spindle ?

[Ron Sutton]

Well I got a 71 c10 and I have been doing a lot of measuring on it. The original spindles are 6.5 degrees. I plan on running a grand national hub so I will run fabricated spindles. The company I have been talking with recommends a 10 degree but that seems a little stout. I think it needs to the other way like a 5 degree but I'm no rocket scientist.

I suspect you're talking to a stock car racing company about the spindle. The rules in stock cars allow for a wide track width but don't allow for long control arms. So the scrub radius in those cars is huge. That's why they run 10° KPI spindles. On ovals, you'll see a hundred different combinations of KPI from left to right, but common variations are 5° on the right & 10° on the left. On road courses, most stock cars run the same KPI on both sides ... of course. I've seen every combo here from 5° to 12°. Another thing to look at is the steering angle length & tie rod end offset for ackerman. Because most stock cars run steering boxes with center links, it is easier for them to get Ackerman. If you're planning to run a rack & pinion, you'll need to make sure you have a lot of offset in the steering arm to get anywhere near the optimum amount of ackerman.

But in road racing & autocross, where the rules allow track width & control arm length combinations that end up with low to zero scrub radius, you don't see those high KPI numbers. 3° to 5° is most common. I build my Track-Star front suspensions & Track Warrior cars with zero scrub & 5° spindles.

Also ... I don't think your spindle measurement is correct. Most GM spindles, including the C10 trucks, have 8.75° KPI. If you're going to end up with a scrub radius above 2" ... I'd stick with 8-8.75° of KPI. If you can get your scrub radius in the 1-2" window with a 7° spindle, that's what I'd suggest. I'd only go down to 5° if you can it under 1" or as close to zero scrub as you can.

You may find the Grand National Hubs & stock car fab spindles produce too much scrub radius. A quick check is to measure the center of the LBJ (lower ball joint) to the WMS (wheel mounting surface). Most of the stock car stuff is over 5". Most production cars are under 5". C6 spindles with hats are around 4.5" +/-. I offer my Track-Star brand of spindles & hubs (my design) for ProTouring, Track Cars & Road Race cars that are only 3-7/8" from LBJ to WMS. This makes it easy to acheive low to zero scrub radius, while running a much stronger spindle & hub with large bearings. My Track-Star spindles & hubs use the same massive bearings that the Grand National hubs do. But the whole package is narrower. Plus my Track-Star spindles use slotted steering arms for quick ratio changes & I offset the tie rod end outward close to the rotor for ortimum ackerman with R&P.

[sccacuda]

...I offset the tie rod end outward close to the rotor for ortimum ackerman with R&P.

Ron, just curious on this. What is the reason for bending the steering link? Isn't it still a straight line from the attach point on the rack to the attach point on the spindle? It shouldn't matter if it was "s" shaped, if the the ends were still at the same attaching points?

[Ron Sutton]

Hi Craig!

Ron, just curious on this. What is the reason for bending the steering link?
Just for inner wheel clearance when the wheel is turned hard ... over 20°. This is from a long arm, zero scrub Track-Star suspension (see photos) ... so the hubs & control arms go deep into the wheel.

Isn't it still a straight line from the attach point on the rack to the attach point on the spindle?
Yup!

It shouldn't matter if it was "s" shaped, if the the ends were still at the same attaching points?

You're correct. The curved tie rod tube is just for inner wheel clearance down at the lower part of the wheel.




Note: Anytime you make a curved tube, it needs to be beefier than a straight tube. Where most straight tie rod tubes in racing are 7/8" OD x .083" wall thickness ... for our curved tie rods, we use 1" O.D. x .156" wall thickness DOM (1026 Steel) tubing.