Wheel Alignment

kiwi ka · 08-10-07, 11:49 PM

Hi Can anybody point me to a link or book on wheel alignment for the set up of a rear engined car set up not unlike the average 70s formula car. I am assembling my semi replica Mclaren M8B that I have built. Its running rear lower adjustable wish bones, top link and at the front we have adjustable top arms and a fixed bottom wishbones.
I have observed Formula Ford style single seaters being stringed so basicly understand what they are doing, its just that I do not know the science. Would you have any toe in on the rear, what toe in at the front, what sort of caster angle would be a good start point etc. If any body can point me to some info, It would be appreciated.

Russ Noble · 08-11-07, 01:39 AM

Russell,

Lots of books on the subject. Staniforth, Herb Adams, Carroll Smith.
GT40 susp is not a lot different to M8. There's some discussion you may find useful here.

What causes heavy steering at racing speeds
Rear suspension bump steer
Front Suspension Geometry

Cheers,

Lynn · 08-11-07, 12:10 PM

Russell,

Russ started this excellent thread which is a great read: What Causes Heavy Steering.....

When you've finished with the thread, you'll have a good understanding of setting up your car. There are a number of really good threads in this section you should probably read. Another is the one that discusses the rear suspension bump steer correction on Jim C's car: Rear suspension bump steer. Ron's thread: Performing Alignments is another really good one to read.

If someone wanted to take the time to compile the chassis information contained in this area, they could publish a world class book on the subject.

Regards,
Lynn

kiwi ka · 08-13-07, 04:47 AM

Russ
I notice that some of the comments relate to rear suspension bump steer, does this only apply to top mounted single trailing radius rod / fixed lower wish bone set ups as I would have thought that twin trailing radius rods would keep the upright in a constant state of toe.
Cheers

Russ Noble · 08-13-07, 05:02 AM

Russell,

That's true so long as the bottom parallel links are the same length and parallel in end elevation. As soon as you alter the caster you will have one pointing down relative to the other and hence will still get a degree of bump steer. So by altering caster you can get either no bumpsteer, or toein, or toeout, on bump depending on what you want.

If you wish it should be possible to completely tune out bumpsteer with twin links. That is certainly not the case with a reversed lower A arm, although it can be minimised with the right caster setting.

Cheers,

Trevor Booth · 08-13-07, 08:24 AM

That is certainly not the case with a reversed lower A arm, although it can be minimised with the right caster setting.

mmmm you sure about that Russ, "there is more to it than meets the eye" so to speak

Russ Noble · 08-13-07, 02:41 PM

Well Trevor,

I was pretty sure about that.....

Even with the lower radius rod running forward horizontally, the rearward end as it moves away from the horizontal is going to describe an arc under movement pulling the upright forwards, which with a reverse A arm must cause toein, I would have thought?

Is there something I have not considered?

Ah yes, I was thinking about my setup where the arms run forward parallel to the centreline of the car. That is why I'm using twin lower links.

If the front end of the radius rod is moved inboard so that it is at the same height as the inboard A arm pick up and the same distance from the middle line of the car. Then the toe will not change.

Just as well there's someone like you Trevor to stop the flow of misinformation!!

Hmmm...... I still haven't figured out the effect of transverse shift of the RC........

Cheers

Trevor Booth · 08-14-07, 08:45 AM

If the front end of the radius rod is moved inboard so that it is at the same height as the inboard A arm pick up and the same distance from the middle line of the car. Then the toe will not change.

Close enough Russ, not always possible to get the forward end where you want it due to space restrictions. They become a very wide based wishbone and with some judicious juggling of pickups points a lot can be achieved, Caster adjustment will alter bump steer

Transverse shift alters the rate at which mass transfers. For the purpose of explanation let us assume that with no transverse shift the mass transfer is linear. With transverse shift the mass transfer becomes non linear. over to you now -: