Kpi

[Pappy]

Does anyone know for sure the Kingpin Inclination (KPI) angle of the Gen 5 upright (spindle)?

Thanks

Pappy

[Roller]

There is no kingpin on the Viper. I believe you are referring to caster. The caster should be around 6 degrees.

Frank

[Pappy]

There is no kingpin on the Viper. I believe you are referring to caster. The caster should be around 6 degrees.

Frank

Hey Frank,

The king pin inclination angle, when viewed from the front of the car, is the angle formed by a line through the center of the ball joints and a vertical line where the first line intersects the ground, whether the suspension actually has a king pin or not. It is a fixed value based on the geometry established by the wheel axis shaft's orientation to the spindle center-line (ball joint center to ball joint center line). Caster is the angle that the spindle is tilted back (positive caster) and you are correct, the static caster recommendation for the Viper is 6 degrees. The Viper KPI will most likely between 6 and 8 degrees, which is common with most of the late model stuff like the Corvette. I build high-travel, low roll suspensions for other stuff, and I am trying to get a feel for how the Viper compares. Mostly I am trying to get a feel for what SRT did to accommodate the high aero downforce that is not common on most other cars. I can, and will if necessary, dismantle my ACR to take the measurements I need, but I was hoping someone already had the KPI number.

Thanks

Pappy

17904

[TrackAire]

Very interesting info on KPI,.....is your other high travel applications for the off road racing market? I am truly amazed at how the suspension on trophy type trucks and similar off road racers perform both off road and even on the asphalt sections when cornering.

[Roller]

Thanks for the info. When I saw kingpin I immediately thought of the kingpin in a straight, or beam axle. I guess I am getting old, LOL! Now I understand what you're asking for but I don't have the answer.

Frank

[Pappy]

Very interesting info on KPI,.....is your other high travel applications for the off road racing market? I am truly amazed at how the suspension on trophy type trucks and similar off road racers perform both off road and even on the asphalt sections when cornering.

Stock cars and road race track cars. My long term road race project car, now on its fourth suspension, has evolved to a high travel/low roll suspension much like the Sprint Cup cars did a few years ago (called soft spring/big bar (SSBB)). The premise is to build the suspension to limit camber gain during compression (old school was to build camber gain and let the outside tire do all the work) and build positive caster during compression that translates to "good" camber once the wheels are turned (more negative on the outside tire, less on the inside). When NASCAR dropped the front ride height rule, the teams just dropped the nose to the ground and set the camber for the track (lots of negative on the outside, lots of positive on the inside). This obviously doesn't work for road race cars that have to turn both directions. High travel/low roll suspensions are designed to force the inside tire to do more work in the turns. High aero downforce contributes to the same condition - more heavily loading the inside tire; therefore that tires' dynamic camber angle is more critical. The ACR, with its low ride height and rake has little front suspension travel opportunity, and what I think I am seeing is that the low turn angles in high-speed sweepers is not allowing the caster to contribute to reducing the negative camber on the inside tire. I don't see doing major design changes to a very well designed system, but I am curious about the strengths and weaknesses of the current design, especially with regards to how SRT is accommodating/using the high downforce. When I get all of the ACR's suspension parameters (control arm pick-up points, KPI, ball joint positions, steering arm and rack measurements, etc.), I will enter them in a suspension analyzer program for my own education. Maybe I will learn something that will help on current or future projects.

Cheers

Pappy

[TrackAire]

Stock cars and road race track cars. My long term road race project car, now on its fourth suspension, has evolved to a high travel/low roll suspension much like the Sprint Cup cars did a few years ago (called soft spring/big bar (SSBB)). The premise is to build the suspension to limit camber gain during compression (old school was to build camber gain and let the outside tire do all the work) and build positive caster during compression that translates to "good" camber once the wheels are turned (more negative on the outside tire, less on the inside). When NASCAR dropped the front ride height rule, the teams just dropped the nose to the ground and set the camber for the track (lots of negative on the outside, lots of positive on the inside). This obviously doesn't work for road race cars that have to turn both directions. High travel/low roll suspensions are designed to force the inside tire to do more work in the turns. High aero downforce contributes to the same condition - more heavily loading the inside tire; therefore that tires' dynamic camber angle is more critical. The ACR, with its low ride height and rake has little front suspension travel opportunity, and what I think I am seeing is that the low turn angles in high-speed sweepers is not allowing the caster to contribute to reducing the negative camber on the inside tire. I don't see doing major design changes to a very well designed system, but I am curious about the strengths and weaknesses of the current design, especially with regards to how SRT is accommodating/using the high downforce. When I get all of the ACR's suspension parameters (control arm pick-up points, KPI, ball joint positions, steering arm and rack measurements, etc.), I will enter them in a suspension analyzer program for my own education. Maybe I will learn something that will help on current or future projects.

Cheers

Pappy

Pappy,
I can't remember for sure the reason, but the Comp Coupes had longer upper A-arms than the standard Viper IIRC. Maybe some of the Comp Coupe racers on the forum can chime in as to what this did to improve handling/camber curve.

Are you the same Pappy that is one the Corvette Forum?

[Pappy]

Pappy,
I can't remember for sure the reason, but the Comp Coupes had longer upper A-arms than the standard Viper IIRC. Maybe some of the Comp Coupe racers on the forum can chime in as to what this did to improve handling/camber curve.

Are you the same Pappy that is one the Corvette Forum?

Yep, I'm on the Corvette forum from time-to-time. I have a C6Z/Z07 optioned car and one of my track cars is built under a modified early Corvette body (56). The 56 is a full independent suspension, high travel/low roll car designed with help from Ron Sutton. It is also somewhat of a downforce car (big wing, splitter, diffuser and diffuser tunnels incorporated into the belly pan, etc), hence my interest in the ACR's geometry - looking to see what geometry changes SRT made because of the ACR's aero, if any. With a little "chain saw work" and moving a lot of stuff I was able to get a 335X18 tire on the front (12.5 inch wheel with 9 inches backspace) with near zero scrub, 4.5 inches of compression, lots of caster gain, etc.

Pappy

18054

18055

18056

[Arizona Vipers]

Your'e HARDCORE Pappy! Good to see you last weekend!

[steve911]

Pappy,
I can't remember for sure the reason, but the Comp Coupes had longer upper A-arms than the standard Viper IIRC. Maybe some of the Comp Coupe racers on the forum can chime in as to what this did to improve handling/camber curve.


Comp Coupes used stock OE A-arms with monoballs. The later Comp Coupes had the REAR upper arm pick up points moved to provide for better trsck alignments.

[Pappy]

Comp Coupes used stock OE A-arms with monoballs. The later Comp Coupes had the REAR upper arm pick up points moved to provide for better trsck alignments.

Thanks Steve. Do you recall if the rear upper arm pick-up point was moved up or down - or inboard/outboard?

Pappy