Pinion angle

[pav8427]

Whats everyone running for pinion angles? Ive heard different angles for different applications, postitive(up) vs.negative(down)-which is better and why? Etc.Etc.


Doug

[silver69camaro]

What suspension are you using?

[MonzaRacer]

Well pretty much it depends but on any live/straight axle if the drive shaft points to the ground you should use a downward pinion angle. For the most part I use pinion angle for tuning launch bite on coil sprung cars. but most will "thrum" with less than 1 degree but I have ran cars with even negative pinion angle(ie pointed up).
But most coil sprund systems will run in the 1.5 to 3.5 degree down angle (figure your driveshaft as the "level" angle) and I have actually hit leaf sprung cars as hard as 5 1/2 degrees down and typicly run them in the 3 1/2 to 4 1/5 range but it depends on the track/condidtions.
Less pinion angle means less bite.
The basic premise for suspension tuning (for dragracing I always start here then work for the turning handling) is you find the center of gravity ,where the car balances perfectly with driver (kind of like making the car a teeter totter. then you take an imanginarry line from the center/front of the camshaft and draw a line down to the CG then draw lins from the upper and lower control arms in intersecting angle and see where they meet (this is going forward) The theory is if you have the rear arms meet at the CG it is "perfect " but this doesnt hold true, some cars need the "lever arm of the rear suspension farther forward and up or down from CG to make a car hook and lift.
Oh and anotherthing is that the rear suspension should OPEN like opening scissors not close as some think. If the rear dips down (suspesion not tires) it lifting the right rear tire and you spin. Think if your index and middle finger on your right hand, the wheels are tied to the middle finger then think of the car body as a resistance for the upper arm to move up so the lower MOVES DOWN and hence planting the tire(s).
I know of people who used to put light springs in right rear of car 6 cyl springs in left front and super stiff springs in right front/left rear and have the car "react" so violently that they will scrape the right rear bumper corner upon launch and never get good 60 foot times and the car is very inconsistent.
The intersection on the front and rear lines are for reference and tuning (read any book on 4 link drag suspensions , simply triangulate the upper or lower arms ,do away with the panhardbar and switch swaybar/shock rates and tada you have a handling suspension for the most part.
some people even triangulate the upper to point in going forward(ie opposite a chevelle rear suspension)and then simply point hem right or left to tune (rather crudely) how the rear lifts the car.
hope I havent confused you too much.If you have questions just ask me in PM or email.
Lee Abel

[pav8427]

Non parallel, unequal length 4 link w/PHB.

Doug

[Yelcamino]

... but most will "thrum" with less than 1 degree but I have ran cars with even negative pinion angle(ie pointed up).
But most coil sprund systems will run in the 1.5 to 3.5 degree

I apologize for jumping in on this thread, but when you say "thrum" do you mean the cyclic vibration felt at certain speeds?

My 66 Elky has a vibration at 2500 rpm, roughly 80 mph, and the vibration increases as speed increases. I never checked the pinion angle after I installed the Currie rear because I reused the original upper arms. Do you think this could be the cause of vibration? Thanks.

Herb