How King Pin Inclination Angle (KPI/KPA) Works

Today we look at kingpin inclination angle, known as KPI or KPA. Largely a consquence of packaging, KPI does provide a degree of self centreing due to lifting the cars weight, and can help with jacking forces in spool equipped cars. It provides the opposite effect to caster though, so must be balanced accordingly.

[@Daltonleach11]

On dirt tracks, kpi is actually helpful. When initiating a turn, we want to take weight off of the rear left and somewhat the front right tires. Kpi shoves the front left tire down, which helps us accomplish this. Then, when counter steering after initiating the turn, we want the rear left to take the weight again. So, in that scenario, it's actually quite helpful beyond just compensating for building limitations.

[@samonge7]

You can totally have your KPI at 0º in the center of your wheel using a pivot point above the wheel, or using virtual pivots like in 5 link multi link front suspension. Many newer cars use these principles, sometimes even combined like in the Hyundai genesis sedan up to 2016

[@garthrichert5256]

Thank you for all your effort to explain. Most appreciated.

[@jensensmith9391]

thanks Kyle, that was good, I found your explanation pretty easy to follow...subscribed.

[@zdravkomomci7570]

best explanation Ive heard so far thanks

[@galant310]

keep it up good job

[@dethkon2284]

If i have long wheel spacers, will i need to correct this increase inclination angle to maintain the same handling charcteristics

[@ItsJustGilly]

So I'm trying to investigate KPI for my 4-wheeled bicycle (quadricycle). Would the same as you explained in the video, rule for bicycle tires? They're round shaped, instead of being flat like car tires.

[@kedarashtikar6454]

how does kpi counter the camber change due to caster? can you please explain and refer some sources which may help me in this regards? Also how do you calculate the Anti-Dive or Anti-Squat percentage of the buggy if the A-Arm linkages are parallel and H-Arm linkage is parallel to camber control link Linkage....(With regards to Geometry)

[@sourabh19911]

I m making a go kart so cn u plzz tell me how much caster n camber will be good

[@Drum_x_Life]

Ehy man the KPI IS ONLY important for straight line stability or also in turns ? Thank you so much if u can answer me I will be so happy

[@Pedrorodrigues3986]

CAN U DO A MOTORCYCLE VERSION ON THIS SUBJECT(SUSPENSION WORK)?

[@chinmayt99]

Is there practically possible to have a 0 scrub radius by increasing a kpi angle ? @kyle

[@augustdubey9150]

does kpi define for rear?

[@pn42069]

Hey Kyle! How do you calculate the KPI and the scrub radius on a pull rod suspension assembly?

[@AwestrikeFearofGods]

Old comment, I know. KPI and scrub radius have nothing to do with pull rods, per se. Therefore, these are calculated the same as any other type of double-wishbone suspension: KPI is the front-view angle between the steering axis and a vertical line, where the steering axis is defined as an axis between the two outer ball joints of the upper and lower wishbones. Scrub radius is the distance between the steering axis' ground intersection and the center of the contact patch.

[@Ubernoob85]

If you're running inboard brakes, you can get less KPI since you can move your pivot points further inward toward the wheel. Therefore, you can run less caster since you don't have to compensate for KPI which isn't there. Does this reduced amount of caster provide any benefit?

[@noureldinmahmoud1508]

Ubernoob85 since u have less caster angle this means lighter steering but less feed back and less camber gain

[@kshitijbhosale8364]

What is generally value of king pin inclination for passanger car and trucks?

[@onino951]

If I run a certain positive KPI, and when I take a corner and it goes from positive to negative at the outside tire, what are some consequences I can see? Or does it not matter positive/negative as long as my scrub radius is closest to the center contact patch? Im doing some analysis through OptK for my fsae project and by changing the KPI angle, I managed to cause these effects. Was just looking for some guidance, Thanks!

[@dethkon2284]

You and i are on the same wavelength. It doesn't work you will get a brain anurism i have tried, to make the system work.

[@Drum_x_Life]

You can resolve this with caster

[@Drum_x_Life]

If you have the contact patch behind the point of rotation you have no problem

[@edcarver8926]

is there anything worth noting for toe in/out for open wheel race cars other than aerodynamics?

[@KYLEENGINEERS]

+Ed Carver Toe in/out actually doesn't have a huge effect on aerodynamics, it does however have a very large effect on handling, which I will be covering in a later video!

[@swapnalatha8590]

why king pin is placed in the steering mechanism ? I mean the main need of installing kingpin ?

[@ManishKumar-xb8sf]

What is the kpi for a go kart? And how will we decide that angle?

[@seetllee]

kpi for a kart must me much greater due to the fact that no differentials are used. The effect of kpi on weight transfer is such that the car tends to oversteer, while using no differentials leads to understeer. So huge amounts of kpi are used in order to compensate the lack of differentials on kart

[@siddharthbaid6092]

can someone give the link for the website he i stalking about in the start of the video

[@ZyNoOne]

If kpi is 0 degree, what will happen?

[@PhunkBustA]

the theory is all well and good and all but not many people have made any videos or put out any info that i can easily find on the actual practice of it, like how to measure it and find where the lines intersect, on an actual car with wheels on it, on the ground, everyone just explains stuff on a whiteboard

[@PhunkBustA]

its just easy to draw lines through stuff on a 2d surface rather than the actual 3d model

[@noureldinmahmoud1508]

PhunkBustA use a cad program

[@rigvendrakumarsrivastava521]

what is the website he talks abt at 0:20

[@acruzp]

moto IQ

[@koyyavenkatesh]

what is website talking about at 0:20 secs

[@aaronmansfield4758]

motoiq.com Mike kojima is one of the writers and has a ton of experience as well. A lot of great starting information on there!

[@4atu00]

Can you make video about F1's banned/limited aerodynamics, and how they would effect the car if they were allowed (for example bigger diffusers and "fan car technology"). And Aerodynamic Analysis about Red Bull's X2010 would be nice.

[@lurking0death]

You go off into outer space on tangential issues and lose everybody real quick.

[@theresastrickler4143]

He may not be high but he looks stoned

[@Drunken_Hamster]

**I** know how you could have the A-arm pickup points "inside" the wheel. Just build a hub without all the breaking system. And then build the braking system inboard the vehicle/before the A-arms.