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post #1 of 14 Old 04-05-2018, 06:07 PM Thread Starter
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Rear coil over springs

I have a 1988 Coupe that I am changing over to a torque arm rear suspension. Lets say I have Koni double adjustable struts and shocks with M&M coil overs front and rear. I plan on using 325 lb. front coil over springs for the front. What rate springs would I get to match front springs for the torque arm rear? This car is my last project car and need to finish it up soon. Mostly street and lots of interstate with hopefully some track time. Thanks.

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post #2 of 14 Old 04-05-2018, 06:44 PM Thread Starter
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Would the M&M torque arm rear springs for stock location with the double adjustable Koni shocks match the Koni double adjustable struts with 325 rate front coil overs? If so witch ones?

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post #3 of 14 Old 04-06-2018, 09:36 AM
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For coilover rear springs I'd start with 225's. If the balance isn't where you want it adjust via rear swaybar or different rate springs.
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post #4 of 14 Old 04-06-2018, 10:19 AM Thread Starter
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Thanks, I have not given rear sway bars any thought yet. Will be looking at adjustable ones when I do. I have been reading old posts and it sounds like torque arms take a lot more spring rate because of no bind and less friction in components to match what you have in the front. It looks like the rear Koni adjustable shocks can handle up about 450 spring rate.
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post #5 of 14 Old 04-06-2018, 10:34 AM
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I would definitely talk to Jack H. to nail down some numbers before spending any money.

You asked about high rate stock location springs. You could probably go with either one depending how much you want to lean on the rear sway bar. If you go with the lighter 5s then you will probably need one of MM's. The 7s would probably do ok with the stock bar.

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post #6 of 14 Old 04-06-2018, 03:16 PM Thread Starter
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Thanks, yes, I have talked to the tech's at M&M a few times and will talk some more before I spend the money. Just wanted to hear from other people and their setups and what worked for them. I bought the M&M pan hard bar, racing torque arm, heavy duty adjustable lower control arms and the stainless brake line and hose kit to go with the cobra rear disk brakes. I would prefer to not use coil overs in the rear do to tire clearance with bigger tires. I do understand that after a certain front spring rate that I have to use rear coil overs. For the front I will have 350 rate coil over springs to start with and already have the M&M non-offset lower control arms, castor plates, braided front brake hoses, steering rack bushings, sn95 power steering shaft, sway bar stiffing plates and relocation brackets, master cylinder brake line swap kit for the cobra master cylinder, proportioning valve delete kit, along with cobra front brakes, 1995 front spindles with a 2003 steering rack. In the near future I'll have the M&M K-member, already have 2004 spindles for that and get the bolt in bumpstear kit.
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post #7 of 14 Old 04-06-2018, 03:18 PM Thread Starter
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Forgot M&M full length sub frame connectors already on the car.
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post #8 of 14 Old 04-06-2018, 05:38 PM
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Sounds like you are well on your way.

I went to Jack himself and filled out the Tech sheet, told him what I wanted the car to do, etc, he got back to me and it has basically become a shopping list that I have been slowly checking off... bugging him with a few more questions along the way.

Before ever contacting him, going by their tech info, I had in my head what I thought I wanted, but was surprised to find that there were several key differences between my list and his recommendations... many of which were due to the weight and other physical factors of the car. (the platform varied a lot over the years and that skews numbers quite a bit)

jw98lx's recommendation for 225 c/o in the rear sounds pretty spot on. From what I understand, once you go much past that, ride quality begins to deteriorate quick.

225 rear c/o works out to a wheel rate of about 247.5lb ... stock location springs are about 50% efficient (meaning a 500lb spring = 250lb wheel rate) and that puts you into the "43TA7" spring realm. With a 350 front c/o my guess working off the info I have for mine would be that you would also need to add a MM 7/8" x .188 rear sway bar to complement those springs.

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post #9 of 14 Old 04-07-2018, 01:28 PM
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FWIW, I ran H&R Super Race and T/A springs on my 86 with MM T/A, etc.with an MM .75" solid adjustable rear bar. The shocks were Bilstein HDs. The H&R Super Race were progressive from about 270 - 300. The T/As were progressive from about 380 - 420. Same 300# C/Os up front on Bilstein HDs.

The SR springs were too light for the front rate but compression and rebound was pretty good. I tried to accommodate spring rate with the stiffer bar setting. This worked but not optimal. When I moved to the T/A spring the rear rate was more compatible with the front but the Bils were overpowered on both compression and rebound. Rear bar didn't help much here either.

Now I have 225# rear C/Os over the old MM1 race Bils. The rate should be good as well as the valving. I moved to a 325# spring up front over the HD Bils. According to MM's tech, I'm maxed on front rate for the HD valving. I haven't taken it out yet with the new set-up but except for the valving mismatch the rates should be correct for level ride.
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post #10 of 14 Old 04-07-2018, 02:39 PM
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DSSR,

What clearance issue between rear coilovers and wider rear tires? Can you elaborate on this?


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post #11 of 14 Old 04-07-2018, 03:52 PM Thread Starter
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Jack,
On some posts I've read that the coil over protrudes into the wheel area more than just the shock. Granted, they might have been talking slicks or something. I have had some 275-50-15's on 10x6.5-15 Prostars on I have it and things looked tight. What I've read about didn't say what brand of coil over and such. I will be using 1998 five spoke factory 17x8 wheels with 245-45-17 tires now.

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post #12 of 14 Old 04-07-2018, 04:03 PM Thread Starter
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Thanks everyone for your reply's and questions. This is important to me and trying to get it right the first time.
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post #13 of 14 Old 04-07-2018, 04:39 PM
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See attached photo.

The entire shock is inboard of the inner tire well. When a coilover kit is installed, some of the upper spring perch and spring is going to stick outboard of the inner wheel well, however it does this within the diameter of the wheel (from the side view), unless the rear suspension is at full droop. When the rear suspension hits a large bump or the car is cornering hard, the tire is very near the top of the wheel well. Under this condition, the entire spring and upper spring perch is inside the diameter of the wheel, so interference is impossible.

If you had a 15" diameter wheel, with a very wide tire, a coilover kit with a 2.5" diameter spring and the rear suspension was at full droop (the car being airborne for a couple of seconds) it might be possible for the edge of the wheel or tire sidewall to hit the upper spring perch. However this is never going to happen with a real car, because with a tire this wide, as soon as the car is cornered even moderately hard, the top corner of the tire's inner sidewall is going to rub so hard on the inner wheel well that it will be locked up solid and the car won't be able to move.
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post #14 of 14 Old 04-07-2018, 11:40 PM Thread Starter
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Jack,
Thanks for clearing that up. This is why I am posting, to find out about things like this, again thanks for your help. Most of the old posts I find all the pics are gone and now the info on these older cars is getting scarce. I read an old post by myself around 2005 that I bought a 93 Cobra master cylinder. Went out and searched around my parts selves and found the thing, now I have two.
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