View Full Version : Why Different Springs

08-07-2004, 09:27 AM
Ok guy and gals who can tell me why the '03 verts have a different rated suspension than the coupes. Coupes have 600 lbs/in. springs front and rear, while the verts have 500 lbs/in. front and 470 lbs/in. rear. The convertibles are heavier than the coupes, so why the weaker suspension?

08-07-2004, 02:19 PM

I am by no means an authority on chassis design but I'll take a 85% un-educated guess.

Perhaps the reason at Ford is using softer springs on the Cobra convertable is because the chassis are not as stiff as the coup and they want to reduce the road shock and stress transmitted to the frame. Some people don't realize the only structual member between the front and rear end of a convertable is the floor pan. A flat member like that is hard to brace.

That my "theory"


08-10-2004, 10:54 AM
Thanks for your reply Russ. I called and talked to someone at SVTOA and ask them the question and this is what they said.

The convertible are not designed as convertibles but are coupes with the top cut off. The verts come with subframe connectors and other frame stiffing components that the coupes do not have. The softer springs are used to keep the ride and handling similar to the coupe. If the verts had the same springs the ride would be very stiff. I guest that what he said makes sense.:D

08-10-2004, 03:16 PM

What the guy at the SVTOA site said does not make sense to me. How would softer springs in a heavier chassis with less structual stiffness have the same handling qualities then a lighter coup with stiffer springs and a stiffer chassis? Convertables require added structual reinforcement because the body would flex like a rubber 2x4 without it.


08-11-2004, 08:01 AM
I see your point Russ. I think that he means that the convertibles have a stiffer, more ridged frame than the coupe does after the add support. I guess I need to try and talk to a enginer with SVTOA.

08-11-2004, 11:26 AM

It's doubtful that the convertable chassis could be made stiffer then the coup without putting a roll cage on it which defeats the purpose.

Think of it like building a bridge. Each end of the bridge is where the load is ultimately supported (front & rear axle). On one bridge the design requirements call for a flat span with no upper or lower truss allowed for support. Just a flat member from one side to the other. This is similar to the floor pan on a convertable. The other bridge design allows for an upper truss to be used to stiffen the span which is what the roof structure on a coup does.

Wanna scare a convertabe owner. Ask him to bump his engine up to 600 hp, put 4.88 gears with slicks and go drag racing. That body will twist like a gummby doll. After a few hard passes the doors will probaby never open (or close) again

On a coup it's not as much of a worry.


08-12-2004, 11:41 AM
Well I know that I will not be going to 600 hp, I need my doors to work. Iam putting a roll bar in the car in the next couple of weeks, Hopefully. It is not a full cage just a 4 point mounting. I know that I will be working on the suspension at some point but not for a while. I will do the front and rear tower braces first. Also I want to change out my seats so I can add 5 point harnesses.

thanks you for the knowledge. http://smileys.smileycentral.com/cat/23/23_30_114.gif (http://www.smileycentral.com/?partner=ZSzeb001)

08-12-2004, 02:48 PM

I would not worry about it too much. A rollbar would be a good idea in the event of a rollover but those are rare in a car with a low center of gravity. I'm sure the Ford engineers did thier homework with regard to beefing up the Cobra convertable chassis to handle the torque that it's motor produces. If not they would have major product defect headaches and lawsuites.

The 600hp 4.88 gear thing was an extreme case I used just to make a point.

Word of Caution with regard to stiffening a convertable chassis: Be careful if you start bracing various points in the car. It may have bad consequences. All chassis will exhibit some flex throughout the chassis. Stiffening various parts of the chassis will move the stress's to other parts of the frame. It's better to have "a little flexing everywhere" rather then "a lot of flexing in one place".

I imagine you drive your Cobra like the 95% of us do and are not competing in autocross. In that case I would leave the car as the Ford engineers designed it (I never second guess those guys, they are the one's sweating the details) I've seen some neat looking rollbars on Mustang convertables but I would consider those for rollover protection only.

Again, I am by no means an expert. Do not take any one persons advice (including mine) as gospel. Ask around. If you start hearing a common thread then that's probably the way to go.

