Kirkham suspension aligment specs.

[maurice19]

Hi David,

When I was there Dec 17th, you told me about the newer suspension. Is this what you meant with the fixed bearings?

Does #318 have this improvement, and if not, do I need it?

Waiting for #318
Maurice Lawrence

[Morris]

Many of the older suspensions on these cars have way to much Bump steer in them and I'm not sure that folks know how to get the bump steer out of them

The Kirkhams have done a great job working with the rear suspension to get allot of the bump steer out of the suspension..... they moved the trailing link where it mounts to the lower control arm...... but thats just a start...... it's up to you to actually move the hub thru it's suspension travel and measure what the hub is doing as it travels up into bump and down into droop.....

If the bump steer on a rear wheel goes up to .150" thousandth of an inch Toe-out ..... and you have 1/8" toe-in ......you will transision between toe-out and toe-in as the wheel travels into bump or droop..... this will cause the car to act as if it wants to go in 2 different directions at one time..... very unstable condition.... so in the old days the guy's would just crank in more 1/2" toe-in to compensate for the toe-in and out condition......

This is not the right way to fix the problem.... it is just a bandaid... and will have an unstable condition in the rear of the car.....

Most folks don't know how to adjust bump steer on the rear of a IRS car and especially one that has Anti Squat ...... so crank in the Toe-in.....Wrong....

First you have to relocate the trailing link so it's in the same arc as the lower control arm..... or as close as you can get.....

Then.....important......then you can rotate the upright on the axil to change the bump steer and get the wheel going up into bump and droop with-in the spec's of .015" thousandths per inch of travel....... I think on our rear suspension we got it down to .030" thousandths of an inch in 4.5" of travel...... but this is a very small movement of the upper control arm on the rear.....

This is something that has been around for a long time ....just not many people knew about it.....

Anyway do the same thing on both rear wheels....and get the rear end going the right way when it goes into bump or droop....

After you get your Bump steer worked out and I would invite you to go over to Gasholes and see how we did what we did.... then go back thru the alignment and re-do all of the settings..... and only then will you be OK.....

The best thing is that if you can do the alignment with strings or straight edges or what ever.....you can come back after you drive it and make adjustments .... there is now magic to this alignment stuff ...just get yourself some reference points and then go from there.. and don't be afraid to make changes and see what they do......

[Morris]

In the suspensions of our cars you have a thing called Motion Ratio...... and the equation for Wheel rate is

Wheel Rate = (Motion Ratio)Squared X Spring rate

Front..... measure from a straight line going through the mounting points of the of the lower control arm .....to ...... the lower ball joint.......Thats a number....

Then measure from the same point going thru the chassis mounting points of the lower control arm .....to..... the center of the mounting point of the Spring or Coil over......

Divide the longer measurement to the ball joint....into the smaller measurment to the spring mount or coil over......

Example....Example......... 16"= chassis mounting point.....Divided into......8"= coil over mount point......... = .5

.5 X .5 = .25

450#springs X .25 = 112.5 lbs per inch Wheel Rate.....not very much ... wheel will fall over on itself....

That's why Tom switches the front springs around on the stock cars.....

If you go to the rear

16" to center of lower control arm mounts and coil over is mounted at 12"..... then

12"/16" = .75

.75 X .75 = .5625

600# X .5625 = 337.5 lbs per inch Wheel Rate....

So if you have 112# wheel rate on the front and 337# lbs Wheel rate on the rear......your front is way to soft to go around a corner and you need help in the front and then you'll know what to do with the rear......

The weight transfer in the rear with 800# springs may be the right roll couple for the rear of a car ....but if you want to take out oversteer or induce understeer you have to change springs .... where as with Roll bars you just change the bar settings..... much easier.....

So I do like roll bars ...because we've been able to balance the roll couple front to rear to get the car to respond the way it's suppose to .........but I will calculate out the bars and roll couple before we make the rear bar.....

Sorry for the long ....long ..... responses ......

Morris

[Morris]

Jamo

I think they are going to shoot me if I post another long message......

Morris

[427sharpe]

Don't worry Morris...you have friends here! We'll let Turk take a bullet for you so you can keep going...and don't worry about the length. This is the best thread that we've had going in a LONG, LONG time.

[xlr8or]

So Morris if I swap the springs and put the 600's up front and 450's in the rear it will give me a wheel rate of 150 front and 253 rear. Will that help having it more balance or is there a specific wheel rate we should aim for? Do you want the front and rear more balanced?

[Specialk]

Morris,

I guess my point is that if you use a laser measuring from the chassis centerline, you will always get accurate measurements. I haven't read your write up, so I didn't mean to imply you are doing anything wrong. Sorry for the confusion.

[Morris]

Xlr8or

That's right your roll couple will be closer .....

The number that people shoot for is all over the place..... it depends on many different factors of the suspension....

Allot of folks start at a Wheel rate of 200# and then go from there.... depending on what the car or suspension is doing.....

At least now you have a way to start and be consistant in what you are doing and which way to go....

the feel of the car is a personal thing an each one of us drive a different way...

Morris

[Morris]

BTW

The numbers I was using were just picked out of the sky.... I think they are close but you need to work with the correct numbers.....

Also why would you just raise the Front springs up to 550# or some number....

And now you see why I built the bigger Roll bar.....

Morris

[Morris]

Kris

And I agree with you .....

Morris

[David Kirkham]

Maurice,

Improvement depends on your point of view. Some guys like all of the adjustablilty. Others get lost in the forest.

I am not sure which one you have. I will check and get back to you. I am 95% sure you have the adjustable version, but I must check as I can not keep all of the cars straight in my head.

Also,

Many thanks to Bruce Robles for all of the help he gave us on his car as well! He taught us quite a few tricks and had lots of advice on inventory control and such that we have implemented. I don't think he would recognize the shop if he came back!

Frankly, most of our customers are successfull businessmen and we have learned a lot from them--from racing, to legal, to inventory, to customer relations. We have been very fortunate they have been so free with their most appreciated advice.

David

[David Kirkham]

We just had a customer take his car to Tom's Motorsports in Las Vegas to do an alignment. It did improve the car quite a bit and I was very happy to talk to Tom about what he did.

He runs 0 toe, or even a little toe out in the front and a little to in in the rear. I thought it would make the car unstable, but I found it didn't. The car seemed to point much faster but not so fast as to unnerve me. I will have to get his exact spec and we will probably modify our specs to more closely align with his (sorry for the pun). Well, not really!

David

ps. Thank you Tom and Morris for all of the great research you have been doing.

[Dominik]

Morris,

again excellent input, but don’t we have to consider the angle of the damper for the motion ratio?

And multiply the motion ratio with the SINE of that angle?

dominik

[Morris]

Dominik

Yes ..... or you can just do it without the angle because it's a relative number only for you and know on else.....and it pertains to your car..... not another....

It all goes back to if all of these things work .... then you did good.... if not ....then you know where to go to start changing....

Morris