off season pondering pinion angle
 

I have a long time nagging question in ref to pinion angle and it's relation to overall race car performance. When searching the web forums on the subject I find as many theories/suggestions as when asking what motor oil a fellow likes.

From personal experience with a number of different combinations I find that sightly more pinion angle [about 1.5 more pinion down hill in relation to driveshaft] than what "they say" always helps my cars. So instead of 1 to 1.5 pinion down in relation to the driveshaft mine works best at 2 - 2.5 down in relation to driveshaft. And this result is not confined to one style race car or suspension. It has consistently give good performance and results with ladder bars or four link, slow small blocks or fast big blocks.

Also, on some forums you will find written comments about "when the pinion climbs the ring gear" and how a lower [more down] pinion angle gives a mechanical advantage to the climbing effort. So far, I have not grasp the visual or understanding of the mechanical advantage.

And think about a dragster where the driveshaft or coupler is in a straight line. Help me understand how the pinion can have any different mechanical advantage regardless of where the pinion works against the ring gear.

So, let's just open a brain storm session about your results with pinion angle adjustments. And we'll see if any light bulbs turn on for me.

Re: off season pondering pinion angle
 

Asking what the best pinion angle is , is like asking a racer what the best brand of beer is.
everyone has their favorite !
Realistically you have 3 basic groups when it comes to pinion angle, 1,leafspring with caltrak or slapper bar, 2 ladder bar ,and 3rd , 4link type suspensions.
As you discovered what works best for you differs from what others may use... Why, because spring rates ,shock settings and radial movement of the suspension will all influence the effect pinion angle has on the cars launch.
Idealy the sweet spot is one that utilizes the least ammount of pinion angle while the car is under acceleration, think less bind.
After years of setting up chassis, I've found Ladder bars like between 1.5 to 3.5 deg.
4links usually 2-4 deg. and slapper / cal track type 3 to 6 degrees.
As they say your results may vary.

Re: off season pondering pinion angle
 

Tom,

my main puzzlement is [for an example] why does a ladder bar car work better at 2.5 degrees than it does at 1.5 degrees.

Is there something else changing other than pinion angle. I completely understand to have an additional degree of pinion angle the entire housing is rotated thus changing the shock bracket relationship and the ladder bar bracket relationship.

So is some mechanical advantage between the housing and attaching hardware coming into play? It is really not the pinion number that makes a difference but the housing to mounting points that finds a sweet spot?

You understand how some things with a race car "just feel right, or just feel better" My experience it in that area of slightly adding more pinion angle than would usually be expected and having positive results show on the ET slip and reported by the driver.

So what do you think is really happening?

Re: off season pondering pinion angle
 

Larry, If your ladder bar set up allows the housing to rotate and seperate the chassis in the rear, it's likely it likes the added pinion angle because the chassis stays seperated long enough to benefit from the increased angle.
To prove this out ,you will need to anylize a good slo mo video of the back of your car to see if it stays seperated to say,maby the 60' mark.
Once you can see that ,you can jack the rear of the chassis to similuate the chassis lift and remeasure your driveline angle.
You will probably find it has decreased from your static measurement.
if the change is large enough, it's possible that it could go to a negative angle if the starting angle is 1-11/2 deg.

Re: off season pondering pinion angle
 

Hi Larry,
I ended using a Go-Pro camera to record what was happening and found I had too much Pinion Angle. As you can see in the video going down the track I was running a negative angle, so I removed 2 deg. Also at launch it was really never going past 0 or postive degrees.
When using the Go-Pro editing software you can slow it way down and zero in on any area of concern within the lens area.

[ame]http://www.youtube.com/watch?v=3SVoqUKEJNg&safe=active[/ame]

Re: off season pondering pinion angle
 

Hey Don ,nice video.
exactly what I was describing.

Re: off season pondering pinion angle
 

Great video thanks for posting. I believe the misconceptions on the importance of pinion angle go back to when Mopar racers ran pinion snubbers instead of traction bars. ---Trevor

Re: off season pondering pinion angle
 

My understanding is that you don't want the diff to rotate enough to make the angle opposite, meaning pointing up enough to give a reverse angle at that u joint compared to the direction of the angle at the front u joint. Ideally the angle would be the same front and rear, but suspensions allow the angle to change so you compensate by pinting the nose of the diff down a degree or two.

Re: off season pondering pinion angle
 

Awsome video! Now put a strobe light on it and see what happens.

Re: off season pondering pinion angle
 

Mother Mopar was the first to really science out the leaf spring suspension and they published their findings in their Chassis book.

Standard Leaf Springs 5 to 10 degrees nose down, 5-7 best

Leaf Link 3 to 5 degrees down

4 Link (double pivot) 2 degrees down

Ladder Bar (single pivot) 1 degree down

Note:Front Universal Joint Angle ( all suspensions ) 2.5 degrees or less

I run 6 degrees down on the Max Wedge with the real SS Springs. I'm going to switch to Cal traks this year and I figure it might be prudent to ask them about the angle used with the new springs and traction bars.

JimR

Re: off season pondering pinion angle
 

Not sure I could do that without triggering some Flashbacks!!!!! :)

Re: off season pondering pinion angle
 

don :great footage !! are the springs caltracs also ??? is this before removing 2 degrees
gmonde

Re: off season pondering pinion angle
 

Don, you have the right idea, imo. I've always heard all of the different angles for different suspensions. I've always wondered how anyone really knew what it looked like under there to recommend a given angle. I wouldn't know how to put whatever camera under a car to see it working (not to mention I'm hardly ever at a track anymore), but it would be interesting to test a large sample of cars and see if these recommended angles are working.

Re: off season pondering pinion angle
 

What is it that measures shock travel and records it on the data logger? Whatever that thingamajig is called, you need to fabricate one for the nose of the differential and actually measure the movement from the base angle. You could build a mechanical apparatus not using a data logger.
I know a guy that was video'ing the movement with a strobe light on his BBC SS car back in the '80's. I don't remember if it was a 4-link or ladder bar car. But as I recall, it was difficult or impossible to keep the pinion angle below zero with shocks and chassis tuning that would enable the car to launch correctly. This was a National record holding car.

Re: off season pondering pinion angle
 

Performance Trends' 4 Link software has a very good pinion angle program. altho limited to 4 link and ladder suspensions.
it allows you to input all the relevant driveline angles and it will put it into animated motion and allow anaylisis of the changes thru the suspension travel.
Not a 100% susbstitute for on track experiments, but it does give some insite into the possible pinion angle changes a given setup will yeild.

Re: off season pondering pinion angle
 

Yes they are the Caltracs Split mono springs and this video was before I removed the 2 degrees. When having the car scaled this past spring at Victory Racecraft the first thing they noticed was the pinion angle and suggested removing some. That's what made me hook the camera up for that shot.