spring rates?

[wicked68]

I have a watts link on the rear of my mustang - the only thing you can really adjust is the spring rate.

The car slightly understeers. I have 500 lb springs on the front - 245s on the front and 295s on the rear. run a6's

the body also roles a bit - as it does with most older muscle cars. I have put in x braces etc and it has a nice martz chasis clip on the front so I can only possibly put in a bigger sway bar on the front.

I have dual adjusable aldan eagles on the front as well and single adjustable qa1;s on the rear with 200lb springs. the rear bottoms out from time to time as well.

so I think I need to up the spring size on the rear - upgrade the sway bar on the front and run the front tires 2 lbs less than the rears.

the question is how big of springs - my gut tells me 500 as well since that is what is on the front. I know there are some complex calculations - any thoughts on this?

the car weighs 3200 total - I dont konw the weight by corner.

mostly running road course with it and a little bit of autocross - rarely drive it on the street any more.

[David Pozzi]

Can you get a 255 up front?
I'd up the rear to 250, The front spring rate at the wheels is a lot lower than you think due to shock angle and mounting. It might be as low as 250 at the front wheel. I think the Martz setup might have fairly low negative camber gain. How much static negative camber do you run up front?
A stiffer front bar will make it under steer more.
I'm not a Mustang guy, maybe someone with Mustang tuning experience will post up their setup.
David

[Bryce]

What is your wheel rate? If you give me all of your suspension pivot points I will calculate your wheel rate. Then it would be best to know corner weights or at least axle weights. My 65 mustang weighs 2663. If you were in san diego I would invite you over to weigh your car and calculate spring rates with my spreadsheet. You could play around with ridetechs spring calculator. http://www.ridetech.com/tech/spring-rate-calculator/

In my falcon, 2733 pounds 1450 in the front, I run a 300lb spring in the front with a 86% motion ratio and a 1.125 solid sway bar that attaches close to the ball joint on the LCA. I do not know the sway bar stiffness off the top of my head. In the back I have a 3-link with watts. My roll center at the axle centerline. I run a 225lb spring and no sway bar. My car handles really neutral. I have 245 and 275 tires.

I agree with David about upping the front tire width. Can you adjust your rear roll center.

[wicked68]

Can you get a 255 up front?
I'd up the rear to 250, How much static negative camber do you run up front?
A stiffer front bar will make it under steer more.
David

I wish I could but 245 is about as much as I can fit without wheel rub. I run -2 up front. so If I am understeering then I need to stiffen the rear up for sure and should not worry about the front at the moment? My rear set up is this: http://www.totalcontrolproducts.com/...-FD_DS_WEB.pdf

as you can see the rear shocks are laying over at extreme angles. I would estimate 20 degrees from being parallel to the axel

you think 300 would be too much ? that is what I am coming up with due to the extreme angle of the shocks now that I have read up on this more. it puts it at the outer edge of the cpm values

[wicked68]

I see what you are saying now - not tire size - doh - but spring rate- you are saying I should drop my front springs to 255 pound springs?

[Bryce]

I see what you are saying now - not tire size - doh - but spring rate- you are saying I should drop my front springs to 255 pound springs?

I think he was taking tire size.

[Bryce]

I wish I could but 245 is about as much as I can fit without wheel rub. I run -2 up front. so If I am understeering then I need to stiffen the rear up for sure and should not worry about the front at the moment? My rear set up is this: http://www.totalcontrolproducts.com/...-FD_DS_WEB.pdf

as you can see the rear shocks are laying over at extreme angles. I would estimate 20 degrees from being parallel to the axel

you think 300 would be too much ? that is what I am coming up with due to the extreme angle of the shocks now that I have read up on this more. it puts it at the outer edge of the cpm values

Its not just the angle of the shocks but the angle of the push rod and the lever arm on the rocker. Also you may have a decreasing rate during body roll due to the pushrod geometry.

Your RC is really low. It looks like a roll bar may be needed to increase the roll stiffness.

[wicked68]

Its not just the angle of the shocks but the angle of the push rod and the lever arm on the rocker. Also you may have a decreasing rate during body roll due to the pushrod geometry.

Your RC is really low. It looks like a roll bar may be needed to increase the roll stiffness.

they dont make a roll bar - already asked - unless you guys know one that will work with this suspension.

that angle looks like its about 70 degrees

[wicked68]

well I had the car on the lift - measured everything and ran it through bretts ridetech site and came up with 450 for the front springs - and verified I have 500 on there now - which I am going to leave - and it recommended 250 for the rear but the 300 arrived today so I am going to go with them and see how they feel since I am slightly oversprung on the front. another site as well said you can go higher and recommended more downforce - I do have a nice front and rear spoiler and ground effects I have put on the car so I dont think it will hurt. will let you know how it goes.