were you all the way to the left and then came all the way back to the right? or just centered and then turned all the way to the stops?

 

Full lock, all the way left to all the way right and then vice-a-versa. The stops either way are kind of soft. Next time I do this I will get out and look. And to do this right I will head to a parking lot and measure the turning circle.

 

Stock (power steering car) was about 3 full turns lock to lock
Borgeson (12.7: 1 ratio) was about 2.5
Borgeson (10:1 ratio) is just under 2

 

Well I am glad someone is reading / watching this!

It turned out to be more work that I thought.

In for a dime, in for a dollar!
I'm committed now. Or maybe I should be....

 

Will the number of turns on the steering wheel from full right to full left lock to lock also depend on the diameter of the steering wheel?

 

No. The steering arms hit the bump stops on the a arm even before the box bottoms out.
A smaller dia wheel gives you more room to get in/out and changes the ratio, a little stiffer.

 

The circumference of the wheel gets smaller as the diameter decreases so if you are palming the wheel to whip it around faster, a smaller diameter wheel will travel a shorter distance under your hand but the circle is still 360 degrees.... but as stated by Leigh if you are using manual steering you will feel the necessary torque to turn the wheel increase with a smaller wheel

 

No measuring, just an update.
Ackermann causes toe-out in the horizontal plane only. IE: when you turn the wheel.
The bump curve causes toe-in or out when the wheel travels vertically, IE: when you hit a bump.

BUT in a turn both things happen at the same time! And that is where Ackermann is useful.

In a turn, you need to combine the toe-in change from this chart:


AND this chart:


I have all the raw data, and this time I thought a table showed the results better than a chart:
In a turn, one wheel goes into compression (bump) and the other side wheel goes into rebound (extension) and you are turning the wheel (ackermann).
You add all three values together to see what hapens in the middle of a turn.

• All the values above assume you start with the static toe-in set to zero, these values add to that, as the tire moves up/down, or right/left.
• The toe-out change on a one wheeled bump, or a two wheeled bump/dip can cause considerable self-steering. Aka: twitchiness. Even when the steering wheel stays straight ahead. Especially when the toe changes over 1/16" or more.
• Did I really run bump steer curves on 17 different alignment variations? Wow. Only 5 of them (so far) have most of this bump steer effect eliminated.
• But in a turn one wheel goes up, and the other goes down, and it looks like the two (opposite) bump steer effects almost completely cancel each other out. The "total bump steer in a turn" is very low in almost every case, almost neutral.
• Then you add in the Ackermann effect, from turning the steering wheel, and get the total Toe Out, (if you could measure this in the turn).
• The total toe-out is about 1/16" positive in almost every case! And 3/16" pos with the bump blocks.
• A little toe-out is a good thing. It helps prevent you from dragging the tire along. And helps prevent understeer.
• As before, the 45mph turn, (1/4 wheel turn) could likely benefit from the extra toe-out from the bump blocks, if you are worried about lap times.

 

Hey Leigh,
Contact these guys about manufacturing the bump steering blocks.
I’ve never used them but found them looking for the spark plug wire looms .
They are local enough to me that I can be an eyes on contact if you need one.

 

Thanks for the lead OCB!

 

I'll throw this out there as a potential item of interest. I recently bought a 1960 Vintage Race Corvette, and after one test and tune session I decided the front king pin suspension definitely required an upgrade. I am building a new, bolt-in front suspension so the car can be returned to its vintage form at any time. In order to retain the Duntov racing brakes (C-3 calipers and rotors), I decided to use as many C-3 components as I could. These are the new VanSteel 1" drop C-3 spindles - CNC machined 6061 and 1" taller for better roll center. They appear to be high quality, and they are compatible with stock C-3 control arms. I will not use the steering arms as my project will use a front steer rack and pinion, but VanSteel has indicated a willingness to fabricate steering arms of my design for me. I will install the VanSteel spindle/steering arm assembly in a 15" rally wheel and then repeat with the stock spindle and steering arm to get a pictorial comparison of where the tie rod attachment points lie in comparison with each other. It will be interesting to see if standard C-3 bump steer characteristics have been altered. More to follow.

 

Oh My!
Where is my wallet!

 

That steering arm looks to be much lower than a std c3 steering arm.
And a std c3 arm needs to be lowered about ~1.5" to fix the bump steer.
So that design my address that issue.
But only with a c3 idler arm and centerlink height. Not sure how that translates to a 60.

Van Steel has also offered to work with me and is willing to make a custom steering arm for the std c3 spindle to fix it's bump steer issues.
Or some other part that may come out of my research.
Back to measuring tomorrow!

 

Good day to be in the garage. With the heater on!

It's pretty.
But thankfully it is not even enough to worry about shoveling.

 

Ohh my that looks cold.
Yesterday we were hiking with the pups and it was warm enough that I wished I had worn shorts.

 

LOL I put that pic up just for you!

