Steering: Ackerman angles and short `quick` steering arms.

[junior]

Trying to dive a little deeper into the rack and pinion solution and arrived at this question:

When swapping a set of short steering arms on an otherwise stock front end, won't the Ackerman angles change if you keep the same length of tie rods? Most certainly when doing this swap, toe-in would decrease and need to adjusted...but what about the Ackerman angles...would they change for the better, or worse, or does it change so little it just really doesn't matter? What are your thoughts? Thanks, Junior.

[Chipmaker]

Its been a long time but if I member right,the length of the steering arms does not afect the ackerman angle.What does is the angle that the arms are in.Thay (the arms)should be in line with a point midway between the rear wheels.So unless wheel base is changed or the arms are bent wrong should be good to go.

[Jerry Forrester]

Yes, of course it changes, but not enough you'll ever notice it. I think a lot of the auto manufacturers threw the Ackerman principle out the window decades ago. I've seen quite a few new cars drive around a corner at a slow pace and leave black rubber marks on the pavement from the inner tire scrubbing on the asphalt.

Its been a long time but if I member right,the length of the steering arms does not afect the ackerman angle.What does is the angle that the arms are in.Thay (the arms)should be in line with a point midway between the rear wheels.So unless wheel base is changed or the arms are bent wrong should be good to go.

[Dan Timberlake]

The late great Carroll Smith In one of his " XXX to Win" books mentions that Ackerman (zero scrub when turning) is not worth pursuing. I think the explanation was when cornering hard the tires operate at different slip angles anyway, and maybe sometimes it is useful to turn the inner tire a little sharper to get it to help pull the front end of the car in tighter.
At different times in various racing venues "negative Ackerman" has been considered desireable.

Reducing Bump steer is more important.

[Mike Van Veghten]

Correct, as long as the two mounting points are still on the same line (the Ackerman line to the back), nothings changes.
Now if they didn't pay attention when the bent the arms, then yes, the angles could be off some.

Will it hurt the way the tires move, probably.......but no more thAn a set of offset front wheels do with changing the scrub angle...pretty much the same thing.

Mike

[bezhawk]

Correct, as long as the two mounting points are still on the same line (the Ackerman line to the back), nothings changes.
Now if they didn't pay attention when the bent the arms, then yes, the angles could be off some.

Will it hurt the way the tires move, probably.......but no more thAn a set of offset front wheels do with changing the scrub angle...pretty much the same thing.

Mike

Exactly! that's why it's important to get the correct offset wheels. Idealy, the scrub radius should be 0. The centerline of the tire patch should be in the exact center of the king pin pivot . That is....if you took a line drawn vertically through the centerline of the king pin and extended it downwards till it touched the ground, it should contact the center of the tire patch.
Since you are talking Ackerman angles, you know that one wheel turns sharper through turns.If the scrub radius is not 0 then un even forces will act with greater pull.

Olds Toronados had had highly negatively offset wheels to get the scrub radius in line . The engineers discovered with that car with that much power, and front wheel drive...that unless the scrub radius is perfect you'll get torque steer under power (they don't).
What does this have to do with rear wheel drive Studebakers??? Well, just that you will wear tires that much faster if you mess with the scrub raduis.

When you change wheels, with different offset, or change TIRE DIAMETERS then the scrub radius changes too.

[Corley]

Just corner fast enough that all 4 wheels are sliding and you will never notice... Ackerman is important, but not critical to be "exact". Don't sweat the small stuff.

[Mike Van Veghten]

Olds Toronados had had highly negatively offset wheels to get the scrub radius in line . The engineers discovered with that car with that much power, and front wheel drive...that unless the scrub radius is perfect you'll get torque steer under power (they don't).

Not completety true.
If you look close, the reason the wheels had so much offset was the bacic design constrants.
1. a big engine.
2. a big transmission
3. a "relativly" narrow car body
4. forced front wheel location
5. front axle...oh yea...we need a pair of front axles...!

See line #5 above. The wheels are so offset are because of #1 thru #4. And the fact that a SHORT pair of axles will exacerbate the u-joint wear greatly over as long an axle as they can get in there.

My Mom had a 66 Toronado (she loved that monster), and I was the caretaker of the car, so I'm pretty familliar with the chassis....at least as far as my memory allows me to have..!

