Suspension Rear pinion angle

[JD1964]

I’m considering getting some adjustable upper rear control arms to to set rear pinion angle. My goal is to gain some extra tire bite on launch from dead stops. This is mainly a street car but my next set of tires will be drag radials since my tires are aging out before they wear out, so less life of softer rubber is no longer a concern for me. I’m considering the following arms. Any concerns with these or concerns with my idea in general? I currently have aftermarket square steel control arms witn poly bushings but obviously non adjustable.

BMR Mustang On-Car Adjustable DOM Rear Upper Control Arms; Polyurethane Bushings; Black Hammertone BMR-UTCA040H (79-04 Mustang, Excluding 99-04 Cobra) - Free Shipping

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[limp]

since my tires are aging out

I hate it when I have over 90% tread and have to throw away tires........

 

[manicmechanic007]

I would go ahead and get the fancy arms and adjust the angle
But
I would research pinion angle some more
No expert myself, but they told us in school that the pinion angle must match the trans to driveline angle
What makes you think changing the driveline angle will improve your launch?
Big fan of traction bars and leaf springs myself, but since you can't do that, a 4 link system or do the best you can with what you've got
That means get your fancy arms and play with it
My old boss was a national record holder back in the 70s bracket racing
He was always talking about weight transfer, course he had an old Chrysler Hemi and heavy 440's
Are you fast enough to pull the front wheels?
Finally got some 4.56's in my 69 and I can pull the front wheels now but it's still a slow schlep

 

[limp]

an old Chrysler Hemi and heavy 440's

 

[JD1964]

What makes you think changing the driveline angle will improve your launch?

The consensus among racers is that with Foxbody 4 link, shorter uppers will give you a negative pinion angle, say 2 degrees negative or so. This short video illustrates what it does. You’ll see the burnout, then the stage. Watch the wheel when the driver launches. The wheels push downward onto the pavement from the rotational force of the tq on the axle. That instant plant helps prevent wheel spin. You see it again when the driver shifts up.


View: https://youtu.be/sAfCBwVkyBg?si=lGujYXyBJCN7CrBU

 

[LILCBRA]

Just a question - wouldn't the 4 link setup be more stable as far as torsional forces go as compared to that leaf spring car? Wouldn't it be more advantageous to set them up to take advantage of the leverage they provide as compared to shooting for a pinion angle? I realize pinion angle will have an effect on the life of the U-joint and vibration, but it's not computing for me as to how it would help launches in this application. It makes sense to exaggerate the angle in a leaf spring car as they don't resist torsional forces nearly as well, so that extra "twist" of the housing would help plant the tires.

As I said, it doesn't compute for me, but I'm definitely no expert nor do I race anything on an even semi-regular basis. Is the -2 degrees you mentioned to just make up for the give in the bushings?

 

[AeroCoupe]

For me it was wear and tear on the car. Only way I could get the pinion angle correct on my T-Bird was with adjustable uppers. Four links will fix the angle but bushing wear will allow it to change and move which affects your 60 ft and how the car tracks.

On the Coupe it has a panhard bar and torque arm so it’s more of a set it and forget it with the spherical and delrin bushings.

 

[JD1964]

I spoke with my local Foxbody expert and he suggested I try a good set of drag radials before I spend time and money messing with pinion angle. He says I’ll notice a world of difference with sticky tires and for my street application, that’s all I should need.