Shock Spring Rate

[bmccrary]

So after pulling the rear end of the bike apart to grease the bearings I ended up taking the shock down to the motorsports lab for some testing.

It was a job and a half just to get the spring off, which I can not seem to get back on now. However, my suspension guy is just up the road. Anyway, back to the story.

Once the spring was off I took it over to the dyno room to check the spring rate. While the machine is no where near a perfect system, my average spring rate came in to be around 690 lbs/in. Which if you account for 20,000 miles of use, I am thinking it might have started life as 700 lbs/in.

I also took some measurements of the spring. 2.25 inch I.D. and a 7.25 inch length.

I wanted to put the shock on the shock dyno, however that did not end up happening and I dont know it if will even work. I do not think the shock has enough travel to be put on the dyno.

Using the preload adjuster on the shock, we can dial in up to 3/8 inch of preload, or 262.5 lbs.

After having one of my old roommates, who understand this suspension geo stuff much more that I do, come over. We figured that a 900 lbs/inch spring would work well for my situation after some rough calculations. Which is this:

When I ride by myself, I leave the preload at 7, and when my g/f comes along, 110lbs soaking wet, and then gear... the front of the bike feels WAY to light for my taste. I would like something stiffer that what I have now for that situation.

If I were to go with a 900 spring, it would be softer on its lower settings that what I have now with preload, but yet, could be dialed in to be stiffer for when carrying a passenger.

The next step was to find some where that carried springs. Apparently RaceTech doesnt have that sort of spring. However, hypercoil does.

Welcome to Hyperco

If you click on catalog, and 2.25" I.D. you can scroll through the springs they offer.

Tomorrow I will be talking to my suspension guy in Salisbury some about this.

Just thought I would share some info that I figured some of you might enjoy knowing.

-bryan

 

[DefyInertia]

The manual says it's 727...so you were right on.

How much do you weigh and how much sag do you get out back riding solo?

 

[Doorag]

Although this sort of stuff is usually WAY over my head, it points out that I should take my bike over to the suspension guy I know and get him to do some basica maths for me. I reckon the bike was designed for someone much lighter than me and I could do with some uprated springs in both the front and the rear. I'll add that to this year's list...

 

[Wolfman]

Thanks for the info...i sorta worked out the spring rate at about .8 when i changed my shock, i know have a 1.0 spring on my ohlins...yes i am a a fat bugger!

Thanks for posting the detail.

:thumbup:

 

[bmccrary]

The manual says it's 727...so you were right on.

How much do you weigh and how much sag do you get out back riding solo?

Nate,

[Hangs Head]

If I would have known that was in the manual, I could have saved alot of time. Oh well. Now I know what my spring is now.

I have never set the sag on this bike or any street bike for that matter. We set all that on the dirtbikes, but I am sure the sage rates will be completely different between dirt and street.

I weight 185lbs dry, so just round to 200lbs with gear.

What should the bike sag be and the rider sag for street. I have never heard or read any numbers. Truthfully, I have never really looked.:spank:

I will need to do the same for when I ride two up with the g/f and gear, this is when I want a stiffer spring.

-bryan

 

[DefyInertia]

I have never set the sag on this bike or any street bike for that matter. We set all that on the dirtbikes, but I am sure the sage rates will be completely different between dirt and street.

I weight 185lbs dry, so just round to 200lbs with gear.

What should the bike sag be and the rider sag for street. I have never heard or read any numbers. Truthfully, I have never really looked.:spank:

I will need to do the same for when I ride two up with the g/f and gear, this is when I want a stiffer spring.

-bryan

How do you know you need a stiffer spring if you have not measured the sag as is and don't know what it should be? Just feel?

Should be around 25mm to 35mm out back...much lower than in the dirt.

Technicalities: Suspension and Springs

Beyond nuts and bolts

By Paul Thede

Figure 1

What's all this ruckus about suspension these days? It seems everyone is clued in that suspension setup can be a key to riding fast and safely, but how do you do it? No matter what shock or fork you have, they all require proper adjustment to work to their maximum potential. Suspension tuning isn't rocket science, and if you follow step-by-step procedures you can make remarkable improvements in your bike's handling characteristics.
Figure 2

The first step to setting up any bike is to set the spring sag and determine if you have the correct-rate springs. Spring sag is the amount the springs compress between fully topped out and fully loaded with the rider on board in riding position. It is also referred to as static ride height or static sag. My company, Race Tech, (909/594-7755) has an advanced method of checking spring sag that I'll describe.
If you've ever measured sag before, you may have noticed that if you check it three or four times, you can get three or four different numbers without changing anything. We'll tell you why this occurs and how to handle it.

