Shock testing with a scale and press

[CT70_Scotts]

So as some of you know I have those front shock inserts ordered for my Pair of K0's. They are Daytona hydraulic over spring from MotorKit. I also scored a set of Topaz orange rear shocks for my K0H from Beatrice cycle on ebay. I have a set of CHP saphire blues rears on my other K0 for several years now.

Ok so my point...my dad has a hydraulic press the kind that has the Parallel moving top plate. If I put a bathroom scale at the bottom with wood blocking I could in theory test these different shock rates? I could also compare the stock spring set up on the K0's to the new set up.
I am also curious to see the difference between the CHP rear shock and the Beatrice Cycle one. I am 180lbs and like the feel of the CHP, but for $36 and CHP does not carry the topaz orange shocks I thought why not.

Curious on others opinions.

 

[scooter]

I’ve got a similar setup and have done it for the rear springs. Be interested in seeing your data

 

[scooter]

My ciphering post / weight measurement request was related - figuring out an appropriate spring rate for a heavier rider. Be interesting to see what you come up with for the new and old spring rate.

 

[fatcaaat]

When it comes to suspension tuning, spring rate is just a small factor to consider, particularly in a road machine. Not sure what your intention is on your vehicle, but I would personally not run a stock rear shock on a bike I plan on riding faster than 35mph. That has less to do with spring rate than rebound and compression.

See, regardless of spring rate, without proper rebound and compression setup, it's going to be bouncy when you hit something. How the shock manages that absorption and comes back can mean the difference between losing control or just carrying on with the ride.

My experience on the stock style shocks is that they are basically nothing but a pogo stick. I watched a buddy of mine hit a bridge coupling on a hot day once and I swear the only thing that kept him on the bike was that the grim reaper wasn't ready for him yet. I hit the same coupling, at the same speed (45-50) and barely noticed a thing. The difference? He was riding a stock suspended bike and I was riding a plushly suspended bike.

Sagging springs or springs that are too stiff are far less of a concern to me, then how they compress and uncompress when put under load.

 

[CT70_Scotts]

Yes understand this is a static test and will tell me nothing on the dynamic rebound. My bikes are stock appearing and will stay that way. Most of my ridding is back yard grass or dirt roads. The one Lifan powered 140 has been 55mph but in all honesty my comfortable cruising speed is 30-35mph on the dirt roads.

Thinking about the K0 replacement front inserts that are hydraulic with spring vs the original is just spring. I bet the replacements are softer in this test as the fluid displacement is limiting the dampening. I just think it would be interesting, and maybe the rear factory looking replacements are the same just better valving not necessarily heavier springs.

 

[fatcaaat]

I rebuilt a pogo front end completely for one of my builds which has a 108cc takegawa motor in it. That bike will hit 65mph. I rode it...it was pretty scary at speed. Even though it has really nice rear shocks, the fronts were pretty bad. I ended up using a steering damper inverted on the front end. Now while I may only get 2.5-3" total movement, it is plush and I can dial in the rebound and compression. It's now pretty nice on the twisties.

 

[scooter]

I’d offer that your static test is going to tell you a good and important bit of information.

The spring rate along with mass determines the natural frequency of the system. Goes as the sqrt(k/m) where k is the spring rate m is mass. Mass depends on rider and will also change as breaks are applied etc. The tires have their own spring rate and contribute to the equations. The difference in natural frequency between front and back will make a difference in feel. The higher the natural frequency the stiffer the system.

The next piece of the equation is damping and there is another equation for critical damping which is a function of the natural frequency. If a system is critically damped it gets back to normal in the shortest amount of time once disturbed.

Take the measurements and we can do a little math. In reality the system is complex but you can get some good first order approximations with a little data and understanding of the basic equations that govern a spring - mass - damping system.

Your new front end added in an important piece- the damping. Finding out the new spring rate is solid data to have in hand

 

[CT70_Scotts]

So finally got around to test these out. Did 3 rear shocks: CHP, stock used, and DrATV aka Beatrice cycle. I also did stock spring front end with my new Moto hydraulic.

Stock
13.5" 94lbs
13.0" 133lbs
12.5" 180lbs

CHP
13.5" 100lbs
13.0" 132lbs
12.5" 186lbs

DrATV
13.5" 146lbs
13.0" 209lbs
12.5" 270lbs

Conclusion just pushing between the CHP and stock the CHP feels stiffer. I have only used the CHP and really like them, this test proved that the valving is what makes this spring better then stock since nearly the same spring rate. The DrATV I will have to try out this summer. I was always taught you do want want to use your full suspension travel, obviously if a shock is to stiff you will not use it, and have my concerns with this one.

 

[CT70_Scotts]

Next was front ends...
Old stock springs:
22 3/4" 0lbs fork length
22" 69lbs
21" 163lbs
20.5" 202lbs

New hydraulic setup
23 3/8" 0lbs
23" 41lbs
22.5" 100lbs
22.25" 160lbs

Conclusion after having a old spring in one side and a new one in the other and just pushing by hand on the floor what a difference. The old style is just a joke it bounces, the hydraulic you can feel that it would absorb. I am disappointment with the lack of travel, looks like just over a inch. I am also disappointed with the finish on the bottom of the fork, looks like the welds will need to be ground to get the axle to sit flush also there is no welded shim on the brake side and the brake pin stay is smaller in diameter. To end on a good note notice the difference in heights at 0, I think this will make the K0's sit a bit higher with this set up.

 

[scooter]

I posted my measurement of an NOS rear shock in my Ciphering thread and I computed a spring rate of 80 lbf/in very similar to what you computed.

For the front end K0 setup I got a spring rate of 47 lbf/in for one spring very similar to your results