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Discussion Starter #1
I'm getting out of the full drag race scene and moving more towards street performance again. I've got QA1 coil over system in front with 14" 175 rate coil springs. If I move to a 300 rate spring, will I feel a difference? With my current spring, I feel every fricken bump through the strut towers.

Thanks.
 

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What do you mean you feel every bump? Be more specific. Does something sound loose, does the car crash over bumps? Sounds like something is wrong with the coil over or the installation.

I ran 325lb/in. springs in an MM coil over kit on the street for 2 years. The ride was much more compliant than the C-springs and KYB shocks/struts I had on a car years ago.
 

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You'll probably annihilate those QA1's with that rate. Sounds like you got a killer ride, though.
 

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Kenbell89lx, a 175 lb coil over rate is about a 160 lb per inch wheel rate. For example, the 2003 Mach 1 has 600 lb per inch front springs and a wheel rate of about 150. In other words you already have a wheel rate in the range of a performance street application. If you go to a 300 lb coil over you will have a wheel rate of about 270 lbs per inch. This would be the equivalent of about an 1,100 lb per inch front spring in the stock configuration which should be more than enough for road racing and quite stiff for the street. Personally, I would leave your 175's in. With the coil overs this should be a decent ride. I agree with Coupe de Surf that something else may be contributing to your rough ride. Whatever is going on, the stiffer springs will make it worse and I can't see the need for any higher wheel rate on the street.

Ron
 

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Discussion Starter #5
What do you mean you feel every bump? Be more specific. Does something sound loose, does the car crash over bumps? Sounds like something is wrong with the coil over or the installation.

I ran 325lb/in. springs in an MM coil over kit on the street for 2 years. The ride was much more compliant than the C-springs and KYB shocks/struts I had on a car years ago.
The sounds I hear/feel is in the tower. Every bump, its like there is no bushing to absorb the movement. I called QA1 when I installed them and told them about the noise, they replied that is "normal" with a coil over system. I'm pretty sure I installed them correctly as it was pretty straight forward, but who knows. I can take some pictures to show you guys. I dont knwo what else to do.
 

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When you look at your front suspension,are the coil springs completely compressed? Do you have any pics? Does your ride have a/c,ps,pb,etc. Full weight? Had a friend that had the 150lbs. springs and they weren't enough. Think he installed 200 lbs. springs and was Way Happier! The 150 lbs. springs were too weak for him.
 

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I have 275 maximum coil overs and they are soft and comfort on the street. Please be sure you don;t have a preload on the springs because then they will feel harsh. I'm considering going to 325 front.
In the back i have maximum adjustable arms and the H&R sport springs.
Smooth ride
 

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Discussion Starter #10
When you look at your front suspension,are the coil springs completely compressed? Do you have any pics? Does your ride have a/c,ps,pb,etc. Full weight? Had a friend that had the 150lbs. springs and they weren't enough. Think he installed 200 lbs. springs and was Way Happier! The 150 lbs. springs were too weak for him.
I'll get some pics. Its got A/c, p/s p/b everything/ Full weight.
 

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Discussion Starter #11
I have 275 maximum coil overs and they are soft and comfort on the street. Please be sure you don;t have a preload on the springs because then they will feel harsh. I'm considering going to 325 front.
In the back i have maximum adjustable arms and the H&R sport springs.
Smooth ride
I was seriously thinking of the MM stuff. How do I tell if there is a preload?
 

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If your coilover setup makes noises or is harsh over bumps, then there is something wrong with the installation or the design of the system is poor causing interference between parts. A properly designed and installed coilover system doesn't make any unusual noises. The cheaper systems do tend to make noise, because the manufacturers don't invest any time (=money) on development and/or use generic parts that don't work properly on a Mustang.

Comparing the wheel rates of an OEM car with springs mounted on the FCA to an aftermarket setup with springs mounted around the strut is tricky. There are many small issues that affect the resulting ride quality other than the low frequency wheel rates that Ron mentioned.

Here is just one example. The stock Mustang FCA has rubber bushings in the pivot locations that are bonded to the FCA and the crush sleeve. Even if you remove the spring from the FCA, the bushing itself adds some wheel rate since it must twist for the FCA to move up and down. If you use an aftermarket FCA designed for coilovers, they usually have nonbonded bushings that don't affect the wheel rate, since they are not bonded to the FCA and crush sleeve. The OEMs are limited in how stiff a rubber they can use in these bushings because the rubber becomes extremely hard at low temperatures, and can tear during suspension motion as a result.

In my experience, a front coilover spring rate of 250lbs/in is the absolute minimum I would ever use on a 3,200lbs Mustang. Anything softer than that and the customer is going to complain that the suspension bottoms out too easily and the car is too soft. The only exception to this is someone who uses their Mustang primarily for drag racing. They generally don't care what the car handles like and are content as long as they can keep the car from bouncing off of the guard rails.

As a data point, one of the people who posts in this forum is a Ford chassis engineer. He took a 10 minute ride in my 92 LX on the street. At the time, the car had 300lbs/in or 325lbs/in front coilovers, Bilstein front struts and the stock 225 wide 16" tires. He said it was the best riding Mustang he had ever been in.

How much preload (distance) is on the spring, is the result of the weight of the car, the spring rate, the spring free length and the total travel in the strut. It is not any type of adjustable parameter. In and of itself, there is no correlation between the magnitude of prelaod on the spring and the resulting ride quality.
 

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Discussion Starter #13
Thanks Jack. I think I have my solution now.
 
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