How important is KPI on an off road mower?

Just like the subject says, how important is KPI on an off road mower? I was going to make my own spindles, and was thinking if the rear is locked, then I would need all the help I could get in the steering department... However building them without the 10° KPI would be easier...

I am assuming the angle you are referring to is also called the "caster".

If that is the case, then the biggest difference you will notice in having this set correctly is high speed (+25 MPH) on a flat surface, like asphalt. If you are just doing low speed offroading/mudding it won't likely be much of an issue.

The KPI or king pin inclination is different then caster. The KPI is the amount of degrees the king pin is tilted towards the inside of the axle and caster would be the king pin pointing front or back.

http://www.mech.uq.edu.au/courses/mech3100-old/steering/kingpin.gif

This might help explain it. typically you would have about 10° of caster and 10° of kpi. The spindle shaft would then be welded in a 10° offset to keep the spindle shaft parellel with the axle. It helps to shift the weight in a corner. And being that I am going to lock the rear diff I want it to steer without too much understeer... Was just not sure how much of a difference it would make.

Cool... thanks for the info. We set ours up with 10 degrees caster and no camber or noticeable toe at all. They steer fine at speed while offroad so IMO you could get away without it.

Another main reason is I see KPI already built into a lot of stock axles. So I did not know what effect it would have in not having any. This 70's Ford tractor I'm working on had about 10° KPI, but no caster. Most MTD mowers from the later 90's have both.