Pinion Angle
Pinion Angle
(OP)
What is the significance of the pinion angle in a four link live axle setup?
I understand that floor clearances may be an issue in some road cars but I suspect there is a direct effect on the vehicles handling.
The particular example I am working on which has bought this question to my attention is a Westfield style Clubman being built by a freind for a street car. It is four link and uses a panhard bar. I don't know if is is equal or unequal length arms but they are all parallel when the car is viewed in plan.
He hasn't decided on anti squat / anti dive yet either but he is working with a horizontal lower arm at ride height.
I have had experience with one drag car guy who tells me 4° nose down is the go and another person who does street cars stuff who says 1° nose is all you need but neither can back up their claims with any reasoning. They jsut know this!
I understand that floor clearances may be an issue in some road cars but I suspect there is a direct effect on the vehicles handling.
The particular example I am working on which has bought this question to my attention is a Westfield style Clubman being built by a freind for a street car. It is four link and uses a panhard bar. I don't know if is is equal or unequal length arms but they are all parallel when the car is viewed in plan.
He hasn't decided on anti squat / anti dive yet either but he is working with a horizontal lower arm at ride height.
I have had experience with one drag car guy who tells me 4° nose down is the go and another person who does street cars stuff who says 1° nose is all you need but neither can back up their claims with any reasoning. They jsut know this!
RE: Pinion Angle
I remember hearing some Dirt track Speedway, "Super Sedan" racers talking about it once. They were going on about mid corner drive and maybe they should do something with pinion angle.
RE: Pinion Angle
If your rear UJ angle exceeds 4 degrees then you may run into severe rumble type issues, and a typical RWD has 2 or 3 degrees of axle windup at max torque first gear, or reverse, so you don't have much room to play with.
On a race car I would try and keep the diff axis parallel to the gearbox axis at full throttle in (top gear-2), and not worry too much, as a first guess.
Again on a road car it is often important to allow the pinion nose to dip as the suspension rises to avoid hitting the floor.
Cheers
Greg Locock
RE: Pinion Angle
I am still interested to know whether there is an effect on traction caused by pinion angle?
Is this just a Myth?
RE: Pinion Angle
There is no more torque being generated, there is no effect on wheel loads, or compliances, so I really can't see where a traction benefit would come from.
Cheers
Greg Locock
RE: Pinion Angle
RE: Pinion Angle
Kevin
RE: Pinion Angle
Kevin
RE: Pinion Angle
have a look here:
http://buickperformance.com/Pinion.htm
RE: Pinion Angle
The cyclical accelerations are a function of the sin of combined angles of the longitudinal axes of the trans (or output shaft), drive shaft (or halfshaft) and the pinion axis (or carrier bearing), and it is opccilatory and the torque on a 4 link rear suspension (or a simple leaf spring suspension) will torque the axes near normal.
As for the occilatory frequency contributing to the cornering forces... I'm just not sure that it's of a magnitude that it can help or hinder.
And remember, anti-dive and anti-squat are nothing more than the suspension going into a binding condition (read, non-linear and mostly indeterminant).
Peter V
RE: Pinion Angle
With horizontal trailing links, your friend will experience a considerable amount of squat. If the intersection of lines through the links, as viewed from the side, falls on a line passing through the rear tire patch and intersecting two other lines, one a horizontal line through the center of gravity and the other a vertical line through the front tire patch, the car will neither squat nor rise.
All of the above applies to a car with a "beam" rear axle. With an independent rear suspension, the no squat/no rise line is parallel to that which I've described, but passes through the center of the rear wheel.
RE: Pinion Angle
RE: Pinion Angle
As for my reference (in my thread on equal rear tire loading) to "some" racers realizing the traction effects of pinion angle, I would now modify that to "one possible" racer. I have been able to find only one racer, on another board, who knows a guy who says that he adjusts pinion angle for 60 foot performance. And, I'm rather doubtful of even that one example. But, my analysis does have some value, for I now realize that the first Ramchargers car, a C/A with a steeply inclined drivetrain, would have had a sufficiently large pinion angle to have an effect. There was no angularity in the drivetrain, understand. It was just that the engine valve covers were right up against the hood, resulting in a steeply angled drivetrain. We used an asymmetric 3link with the single upper link offset to the right. But, I did not take pinion angle into account in the setup equations. That upper link should have been offset a bit more for equal rear tire loading.
