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Suspension Coil Compressors

Note: Allpar does not endorse and cannot take responsibility for any of these modifications.

The late, great Gus Mahon wrote:

I bought some spring clamps for $4 per pair. When you shorten springs, you lower the center of gravity (good for handling), and you stiffen up the spring rate (good for handling). Merely shortening the spring actually changes the spring rate.

Imagine a 10 coil spring sitting upright on a table. You place 200 lbs on the spring. The weight moves the top of the spring down 1 inch. So your spring rate is 200 lbs per inch. Each one of the ten coils has shrunk 1/10 of an inch.

Now cut the spring in half. You have 5 coils now. When you place the 200 lbs on it, each coil still shrinks 1/10 of an inch. (same diameter coil, same amount of deflection.) Because there’s only 5 coils, the spring will only move down 5/10 of an inch.

This gives you a new spring rate of 400 lbs per inch. Twice as short = twice as stiff.

Say there’s 6 coils on your springs. You can stiffen them up by 1/6, if you cut off one coil. Clamping two coils together is very similar to cutting off a coil. Cheap and effective; you get the same two-fold benefits. So instead of buying stiff expensive “sport” springs for my Plymouth Acclaim, I clamped two coils together on all four wheels. There was a major improvement in the Acclaim’s handling. Then I put a little negative camber in the front wheels, and got rid of the factory’s toe-in.

There was no need to buy new sway bars! You can ask the owner of the new Corvette that I wasted on the Cross Bronx Expressway (very twisty) on the way home from Atco’s ID Drag Wars 3 weeks ago, after blowing away a twin turbo Supra at the track. (The standing ovation from over a thousand people sent chills up my spine; what a hoot!)

My car weighed 3,000 lbs when I put them on, and my van weighed 3,250 lbs when I put them on. If you use one clamp per spring, it lowers and stiffens like cutting off half a coil. If you put two clamps on the same coils, almost opposite each other, you get the effect of cutting a full coil. By sliding the coils closer together and farther apart, you have a “tunable” spring rate, and adjustable vehicle height.

Installation of coil spring compressors

After you jack up the wheel to compress the spring, then you take a large pair of Channel Lock pliers, and compress the 2 center coils a little more. Then they fit. After the installation, hacksaw off the protruding bolt ends.

harber wrote: You don’t have to remove the tire or the spring. In the case of the front springs (at least on the last car I did) I had to compress the spring, using a floor jack to raise the car by its A-frame.

harber agreed: Those things are a piece of cake. They are essentially a U bolt with a clamp at the bottom side. The U bolt slips over the spring, then a slip-on clamp goes on the bottom spring, then you tighten two nuts to compress the spring.

Bradley Miller added: Just changing tires can make a killer effect on the car. I went from 195-60HR15 to 195-50 and got immensely different handling from my old 2.5L Duster. The tires are the biggest key to making anything work -- too much sidewall deflection, and suddenly you’re squirming around on an inch of tread on the sidewall. Between that and a decent alignment, you’d be surprised what can be done.

Mike Swern wrote: For MacPherson strut suspensions, it is generally not a good idea to lower more than 0.5-1.5 inches. After that, bump steer is greatly increased. The advantage of sport springs over clamps is that the spring rate is higher on a sport spring and many sport springs are progressive rather than linear. Yes, the spring ratio is raised when you use the clamps, but you lose comfort and cushioning with the clamps. Lowered springs don’t have as high a rate and can hit the bump stops under maximum load.

If you live near potholes, especially with a more aggressive wheel combination like 50 or 40 series tires, be prepared to shell out some dough for new rims if you hit your bump stops in a pothole. Also, progressive springs give a nicer ride while keeping good handling characteristics because they soak up the small bumps while hardening up for the twisties.

Bob Sheaves wrote: A spring designed for 200lb/in and a certain length is a certain wire diameter. When you “shorten” the spring, not changing the wire gage diameter, the rate goes up becasue the rate is a function of the diameter of the wire times its length (if uncoiled).

Think of the coil spring as a long torsion bar. Keep the diameter the same and shorten the bar and it gets stiffer (more resistant to twisting efforts). Keep the length the same and increase the bar diameter and it also gets stiffer. A coil spring is a “dual axis” torsion bar, in rough terms—a mandrel centerline, and a wire gage centerline.

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