Spring selection

[fabr]

Bottom line is that spring rate/shock valving is voodoo science. Best guess and then test,test,test.

[Boostinjdm]

that's kinda what I meant in my last post, I just didn't spell it out.

[Admin]

If you figure motion ratio from the center of the tire and not the ball joint, there would be no correction factor correct? for wheel rate..

[Boostinjdm]

Bottom line is that spring rate/shock valving is voodoo science. Best guess and then test,test,test.

It is only voodoo science when you are going for a ride quality judged by the seat of your pants.
When going for traction in a straight line and around corners, it can be figured mathmaticaly if you have enough information.

[Boostinjdm]

[Admin]

no, because that "center of tire" is still at the end of a lever that still causes the shock to approach and retreat from 90 degrees.

close enuff for the available spring rates on the market...

[Boostinjdm]

[Engineer]

I kinda agree with ya Bug.  however,  the motion ratio changes throughout wheel travel as the shock approaches or retreats from 90 degrees to the arm.  If you are going for an average,  wheel travel to shock shaft travel is ok.  You just have to know that it is an average.

I think Boost sumed it up.

[Boostinjdm]

I think Boost sumed it up.

Does that mean I'm right?  I was just talking out my ass as usual.  I guess everybody gets one right sooner or later. 

[fabr]

It is only voodoo science when you are going for a ride quality judged by the seat of your pants.
When going for traction in a straight line and around corners, it can be figured mathmaticaly if you have enough information.

Sort of but pretty damn close.IMO.

[LiveWire]

My motion ratio is more than 2:1 from full droop to ride height and less than 2:1 from ride height to full bump giving me a rising rate suspension. From +/- 1" of ride height it is 2:1, so that is what I am going by. I calculated spring load needed at ride height to support the machine using the motion ratio at ride height. Taking an average of the entire travel would yield a similar result, but it could be off a little. Using the overall motion ratio from the shock to the tire is going to factor in all the details that the spring calculators ignore. If a calculator takes shock angle into consideration, that is just an attempt to better estimate the motion ratio. Since they assume the arm is level, it will be off. Neither ride height nor the average angle puts my arms at level to the ground. All the calculators are flawed in that they all are trying to calculate a number that most on this board already know, but without all the needed inputs. You don't need to even do it that way if you can just measure the result. It's like having an elaborate calculation with gearing charts and tire diameter when you can just use a GPS to check your speed at a given RPM, voila, you know your final gearing factoring everything in. Calculations with crap in give crap out. If you can measure the real thing then just use it.

[fabr]

That's really my point about the calculators.They are just guesstimators to give a HUGE point to start from.

[Engineer]

Actually, they always spit out a specific number, which most people assume to be precise.  Actually understanding your suspension and motion ratio and ratio change through the travel range, like Livewire pointed out, is the best way to get a good pick to start with.  I think his plan of looking at the motion ratio 1" either side of ride height to use for the calculations would be an excellent way to start.  If I had my buggy together enough to weigh, I would be ordering springs off of this formula today. 

[fabr]

A specific number yes,but,it is a huge guess at any rate.

[Engineer]

Yah they really don't take enough variable's into account.  We have talked about the shock layed over, and possibly in two axis on a 5-link, how about rake in the front...  That will change it just like angle from the shock to the arm.