Front End Geometry

[sjelby]

tAnyone know how independant
front ends work?
I am putting together a front end with mustang 11 upper and lower control arms from Heidts.
I would think they would be parallel to each other.
The crossmember plans i have seem to be out of proportion in some aspects.
IE: top contol arm hitting the shock tower.,
arms not parallel.
photo added where the top one is going to be located.
i think i need to make it sit higher.

[Tenrocca]

You will always find the top arm short then the lower - this being the case there is no way they can remain parallel through the full range of travel.

They are desgned to pull the top of the wheel in at bump - my understanding is that if you were going round a corner the outside wheel would have more weight on it, compressing the suspension - as the wheel gets pulled in at the top it helps the tyre maintain a flat contact with the ground to counteract the body roll.

Hope that makes sence.

Cheers

[Wbulk]

Heidts use to have some really good technical articles on their website explaining theory of design. One of the critical things is that the steering rack inside joint, the lower A arm pivot point, and the upper A arm pivot point should all be in a straight line. At ride height the lower and upper A arms should be close to level. Make sure you have the right width steering rack to make those pivot points line up or you will have some bad bump steer. The location of that rack, up or down, can also throw the alignment of those pivot points off. Lay it all out on a large piece of paper before you start welding. Most suspension have about 4 deg. of anti-dive built into the angle of the upper A arm.

[vector1]

generally lower a arm horizontal to sloped 5 deg. lower toward center, generally.

[xb-60]

Originally Posted by sjelby

tAnyone know how independant
front ends work?
I am putting together a front end with mustang 11 upper and lower control arms from Heidts.
I would think they would be parallel to each other.
The crossmember plans i have seem to be out of proportion in some aspects.
IE: top contol arm hitting the shock tower.,
arms not parallel.
photo added where the top one is going to be located.
i think i need to make it sit higher.

Generalizing here....typically, the upper wishbones /arms are around 75% of the length of the lower arms. The arms are not parallel. The upper arm chassis mounts will be higher that the upper arm ball joint.
Basic reasoning...if your wishbones /arms were the same length and parallel, all OK when going in a straight line and hitting a bump, but when cornering and body rolling, the wheels would still move up and down parallel to the body, so you would have significant positive camber on the outside wheel (with reference to the road surface).
Steering rack length (the actual rack itself without the links) needs to match the distance between the lower wishbone inner mounts.
Height of rack needs to match the vertical position of the lower wishbone inner mounts.
Angle of the links on the ends of the rack needs to match the angle of the lower wishbones. All of this is so that if you hit a bump, the wheels don't toe-out or toe-in excessively.
To top it off, the steering knuckle (on the stub-axle) needs to be the correct length and the correct angle to achieve 'Ackermann steering'. This needs to be reasonably correct so that when you're on full lock, the inside wheel turns through a greater angle than the outside wheel. It's related to the angle of the steering knuckle being in line with the midpoint between the rear wheels.
It might sound involved, but the principles are reasonably simple. Remember that a manufacturer spends a lot of time trying to get this as good as he can, so you spending a while working out the what and the why, will pay off with better and safer handling, better braking, less scrub on the tyres, and a nicer 'feel'.
Cheers,
Glen

[sevenohms]

Originally Posted by sjelby

tAnyone know how independant
front ends work?
I am putting together a front end with mustang 11 upper and lower control arms from Heidts.
I would think they would be parallel to each other.
The crossmember plans i have seem to be out of proportion in some aspects.
IE: top contol arm hitting the shock tower.,
arms not parallel.
photo added where the top one is going to be located.
i think i need to make it sit higher.

Hey Stan,

There are good books on this, try an engineering library or the technical bookshop (used to be in elizabeth st).

Its pretty straight forward once you get the general concepts!

If ya want some help, give me a buzz

Nathan

[Maurice Butler]

A good book is "Competition Car Suspension" by Allan Staniforth (isbn 1 84425 328 7). has a section on string computers (no keyboard involved), get for getting you head around some of the principles and learning what the compromises are.

[FWB]

you don't need a book, and there is nothing wrong with the crossmember, get the crossmember proped up off the bench and let the rotor swing down and bolt it together.
i put the heidt's on my car and trust me it will be fine.....the lower arm as stated in a previous post, will droop a little at rest, and the upper will be angled toward the spindle too at rest....to quote a politician......trust but verify....

[mickmate]

Follow your instructions, here's a sample http://www.heidts.com/_uploaded_files/in-032.pdf

[Wbulk]

The information on suspension design is in the Heidts catalog pages 5-6.

http://www.heidts.com/_uploaded_file...10_catalog.pdf

[sjelby]

Thanks all. I'm on the iPhone this weekend so im limited but I knew what I got was incomplete. I didn't get any instructions . Lol . Looks like I haven't done too bad flying blind.
Stan.
Again thanks all.

[sjelby]

Thanks all. I'm on the iPhone this weekend so im limited but I knew what I got was incomplete. I didn't get any instructions . Lol . Looks like I haven't done too bad flying blind.
Stan.
Again thanks all.

[sjelby]

A little further to finishing the front end.

[renovationinnov]

hey stan looking good is that your chassis rails you are going to run or another mock up
rob

[sjelby]

Hey Rob,
Just setting it all in to 75 x 50 x 3 ml box and it can then be grafted into the chassis as it is getting built.
getting the front end sorted, the jag rear shortened , then take them down and get the chassis finished.
Stan.
ps . beers at the winery were good last w/end.

[Aussie Mike]

Nice fabrication work there Stan. Looking good.

Cheers

[sjelby]

Thanks Mike,
your changes to your f/end are looking impressive.
Some more welding tomorrow then assemble and then its onto the steering rack.
Im looking for a torana steering rack as mine is front mounted.
Any one got one laying around??????????
Stan