Front Coil Overs and Rear Traditional Springs within a Maximum Motorsports K-Member Kit

[Habu135]

I’m finishing up my ’93 Notchback this Fall, 12th Owner: My '93 Notchback Restoration & Performance Build, by finally ordering a Maximum Motorsports (MM) K-Member. I plan to purchase all the associated hardware to run coil over struts in the front.

I had a good technical discussion with MM’s staff, but wanted to get current K-Member and suspension enthusiasts’ input as well before I pull the trigger. My concern is this, and I’d appreciate any feedback:

My car is 100% street driven and I’ll likely be going with the Bilstein Front Struts with 275 lb/in, 12” long, 2-1/2” diameter coil over springs. This is per MM’s technical suggestion for “Good handling on the street while maintaining excellent ride quality”. My concern is twofold:

1. Is 275 lb/in too soft up front as I’m coming from Ford Motorsports B Springs which are Front: 425/500 lb/in., Rear: 200-300 lb/in. I want good street manners, and a suspension that doesn’t beat me up, but I don’t want the car too lose.

2. If I go with the 275 lb/in coil overs, will that be compatible with traditional 200-300 lb/in rear springs? I was planning on leaving the rear 200-300 lb/in rate Ford Motorsports B Springs alone as the rear height is perfect and the car squats very nicely when accelerating hard. My car already has Bilstein rear shocks and a MM Panhard bar which was part of MM’s suggestion. So then the only addition from my current rear setup of Ford Motorsports B Springs, MM Panhard Bar and Bilstein shocks would be the addition of an Eibach 1” solid anti-roll bar.

Is there a formula or equivalence between non coil over springs, such as the Ford Motorsports B Springs rated at 425/500 in the front, and coil overs? It seems that MM’s suggested 275 lb/in is far softer than what I’m currently running. I’d like to get this right on the first try and have concerns about the 275 lb/in coil overs in the front with 200-300 traditional springs in the rear. Thanks

 

[Mustang5L5]

I have the same setup pretty much. Yes, there is a difference between coil-over spring rates and standard spring rates in terms of how much "poundage" you need. The reason for the difference is due to the springs location. The closer into the spring pivot's point you go, the stronger the spring you need due to leverage of the control arm. Since the coil-over spring is located on the strut and further from the control arm pivot, you can get away with a lighter spring.

What you would do is convert all your spring rates to wheel rates and then you can conpare.

For stock location springs, take the spring rate and multiply it by 0.25. That's your wheel rate.

For front coil over springs on a fox, take your front spring rate and multiply by 0.9. That's your wheel rate.


I'm running 250# front springs on bilstiens and think the ride is fantastic and it handles well. In hindsight, if i could do it again i might have gone 275#. Our back i'm running an H&R spring per MM's recommendations, but i'll need to look up what it is.

 

[gkomo]

I have the MM coilover kit with Bilsteins sitting in the garage waiting to go on. I went with the 250# coilover springs and am running the H&R Race Springs in the rear. Can't comment on ride quality due to them not being installed, but i did do the wheel rate calculations and i believe the rear H&Rs fell within the range to pair with the coilovers. This was like almost a year ago now when i did all this so my memory could be spotty.

 

[AeroCoupe]

Running 325# springs up front and they are a bit stiff for the street. I was going to track the car more than I do which is basically never so it’s on the list to go to 275# springs at some point.

 

[Habu135]

Running 325# springs up front and they are a bit stiff for the street. I was going to track the car more than I do which is basically never so it’s on the list to go to 275# springs at some point.

What springs and rating are you running in the rear?

 

[Habu135]

I have the same setup pretty much. Yes, there is a difference between coil-over spring rates and standard spring rates in terms of how much "poundage" you need. The reason for the difference is due to the springs location. The closer into the spring pivot's point you go, the stronger the spring you need due to leverage of the control arm. Since the coil-over spring is located on the strut and further from the control arm pivot, you can get away with a lighter spring.

What you would do is convert all your spring rates to wheel rates and then you can conpare.

For stock location springs, take the spring rate and multiply it by 0.25. That's your wheel rate.

