Front End Drift

[PCC]

OK,

Next technical problem for you Cobra Whiz Kids:

Soon to get the front end lifted so that the wheels don't catch on the front guards.

Notice that when driving on anything other than a smooth asphalt surface that the steering is very light (you think the front tyres are off the ground - maybe they are!). Once you traverse the rough area the steering is responsive again.

Any ideas or is this is characteristic of these cars?

Running Jag suspension front and back.

I'm sure Scott will put me right when I get back from the UK at the end of January.

[Excaliber]

Could this be quick "bound" (compress) and a to long "rebound" (extend) on the front shocks?

Like drag racing shocks. They compress real quick and then HOLD their position in order to shift the weight to the rear. Making the front end light. Maybe you got this going on with the FRONT shocks?

Ernie

[PCC]

Ernie, I think you are close to the mark.

I've got a leaking shock which is probably contributing to the problem.

Time to get some konis - any ideas on the size?

[Excaliber]

I have seen some excellent math for sizing your shock and spring rates on the various "Shock Selling" Web sites (like Koni).

Suspension is perhaps the most complex area of a car to "nail down". Good hunting!

Ernie

[John S Peterson]

The shock "ratio" is what determines how they react to "jounce and rebound" Typically you find ratios of 50/50 on most passenger vehicles, meaning they react equally in each direction. Aftermarket shocks ie Koni, Alden and so on can be purchased with an adjustment that allows you to taylor the ratio slightly to get it to preform to your needs. On the drag racing shock, they are usually a 90/10 shock which allows them extend very quickly to get the front end up and transfer the weight to the rear, and slower compressing.

John

[PCC]

Adjustment konis - trial and error

Too easy.

One question though - what initial size to you buy?

Or do you simply measure the existing shocks and order same size?

[Excaliber]

Ha ha,,,,to easy huh? Yeah right!!!!

You gonna HAVE to do some research, there is no free lunch! But yeah, I'd start with the deminsions of your existing shock. And there IS a formula as to figure out HOW and WHAT to measure with your existing shock to get an exact replacement.

Exact replacement? Nah, to easy! Do the math thing.

Check it out here:
http://www.koni.com/_cars/frame.html

Ernie

[John S Peterson]

It has to do with the amount of travel of the suspension. One way that has worked for me is to figure out the minimum and maximum of suspension travel so when the shock is installed it is usually extended to about half of it's travel. Just about every kit I have seen this is figured out making it just a matter of what brand you want. As far a spring weight goes it depends on how much weight is on the front end and how stiff you want it. Remember the spring holds the weight, the shock just dampens the oscillations of the spring. Club Cobra has been a valuable source of information for me and I'm thankful for the "brains" in this group of very special people. Take a look at some of the other posts in here and you will find more valuable info.

John

[speed220mph]

Peter: The problem with your car isn't shock valving since what you described occurs during a steady-state situation. Sounds like your car is running with a "bad attitude", or the front is higher than the rear. Air is packing under the car, causing the front to lighten up, increasingly so at higher speeds, causing severe understeer. When you run over rough surfaces, the front seems to be "ratcheting down" due to excessrive shock-absorber jounce control.

I hestitate to give you a quickie fix suggestion, but I have an appointment to meet. But here goes: Set the front end ride height lower and dial out some REBOUND control. I hope your shocks are adjustable as is the ride height. Give that a go and report back. No use spending big $$$ for shocks and find the shocks weren't the problem. Use the KISS (keep it simple stupid) principle first and see what happens.

[wilf leek]

Could I ask if you have had the suspension properly aligned on your car?

With the jag front end, you definitely have adjustment on toe and castor angle, both of which can have a marked effect on steering "feel".

Dependant on your car, you may have camber adjustment as well.

If you have not had a full alignment done yet, it would be well worthwhile, no, essential, before you start suspecting dampers etc.
As Tom suggests above, setting the ride height up properly is an essential move first, before you set the other suspension parameters.

Your kit manufacturer should be able to give you all the relevant settings.

HTH

[speed220mph]

Peter: Like I said, I shouldn't have hurried. What I meant was to dial out some rebound control. Sorry if I caused any confusion.

As Wilf suggests, the car should be checked for alignment, but the characteristics you describe wouldn't cause a light feel. Regardless, always make sure alignment is spot on before you make any drastic adjustments.

[maxrpm]

Instead of softening the springrates in the front coils(which I believe is the cure) you could add approx. 200lbs to the nose of the car with a nice 427... Seriously, I had the same problem. A light engine with aluminum heads & high spring rates caused the front to easily lose road feel with any road imperfections. No amount of toying with the adjustment on the shocks helped. Have your front coils rate-checked, they might be too heavy.
Just trying to help.

[coyled]

I woul check that alignment. Little or no castor will make it really easy to steer in parking lots but give you no feel at high speeds. I would also look at the tires, swap sides maybe. Scott

[speed220mph]

Max: When you're talking spring rates, springs must be designed so the static deflection of the front is slightly more than the rear, or travel from full droop to ride height, which should be abut 3 inches at minimum. It gets complicated, but spring rate translates to wheel rate depending on the lever ratio of the suspension, or spring travel to wheel travel.

