if designing an upright to be able to vary the scrub you simply have a spherical bearing housing on both the top and bottom points on the upright which you can fit shims behind to space the upright out whilst not changing th steering axis. Its similar to a racing car upright with the top joint able to fit shims on the upright to change the camber angle without having to go through the painful process of changing arm lengths. this way you dont effect the KPI with changing camber whereas lengthening arms you change the KPI with camber

 

Interesting read.

I'm planning on using a maval manual converted FC PS rack on my car. And also as large of tires as I can fit up front w/o adversely affecting steering. What I read was that w/ manual steering and large tires any bumpsteer will rip the wheel out of your hand.

FC has mc-strut (i like that, kind of like the mcdonalds version of suspension.....). I noticed some adjustable steering links (for wider steering angle for dorifto kiddies) that they also had something for bumpsteer adjustment.

I'm a hands on learner, with a shitty memory to boot. I'm grasping some of this, but as far as how I could utilize it properly on the FC eludes me.

http://www.mazdatrix.com/SteeringAngle.htm <---steering angle thingies w/ bump steer adjustment


Now what I'm getting at.
Is with a offset that will fit a wide enough tire and fit flush (17x8.5 +30 or 17x9 +25).
Can I just dial out the bump steer w/ this adjustment point? Or am I only dialing out the gained bumpsteer from the added steering angle (which I once again have no idea how it affects bump steer or the steering geometry) which would just put me back at the scrub radius of the new wheels offsets?


Great thread and I'm learning some new stuff which is great.
I can't wait to learn more about my McStruts and how I can make them function properly
-Ben Martin

 

Alright, a friend explained to me how lowering a car can change the relation of the steering rack to the hub/tie rods, and how bump steer is created through changes in the way that the toe geometry functions.
Now I understand the bump steer adjusters
http://www.mazdatrix.com/pictures/ra...umpSteer1w.jpg


Now. Am I correct in thinking that these will only fix bump steer from lowering the car, and have jack **** to do w/ scrub radius?

Slowly learning,
Ben Martin

 

just to add some fun info for this incredibly detailed and well written/debated topic.

if one was to put thier ball joint in something of a cam where the joint's centerline could be moved seperately from the a-arm itself a scrub radius "adjustment" could be made(yes damon this would still adjust camber and caster bet you can work that out of the a-arm alignment adjustments). alot of aftermarket honda alignment parts include this style ball joint. one could also build it similar to desert trucks with uniballs mounted in camber plate style flanges.

sorry to add to the fire

 

bump steer discussion:
https://www.rx7club.com/suspension-wheels-tires-brakes-20/bump-steer-explained-625500/

 

a lot of that doesnt concern me as FCs are one armed wonders.

And doesnt answer my question of can this alleviate scrub radius.

I'll just have to reread it a few times and hope for the best as its rather technical, not to mention no f'in clue what ackerman is.

 

Yes.

 

If you've moved the centerline of the ball, then you have done nothing but shorten the distance between the joint and arm pivot on the chassis.

-Aaron
Synaptic3.com

 

If you move the centerline of the joint attached to the up-right, you will change the scrub radius because you have changed the distance between the ball joint and the upright. If you only change the way the arm attaches to the joint above, you do nothing.

 

Pulling this up, as I haven't seen any more recent discussion. Anyone have data on wheel width to offset for ~0 scrub radius on an FD?