RE: Pinion Angle
RE: Pinion Angle
Your description of an offset, or asymmetrical, trailing link is the best solution for equalization of rear tire loads. This was used by Jaguar in their early C-Types. (Late C-Types had IRS.) The Jaguar design, however, used 3 links. Two were symmetrically placed below and the third was above, offset to the right. (Your suggestion will work, of course. It's just that the 3link is more easily implemented.) This was copied, by the Ramchargers, in their first car, a C/A. Unfortunately, I had not then correctly solved the equation set and the suspension never exhibited its true potential during the competition life of the car. The proper setup equations, offering both equal tire loading and no squat or rise, are included in my contribution to the Student Workbook which accompanies the Millikens' "Race Car Vehicle Dynamics," available through the SAE or Amazon.com.
Braking problems exist only if the fronts are "locked." Of course, with one tire more lightly loaded, dynamically, such a situation is more likely. But, Jaguar seemed to be satisfied with the braking peformance of the C-Type.
RE: Pinion Angle
I am more an engine man than a suspension expert, but as we got the car ready and raced at out Supernats last weekend, I have since found some time to contemplate your comments re pinion angle and torque reaction on tyre loadings and traction. I have also seen some discussion on this matter in another forum.
After this disacussion and contemplation, my thoughts go like this:-
For every action there is an equal and opposite reaction.
The original action is the torque generated by the motor.
On a race car, this is transmitted directly to the chassis rails via the solid engine mounts.
The torque of the motor is also transmitted via the longitudinal drive train to the pinion gear.
The pinion gear acts on the crown wheel in several ways.
One action is to turn the crown wheel, axles, wheel and tyres until there is a reaction at the contact patch This moves the car forward. The reaction to the turning of the crown wheel, lifts the pinion and front of the car.
The other action is for the pinion to try to twist the axle houseing in the opposite direction to the pinion rotation.
On a rigidly mounted rear axle like a hard tail dragster, this reaction is applied to the relativly rigid chassis, and is equal and opposite to the reaction at the engine mounts, so they cancel each other out, except for any twist generated in the chassis rails between these points. This twist should be minimal, and easily accomodated by the very flexible tyres, with negligable difference in loading
On a car with IRS, the differential houseing is rigidly mounted, so same situation as a hard tail dragster.
On a beam back axle with suspension, the reaction is transmitted to the chassis via the springs, allowing considerable movement, thus unloading one wheel.
This unloading can be roughly counteracted by preloading the wheel that lifts to try to obtain equal weight under near maximum torque, to get best average weight dureing the phase when traction is most critical.
I wonder if a better solution might be an extremely rigid anti roll bar, like say, one made from 2 or 3' chrome molly tube, with as short as possible longitudinal links.
This would have the effect of makeing the car effectivly rigid in roll, but still retain longitudinal compliance. Is that yaw or pitch? I did say I am not a suspension man.
Sorry for the very long post, but you did get me thinking.
Am I wrong in my analysis, as no one seems to do it this way
Regards
pat
RE: Pinion Angle
RE: Pinion Angle
I would like to implement no squat or rise on my clubmans style car with a beam axle and 4 link rear.
John
RE: Pinion Angle
Basically you jack one axle of the car up, and measure the increase in wheel load on the other end.
You need to pack the springs, and empty or completely fill the fluid tanks.
http://www.jeepaholics.com/tech/cog/#_To...
doesn't include either of those tips, but shows you what to do.
Cheers
Greg Locock
RE: Pinion Angle
I prefer what I call the "tabular" method. You tabulate the height, weight, and height*weight products for as many components as you can and then select a reasonable height value for that which remains and include that product. Dividing by the total weight, you then have a fairly accurate measure of CG height.
RE: Pinion Angle
The method Greg suggests becomes more accurate as the car is lifted higher at one end. The method used among some of us LandRover enthusiasts is to lift one side of the vehicle, having placed some hay bales at the other side. The jack is raised until the vehicle reaches its balance point, when a plumbline gives an accurate indication of the CofG.
Don't try this at home, kids!
RE: Pinion Angle
http://www.accessiblesystems.com/60Degre...
RE: Pinion Angle
I need to fix now some angles of the suspension, whereby the only fix point is the front fixation of the lower trailing arm which is about 46cm, the upper one will be about 40cm and sit further back (like Steeda's link for the Ford Mustang). Hence the a line through the front pick up points of the trailing arms leans massively backwards. The distance from the middle of the back axle would at max 7cm. What are the ideal angles for the lower and upper trailing arms, when the suspension moves 4.5 cm upwards and 2.5 cm downwards from rest?
cheers
Tommog