Springs rates too stiff?

v8hgt

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I’ve been thinking lots recently about my suspension and I’ve come to the conclusion my rear spring rates are too stiff and the dampers too lose. The fronts are slightly too stiff too but no where near as bad. I’m running BMR min drop springs front and BMR sp080 rears on PP dampers which give rates very similar to a gt350. They are fine on smooth roads but not great on typical U.K. roads. I would really like to try some softer lowering springs with adjustable dampers to see if that sorts the problem. Lotus always used soft springs and firm dampers. I think Ford are using stiff springs and soggy dampers…

anyone tried this approach on a road driven mustang? I know the top rear shock mounts are weak on mustangs. Would firm dampers and soft springs rip them right off?

 

TeeLew

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I'm one of the few who will agree with you. I like the front of my car relatively stiff, because it drastically improves the front half of the corner. The BMR min drops have a 170 #/in front and we don't know the rear rate, but it's probably around 750-800 #/in.

As far as rear spring rate goes, that's about the point where the rear of my car starts feeling a little too stiff in terms of bump compliance and a little too 'flat' while cornering/accelerating. I've been on several front and rear springs. I'm presently at 450F/750R. On the street, this combo feels pretty good, but I haven't tested it in anger, so it's tough to know if I've improved the car in terms of lap time. It's definitely better in terms of accepting throttle, though. Any increase in understeer has been minimal. Interestingly, Ford has turned a 180 on their chassis philosophy. The Shelby cars are relatively rear stiff, but the Mach 1's have a lower rear spring rate. The base is about 650 #/in and the HP version is ~725 or so? It's worth noting that no one complains about the rear spring rate or chassis motion of these cars.

Along with the spring rate, the ride height is equally important. Every aftermarket spring package lowers the front more than the rear. So everyone is taking a car that has traction problems stock and to make a 'better handling' car, they stiffen the rear spring and add rake. Whatever understeer was in the stock car to start was mostly a product of front camber. Once camber is set to a reasonable number, understeer is pretty minimal. Most aftermarket spring packages reduce rear grip unacceptably in my opinion.

I use the Maier weight-jackers on the rear of my car, so I can vary spring rate and ride height separately. I feel that rear ride height is a more powerful tuning tool than rear spring rate. It's definitely a better tool to use at the track.
 
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v8hgt

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I'm with you on the front end. The BMR min drops on the front are stiff but they have some compression. To be honest a very stiff ARB would probably serve just as well, but the springs give the required stance drop etc and add just enough camber to overcome any font end issues. The rears however feel way way way to stiff in normal driving on poor roads. On a track they are probably fine. What I want to try at the back is the following combo.
1. much stiffer ARB
2. dampers with adjustable compression and rebound
3. springs that give a 1/2" drop, but have a rating of aporox 600 - 650 #/in (might try stock Mach 1 springs)

My only fear here is that the top shock mounts are known to be a sacraficial weak point. Adding stronger mounts has been known to tear them clean out of the shell. Go too stiff on the compression damping and you may risk structural damage, without ripping out some of the interior and welding in reinforcement first. Most of these aftermarket bits are really aiming at the track/strip market, not at the real world GT market. If I can get the back end riding just a bit more like a Maserati Grantourismo I will be happy. Got the front end dialled in almost the same :)
 

sabtaj1

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I’m running BMR drag springs. I stiff have the pp1 front struts but when I had threat factory shocks on it, it road like a lumber wagon. Could feel every crack in road n just bouncing in the e seat. I switch to Viking crusader rear shocks and absolutly night n day. Now you don’t need those, they are pricy but those stock rear shocks are stiff.
 

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The stock GT non PP rear springs pair very well with the bilstein B6 rear dampers.
 


TeeLew

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The stock GT non PP rear springs pair very well with the bilstein B6 rear dampers.
For a non-adjustable plug-&-play setup, I think you're hard pressed to beat the Bilstein. B6 for close to stock rates & B8 if you're going stiffer.
 
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v8hgt

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Im actually tempted by the bilstein B6 rear dampers. Good price, quality product, non adjustable but I hear very good things about them. If I could get some Mach 1 springs (non HP) to match them with that could be a good shout. Almost impossible in the UK though. what rear springs are you pairing the bilstein B6 with?
 

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I believe the non PP rear springs to be right at 670. I think the PP's around 740?

I swapped mine out for some 800# and it was a mistake with the B6's. At least for rough roads.
 

NeverSatisfied

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I’ve been thinking lots recently about my suspension and I’ve come to the conclusion my rear spring rates are too stiff and the dampers too lose. The fronts are slightly too stiff too but no where near as bad. I’m running BMR min drop springs front and BMR sp080 rears on PP dampers which give rates very similar to a gt350. They are fine on smooth roads but not great on typical U.K. roads. I would really like to try some softer lowering springs with adjustable dampers to see if that sorts the problem. Lotus always used soft springs and firm dampers. I think Ford are using stiff springs and soggy dampers…

anyone tried this approach on a road driven mustang? I know the top rear shock mounts are weak on mustangs. Would firm dampers and soft springs rip them right off?
I think the problem lies in the high speed section of Ford's damping curves.

I run BMR Handling springs on Bilsteins and as crazy as it sounds, it handles rough pavement better than the Base GT springs/shocks did.
 

WD Pro

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If I could get some Mach 1 springs (non HP) to match them with that could be a good shout. Almost impossible in the UK though. what rear springs are you pairing the bilstein B6 with?
Putting problems with getting any product thanks to covid aside, I can’t see why non HP Mach springs would be a problem in the U.K., isn’t that what our M1’s come with anyway ?

Just check if a rear magneride spring will fit on a non magneride car - I know one is wound the opposite way, but I don’t know if that’s accounted for with the rubber insulator or if the cast arm is slightly different too ?

WD :like:
 

TeeLew

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Stock rear springs cut to achieve a lower rear ride might be a nice combo with B6's. I'm on Magneride, so not a great comparison with a base setup in terms of dampers, but I found lowering the rear of the car gave much better rear stability on corner entry. I've dropped the rear of my car much more than the front.

The damping loads going into the chassis are not crazy high. People have had trouble with using the stock damper mount when putting a coil-over in that spot, but that is putting spring and chassis load in the same spot. I haven't heard of anyone having trouble with just the damper. A large doubler plate on the inside might be cheap insurance if you're concerned.
 

TeeLew

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Just check if a rear magneride spring will fit on a non magneride car - I know one is wound the opposite way, but I don’t know if that’s accounted for with the rubber insulator or if the cast arm is slightly different too ?

WD :like:
I'm trying to remember, but I think the arm is different, not just the spring isolator.
 

MidwayJ

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The BMR min drops have a 170 #/in front and we don't know the rear rate, but it's probably around 750-800 #/in.
The rear rate is 740 as stated on BMR's web site.
 

TeeLew

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MidwayJ

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Who updates the spreadsheet? We should put this in.
The SP763 package is the minimum drop front springs matched with the same rear springs as the SP080 performance set, which have a 1/2 inch drop and 740 spring rate.
 

 
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