# Daily Archives: June 21, 2017

## Feet still hurt and other things

Well I was supposed to go run errands in Carrollton today but I could barely walk to the mailbox in front of the house so no trip to Carrollton. I seriously did something bad to my feet, and I wish I knew what it was so I could not do it any more. I mean this is highly annoying not being able to leave the house except to get the mail.

Anyway I didn’t log on to post about my feet, I’m here to post about THINKING! > thunder, lightning, dogs and cats living together < No need to panic I’m just going to discuss on how my brain works > spooky music, portals to strange dimensions, screams of the damned <. NOW STOP THAT! I swear I will turn this blog around right now if this doesn’t stop > … <

OK now as I was saying I’m going to show I knew about how much to move the springs in on the front and rear axles so I could balance the car’s handling without resorting to heavy anti-roll bars. It has to do with single and double wheel rates and how they differ on a beam axle.

On double wheel rates or technically a “two wheel bump” the wheel rate is whatever the spring rate less whatever is lost if the springs are not vertical. Plus the motion ratio for springs not mounted directly to the axle which doesn’t apply here. What starts getting weird is when you get body roll or looking at it from a static body reference a “single wheel bump”. Then you start getting all kinds of motion ratios involved.

I should explain what a “motion ratio” is before I continue with this post. On a beam axle like both the ones on all of the iterations of the bucket from Sprint-T to TGS2 the motion ratio is the ratio of the tread (the distance between the center of the wheels looking from one end) to the distance from the center of the wheel to the point that the spring affects the axle, on the slant height. I guess you could use the distance on the horizontal plane because there is only a few % difference, but if you know the slant height between the contact point of the stationary tire and the spring closest to the affected wheel, why not use it?

On the front axle the springs are mounted as close to the ends of the axle as is physically possible, so the motion ratio for the spring closest to the bump is nearly 1:1 and the motion ratio on the other end is effectively 0, after taking the effect of applying the motion ratio into consideration. (The effect of a spring on the wheel rate is effective spring rate at the mounting point times the motion ratio squared.)

On the rear axle the spring away from the bumped wheel is actually close enough to be affected in a single wheel bump and contribute a significant amount to the spring rate at the wheel, so it has to be added in to find the wheel rate. To explain why I present a reductio ad absurdum where there is a single spring mounted on the center of the axle. The effective single wheel spring rate is ¼ the two wheel spring rate with zero resistance to rolling over in a turn, demonstrating the three spring rates for a beam axle: the two wheel rate, the single wheel rate, and the roll rate.

And I bored myself writing about it. I don’t get it, this is exciting to do, why can’t I convey that excitement when I write about it? Seriously this is giggly hand-rubbing exciting to do with the calculator and the graph paper, why can’t I make it sound as fun when I’m writing about it? I make it sound like homework instead of the nuts and bolts of deciding where the nuts and bolts go.

I guess I’m just tired and need to take a break from writing and go do something.