We have gone through full testing of Bump steer inducing tie rod end locations and have found that the inner joints need to be moved up 15mm and in towards the centre 75mm We tested multiple locations and combinations to for both inward outward location and height above and below the OEM location to rectify our bump steer problem. This also requires you to extend both ties rod tubes by 75mm due to the new inward location of the inner ball joint. This change eliminates any bump steer diving and weaving problems. You can then use OEM front alignment settings and your C3 will drive like a new car. We have designed and made a plate that bolts on to the original drag link tie rod loactions to achieve this relocation of the inner tie rod ends.

 

OK, so you believe that you have solved the problem. Some data would be great.
And longer tie rod tubes sound easy enough. But this plate you designed? Can we purchase one? Can you give us a blue print to make one?
And, lastly, where in Australia are you? I'm up Sunshine Coast way.

 

They are at the lazer cutters right now and I will do a few extra's, my test unit is not available but once dressing, taper cutting and finishing is done they will be available.

 

Sounds good, keep us all posted. And yes. Some data on the results of this would be nice.

 

I agree with you 100% and have seen this mod once or twice.
Do you have any pics of the plate?
Would you be willing to "produce" a couple?
Count me in for the first one!

Here is a somewhat similar? design from Ridetech. Looks like a bolt-on plate to me.


And the Hotchkiss still-born prototype. Similar in design pickup points, but they were heading towards a single custom forged centerlink. This is the welded up prototype.


Both the above designs use raised and closer together inner tie-rod pickup points.
Seems like everyone came to the same conclusion.

Front toe-in change (bump-steer) can be reduced dramatically. Factory C3 toe-in change is an absurd .400" !!! It can be lowered to .010" when done correctly. That is Nascar race car levels. 40 times less STEEERING effect!

 

Bill is right here somewhere in Australia. So I'm thinking I should be on the top of that list when he gets some of these made.
Providing there not 9 million dollars of course.

 

Ah just cause you are closer you are going to cut to the front of the line?



LOL!

 

@4-vettes does have a 12 hour head start on us...

 

Ahhh, I think I was also the first to express interest.
And the shipping won't be as bad for me.

 

I have the VBP blocks installed for over a decade. Work very well.

 

Ackerman

What the heck is Ackerman geometry anyway? And how does it affect my steering feel?

Basically it affects the toe-in, just like bump steer, but it is also different.

Ackerman Geometry

Ackerman geometry is when the front ball joints and steering arm joints are aligned in such a way as to cause the INSIDE tire, to turn MORE than the outside tire, but only in a turn. It causes TOE-OUT to INCREASE more & more the farther you turn the wheel. This is needed because the inner tire actually travels on a smaller radius circle, than the outer tire, on a larger circle. This allows all four tires to roll freely, without any scrubbing involved. At max cornering all 4 tires will have the same slip angle.


The axle of all 4 tires points to the same center of the same turn.

In the pic above, all 4 tires are smoothly rolling around the center of the same turn, with the same radius. If you look at the front tires, there is significant toe-out required to do this. But that is what the tires want to roll smoothly.

Factory C2 / C3 setup:

Now Ignatz measured the existing factory C3 Ackerman angles, and found the ball joint / steering rod joint lines did not cross near the rear axle as required, for perfect Ackerman. They were much closer to a parallel system, than true Ackerman geometry. If they crossed at all, it was far behind the car. For explanation purposes, let’s consider what happens when they are parallel, in a turn.




What problem does parallel steering cause?

The two front tires are almost parallel in the turn. IE: the toe-in is the same as it was set statically, at rest. But the tires require significant toe-out to roll smoothly. So what happens instead? The heavily loaded outside tire carries 75% of the load in a turn, and will track the way it wants, and follow it’s circle diameter. Since there is not enough Ackerman induced toe-out for the inner tire to track smoothly, it becomes toed in too far versus what is required for smaller diameter circle. It does not roll smoothly. It must endure large (reverse) slip angles, and is in fact being dragged thru the turn by the outer tire that has the stronger traction. By looking at the extreme example on the right you can see this inner “tire drag” happening.

What does the driver feel?

• A large understeer or push, that gets larger the more you turn the steering wheel.
  
• This understeer and dragging of the tire slows the car down.
  
• The inner tire is not operating at it’s maximum traction slip angle, and generates less cornering force than it is capable of. Less traction causes the front end slips more. When the front has less traction, you feel it as understeer. Or push, or plow.
  
• The understeer deadens the response of the steering wheel. Larger steering wheel motions are required to get the front end to respond. It feels sluggish to inputs, by the driver.
  
• Tire wear is increased due to dragging of the tire, or caused by large slip angles.
  
• All the above causes the car’s track times to be slower.
  

VBP “Bump steer block” setup:

These bump steer blocks do more than just correct some of the bump steer, They correct the geometry much closer to Ackerman geometry. IE: They get the toe-out correct in a turn. They do this by moving the tie rod joint on the end of the steering arm, inward, roughly an 1-1/2”. This makes the two lines almost cross, near the rear axle, which would be closer to perfect Ackerman. Ignatz showed this in his string picture above, with the two strings crossing under the gas tank. In the factory setup, they either never cross at all, if perfectly parallel, or cross way behind the car.