For front coil over springs on a fox, take your front spring rate and multiply by 0.9. That's your wheel rate.


I'm running 250# front springs on bilstiens and think the ride is fantastic and it handles well. In hindsight, if i could do it again i might have gone 275#. Our back i'm running an H&R spring per MM's recommendations, but i'll need to look up what it is.

That's good information, thanks. Can you explain why you'd go with 275 lb/in compared to 250 lb/in if you had to do it again?

MM suggested I go with "Torque Arm rear springs, 375-440 lb/in." springs only in the rear which seems odd as my current set up is 200-300 lbs Ford Motorsports springs.

 

[Mustang5L5]

51651.77R rear springs are what I have.

MM recommended me the 94-95 versions as i had the adjustable control arms. I think it's spot on as i am able to adjust down to touching the top of the tire and to about 1" of gap

H&R Mustang Super Sport Springs, 1994-95 Mustang

H&R doesn't publicly publish their spring rates, but from searching online i think they are 275-300# springs.

 

[Mustang5L5]

That's good information, thanks. Can you explain why you'd go with 275 lb/in compared to 250 lb/in if you had to do it again?

MM suggested I go with "Torque Arm rear springs, 375-440 lb/in." springs only in the rear which seems odd as my current set up is 200-300 lbs Ford Motorsports springs.

Because they aren't as harsh on the street as I thought they would be. I think i have alittle room to go stiffer without it getting too harsh.

Plus they recently repaved all the roads I regularly travel on with the car, so i figure I can go stiffer. I kinda half-heartedly keep an eye out for a set of used 275# springs. They offer a 12" and 10" lenght so not sure which would be ideal for me

Torque arm springs in the rear seems a bit stiff. What's the full suspension setup? Usually you go that stiff in the rear if you decrease bind. If oyu have a standard 4-link setup. that seems extreme IMHO

My rears are 275-300# it seems

 

[AeroCoupe]

What springs and rating are you running in the rear?

I have a MM panhard bar, MM torque arm, and MM LCA's with Griggs Racing valved Koni's. I want to say the rear springs are 225# but I would have to confirm that later today.

 

[Habu135]

Because they aren't as harsh on the street as I thought they would be. I think i have alittle room to go stiffer without it getting too harsh.

Plus they recently repaved all the roads I regularly travel on with the car, so i figure I can go stiffer. I kinda half-heartedly keep an eye out for a set of used 275# springs. They offer a 12" and 10" lenght so not sure which would be ideal for me

Torque arm springs in the rear seems a bit stiff. What's the full suspension setup? Usually you go that stiff in the rear if you decrease bind. If oyu have a standard 4-link setup. that seems extreme IMHO

My rears are 275-300# it seems

I also thought that spring rating seemed extreme.

My current rear setup is 200-300 lb/in Ford Motorsports B Springs, a MM Panhard Bar, MM LCAs with stock uppers and Bilstein shocks. MM suggested I go with an Eibach 1” solid anti-roll bar which I plan on getting. My concern, other than the odd highly rated spring MM suggested, was that my exisitng rear setup would not be complimentary to the 275 lb/in front coilovers. But it sounds like my current rear set up + the 1" solid anti-roll bar may be just right.

 

[Habu135]

I have a MM panhard bar, MM torque arm, and MM LCA's with Griggs Racing valved Koni's. I want to say the rear springs are 425# but I would have to confirm that later today.

The springs are just springs, right? No rear shocks?

 

[AeroCoupe]

The springs are just springs, right? No rear shocks?

Griggs Racing valved Koni coil overs. And that was a typo on the spring rate. Should have read 225#.

 

[Habu135]

Griggs Racing valved Koni coil overs. And that was a typo on the spring rate. Should have read 225#.

So does 275 lb/in coil overs in the front with traditional 200-300 lb/in rear springs sound like a good pairing?

 

[gkomo]

 

[Habu135]

I'm tracking the MM website. I've read it a few times trying to decode the tech's suggestions. Kind of looking for real world suggestions based on personal experience and knowledge of combing front coil overs with traditional rear springs before I drop the money.

 

[Mustang5L5]

My full setup is as follows. Some of this may not be relevant to your needs

Everything is MM unless noted.

