Steering Axis Inclination - Explained

What is steering axis inclination? The second of four short videos on wheel alignment. This video provides information on steering axis inclination, and the role it plays on automobiles.

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[michaelskalecki]

University is where I go for my engineering degree, your youtube is where I go to learn what I'm really interested in

[EngineeringExplained]

@yamenad When you're looking at the diagrams on the board, imagine that you are sitting behind the front right tire at looking parallel to the ground at it. The dotted red line is the line about which the wheel/tire rotates. The dotted green line is the center of the wheel/tire. The closer these two lines are at the bottom of the tire (scrub radius) the easier it is to turn, and less wear will occur. Hope this helps!

[EngineeringExplained]

[1] No, having a large scrub radius will make it more difficult to steer. However, at high speeds little effort is required to steer.
[2] Scrub radius is the distance between where the center line of the tire meets the road, and the line of the steering axis meets the road. By changing the camber the tire's center line moves closer to the steering axis.
[3] It doesn't heavily depend on caster. Caster moves the steering axis in a different plane, making the scrub radius change minimal.

[EngineeringExplained]

Bigger scrub radius means more tire wear when turning, and by altering the camber they're also going to change the tire patch, likely making it smaller. The trend goes, smaller tire patch = less overall grip, as there's less surface area of the tire "meshing" with the pavement.

[drahkas]

Dude, thanks. I have been noticing a slight *bump* in my WRX when I reverse and lock the wheels in one direction or the other and was worrying that there might be something up with the wheels or axles. You've saved me some embarrassment asking a mechanic about it at the shop!

[rsn]

These videos introduced me to vehicle dynamics. This channel is legendary.

[EngineeringExplained]

@PhilTheBroatian Because there are things between the steering axis and the center of the wheel. Brakes, suspension components, the wheel itself has an axle in the center obviously, from which it is driven. These components make it difficult to decrease that distance, though it would be beneficial if possible.

[EngineeringExplained]

Yes, many people have requested this kind of idea. I've started to incorporate real examples in my latest videos. It's difficult to pair with some topics though, but thanks for the feedback!

[rafaelrego]

Excellent videos.
I'm watching one by one, since the firts one. I'm almost an mechanical engineer (graduating at the end of the year), and this videos are such a precious thing for motorsport and cars in general interested.
Congratulations

[EngineeringExplained]

Oh my. Well, I don't really know. You can read on forums or just test things out. Make slight variations in each, and then see how the car performs. Make minor adjustments, and see how it changes. Work in small steps until the car behaves the way you want. Though I'm assuming there isn't time for all this, so I would check out forums and see what setups people like to use.

[EngineeringExplained]

Well, negative camber can be beneficial in corners where the tire will sort of even out with the ground and hold the car better. If you move the pivot of where the tire rotates you can also reduce the scrub radius.

[mojtabakomeili]

I have teaching experience in engineering. But what you are doing is awesome dude.Keep it up and thanks for making such an effort in amazing videos.

[EngineeringExplained]

Seems sound, glad you enjoy the videos!

[EngineeringExplained]

@Nicosh1471 It is also due to positive caster, which will be another video posted shortly. Positive caster plays a very important roll in keeping the tire straight. Glad you enjoyed the video!

[CR]

wow your channel blew up... good straight forward clear information... this is one of the very few channels that are actually useful for the world

[Nicosh]

I never knew this is what caused the steering wheel to return to centre. I always presumed it worked by some kind of elastic or spring operated mechanism! Thanks! :)

[EngineeringExplained]

Well for racing purposes you may use negative camber, at the sacrifice of tire wear. But when you're racing negative camber isn't going to be the major cause of your tire wear. It's the fact that you will frequently be hitting 1g of deceleration and close to 1g in the corners. Put's quite a beating on your tires. So for racing purposes you might ignore things like the scrub radius. Probably didn't make that too clear in my camber video.

[EngineeringExplained]

@HawaiiJackJr The amount of contact between the tire and the ground is almost identical in both scenarios. Regardless, power would not be affected.

[EngineeringExplained]

Because of the angle of the SAI, as the video describes. It forces the tire downward.

[JeromeDH]

Just for completeness, the angle of the steering axis on the y-z plane (the board in the video) is called King Pin.