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springs for f56

13522 Views 18 Replies 9 Participants Last post by  Ryephile
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Here is some information to put things in perspective, snipped from my JCW Pro coilover unboxing thread:

Stock Sport Suspension:

Droop @ 17.375" front and 16.5" rear
Ride Height @ 14.75" front and 14.375" rear
Free Compression @ 13.75" front and 13.125" rear
Bumpstop Compression @ 11.875" front and 11.625" rear

Put into a different context:
Total Possible Stroke is 5.5" front and 4.875" rear.
From Ride Height to full Droop is 2.625" front and 2.125" rear
From Ride Height to first bumpstop contact, or "free compression travel" is 1.0" front and 1.25" rear.
Full bumpstop compression adds another 1.875" front and 1.5" rear of compression travel, but it won't be comfortable.

To have this make sense for lowering springs, let's look at the re positioned ride height per the manufacturer claims. NM claims on an F56 Cooper S the front will lower 1.3" and the rear 1.22". That means the front suspension will be compressing the bumpstop 0.3" and the rear will basically be almost resting on the bumpstop. This means you'll have about 1.5" front and rear of very stiff compression travel, because the effective spring rate of the bumpstop, being exponential to infinity, is significantly higher than the coil spring.

Just to put it in perspective regarding bumpstop spring rate, the MINI's springs [having not measured them yet] are probably in the realm of 250 to 300 pounds per inch of compression and will be fairly linear. So hitting a 2" bump would mean between 500 and 600 Lbf. A typical Penske black bumpstop has about 1.5" of total compressability. The first inch needs only 250 pounds force, but since it's exponential the last half inch needs an additional 1750 pounds force, and any additional compression approaches infinite force. The big nail in the coffin is the car is setup by MINI's chassis and suspension engineers to use several hundred pounds of force deflection [when you hit the majority of bumps in the road] to maintain a rational ride quality and chassis composure, and lowering springs get rid of that buffer, putting you right on the bumpstops.

Lowering springs are an affordable solution to primarily achieve an aesthetic, as having no free compression travel means you the suspension has no ability to comfortably absorb bumps on a straight road, let alone during a corner when you need the bump travel the most to maintain confident chassis composure. In terms of day-to-day with lowering springs, certainly the F56 with its greater suspension travel will be less harsh than an R53 on lowering springs, which most of the time felt like you had tie-rods for dampers. I haven't studied the Countryman damper arrangement, so I unfortunately can't comment with regards to your previous MINI.

If you live on glass smooth roads, none of this will matter. For those of us in the rest of the world, lowering springs aren't the wisest idea.
.the math does not work one to one. Just because the lowering spring lowers the front of the car 1.3", does not mean the car is resting on the bumpstops since there is 1 inch of free travel on the strut assembly. Since the strut it located more inward, it translates to a ride height change that is not one to one, I.e if the car is lowered 1.3 inches, the strut might compress .8 inches. the further inward the spring, the more this affect is applified. The end result ia still the same though...most lower springs on modern suspensions make your car handle worse since they ruin geometry, spring rates mismatch dampers, inadequate travel, so on and so forth. Want to make your mini handle better....keep the stock springs, add negative camber up front and stiffen the rear sway bar a bit. This will out handle a mini with any lowering spring on the market. Car and driver actually complained about how horrible the jcw suspension was on track...makes me wonder if the best mini setup it stock suspension with negative camber up front and a better rear sway.
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Woah pump the brakes. Just trying to provide advice to 99.9 percent of people who mod their cars. If you want you car to handle better in the real world, the lowering springs will make it worse on most cars, which I know you agree with since you used the term motion ratio. I have been working on suspension for a decade now from simple setups to trying to maintain desired suspension frequencies on one off setups.

I just want to keep it simple for the majority of people. The vast majority of lowering springs place cosmetics over handling and I bet you agree :)
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