Mike

[1962larksedan]

Trying to dive a little deeper into the rack and pinion solution and arrived at this question:

When swapping a set of short steering arms on an otherwise stock front end, won't the Ackerman angles change if you keep the same length of tie rods? Most certainly when doing this swap, toe-in would decrease and need to adjusted...but what about the Ackerman angles...would they change for the better, or worse, or does it change so little it just really doesn't matter? What are your thoughts? Thanks, Junior.

I don't see why using 'Avanti' steering arms would hurt since the 1985 down model was built atop the 1951-66 Stude car platform.

[junior]

okay, thanks for your thoughts...so I gather it's really a non-issue. A little knowledge is indeed a dangerous thing...more questions to follow as I self educate on this topic. (r&p steering that is) cheers, junior.

[Corley]

One thing to watch out for when making this switch is that different cars use different amounts of pressure for the PS. You can adjust this with the pressure relief valve on most pumps, but if you just connect and hope, you might easily wind up with some very twitchy steering, or perhaps something worse... Research the specs for the pump and rack you use. (Assuming you use a power rack, which you may as well.) Another thing is be sure your rack is for rear steer, and not front steer. Use the wrong one, and you will have an exciting time of steering backwards (turn the wheel right, and you go left). Still another thing is how you are hooking it to the steering column. Lot's of U-joints out there that can marry this to that, X# splines to double D, etc. but you will either have to cut and modify the stock column, or use some other makes column, or maybe an after market column. This can get dicy hooking everything up, cutting a new firewall hole, securing to the dash, etc. If you are an automatic with a column shifter, that can be an issue, (different shift pattern, lighted indicator, linkage differences, etc.), and even the horn button hookup can be a pain on some after market columns. Hec, just getting the column shaft to not interfere with the manifolds can be a hassle, since it extends further forward and lower down that the old steering gear. Above all, if you do this, make it safe. Don't cut corners on the mounting brackets, the U-joints, etc.... Let us know how it goes!

[Alan]

If you find a non power center steer unit let us know. I have been at Pick a Part looking under all of the late 80's through late 90's Old's and Buick's and all I can find are power.

[Jerry Forrester]

One thing to watch out for when making this switch is that different cars use different amounts of pressure for the PS. You can adjust this with the pressure relief valve on most pumps,

Here's the pressure adjusting valve you need to use. Both the pressure line and the return line go through it. Adjusting it just allows unwanted pressure to enter the return line.

[48skyliner]

Converting to a rack and pinion steering is not just a bolt-in project. It is highly unlikely that you can do this without some welding at some point, whether it is the steering shaft, mount brackets or whatever. We fitted the Skyline steering column and found that the steering shaft was about 3 inches too short to fit the 240SX rack, so it was extended. So far as we can tell, the Nissan power steer pumps are the same. Notice the shiny piece of 1/4 inch aluminum plate under the motor mount - necessary to provide clearance from the turbo downpipe (which is cast iron and cannot be easily modified).
The power steering rack is a good idea, maybe consider using the pump from the same car, or at least the same manufacturer. If there is an issue with pressure or flow rate it may be addressed by changing the pulley on the pump to raise or lower the speed.

Regarding the Ackerman, I spent a lot of time studying Carroll Smith's books, building a model, and contemplating my navel when I designed the Stiletto, and I constantly reminded myself that his books are oriented to building and tuning RACE CARS. The average old Studebaker is going to spend more time making tight turns in the grocery store parking lot than hard turns near the limit of adhesion at 100 mph, and the old school theory about the steering arms lining up with the center of the rear axle is certainly close to optimum.

The most important factor when you are selecting a steering rack is the length of the rack between the ball joints, because that affects bump steer. In a simple design, the steering rack ball joints should be on the line drawn between the upper and lower A-arm pivots as seen in the front view. This gets more complicated when the A-arm pivots are not parallel to the vehicle centerline. If you are using a center steer rack, similar issues apply,but I have no experience with it.

[bezhawk]

Ackerman angle is designed in because cars have width to them.Therefore the inside tire turns in a different arc in a turn than the outside tire. If they don't you will slide the outside tire thru the turn.
We had 4 Toronados, 66,67,69,70GT. The main reason they tucked the wheels in is so the centerline of the wheel is in centerline of the outer constant velocity U-joint. If they are out they will not steer straight and true under torque. They are great cars.