Guldstrand or VBP Bumpsteer Block


Bumpsteer block installed, moving steering rod joint inward. You can see the anchor points of the string lines.

In the above pic, the bump stops cause the string line to move inward, and the two lines cross under the gas tank.


Ideal Ackerman Geometry where the two string lines cross under the rear axle.


Ignatz stringlines after the addition of the bumpsteer blocks. They cross under the gas tank, but at least near the rear axle. They cross point was much further back before the blocks.

What does the driver feel now?

• The exact opposite of the above bullets
  
• Less under steer in turns
  
• More lively steering response or driver feel in the middle of the turn, as reported by both Ignatz and Staley.
  
• Less friction.
  
• Faster lap times.
  
• Decreased tire wear.
  
• Higher cornering G-forces
  
• More traction in the front end. Basically less understeer.
  
• Quicker turn-in
  

We should more correctly call these things, “Correcting blocks for both Ackerman and Bump Steer”.



No wonder they are called just “Bump Steer blocks”, for short! LOL

 

OK, so basically your saying these little adapter blocks are a really good thing.
But are they sold anymore? They look like a affordable solution. They also look like drilling would be required on later C3's as they don't have both sets of holes in the steering arm.
The bump steer kits I see sold show new tie rods and special ends. And get stupid expensive when looking at shipping overseas.

 

So how do we fix both bump-steer (toe-out on bump) and low Ackerman (toe-in on turn)?


Zero bump steer would have all three links point to the same "instant center"

The Bump steer blocks help with this because they lower the steering rod joint down roughly 1"

The bump steer blocks move the steering rod pivot point down 1" from green to purple circle. This corrects the angle of the steering rod pretty well and makes it aim at the instant center point of the two a-arms.

That change makes the bump steer curve change from a tilted line to kind of straight up. It is even above and below the ride height.
This chart also assumes you are using a 1" longer upper ball joint, which changes the height and location of the instant center.

The pink line is much improved. Almost zero bump steer at 1" above or below ride height, during compression or rebound.

But this chart still has a curve to the improved pink line. It makes the car go into toe-out at 1.5" of suspension movement. The reason it still has a curve shape to it is because the tie rod itself is too short. We need to lengthen it.


Back to this same picture. The correct length of the tie-rod (joint to joint) is either the yellow or the green line, depending on it's height.
The existing red line is too short. Shortening the tie rod by 1-3/8" to add the Bump Steer Block, did not help. It actually made the curve worse.
We need to maintain the position at the steering arm bump blok (purple circle, not green) and extend the tie rod length by an inch or two, (from red line to purple line).
The correct location for the inner tie-rod joint is now above the centerlink, and an inch or two to the inside., in Purple Circle.

This is exactly what Bille3821 has found in Australia (post #81 ), Detroit Speed, Ridetech, Hotchkiss, and several old racers. There are several ways to address this new joint. Probably the least expensive, and most DIY, is to fashion a steel/aluminum plate that bolts to the existing centerlink, and re-locates the inner joint. Bille3821 says up 15mm and inward 75mm. That's 0.19" up and 2.95" in for the non-metric speaking crowd. That looks to be about right just to my eye.

Recommendations:
Longacre recommends .005 to .015" toe-out in bump. Never toe-in. Definately under .050" toe-out, or the car slows down. Looking at the VBP graph there is ~.075" toe-out at 1.5" bump. At least it came way down from the .200" stock bump-steer. I still feel like there is room for significant improvement. But then the Ackerman makes it go into toe-out. Do they cancel each other out, or just make the car squirelly as it moves around. I vote for squirelly.

My Plan:
I am inclined to pursue how to make or buy one of these centerlink plates. And maybe the bump steer blocks too. Those two items would fix 90% of what is wrong with the front geometry, without buying thousands of $ of parts I do not need or want. Unless I can get one from Bille3821. I have already contacted Ridetech and they are not interested in selling their similar centerlink plate separately. And I am not interested in their $6,000 dollar turn one system with everything from new aluminum spindles, sway bars, to coilovers, etc.
I would guess I can build one of these for $100-200. Even if I am way off and it is a few hundred it would be worth it to me! Maybe as a "team" we can make this work.

I guess the next step is to build a wood prototype and test the Ackerman and Bump Steer.

Duntov Corvettes has the bump steer block available for their race car builds. They now sell it complete with modified steering arms, etc. for $300. Maybe I should carve one of those up also and see if it can be produced for me somewhere. Or just bite the bullet and buy one.

Bikespace, if I make a Bump Steer Block out of wood, could you copy it and 3-D print it? I am not good with CAD. Maybe someone else here is?

Go TEAM GO!

Anybody else up for this?

 

I would be happy to!

I'm assuming you have steering arms with two holes in them (4 holes, each, for the nit-pickers).

This will give me an excuse to buy a proper drill press.