Comparing tri5 to C4 front suspensions

[Rick_L]

I'm running a tubular upper arm for a 55-57 that's been shortened. The taller spindle and increased SAI requires a shorter arm - should be obvious. I have no idea what a C3 upper arm looks like or where its pivot is located.

I don't think anything is different in tire scrub between stock suspension and a suspension with the C3 spindle. 0.4" seems like a lot based on the geometry, I'll check my layouts.

Edit: my layout shows 0.17" scrub in the first inch of travel when you lower the car 2" with a shorter spring.

[chevynut]

I don't think anything is different in tire scrub between stock suspension and a suspension with the C3 spindle. 0.4" seems like a lot based on the geometry, I'll check my layouts.

Edit: my layout shows 0.17" scrub in the first inch of travel when you lower the car 2" with a shorter spring.

It's really not the spindle, it's the fact that the lower a-arm is angling upward at ride height by 2" at the end, then goes up another 2" at full suspension travel. At least that's what I modeled for a 2" cut spring and got 0.417" of lateral movement of the balljoint. That is somewhat offset by the negative camber gain to get a net of .22" of tire scrub at 2" of compression. That just seemed like a lot to me. A stock suspension has 0.180" of tire scrub so maybe that's not that bad, but the 2" dropped spindle with tall balljoint showed only 0.039".

[Rick_L]

Yes I know. Check your numbers, I stand by mine.

[markm]

Does it make a difference that a 57 has shorter springs, and tires than a 55/56. I remember sales lit. that talked about a newlower stance for 57. It has appeared you discussions have not been year specific.

[chevynut]

The 57 springs are the same as the 55-56. The tires are shorter, as well as the rear spring being mounted higher in the frame at the front leaf spring mount. It makes it about 1/2" lower overall.

[chevynut]

Yes I know. Check your numbers, I stand by mine.

I don't know why you didn't address this in the other thread.

I just checked my numbers.

I put the datum at the lower a-arm pivot with the arm 14.75" long. Starting with the lower balljoint 2" above the pivot, then raising it 2" you get a horizontal movement of the balljoint inboard of .417". It starts out at 14.614" outboard of the pivot, and ends 14.197" outboard of the pivot. The difference is .417". Do you agree so far?

The change in camber is -1.49 degrees at 2" compression. If the tire is straight up at ride height, then it rotates 1.49 degrees around the lower balljoint". If we use the assumed 225-60-15 tire the balljoint is 7.59" off the ground. So simple trigonometry says the tire contact patch moves .197" outboard with that camber change alone.

The net tire scrub is the difference between the lateral movement of the balljoint and the lateral movement of the contact patch, so you get 0.220" tire scrub.

Check your numbers, I stand by mine.

[Classicgary]

yes to the talk on chevytalk a LONG time ago.
i did the C3 thing on my '56 way back in the 90's. Drove that car for many many years with that setup.
Funny thing, the guy i sold the car to changed everything thinking "bolt on" stuff from a classic chevy parts place was better
than my "home done" stuff. HaHa joke was on him.
Anyway. i'm going to do the C3 thing on my '57, because i know it works, even though it ain't the latest "trickest" deal in town.
and parts are pretty much everywhere and the whole thing is just about a bolt on, the hardest part being "narrowing" the upper
control arms. But how offen do those need replacing once it's done?
SO, back to my question.
I was just curious as to the numbers. It really doesn't matter, 'cause i know it works FOR MY NEEDS.
And, the way i "narrowed" the upper A arms, was cut it, remove 5/8" (cause the cutting tool takes out 1/8" on each cut),
weld it back together with the bias to the rear of the car. Easy peasy.....

[chevynut]

Gary, go visit the thread on suspension analysis. If the spindle height changes to 10.75" it's pretty close to the 10.65" for the .9" extended balljoint. The additional SAI should help and I think it may even help with camber gain, especially while turning. That's one factor we didn't look at extensively.

[55 Rescue Dog]

So, what exactly is the perfect camber gain? Sure, it is a big factor at max g's in a corner, dependent on body roll, etc. But it has no benefit going straight down the road, or low G cornering speeds, and cannot possibly help under heavy braking loads either. Camber gain it seems, is always scrubbing the tire in, and out, even when not needed. It is all a balancing act, depending on it's intended use.

[Rick_L]

If the spindle height changes to 10.75" it's pretty close to the 10.65" for the .9" extended balljoint. The additional SAI should help and I think it may even help with camber gain, especially while turning. That's one factor we didn't look at extensively.

Who is we? I published analysis for the C3 conversion and several others. You never commented. I guess you figured it wasn't worth reading since you didn't write it or do the analysis.