[Spunger]

I am pretty sure my Cortina Joyride is a falling rate. Probably why the dumb thing bottoms out constantly

I know the stable platform shocks help bandaid the falling rate suspensions. I thought about it for a while but figured we'd just keep the Float RL and use it till it busts.

 

[thaflyinfatman]

i dont have the math at hand, and am to lazy to figure it out, but the relation in a single pivot between the shock lenght and the delta of position in the wheel is a matter of sines and cosines of the delta-angle of the swingarm, instead of an exponential (non-linear) relationship.

Uh, you are aware that sinusoidal (and similar) relationships aren't linear functions.... hence why they're called "circular" functions.... right?

No bikes are truly "linear", but some singlepivots are close to the point where I don't think a person would be able to tell the difference.

What makes a significant change in rate (ie to make it noticeably rising-rate or falling rate) is when the angles of the suspension members (esp. relative to the shock's axis) change quickly. Shorter links = greater opportunity for rate change. You can set up a single pivot to be mildy rising-rate, but you can't do it as much as you can with a linkage design because the swingarm has to be at least the length of the wheel's radius + a bit; with a linkage you can make the links waaaay shorter than that and get a much greater change in the angles. [/basic explanation]

 

[binary visions]

Uh, you are aware that sinusoidal (and similar) relationships aren't linear functions.... hence why they're called "circular" functions.... right?

I'm not sure I've ever heard a logical argument out of Alexis.. Anyone remember that wild thread about Dorados and how he would type pages of pages of arguements that said, basically:

A) Nobody was a "real" DH racer if you weren't a South American, flying-all-over-the-world, world-cup-winning racer, and

B) Because his friends didn't have Dorados, they were unreliable, high maintenance, terrible forks.

 

[BRacing]

Remember guys, this is a technical discussion. You all have brought some interesting points to the table so far, so keep the 'name calling' out of it.

FlyinFatman: A very good explanation thus far.

I wish we had a list of popular bicycles, and could list them as rising, linear (or close to it), or falling.

-B

 

[binary visions]

Remember guys, this is a technical discussion. You all have brought some interesting points to the table so far, so keep the 'name calling' out of it.

Okay mom

There was no name calling; sometimes it is wise to point out when you are arguing with someone who will not answer to or be swayed by logic. It avoids what I mentioned had happened before in my post: pages of illogical and inane argument.

We now return you to your regularly scheduled program...

 

[Spitfired]

The best description I can give for a single pivot:

Visualize a single pivot. If you draw a line from pivot to shockmount(swingarm) and then to shockmount(frame) and measure the angle between those at full extension and full compression you can get a good idea of rising for falling. If the extended angle is less than 90 and the compressed angle is less than or equal to 90, you've got rising rate. If it's initially greater than 90, chances are under compression that angle will go up (heckler for example).

For rising rate, the shock's mechanical advantage at the 90 degree is higher than that of the fully extended less than 90 degree angle. At full compression, it's pushing sraight against the swingarm - all of the springs force is concentrated in that line. As the swingarm goes back towards full exension, and the angle gets smaller, the shocks pusing force is going to be less on the swingarm.

Likewise, on a falling rate, as you compress he swingarm hat angle gets even larger than 90 making the mecanical advantage go down throughout the travel.

Heres a picture of a rising rate SP I made for you right quick

 

[FlipSide]

Good explanation Spitfired...I was about to post something similar!

 

[thaflyinfatman]

I'm not sure I've ever heard a logical argument out of Alexis.. Anyone remember that wild thread about Dorados and how he would type pages of pages of arguements that said, basically:

A) Nobody was a "real" DH racer if you weren't a South American, flying-all-over-the-world, world-cup-winning racer, and

B) Because his friends didn't have Dorados, they were unreliable, high maintenance, terrible forks.

ahaha, did you see the 24/26 debate? He was pro-24" because it accelerates faster and you're "always accelerating" (in response to me saying "you're not always accelerating" taking "acceleration" to mean positive and "deceleration" to mean negative)... never mind that you'll average a lower speed with the greater rate of positive AND negative acceleration. But that's just what you want for dh racing!

 

[Gravity Ho]

Anybody else getting a nose bleed from reading all this? And here I thought I was a geek!

 

[zane]

The best description I can give for a single pivot:

Visualize a single pivot. If you draw a line from pivot to shockmount(swingarm) and then to shockmount(frame) and measure the angle between those at full extension and full compression you can get a good idea of rising for falling. If the extended angle is less than 90 and the compressed angle is less than or equal to 90, you've got rising rate. If it's initially greater than 90, chances are under compression that angle will go up (heckler for example).

For rising rate, the shock's mechanical advantage at the 90 degree is higher than that of the fully extended less than 90 degree angle. At full compression, it's pushing sraight against the swingarm - all of the springs force is concentrated in that line. As the swingarm goes back towards full exension, and the angle gets smaller, the shocks pusing force is going to be less on the swingarm.

Likewise, on a falling rate, as you compress he swingarm hat angle gets even larger than 90 making the mecanical advantage go down throughout the travel.

Heres a picture of a rising rate SP I made for you right quick

This was practically what I was planning to say.

 

[towelie]

Hmmm...I was just thinking about something that may through a wrench into the works here.

While my statement a few pages back says essentially the same thing spitfire just said, I think we may be neglecting something important. That is, the further the swingarm gets from horizontal (horizontal line from the pivot to axle), the more degrees of rotation are needed to get a vertical inch of travel. In an extreme case, if the swingarm went totally vertical you'd get practically no travel for large swingarm rotations. Because of this, a higher pivot location may give more of an effective rising rate, and a lower pivot location may give more of an effective falling rate, even if shock locations are the same. This is because in the higher pivot location, the swingarm is becoming more perpendicular to the direction of desired wheel travel (up). Of course, the higher the pivot, the shorter the bar between the pivot and shock mount, and the tighter the arc the shock mount follows. Tighter arcs will always keep it from being more linear, so maybe inches of travel per degree of pivot motion are in the wash here. Still, something to think about.

 

[zane]

Yeah, that's true. I was thinking about this the other day when I was modeling suspensions. You'd have to take the rate by the swingarm into account when calculating overall rate.....

You'd basically have to graph all of the rates of each link (the more links the more separate rates you'd have) and take the superposition of all the graphs to get the overall suspension rate. This is the most accurate way I can think of to calculate the final overall rate.