Front:
Bilstiens w/MM coil-over kit
250# 12" springs (although I would go 275# if I didn’t again)
K-member kit, and standard A arms
caster/camber plates
bumpsteer kit
Stock fox sway bar
Strut tower brace

Rear:
MM adjustable HD lower control arms
Steeda boxed OE style upper control arms
new Ford OE axle bushings
Eibach rear sway bar
Bilstien rear shocks
H&R super sport springs 94-95 (51651.77R) guessing about 275-300 lb
panhard bar (this was added later to all the above)

Other:
MM full lenght subframe connectors
MM steering shaft w/SN95 rack conversion
MM steering rack bushings


I did have plans to install a torque arm, so I did buy the lower range torque arm springs. Haven't gotten around to buying/installing the TA yet as I kinda want to do that on a lift. 50/50 on if i actually do it.

Car has a very nimble go-kart feel to it in terms of steering and response. Ride is comfortable (for a fox) but it definitely handles well for the street driving I do. Probably VERY overkill for what the car has become.

 

[2000xp8]

I have 275 coil over in the front with bilstiens.
The rear were H&R Race.
The rears were notably softer than Eibach springs.

I don't have that setup anymore, i have the HD Torque arm springs in the back.
But if i didn't have the torque arm, i would absolutely do it again.
For the fronts I think any set 300lb +/- 25lbs is probably fine.

 

[AeroCoupe]

It was 2007 when I bought all of this for the Coupe so I had to dig to find the paperwork and found that the fronts are 350# and rears are 200#. Also found my note that if I did not want to put the car on the track to move down to 275# springs up front. Not what MM would recommend but that is what I have wrote down in some notes from my buddy that used to sell and race MM.

I would run what MM told you to run in the rear if you are running coil springs in the stock location. I swapped my car from traditional coil springs to coil overs when the torque arm was installed. Prior to that I ran H&R Super Sports with Tokico Illumina dampers and that was a super nice street setup.

 

[Habu135]

Tracking all. It seems that the 275 lb/in. coil overs is the way to go in the front for a street driven application. I suspect the Ford Motorsports B Springs (200-300 lb/in.) in the rear will work well with the planned front set up. I just get a little hung up on the conversion from suggested rear coil overs to my existing B Springs set up. I suspect the 1" solid anti-roll bar will displace any "slop" from the slightly soft rear springs, but at the same time I believe the stock rear springs were 200-300 lb/in.

 

[Habu135]

My full setup is as follows. Some of this may not be relevant to your needs

Everything is MM unless noted.

Front:
Bilstiens w/MM coil-over kit
250# 12" springs
K-member kit, and standard A arms
caster/camber plates
bumpsteer kit
Stock fox sway bar
Strut tower brace

Rear:
MM adjustable HD lower control arms
Steeda boxed OE style upper control arms
new Ford OE axle bushings
Eibach rear sway bar
Bilstien rear shocks
H&R super sport springs 94-95 (51651.77R) guessing about 275-300 lb
panhard bar (this was added later to all the above)

Other:
MM full lenght subframe connectors
MM steering shaft w/SN95 rack conversion
MM steering rack bushings


I did have plans to install a torque arm, so I did buy the lower range torque arm springs. Haven't gotten around to buying/installing the TA yet as I kinda want to do that on a lift. 50/50 on if i actually do it.

Car has a very nimble go-kart feel to it in terms of steering and response. Ride is comfortable (for a fox) but it definitely handles well for the street driving I do. Probably VERY overkill for what the car has become.

I think my suspension's final results will be very near your setup. I already have most of your ancillary parts, just need to finalize and install the coilovers and odds and ends (bump steer, etc.).

Based on all of yours input, it seems that the 275 lb/in. front coilovers is a great set up for the street. Thank you. As I mentioned though, I don't really want to change up the rear too much as the height is perfect for me (want some tire space for all the steep driveways and speed bumps in deserty SoCal) and the car squats nicely during acceleration. A torque arm would just scrape as the cats and header collectors currently do, and the torque arm would add another 1/2". I need to do a bit more research and see if MM gets back to me on the rear springs.