I believe the spacer is 20cm long and I put 375mL of fluid in the forks and measured it to 120mm oil height.

The suspension feels perfectly fine when I ride it. It doesn't feel too harsh or stiff, to me. Though, I would like to have the knowledge to fine tune it with precision to my liking.

[RichDesmond]

Just for for clarity's sake, I'll post my pertinent information...

This is the method I used to generate my sag number:

With the front wheel off the ground, measure the distance from the top of the lower fork leg (the big part of the fork) to the bottom of the bottom triple clamp. This is L1.

Push down on the forks and let them rise slowly. DON'T BOUNCE. Measure the distance from the same locations of where they stop. This is L2.

Pull up on the forks and let them sink slowly. DON'T BOUNCE. Measure the distance from the same locatins of where they stop. This is L3.

For L2 and L3 you need to balance yourself on a wall or have another friend balance the bike while you sit on it in your normal riding position. Feet should be off the ground.

Sag is:

S = L1 - (L2 + L3)/2

It is entirely possible I did this incorrectly, or that there are better methods.

I weight approx. 175lbs with gear on. and I have 0.85 sonic springs with 15w spring oil. I believe the spacer is 20cm long and I put 375mL of fluid in the forks and measured it to 120mm oil height.

The suspension feels perfectly fine when I ride it. It doesn't feel too harsh or stiff, to me. Though, I would like to have the knowledge to fine tune it with precision to my liking.

Do you have someone helping you when you did the sag measurement? Also, are you getting the weight completely off the front end of the bike for the initial measurement?

When you installed the springs, did you size the spacer according to the instructions, or did you cut it so that the total spring/spacer length was the same as stock?

[Iarn]

I did. I had two others helping me. I took the measurements and I followed the measurement locations precisely. All weight was off the forks when I took the initial measurement. I put her on her centerstand, then lifted the rest of the way with a jack. The unloaded measurement was 161mm*. 

I didn't follow the instructions that came with the Sonic Springs at the time because I had lost them (and forgot that they came with instructions to begin with). I later found them but I had already completed the whole ordeal. The spacers are no where near as long as the stock metal tubes I removed.

I suppose I could remeasure the sag and see if I get the same outcome, and if so, shorten the spacer significantly.

Does having the front suspension warm or cold affect this in any way? I hadn't ridden Ele the first set of sag measurements.

[RichDesmond]

First thing to do is see how much preload you have. 15mm is good.
Do you remember how long the spacers were relative to the top of the fork tube? Did they stick up much above the top? Did you have to push a lot on the fork caps to get them to start threading into the tubes?
On the GS500, the spacer should be close to flush to the top of the tubes.

[Slack]

Just for for clarity's sake, I'll post my pertinent information...

This is the method I used to generate my sag number:

With the front wheel off the ground, measure the distance from the top of the lower fork leg (the big part of the fork) to the bottom of the bottom triple clamp. This is L1.

Push down on the forks and let them rise slowly. DON'T BOUNCE. Measure the distance from the same locations of where they stop. This is L2.

Pull up on the forks and let them sink slowly. DON'T BOUNCE. Measure the distance from the same locatins of where they stop. This is L3.

For L2 and L3 you need to balance yourself on a wall or have another friend balance the bike while you sit on it in your normal riding position. Feet should be off the ground.

Sag is:

S = L1 - (L2 + L3)/2

It is entirely possible I did this incorrectly, or that there are better methods.

I weight approx. 175lbs with gear on. and I have 0.85 sonic springs with 15w spring oil. I believe the spacer is 20cm long and I put 375mL of fluid in the forks and measured it to 120mm oil height.

The suspension feels perfectly fine when I ride it. It doesn't feel too harsh or stiff, to me. Though, I would like to have the knowledge to fine tune it with precision to my liking.

Pop off a fork cap and check what your preload is. Just the length of the spacer doesn't do it.
You mean the oil level was 120 mm from the top of the tube? That sounds a little low as memory serves (but I didn't go look it up).

[Iarn]

Yeah, 120 mm is oil height with the springs and spacers removed and the cylinder completely compressed. As far as I'm aware, that's within the acceptable range for my sonic springs.

I just put on my R6 shock today. So I'll be checking my fork preload some time this week.

[RichDesmond]

Yeah, 120 mm is oil height with the springs and spacers removed and the cylinder completely compressed. As far as I'm aware, that's within the acceptable range for my sonic springs.

I just put on my R6 shock today. So I'll be checking my fork preload some time this week.

That 120mm is fine, as long as it's the air gap that you're measuring. I.e. the distance from the top of the fork tube down to the surface of the oil.

[Iarn]

I finally got around to measuring my fork sag again after installing my R6 shock. The result was vastly different. 33mm of sag.

I did two things differently this time around. I used the measuring method from the Sonic Springs website that Rich provided links to. The rider stays still and someone else moves the suspension up and down instead of the rider. I also rode my bike for about 5-10 miles to warm up/loosen the suspension first.

Turns out I'm within acceptable range. I wanted 30mm, but I can live with 33mm.

Thanks for the tips, all.

Just for lagniappe, I measure my rear sag at 40mm, with 10mm of sag with bike off the stand and no rider. Acceptable?