 

I'm not going to put up a pic of my back yard. You'll all want to shot me! I mowed the lawn on Saturday. It's Tuesday evening and it looks like I should do it again.
I will say I keep watching this thread. Although I never realised I had a bump steer problem. I just let the wheel do it's thing over rough bumps in a curve. Just a very losse grip on the wheel, let it shake as it wants to. Car still goes where it needs to go. Just how old cars are. I'm pretty used to it.
If this thread ends. Perhaps the perfect answer for us guys with mostly stock cars will pop up. And hopefully it won't cost a Kings ransom. If so, I'll be all in. If it costs a small fortune. Count me out.
Anyway, I keep watching.
The lowered steering arm certainly sounds good. But at what cost?

 

Doc;
You described bump steer perfectly from the driver's perspective!

The wider a tire you put on the car, and the tighter you make the suspension steering, the more you notice this movement or "shake"

There are entire suspension solutions out there now that correct this, but yes, I would call $8000+ a "king's ransom"!
It is not enough of a problem for me to spend that much money.

But if you want a sneak peek at where I am heading, just promise not to laugh at my backyard engineering:

Protoype #1
Yes it is made out of 3/4" cardboard! LOL

This is a bolt on draglink/centerlink adapter plate that raise the inner tie-rod points both upward, and inward, about an inch each way..
Before you laugh, both racers and Ridetech do something very similar, but Ridetech changes almost every part in the front suspension at the same time, that drives the cost very high. I am doing it the racer way. Just change what you need.

This is a mockup just to check clearances. And see if I can get any kind of bump readings off of it.
It obviously still needs a large scoop out of the center for oil pan clearance.
If it works, wood or metal is the next prototype.

My target is one or two pieces to cure just the bump steer in these cars, and for it to be an affordable, bolt-on, and not require other changes. The Ridetech solution cost $8000 for the entire front suspension, and will not let you run C3 brakes. That is about 6 more changes than I need, just to fix one issue.

I considered lowering the steering arms themselves. But they would have to be be much lower than they are now. And then they could easily interfere with tire sidewalls, wide wheels, etc. And billet arms would likely be costly. Geometry wise, this plate works the same to raise the inner point instead. All we need to do is change the tie-rod "tilt" angle, it does not matter which end we change to tilt it. I see some other advantages to doing at this end as well.

Today is measuring day again!

 

Here is my mad scientist reason behind moving the tie rod pivot.

To get a linear bump curve both tie-rod ends need to land on this suspension pivot line. Even the stock OEM inner location was 1.5" too short. But it still yielded a pretty straight line bump curve graph. Just tilted.

The main problem I have with the bump blocks is they shortened the tie-rod another 1.25". That is what produced the pronounced curve in the bump steer version of the bump steer graph. The OEM steering arm locations are exactly in the laser line of the a-arm pivot points. I mean perfect! Adding the bump block moves the pivot point 1.2" inside of the laser line. Wrong direction. That is a negative for no noticeable gain. According to many, there is "supposed" to be be a gain in Ackermann.

Second issue I had with the bump steer blocks:

The bump steer block hits the frame, well before the normal turn bump stop.
Reducing the turning radius. At parking lot speeds anyway.

Steering box movement one side only:
1-3/4 turns to hit box internal stop
1-1/2 turn to hit a-arm turn stop OEM Fast Ratio hole
1-1/4 turns to hit a-arm turn stop with bump block

Third bump stop issue is the lack of any help with advantageous Akermann steering effect at any speed above 40mph, or steering wheel turns at 1/4 turn. The effect starts to become noticeable at 1/2 turn but this is at a very slow 30 mph speed. The primary effect is at 1 full turn, which is parking lot speed. According to myth, and theory, there is supposed to be a positive effect from more Ackermann Steering. But on this car, the measured effect is miniscule at 40 mph, and only comes into play at even lower speeds. Myth busted!

So between all that, and the cost of a billet steering arm, and possible tire or wheel interference issues, all that "steered" me away from dealing with the "bump blocks" The blocks are just easy to measure, and to manufacture. And a quick fix. I am convinced that is their main advantage. And the reason for their existence. They are easy.

So we know the engineers could have done better, even in 1963. So why did they design the suspension this way? My theory is they designed in the large 1/4 inch of bump steer toe-out ON PURPOSE. It would help the car in a turn on the race track, at any speed, not just higher speeds, and be consistent. Yes it would give a bump steer effect on bumps, but with the skinny 5" wide tires of the day, that became a trade-off. And most race tracks are smoother than public roads anyway. We know Duntov favored the racers. It must not have mattered too much. Just put up with the steering wheel "shake" as Doc mentioned. You "saw" at the wheel anyway on the racetrack. But with today's 50 year newer and twice as wide tires, it just becomes very annoying. These tires operate at very low slip angles, compared to the skinny tires of old. It is hard to feel a narrow slip angle when your steering is "shaking" even more than that! And on the street, it is just annoying.

There is a better way than "bump blocks". It's just harder to figure out.

 

As promised, here is a comparison of the OE spindle and the VanSteel dropped spindle. Both have OE-style hubs and a C-3 rotor in a 15" rally wheel.

Edit: For some reason the photos are not uploading. I will try again later.