Concerned about front track increase affecting ackerman?
 

Has anyone given any thought to the affects of increasing front track (using lower offset wheels for example) on stock ackerman?

I would think that the ackerman as been calculated based on the stock offset wheels. Going to say a +35 wheel on the front increases front track by 26mm, which would have a toe-in type effect when cornering.

Thoughts?

I don't think offset would affect ackerman at all, it just affects the scrub radius.

Ackerman is just the difference in steering angle between the two knuckles, offset doesn't change anything inboard of the wheels.

My understanding is that ackerman is present to account for the difference in the radius' of the arc that each tyre is travelling.

Given that the outside wheel is now on a greater radius than it was before, and the inside wheel is on a lesser radius than it was before, then both are (in my mind) experiencing a toe-in affect, as the out wheel should be turning less the further out it is positioned, and the inside wheel should be turning more the further out it is positioned.

The math doesn't support the concern.

The Ackermann Angle is measured as a equilateral triangle that is created by connecting the pivot points of the front axle with a line drawn to the center of the rear axle. Or more simply, a right triangle that is the distance between a pivot point of the front axle to the center point of the front axle (line A), then creating a right angle to the center point of the rear axle (line B), then extending back to the pivot point (line C).

The wheelbase of the car is 2570mm with a front track of 1520. This scribes a triangle where line A=760mm (1520/2), line B=2570mm & line C=2680. Angle AB is 90 degrees so angle BC (angle X) is 16.47 and angle AC must be 73.53.

Changing line A to 773 (adding 13mm) has the effect of changing angle AC to 73.26 degrees; a difference of 0.27 degrees (or an difference of 0.36%).

Keep in mind that you rarely drive with the front wheels at full lock, further reducing this effect.

I recently had 20mm spacers installed on my car (to fit a BBK) and there is a *very* pronounced change in the car's steering feel.

Best I can describe it is as being more reponsive but much less precise overall. More darty and 'go-kart like' but not in a good way if that makes sense. The steering effort feels higher and the steering feel versus chassis response now lacks linearity. I've also noticed additional understeer on corner entry unless you take care to shift the car's weight around and get a nice 'set' into the corner first, after which there seems to be more overall grip.

I'll leave it to the suspension geeks to figure out whether it's increased scrub radius, ackerman, effective changes in the spring rates, track width or whatever.

All I do know is that I've got some 10mm spacers on order to try and remedy the steering feel by narrowing the track and am prepared to go down to 5mm spacers if the 10mm spacers don't improve things much.

TL;DR IMHO adding wide spacers (and maybe low offset rims) *will* change the way the car feels for the worse.