GTD quick rack.

[John Milmont]

Re: Bump Steer Elimination - GTD quick rack.

Hi from new member,

Maybe I can post a chapter from a book I have that covers steering systems. In it anyone can find information on how to correct or redesign a steering system so it works properly all the time. Not sure why this wasn't done back when the GT40 was first designed and built.

I would like to know what book you're reading. The steering system, like all other aspects of the car, is a compromise and cannot be designed to be perfect for all situations, especially concerning ackermann geometry. Formula 1 even has whole different front ends with different steering racks and geometry for different tracks.

The original GT40 was the first car to use a computer to aid in the development of the steering geometry, does the GTD use the same geometry as the original 40?

But anyway, I think an aspect of suspension geometry that impacts bumpsteer which is often overlooked is anti-dive. GTbob posted a 2D drawing of your typical double wish-bone suspension layout, if it was this simple, finding the optimum location for the steering rack would be a snap. The problem is when you have anti-dive in the suspension, the path the steering pickup on the upright follows is no longer a 2d arc, but a 3d movement. This means that the pickup is not just moving up and down and in and out, but also forward and back.

There is suspension design programs out there that, after you model your suspension into it, can solve for the best location of the rack to minimize bumpsteer. Has anyone thought about this?

 

[Dylan]

Suspension software like that is not trivial to use and requires EXACTING inputs to get good numbers out.

 

[RichardH]

Raising an old thread...

What make/model is the "standard" GTD rack? As I might need to get mine refurbed.

Or is there a better replacement available now?

 

[Brett James-McCall]

I think it was a Cortina Mk4

 

[Robert May Eng.]

Re: Bump Steer Elimination - GTD quick rack.

I would like to know what book you're reading. The steering system, like all other aspects of the car, is a compromise and cannot be designed to be perfect for all situations, especially concerning ackermann geometry. Formula 1 even has whole different front ends with different steering racks and geometry for different tracks.

The original GT40 was the first car to use a computer to aid in the development of the steering geometry, does the GTD use the same geometry as the original 40?

But anyway, I think an aspect of suspension geometry that impacts bumpsteer which is often overlooked is anti-dive. GTbob posted a 2D drawing of your typical double wish-bone suspension layout, if it was this simple, finding the optimum location for the steering rack would be a snap. The problem is when you have anti-dive in the suspension, the path the steering pickup on the upright follows is no longer a 2d arc, but a 3d movement. This means that the pickup is not just moving up and down and in and out, but also forward and back.

There is suspension design programs out there that, after you model your suspension into it, can solve for the best location of the rack to minimize bumpsteer. Has anyone thought about this?

Someone wrote that getting to grips with suspension and finding the ultimate setup is like trying to get a ball to be in the middle of a triangle and the more you go one way with set up the the ball goes to a different corner rather than the middle. I asked a friend of mine that works within the drawing office of f1 team if he could redesign the front suspension of the gtd , in short the answer was no because I could not give him a fraction of the data needed to even start the program. When he popped round to see it in the flesh he just laughed and said "best of luck". So I will when I get round to the front end have a good dig about and attempt to better it.

Bob

 

[Jim Cowden]

Their are suspension programs out on the market I consider good value.
I have susprog 3, it requires lots of input but once you get your head around it its a good tool.
I have the program because I did redesign my suspension and it allows you to make changes ,get the data and go do it you are happy.
You still need to check manually on some stuff like bump steer camber gains ect to check your model against your car.

I used rosejoints instead of tie rod ends and shimmed it to adjust bump steer , it worked fine , you maybe able to do the same.

Jim

 

[RichardH]

Two Q's regarding the steering rack...

Is the "standard" GTD rack the Cortina MK4 rack, and if so, any particular year?
is a Southern GT rack the same or a special?

 

[Kev Farrington]

Hi You are right re the GTD rack being Cortina. I started with a Mk3 just because I had one and it stayed on my car for years until it was worn out and I bought a new Mk5 rack from Burton. It was identical to the Mk3 one. I`m not sure about Southern GT but their car is based on the GTD so it would make sense for them to use it unless parts supply is a problem for them. Burtons were very cheap when I replaced mine. Kev Farrington

 

[RichardH]

Thanks Kev.