All 2st Suspension Spring rates, Sags and Damping adjustment setup.

I have come up with a formula that I use for setting the suspension up on my bikes. This info was collected the past few years from several different tuners and applied. I have broken this down into a formula using percentages of available travel so this will work on most any bike. (KTM PDS is slightly different but close). I thought I would share this knowledge with you.

Your shock spring preload should be less than 10mm on linkage suspension but not less than 5mm. You don't want to over preload a weak spring as you will just get a harsh ride that still will allow hard bottoming. I usually shoot for about 5mm preload on fork springs. If you have the right spring.

You can figure your correct sag numbers by using percentages. That way you can get the correct springs for you and your bike. Base these percentages on the available travel front and rear with a variance or leeway of + - 3 mm.

Front suspension static sag should be 14% ( available travel in mm X .14 = static sag in mm)

Front suspension rider sag should be 25% (X .25 = Rider sag)

Rear suspension static sag should be 11% of available travel (X .11 = static sag)

Rear suspension rider sag should be 34% of available travel (X .34 = rider sag)

Using these principles you can figure the correct sags for any bike and thus the correct springs without guessing and compromising.

Once you get the springs set correct you can get the forks and shock revalved if need be. I usually like to take 20-25% of the high speed compression out with the correct spring rates.

I usually leave rebound stock or change according to the replacement springs. I usually will change rebound one click per .2 kg. on rear shock. If I go up on spring rate say from a 5kg to a 5.8kg , I will go in 4 clicks. That is a good place to start. After setting rebound and spring sags (and getting correct spring rate installed). I find a G out or a ditch that I can jump into and expect to bottom front and rear at same time. I will back off compression till I am bottom softly front and rear. NOT DRIVING FOOTPEGS THROUGH YOUR FEET OR METAL TO METAL BOTTOMING.. Just bottoming softly. Then I go back in about 2 clicks to compensate for heated suspension. I then will ride extensively to see if I need to go in or out slightly to fine tune. Damping I find is a very personal thing it you take the time to dial it in. I like a plush and compliant suspension but not wallowy. Many times lately I find that I have to go down on fork springs and up on shock spring rates. I weigh 180-185lbs and ride a 2011 WR150. It came with .42kg fork springs. That is what my KTM 525 / 530 had in the front forks. For sure there is a big difference in weights. I tried .44kg on my 525 and the bike would not turn. The bike should settle into the corner front and rear when turning. My bike would not settle. The forks were way off static and rider sag. I was on the cusp whether to go to a .38kg or .40kg. If I were 10lbs lighter I could have used a .38kg. But as it stands the .40kg allowed my sag numbers to work perfectly. 40mm static and 75mm rider. I had Hall's Cycles take out 20% of my compression on front. I am using 5wt Maxima Racing fluid. I am 10 clicks in from full out. My WR150 came with a 5kg on the rear. When I had the correct rider sag , I had NO STATIC SAG. I kept going up on my spring rate till I was at 6kg. A huge difference. A full Kg or 5 sizes heavier spring. But I had to do this to get the needed 30mm static sag with 101mm rider sag. With the correct sag rates the bike is not nearly as tall feeling. Much easier to throw a leg across. Turns perfectly and is very stable on straights. I had Hall's Cycles take 25% of my compression out of the rear shock. I am very happy with the results. Use the formula and you can get the perfect spring rates for you and your bike. Don't ride the bike till you are satisfied you have the correct spring rates as most shops will exchange unused springs for different rates. If you ride with them they will look used and can't be sold as new. I think you will be very happy with the results if you don't compromise.

Thanx for all your work! This really helps me understand the boinkers and how they need to be set up.

Maybe we could get one of the Moderators to also move this up to a suspension set up posting.

Darin

How are you determining available travel? Using the published numbers or measuring it?

Great information!! What brand of springs did you end up with?

I got my springs from Hall's. Not sure what brand. Didn't look. Straight rate for sure.

Using the bikes spec sheets. That will be closer than measuring it yourself. I also convert inches to Millimeters (inches X 25.4 = Travel in Millimeters). Using this method really works. I have been extremely happy with the results when I get the spring rates right and not relying on some MX tuner out in California who only sets up SX bikes for factory riders. Ever notice that the forks don't move on SX bikes when going through the whoops. I honestly don't think this is correct but I guess it works for them. But did you also notice that they have to have a berm to make a turn. The few riders that have forks that actually move in the whoops on a SX Nat'l can turn inside the ones whose front ends don't move in the whoops. I think they should be using more damping with slighter springs IMO.

How much preload did you end up needing on the shock? With light bikes like a 125 do you think the static sag is still a good rule to go by or should the amount of preload be more important?

With the correct spring you can get the correct static and rider sag. DON'T COMPROMISE ! Having OCD means that I wouldn't let it go till I had it perfect. I ended up with about 8mm or less preload. I quit measuring when I got below 10mm. At 10mm I knew it was too stiff. Craig Hayes of Keytime Motorsports confirmed that. He encouraged me to keep going till I had it right even when others were saying that it was good enough. So YES, using static sag is ALWAYS a good rule to follow. But Static and Rider sag both need to be right.

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Excellent post! (I've used Vinduro's advice setting up KTM's PDS suspension, too)

Vin - How does a tuner "take out 25% of the compression damping?" Are you testing on a shock dyno? Are you talking across the board, or just low speed or high speed? So far, BTW, my experience with the 09 TE is exactly as you say... at my weight I could use stock or slightly softer fork springs, and stiffer shock spring with less preload. Yup.

I don't know as much about valving as I do about springs and fine tuning. I tell my suspension guy to take 25% of the High Speed Compression valving out. He may change out a percentage of the shims and replace with thinner shims and or remove shims. I removed 3 shims from my XR250 forks myself and was happy. Remember High Speed is for roots, rocks and sharp edged holes. I think to some degree it effects the whole range. As does changing rebound effects compression slightly.

Dwight,

On your 11% static figure, how much leeway do you allow? If it is at 8% and still have rider sag at 34% is that close enough or do I need to go stiffer on the rear spring?

Go 2 steps heavier. You are at 23.5 and need 30-35mm IMO. I have stated a 3mm leeway but I think 2mm is better. You gotta give a little room for those not as particular as I am. LOL
I have 30mm static and 101mm rider sag. I was at 25mm static and when I went up from 5.8kg to 6.0kg the static sag went to 30mm.

Thanks Dwight. I am going to see if I can't get it done.

I must be screwing somthing up.My bike has 320mm of available travele in the rear.If i mutiply that by 34% wich is .34 it comes to 108.8 mm of sag! It's gotta be me.

What are the stock spring rates on 2012 cr 125 and are 2011 and 2012 the same suspension ?

As far as I know they are the same and come with 5kg spring. If you weigh 170 to 200lbs you will need at least a 6kg spring

Thanks, do you know the front rates for the cr with KYB ?

No clue

I know I have seen it on the Cafe H somewhere but what springs are in the 09 WR250s Zoke forks? The manual says it has a K=4.5Nm My static sag is 38mm but total sag is only 70mm which means I need another 60mm of rider sag. I'm thinking a 4.2 spring.

I just had mine serviced and valved by EE and the paperwork that came back stated they were 4.2kg. Anyway, if your numbers aren't right you need lighter springs.