What we try to do here is make sure ride frequencies are basically the same front to rear, or the front is slightly slower--read softer--than the rear. But the concern over sufficient wheel travel, or static ride height to jounce, is sufficient. But this is not the problem as Peter describes it. His is one of floating. If the front were running out of wheel travel, the car would PUSH badly over bumps as the front wheel rate goes out of sight. Sort of like having extremely stiff springs. But his car reacts just the opposite.

Having designed and set up a lot of race cars, I'm aware that suspension problems can drive you nuts. I've been flown across the country to cure what seemed to be "incurable" problems. However, taken logically, eliminating known problems, and driving the car under controlled conditions, you can zero in on any any suspension problem with relative ease.

[PCC]

I think maxrpm has hit the nail on the head.

He has described exactly what is happening.

I can't drop the front end any further as the wheels / tyres hit the guard as it is (see pic).

I intend softening the springs lifting them at the same time and trying on some adjustable konis.

I'll refer to what's been said on here regards shock adjustments and take it from there.

Will have to wait until end of Jan as across in the UK getting frozen.

Thanks for your help guys - very informative.

[BMK]

PCC

Sure is nice and warm here. Missing the Meter maids??



I have experienced a smiliar situation under extreme acceleration where I have the float effect.

I have used the QA1 shockers - see my file picture - and now understand the problem I may have caused by using the drag racing type of shocker.

I took the Cobra for a run on a narrow back country road and really pushed along finding that it was not responding and floating. I corrected it slightly and it started to tank slap through the steering - float.

The road surface was good but did have a few dips.

Glad I'm not the only one experiencing this. I thought it was my driving or lack of. If possible keep me posted. The QA1 have a number of adjustments so I will experiment here and let you know.

Keep me Posted on your findings when you get back.



Cheers

Bernie

Bernie Knight
Mt. Gambier South Australia. www.mountgambier.gov.org

Home of "Weekend at Bernie's #2" March 13th/14th

[Excaliber]

,,,yeah it's been cold as heck here too. Dropped all the way into 60's last night........

ernie

[wilf leek]

Whaddya mean "frozen"? Tis balmy in jolly olde right now. And I don't have anywhere warmer to call "home". You want to try driving a cobra in this weather - takes me 1/2hr to get enough layers of clothing on to make it, umm, "enjoyable". Last trip out I had the thermometer was just getting above freezing point, but the roads were dry so I had to go.

Your pic shows a very low ride height all round. Have you checked with your kit manufacturer that the suspension will work properly with the car set that low front and rear?

I know race car ride height set up is "just high enough to stop it scraping", but I see many cobras here running far too low. The suspension just can't work properly in that situation. For a comparison, look at a Kirkham or Shelby on their respective websites - or indeed my car in my own gallery here - they sit far higher up relative to yours.

I know each guy likes their car set just so, but it could be that your low ride height is compromising the suspension??

[PCC]

Wilf, with my car the manufacturer setup the suspension. I think for cruising ready for a set of neons to compete with the jap imports we have here (like mosquitos - everywhere).

The number of times I get a skyline pulling alongside with his turbo blow off valve piercing through my ears - not funny. That's when the V8 switches to full torque and glides away.

You may be right that the height is compromising the suspension and that is why its in the process of getting lifted (already an inch higher at the back - since that pic). Front to sort out.


Bernie - am I touching upon a subject which is common to Cobra's although nobody raises it, rather tweeking their own suspension until happy.

All I know is that when it doesn't feel right it generally isn't right.

My experience is similar to driving an RS2000 in a gravel forest - no feel no traction (just shut your eyes and foot to the floor until you can't do no more)!

[BMK]

Wilf



Thanks for the reply.

We built the chassis at McDonald Bros. Racing who do a lot of race cars but mainly concentrate on drag cars.

I think that could have been the reason for the QA1 shockers.



Just taken off the shelf.

I have since been told that they may not be suitable and have just noticed comments on the Thread here.

I will follow up on this with the guys there at McDonald Racing, as I am heading there tomorrow.

The description that was given to handling problems is very similiar to my problem. I have really been pushing the car to its/my limit and I have had a bit of a scare with the float effect.

Have used a 9" rear with four bar. Two at approx. 90dg and 45dg. 3.25LSD. No panhard. Suspension has full travel ability as the chassis was built to suit.

I don't know if you can see the chassis detail in the photos.

The front is fabricated with tube upper and lower arms. Both front and back suspension has been hung high on the chassis to give the lower stance.

There is little to no flex in the chassis. I sit on a floor welded below the chassis and look through the middle of the screen. I thought this low position may have caused me to over correct.

In lower gears I am getting considerable wheel spin but straight and direct in direction. This is consistant with what has been said regarding the QA1 shocker being suitable for drag racing.

Handling is very good through the curves and it hangs on like a kart, BUT as described it floats about if there is any dips etc. in the road.

Will keep watching this space and do some adjustments on the shockers.

Thanks again

Cheers

Bernie

Bernie Knight
Mt. Gambier South Australia

City site is - www.mountgambier.gov.org