Rear end

Step 1: Extend the suspension completely by getting the wheel off the ground. It helps to have a few friends around. On bikes with sidestands the bike can usually be carefully rocked up on the stand to unload the suspension. Most race stands will not work because the suspension will still be loaded by resting on the swingarm rather than the wheel. Measure the distance from the axle vertically to some point on the chassis (metric figures are easiest and more precise; Figure 1). Mark this reference point because you'll need to refer to it again. This measurement is L1. If the measurement is not exactly vertical the sag numbers will be inaccurate (too low).

Step 2: Take the bike off the stand and put the rider on board in riding position. Have a third person balance the bike from the front. If accuracy is important to you, you must take friction of the linkage into account. This is where our procedure is different: We take two additional measurements. First, push down on the rear end about 25mm (1\") and let it extend very slowly. Where it stops, measure the distance between the axle and the mark on the chassis again. If there were no drag in the linkage the bike would come up a little further. It's important that you do not bounce! This measurement is L2. Step 3: Have your assistant lift up on the rear of the bike about 25mm and let it down very slowly. Where it stops, measure it. If there were no drag it would drop a little further. Remember, don't bounce! This measurement is L3.

Step 4: The spring sag is in the middle of these two measurements. In fact, if there were no drag in the linkage, L2 and L3 would be the same. To get the actual sag figure you find the midpoint by averaging the two numbers and subtracting them from the fully extended measurement L1: static spring sag = L1 - [(L2 + L3) / 2]. Step 5: Adjust the preload with whatever method applies to your bike. Spring collars are common, and some benefit from the use of special tools. In a pinch you can use a blunt chisel to unlock the collars and turn the main adjusting collar. If you have too much sag you need more preload; if you have too little sag you need less preload. For roadrace bikes, rear sag is typically 25 to 30mm. Street riders usually use 30 to 35mm. Bikes set up for the track are a compromise when ridden on the street. The firmer settings commonly used on the track are generally not recommended (or desirable) for road work.

You might notice the Sag Master measuring tool (available from Race Tech) in the pictures. It's a special tool made to assist you in measuring sag by allowing you to read sag directly without subtracting. It can also be used as a standard tape measure. Measuring front-end sag is very similar to the rear. However, it's much more critical to take seal drag into account on the front end because it is more pronounced.

Ffront end

Step 1: Extend the fork completely and measure from the wiper (the dust seal atop the slider) to the bottom of the triple clamp (or lower fork casting on inverted forks; Figure 2). This measurement is L1.

Step 2: Take the bike off the sidestand, and put the rider on board in riding position. Get an assistant to balance the bike from the rear, then push down on the front end and let it extend very slowly. Where it stops, measure the distance between the wiper and the bottom of the triple clamp again. Do not bounce. This measurement is L2.

Step 3: Lift up on the front end and let it drop very slowly. Where it stops, measure again. Don't bounce. This measurement is L3. Once again, L2 and L3 are different due to stiction or drag in the seals and bushings, which is particularly high for telescopic front ends.

Step 4: Just as with the front, halfway between L2 and L3 is where the sag would be with no drag or stiction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true spring sag: static spring sag = L1 - [(L2 + L3) / 2]. Step 5: To adjust sag use the preload adjusters, if available, or vary the length of the preload spacers inside the fork.

Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm. This method of checking sag and taking stiction into account also allows you to check the drag of the linkage and seals. It follows that the greater the difference between the measurements (pushing down and pulling up), the worse the stiction. A good linkage (rear sag) has less than 3mm (0.12\") difference, and a bad one has more than 10mm (0.39\"). Good forks have less than 15mm difference, and we've seen forks with more than 50mm. (Gee, I wonder why they're harsh?) It's important to stress that there is no magic number. If you like the feel of the bike with less or more sag than these guidelines, great. Your personal sag and front-to-rear sag bias will depend on chassis geometry, track or road conditions, tire selection and rider weight and riding preference.

Using different sag front and rear will have a huge effect on steering characteristics. More sag on the front or less sag on the rear will make the bike turn more quickly. Less sag on the front or more sag on the rear will make the bike turn more slowly. Increasing sag will also decrease bottoming resistance, though spring rate has a bigger effect than sag. Racers often use less sag to keep the bike higher off the ground for more ground clearance, and since roadracers work with braking and steering forces greater than we see on the street, they require a stiffer setup. Of course, setting spring sag is only the first step of dialing in your suspension, so stay tuned for future articles on spring rates and damping.

And this is good: Motorcycle Suspension Set-up