TCI to start new R&D Project with a C10!

[slow4dr]

http://www.pro-touring.com/threads/1...-amp-D-Project

[68c10airstream]

A few geometry questions, how do you adjust caster and camber? Shims behind upper control arm cross shaft. If so doesn't this effect the center line that is supposed to run through the center of the cross shaft through the inner tie rod end and down through the lower cross shaft to eliminate bumpsteer? I have been curious about the factory bumpsteer values in comparison to this newer style front end. I noticed the bumpsteer gauge being used but no values. I believe the front ends on the market that have adjustable upper control arms that lengthen or shorten as needed for caster and camber would not alter the bumpsteer values. Anybody ever dig into scrub radius, what backspacing in conjunction with wheel diameter to yield a certain scrub radius value? In the early 80's as a subaru mechanic, the factory advertised zero scrub radius. This was the center of the footprint at the pavement was exactly where the SAI (steering axis inclination) imaginary centerline through the ball joints ran down to the pavement and contacted at exactly the same point as the center of the contact patch of the tire. Our dealership installed aftermarket wheel that were dished outward ( wider track width) and we battled with steering wheel shake, sensitive steering, etc. Reinstalled factory wheels and all problems gone. Obviously manual steering on this application.

[slow4dr]

Originally Posted by 68c10airstream

A few geometry questions, how do you adjust caster and camber? Shims behind upper control arm cross shaft. If so doesn't this effect the center line that is supposed to run through the center of the cross shaft through the inner tie rod end and down through the lower cross shaft to eliminate bumpsteer? I have been curious about the factory bumpsteer values in comparison to this newer style front end. I noticed the bumpsteer gauge being used but no values. I believe the front ends on the market that have adjustable upper control arms that lengthen or shorten as needed for caster and camber would not alter the bumpsteer values. Anybody ever dig into scrub radius, what backspacing in conjunction with wheel diameter to yield a certain scrub radius value? In the early 80's as a subaru mechanic, the factory advertised zero scrub radius. This was the center of the footprint at the pavement was exactly where the SAI (steering axis inclination) imaginary centerline through the ball joints ran down to the pavement and contacted at exactly the same point as the center of the contact patch of the tire. Our dealership installed aftermarket wheel that were dished outward ( wider track width) and we battled with steering wheel shake, sensitive steering, etc. Reinstalled factory wheels and all problems gone. Obviously manual steering on this application.

Sorry for the late reply, we just got back from the Street Rod Nationals today.

I forwarded your message over to Sal for a reply. Here is what he said.

"The front end was designed with the front wheel centered and 6 degrees of positive caster. This will equal .015 bump steer(Toe Out) at full compression. The upper control arm mount has 10 degrees of anti-dive. The spindle inclination is 8 degrees which I is the same as the factory spindle and the camber will be adjusted via the shims. There is .5 degree negative gain at 1 inch of bump. We purposely kept the stock track width so the scrub value would be as close to zero as possible. With a wider front wheel the value will change. With a 9.5" x 3.25" back spacing and a 27” diameter tire the scrub radius was 2.25". By eliminating the steering box we will be able to run at least an 11" wheel up front. We made the steering arms bolt on so we could test and make any changes necessary to improve the suspension even further if necessary and run a 15” wheel. -Sal"

-J

[68c10airstream]

Sal, thanks for taking the time and posting the results. I'm opting to go to about a 29" diameter tire, 20x8 rim with 4" backspace, which if my math is correct will yield just under 1" scrub radius. My next concern will be if the tire will fit inside the wheel well without rubbing. I'm currently running stock new ece coils with a ece 2 1/2" drop spindle, 72 and up thick stock rotors with 15x8 factory rallies with about 4" backspace and a 26 1/2" diameter tire. If you feel the hub face is in the same spot as what you are designing i will take my existing tire and add additional dimension to it and check for rubbing. Thanks again for your help, Brian Fuller