Caster settings keep your wheels travelling in a straight line, because it gives it a center point to follow. Both caster settings and KPI affect how the front end will track and will cause it to center after a turn. Most big rigs are set up with a zero caster angle, or slightly positive, however most people add caster shims on the front axle to keep it tracking in a straight line better. Both these things effect how your front end will track, each working with the other.

Im in a truck shop every day and see hundreds of front ends pass by me. When it comes to centering the wheels after a turn KPI has just as much to do with it as caster, Fact.

Also, did you not just say that front end spacers have no effect on stability, but yet you continue to say it provides a higher G turn before it flips? Is that not stability?

 

BUT

I can see where this conversation is going, and Im not one for arguing on the internet, its lame[img]i/expressions/face-icon-small-tongue.gif[/img]

 

Man, you are getting technical about stablity. That's why I refered to it as handling stablity.

I guess it does help over all stablity if you look at it that way. But, it don't make make it corner any flatter, whick is the Raptors only real defect. So, you can have that one.

Dude, KPI has no affect on self centering. It is actaully an undersirable geometry trait because it causes goofy camber angles when the wheels are turned. KPI is only there to control road and braking forces that are transfered to the tie rod.

Do some internet searches and check it out.

But, I am not a mechanic like you. I was on a front end design team in College though. So, the experience I have is text book Senior Design and trying to make the Raptor corner good.

 

I concur. I will drop it.

 

I do agree with the raptor having the rear wheel turn problem, and that is somthing that defently should be addressed.

KPI gives you a pivot point for your wheels so that they don't scuff around cornors. As you cornor your camber changes, and it is the weight of the truck, and the KPI that brings it back to center. Because the camber is set at a resting straight ahead position it naturally wants to center its self as your driving down the highway. So as you turn your wheels start lean outwards, or positive camber. The weight of the truck forcing down on them pushes them to go back to center. <u>As you said the KPI changes your camber settings on turns. Because the camber is now changed they naturally want to return to their resting position.</u> Like I said, Caster, camber, toe, and KPI all have a effect on front end geomoetery. In order for the front end to track straight everything must be working together.
Most heavy duty rear ends use torque rods to control the axle from spining in the housing, and this is also similar to what KPI helps to acchive. Trucks with zero KPI will handle like a shoping cart. [img]i/expressions/face-icon-small-wink.gif[/img]

Im not a mechanic dude! Not yet at least. Im still going to school but spend 8 hours a day in a truck shop working on real life technicial problems, and I see alot of front end alignment problems.
I don't mind continuing this converstation, Its actually quite intresting. I just don't want this to turn into a internet war like 5 year olds throwing crayons.[img]i/expressions/face-icon-small-happy.gif[/img]

 

Cool. I can continue if this thread stays technical, not crayon throwing.

Think that the only way the weight of the bike can straigten the wheels is if the axle centerline is forward of the caster line and KPI line....like on a bike or motorcycle. The front axle is forward of the forks. On a bike, the forks are curved forward. This is so the weight straitens the wheel. The front of the bike actually lifts up when turning the wheel.

If you turn the wheels and front end doesn't move upward, then the weight of the bike is not causing the wheels to straighten.

The front end does not lift on a Quad when you turn the wheels.

 

Hey I was thinking about it more. If you have spacers on the front or reversed wheels, your front end will lift when you turn. If you have stock geometry and the KPI line intersects the tire where it touches the ground, you front end will not lift when you turn the wheels.

 

ok, im going to just get the rear spacers then. Should i get 1.8 inch in back, or the 2.5 in back ( both each side ) ? i ride in roads, snow, sand... plz help, thanks so much! oh, i dont jump at all.

 

On a raptor, the wider the back, the better. Get the 2.5s. It will be the single best purchase for your bike. It totally changes how it corners. The back end will slide now when you power up in the turns. Before, the front end would lift, and you would understeer.

I was ready to turn the Rap in for the Z400 at the time until I put those spacers on. What a mistake that would have been!

 

When you turn the outside of the truck or whatever lifts up, hence the whole I idea behind sway bars.