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I need an opinion please. I’m building a street rod with a long wheelbase. The front tires will be about 3” wide with rear tires 14” wide and most of the weight on the rear. I’m getting ready to make my steering arms. My question is should I make the rear intersection at the center of the rear end or forward of axle centerline to give turn in authority and if so how much? Thank you for your time.

The ideal Ackermann for a street machine is going to be the center of the rear axle. But to be honest you are not going to see any real difference in turn in capability with minor changes in the intersection point. I can tell you for a fact that OEMs use the same steering geometry for three different wheel bases without any issues. Davew

Thank you for the quick response. I have been a lurker for years and knew you guys could help me out. I’ll be posting progress on “Birth of Long John”

I should have asked if you are using a straight axle? Is the objective to minimize steering effort during turning? Davew

I wouldn't be overly concerned about exactly where your ackerman ends up. Sure, some is better than none, so add a bit of it. But there isn't enough ackerman in the world to give you 'turn-in authority' with those pizza cutter front tires.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

You are right about the tires. I don’t expect to be diving into a hair pin turn or anything. This will be a street driven fun car. I’ll just get to the speed limit REAL FAST!
I’m not real concerned with steering effort. I’m using a Unisteer half rack.

Back when skinny tires were all that existed, OEMs used all sorts of Ackerman, and even anti-Ackermann. Didn't matter much to skinny tires, and matters less as wheelbase goes up.

It's a little-known fact, but every once in a while luck can run your way...

If you have steering arms already, whatever they give will probably work OK. If you have to make the arms, just go parallel so bump steer hassles are reduced.

"I’m getting ready to make my steering arms." Drill an extra hole or two and use the hole that suits yer driving venue. I'm using replaceable arms for that reason.

Forgot to mention the arm attachment to the upright is height adjustable for bump steer correction.

From a practicality standpoint, it can be very hard to push a car while turning if it does not have Ackerman. How much so depends on a number of variables, such as amount of Ackerman, weight on wheels, tire width, tire compound, road surface. Also, you have to ask yourself how often the car might need to be pushed. I suspect anyone building a car from scratch has to honestly say, "a few times, yes."

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Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
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