Cobra Geometry Challenges!

[Silverback51]

Originally Posted by DocDirk

Thanks again for the pearls of wisdom on this topic! Maurice, by correct ride height do you mean simply to make sure all four corners are at the same height.... or is there a specific "correct" ride height for optimal performance?

Also should this be done with weight placed in the driver's seat to simulate the driver and take that into account?

Thanks, there's a lot I don't know,that's for sure!

Regards,

Dirk

Just noticed you are not all that far from Roger Krause in Castro Valley. You may want to consider making an appointment with him and letting him set up the car for you.

[mickmate]

The misconception with ride height is people think it's what looks good. Ride height should be engineered for a specific roll centre and centre of gravity on the car and should have the lower suspension arms level with the ground. From your description you simply need more caster. Recommended settings for a car like this would be about 4 deg. I would get it into a good alignment shop that does race cars and have the MII specs handy and have the alignment guy explain to you after he's worked his magic how it started out and what he's done to correct it. With the fat back tires trying to push in the direction they're pointing these cars are nothing short of dangerous if they're not carefully aligned and predictable in their response. That's before you try and slow it down with weight transfer, anti dive etc. Now it's almost time to look at bump steer and try and go round a corner.

[Maurice Butler]

Originally Posted by mickmate

The misconception with ride height is people think it's what looks good. Ride height should be engineered for a specific roll centre and centre of gravity on the car

This is why didn't specify a figure. The started with orginal had 5" between the chassis and the ground at the front and 51/2" at the rear. As these were modified over the years by owners. These figures changed dependant on tyres, rims, modified suspesion arms, etc.

As every kit has there own thoughts on what makes a good handling car the suspension mounting points, suspension arms, uprights all could have slight varations due to enginneered improvements. Therefore you need to start with your with the manufacture recommendations.
You could also spend time with a string computer and reverse engineer the ride hieght, only still be out.

In NZ the law states for road registration the ground clearance between the chassis and the ground must be 4". All the young lads & girls with there lowered jappers keep running fowl of this.

[Bobcat]

One more comment on the sway bars . After setting the wheel weights , cross weights , alignment etc , make sure the sway bars do not have to be pulled into position as that will undo everything you just did . On mine , we had to fabricate a new connecting rod as when we got the first side connected , the second was off about 3/8" . Now the bars are installed with zero preload ..... front and rear .

[Jerry Clayton]

and then sometimes when you get them to go straight really nice---they won't turn----

[DocDirk]

Some references to ride height have mentioned 5 or so inches. My front frame ground clearance is 7 1/2", the back about an inch higher.... however, my oil pan drops well below the frame and clears the ground by about 5". Perhaps a shallower oil pan is in the offing now, if 7 1/2" seems to be a bit high for the ride height.

My WCC is heavier than most other cobra builds, don't konw if that would up the need for height in itself or just require stiffer springing.

I never got straight what the corner adjustment spring compression changes and subsequent preload does to handling, since it might wind up being different at each corner.

Roger Krause is indeed less than 100 miles from my home, (thank you!) I'll be giving them a call today to see if they would consider give my car a look see.

Thanks again - where is it I can make a donation to keep this wonderful forum up and running??

Regards,

Dirk

[rustyBob]

just keep asking questions Dirk.......i'm learning just like you are on how to do this....
I was told that your lower control arms should parallel with the ground ???
is this true ???
and will that give a ball park figure on your ride height ??? for the front..

[DocDirk]

I called and discussed my handling dilemma with Roger Krause, very nice guy over the phone...we set up an appointment for next week for them to go over the car thoroughly with regard to gear, basic setup and recommendations to improve response. I don't know how much they'll leave to me, but I plan to be in on the analysis and get an education while I'm there lol

Regards,

Dirk

[Silverback51]

Be sure to let me know how it goes. I'm thinking about stopping by there while I'm on vacation and having him do a professional set up on mine.

[lal Naja]

How many of you discussing this topic have a Jaguar rear IRS in your car. And have you done any alignment on it. Does it need any toe-in?

I started doing my alignment. I set up my wheel base measurement to be exact on the left and right side. Then when I did two diagonal measurements to check for squareness one measurement was 3/16" off. So I now need to check if my IRS has more tow-in on one side, or if it or the IFS is not centered to each other.

It takes a lot of planning and measuring to figure this out. It is a bit frustrating too.

Thanks, I look forward to your comments.

Arthur

[bobcowan]

I have IRS, but it's not Jag.

The first step is to ensure the wheels are centered on the chassis. Intially, try to make all your measurements off the chassis, and not to the other tire. It's more accurate that way.

I use 1/32" toe in, and -0.5* camber. That seems to keep it tracking straight and true.

[RICK LAKE]

lal Naja Arthur As far as alignment numbers with a jag rearend with 335 tires, running -.75 camber both sides and 1/16 toed in on both sides. This is with a 1/2 tank of car in the car and your body weight in the drivers seat. I used to run -.50 on camber both sides with 295 tires in 15" rims. You can run more but getting the WHOLE tire on the road is more important along with tire pressures. Auto cross and roadracing you end up with higher tire pressures after a 20 minute run. 8-10psi higher is about the norm. I have gone to nitrogen filled tires and cut the tire pressure increase in half.
I am running poly bushings in my rearend and have almost no deflection of the bushings. They are greased before going to the track. Some Jag rearends are running needle bearings in the carrier arms to the hubs. Again as along as they are grease to remove any play they work ok. I like the polys better.
IMO the most important spec is THRUST angle of the car. You want this a "0" if possible with you in the car. With all things being equal from side to side weights on the car, tire pressures,clean tires, same size curcomfrence, the car should go in a straight line forward every time. No side dances unless you are not straight from the start.
Art I would get CRAZY with how straight the body is on the frame, you can move it around later. Having the suspension right ( wieghting corners ) setup of a 49/51 bias of the car and alignment. will make your car a great handlier.
Some great people have said it's the little things that make a car handle better. I agree with this. Good Luck Rick L.