I was arguing with some of the oldschool guys on Facebook, Kelvin pipped up with his car that had the "Penultimate" rear crossmember. He raised the crossmember to some crazy height in his tube frame car. Which to me was odd. I would have put Miata suspension or something good back there before putting the stock stuff back in. Never the less, I couldn't remember how the roll center works with semi trailing arms. It looks like it's not ride height dependent, it's calculated using the rear swing arm pivots point angles. Yes a super low car will have really bad squat when accelerating. So for fun I thought I would scan the rear suspension and make a model out of it so see what exactly happens.
So guys what do we really know? Looking up pictures of how the roll center works it's hard to see exactly what happens since the sketches are always with level arms...... Is it just squat that makes are cars feel odd in the back when they get super low?
Yes my model is crude, maybe later I will clean it up.
"People don't like it when shit doesn't match their rule of thumb." Sam
The model will end up confirming what Fred Puhn wrote in his old suspension book - the rear trailing arms are squirrely and the best solution for a competition car is to lock them out with 10,000,000lbs/inch springs.
I believe raising the semi-trailing arm pivots increases anti-squat. In defense of Kelvin, that car was built well before Miatas were recognized as the answer to every automotive question. Also, I'm pretty sure swapping in a Miata rear suspension would kicked him into the Modified class.
Tedman wrote: ↑27 Feb 2021 23:07
I believe raising the semi-trailing arm pivots increases anti-squat. In defense of Kelvin, that car was built well before Miatas were recognized as the answer to every automotive question. Also, I'm pretty sure swapping in a Miata rear suspension would kicked him into the Modified class.
+1
That would put you into the same class as that guy up here who used to run a "Lotus Europa", which was actually a Formula Atlantic chassis with a built N/A Buick GN V6 (ie a F3000 engine) with the Lotus fiberglass body (or an even lighter weight replica body) lowered onto the thing to make it look like a 'car'. I'm sure Keith will remember that guy.
That car seemed to defy physics...I have NEVER seen a car that could change direction as SHARP and hard as that car, My God it was impressive to watch, driven by North America's fastest driver in that class!
His A-Mod car was even crazier to watch.
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan
Keith Law
1973 2 Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1971 Vintage 13' BOLER trailer
Tedman wrote: ↑27 Feb 2021 23:07
I believe raising the semi-trailing arm pivots increases anti-squat. In defense of Kelvin, that car was built well before Miatas were recognized as the answer to every automotive question. Also, I'm pretty sure swapping in a Miata rear suspension would kicked him into the Modified class.
Yeah it for sure changes anit-squat but lots was claimed to what else it does. I just want to check for myself.
"People don't like it when shit doesn't match their rule of thumb." Sam
I'm definitely keeping an eye on this. I know a lot of BMW guys have made semi-trailing arms work well, so why can't the Datsun do the same?
That being said, my ultimate dream would be to switch to a multi-link setup of some sort. I'm actually surprised no one has created a custom crossmember to mount something up using "standard" aftermarket parts for S chassis cars or something. Maybe there's no room. But this is off topic.
One of the guys on Ratsun narrowed the various components of an S13 rear subframe/suspension assembly and mounted it into a 510. Jeff H. saw that car so he knows it physically existed.