Kim, all you asked for was why he spring rates were diffrent on the convertable and look where it's gone. I hope I have not confused you. Enjoy your Cobra Convertable. I got mine (coup) last month and I really glad I did.

Be well



08-13-2004, 12:31 PM
I like the exchange of knowledge. I have had my '03 since April or May. This car is going to beome my track car in stead of my Lightning. I have to put the roll bar in in order to do the HPDEs that I am hooked on. I do not drag race so I do not have to have a six point type bar. You need to think about this coming March when SCMC does a High Performance Driver Education (HPDE) at Carolina Motorsports Park (CMP) in Kershaw,SC. This will be the third year for the event. I did the first two with my truck, this will be the first for me with a car. Besides tthe HPDEs I also AX the car so far I have done two since I got it and will be doing my third in Oct. at the Tail of the Dragon Run. If you are in the area should bring your car and play with it. If you are not in the area there are other SCMC event around the country that you might want to take a look at. These car are meant to play with and not just to drive around in.

I just saw that your are in LA, a little far from the east coast. I know there are a lot of tracks out your way. Find an open event and go watch or better yet but a helmet and sigh up for an HPDE. You will learn more about the car and yourself and if your like me you will want to keep doing them.


08-13-2004, 03:36 PM
Golly Kim, with that experience I'm surprised you even asked the question regarding the spring rates. Dangl I bet you would hand me my ass on a platter on the Angeles Crest Hwy.

Now I have a question:

Why did you get a convertable if you plan on competing in road race events?

I would think a coup would be a better choice. Your gunna beat up on that car pretty hard road racing.

Just make sure that SVT is in the winner's circle and make us proud.

Russ :baby:

08-13-2004, 04:38 PM
It was my understanding that the 03/04 verts were made geared towards ride quality and "cruising" rather than performance handling. Not much changed from the 99 verts all the way to the 04 as far as how the chassis was setup, they just chose to go a different route for the 03/04 verts (keeping the same rates) and make the coupes more performance oriented (bumping up the rates). Some of that was dues to the scrutiny that heavier 03/04 were going to handle badly due to added weight.

That surprises me that you were given that answer from SVTOA because it is sorta misguided. They are right about the part about verts being coupes with the tops cut off and the fact that they have bolt in subframe connectors, but they do nothing for the car compared to welded full lenght aftermarket subframes, then on top of that you can add a cage like mentioned. So basically, the verts are pretty sloppy stock and the higher springs would twist and turn the body way to much after some good beating withough further chassis stiffening.

Thus the softer spring rates to give them a more lush ride.

08-13-2004, 05:38 PM
Russ you are right about the vert not being as good as the coupe for a track car but I got a good price on it. It was sitting around the show room and the '04 were there also. Mine is the 10 anni. edition that no body wanted. Also my wife wanted a convertible. Beside that it will do better than my truck will. I do have some track time but it is all in my Lightning. I have never owned a Cobra and no nothing about them. I thought that when I bought my Lightning in'01 that I was getting a sport car. For the twenty years before that all I drove were extended cab long bed pickups, so going to the L was like a compact car to me.

Trying to keep brakes on the L was a pain. So we bought the Cobra which is a daily driver as well as a track car. Part of the fun of owning a SVT product is making it your own. Beside doing the HPDE and AX is not like Road Racing, I do it for the fun and a place to drive the car as it was meant and not havae to worry about tickets.

Thanks Firme for joining in. Knowing me I misunderstood what was told me. I suffer from CRS (Can't Remember ****) I guess I had too much fun in the 60's and 70's.:thumbsup:

08-13-2004, 06:58 PM
Russ you are right about the vert not being as good as the coupe for a track car but I got a good price on it.

A vert will do just fine with the right modifications (and cage)

03/04, when setup right for track use, can terrorize the competition

check this out

08-15-2004, 08:41 AM
Wow!!!! those are some mods. I might get to do some of the undercarrige bracing and some of the front and rear suspension stuff but not all of it. I will have to look for it next time I am at an event where it might be.:eek: