Ackermann steering affected by wheelbase

This question is not motorsport related but I can't find an answer. How could the Ackermann steering geometry be affected by drastically changing the wheelbase of a vehicle? In my case, a Ford F350 with the rear wheels moved right behind the back of the cab. The front steering has not been modified so the Ackermann geometry or TOOT angle is still set for the original wheelbase. I have noticed feathering on the outer edge of the tire tread and was don't think I can fix this without major modification to the vehicle.

This entire scale of this drawing is completely arbitrary, but it should illustrate the point. If the F350 had perfect Ackermann to begin with, it would look about like this. When you shorten the wheelbase the point where the 2 front tires meet won't be inline with the rear axle, and will result in some scrubbing. Ackermann is effectively just a trapazoid, and adjustable ackermann is an option for some vehicles. The difficulty of modifying it is going to vary depending on what aftermarket is available, or how the vehicle is setup so it's hard to say how major of a change it might be.

As Robbie said, the axis should meet at some point, when projected.

There are other things to take into account, like tyre slip angles, if it were a performance vehicle, and some manufacturers use excessive angles to promote safe (?) understeer in production vehicles.

In this case, it may be possible to selectively modify the stock steering arms either by bending them - this is a specialist job, so make sure the person(s) doing it know what they're doing, as it can affect the forgings, or by machining the mating surfaces where steering arms are bolted to the stub axle assembly.

It isn't that difficult, if one knows what one is doing - you may even find a steering specialist who specialises in this type of work - try companies that sell dropped spindles and lift kits - they may be able to further advise you.

hi brady i work in the airforce with f350 for towing aircraft (also with f150,250,450 y 550) and we have the same problem. i noticed that, in our case, we have some extra weight in the rear for help the tow of heavy aircrafts, and the front suspension tend to up, so the contact of the tire is in the out. maybe is you try to put the correct rear rate spring can help to solutionate your problem. regards

Sadly, spring rate doesn't change the tyre loadings - that's down to mass distribution.