Evolution of the FOX (Part II)

[marshall_mosty]

So... as most of you guys know, I can't leave well enough alone. Also, trying to find the mysterious 1/2 second that separates myself and Mike Patterson has me digging further into my brain for great ideas to make the car faster. My current suspension (prior to this post) was a Griggs Torque arm and Watts Link. The torque arm is very long, so with the subsequent instant center being very far forward in the car, provides less than ideal bite out of the corners. The benefit of this type of suspension is the axle also doesn't want to lift much, so axle hop under braking is non-existent (good thing). I've read a lot about decoupled torque arms and was trying to think of how to utilize that idea on my car.

While scrolling thru a Coleman catalog, I came across a decoupled three-link from roundy round cars. This looked appealing, as the packing was pretty compact and it would all go in from the top. After gathering up the required chassis parts, I went to work.




I didn't take any progress pics on this one due to a compressed timeline and time at the shop before the next event. So... here is the final product.








This design should provide the same braking effect as I had before, but more bite on acceleration.

[RichardP]

This design should provide the same braking effect as I had before, but more bite on acceleration.

Cool stuff. I'm anxious to see how it works out for you. You will probably have to experiment with different lines, braking points, throttle pickup, etc. to optimize.

Have you measured the geometry to figure out your new effective torque arm length under acceleration?

As far as braking, you should be able to have slightly more rear braking because the brake torque is no longer trying to lift the rear axle off of the ground. The cool thing about your setup is that you can adjust that. You can tilt the brake link to get back to where you were or you can even have the brake torque jack the rear end up. It will be fun to play with...


Richard P.

[AI#97]

That looks complicated. 1/2 seconds are easier to find in the driver!

is the front mount fixed only to the cross bar? If so, you might want to triangulate it a bit more as you would not believe how much flex there can be in a piece of 1.75" DOM that is 3-4 feet long! Could oscillate and cause tuning issues especially on a bumpy track. Is the red "flex link" adjustable for spring weight? How did all this factor into weight of the car compared to what you had?

Curious to see how it works for you.

[marshall_mosty]

Is the front mount fixed only to the cross bar? If so, you might want to triangulate it a bit more as you would not believe how much flex there can be in a piece of 1.75" DOM that is 3-4 feet long! Could oscillate and cause tuning issues especially on a bumpy track. Is the red "flex link" adjustable for spring weight? How did all this factor into weight of the car compared to what you had?

Matt,
The front mount is currently just mounted to the cross bar. I can always triangulate to the ballast plates in the floorboard if need be. You can tune the red bits with different donut sizes. With regards to the weight of the car, I really won't know until I hack up part of the torque arm that I don't need. I'm betting it will be a smidge heavier in total weight than what I have now. But I am carrying around 160 lbs of ballast (8 20lb plates), so could pull a plate if need be.

Have you measured the geometry to figure out your new effective torque arm length under acceleration?

Richard,
I haven't done the math yet, but if I have time next weekend to get some measurements, I will. Should be easy to measure the pivot point heights and location.