Cygnus Performance

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Spring Rates, Brands and Conversion Charts

– Introduction –

The two most popular units of measurement for coilover spring rate are kg/mm which refers to how many kilograms it takes to compress the spring 1mm and lbs/inch which refers to how many pounds it takes to compress the spring 1 inch. Here are a couple of quick spring rate conversion charts: 

Spring Rate Conversion Charts
kg/mm to lbs/inch Conversion Chart

3k = 167.994lbs/inch
4k = 223.992lbs/inch
5k = 279.990lbs/inch
6k = 335.988lbs/inch
7k = 391.986lbs/inch
8k = 447.984lbs/inch
9k = 503.982lbs/inch
10k = 559.980lbs/inch
11k = 615.978lbs/inch
12k = 671.976lbs/inch
13k = 727.974lbs/inch
14k = 783.972lbs/inch
15k = 839.970lbs/inch
16k = 895.968lbs/inch
17k = 951.966lbs/inch
18k = 1007.964lbs/inch
19k = 1063.962lbs/inch
20k = 1119.960lbs/inch

lbs/inch to kg/mm Conversion Chart

150lbs/inch = 2.685k
200lbs/inch = 3.580k
250lbs/inch = 4.475k
300lbs/inch = 5.370k
350lbs/inch = 6.265k
400lbs/inch = 7.160k
450lbs/inch = 8.055k
500lbs/inch = 8.950k
550lbs/inch = 9.845k
600lbs/inch = 10.740k
650lbs/inch = 11.635k
700lbs/inch = 12.530k
750lbs/inch = 13.425k
800lbs/inch = 14.320k
850lbs/inch = 15.215k
900lbs/inch = 16.110k
950lbs/inch = 17.005k
1000lbs/inch = 17.900k
1100lbs/inch = 19.690k
1200lbs/inch = 21.480k

– Why Does Spring Rate Matter? –

One of the most important decisions you will make when you purchase coilovers is deciding what spring rates to go with. How stiff or soft would you like the car to ride? How much understeer or oversteer are you looking for? Is your top priority smooth ride quality or the best possible handling or a combination of both? How far below stock ride height would you like to lower your car?

These are the questions you need to ask yourself. Then you need someone who truly understands your chassis and how it reacts to different rates to advise you if you want to get the results you’re looking for the first time without doing an enormous amount of research. No one has more experience with this than Cygnus Performance, LLC. We have specialized in custom coilovers since 2006. Day in day out for more than 16 years we have advised customers on spring rate. Spring rates dramatically affect the way your car performs and rides, so getting this right is absolutely mission critical.

– Can You Change Spring Rate In The Future? –

This all depends on what coilovers you buy. On many lower quality brands you cannot change spring rate without revalving the shock which is a costly and time-consuming process. Our coilovers feature industry-leading levels of rebound adjustment which will allow you to change spring rates in the future without revalving. If your needs change and you want your car to be more or less aggressive you will have the flexibility to significantly change rate with Cygnus Performance X-1 coilovers. All of our products offer a large rebound adjustment range, and some of our products offer more rebound adjustment than anything else in the industry. When it comes to damping adjustment range more is always better. Damping adjustment range has nothing to do with the number of clicks a rebound adjustment knob has. It’s what these clicks do that matters. All Cygnus Performance X-1 coilovers provide a very large difference in damping force between full soft and full stiff.

– Why Is Spring Brand Important? –

In a word: Accuracy. Low quality springs tend to have a lot of rate distortion. If you have a 7k spring and you hit a pothole even though the spring is supposed to be linear and stay close to 7k throughout the range of compression it will often jump up by 20% or more which is very bad for ride quality. It’s also not good for consistency when you’re cornering. Low quality springs often don’t match the rate printed on the side. A 10k spring might actually be closer to 8k or 12k. One supposedly identical spring might not match the next. This is obviously not good for handling. The car may not feel the same when you are turning left as when you are turning right. You may have different amounts of understeer or oversteer than you desire, and the overall neutrality of the car could end up being pretty inconsistent. Low quality springs also tend to sag and change over time. This means you lose preload, ride height changes and rate likely changes as well. A spring may seem like a simple part because it’s just a piece of steel, but as you can see it’s a very important piece of steel. After the damper this is the most important component of your entire suspension.

The most accurate springs that we have experienced after 16 years of custom coilover builds and running hundreds of springs through rate testers are not 100% perfect, but they are massively better than the entry level springs that come on most coilover brands. They are much more linear, they have very little distortion, and they typically don’t sag, settle or change rate over time. This will have an extremely positive impact on both ride quality and handling. If your springs are not working properly the rest of your suspension does not matter. We always highly encourage people to upgrade their springs if it’s within their budget.

– The Springs We Offer –

We work closely with both Swift and Hyperco to custom manufacture the highest quality coilover springs in the world. These springs are manufactured both in the United States and Japan. The springs we sell are extremely accurate. They are almost perfectly linear, and they have very little distortion. They don’t sag, they don’t settle, and they have a lifetime warranty that you’ll never have to use.

We work with the best manufacturers in the world to create specifications that are not available in their standard catalog when necessary. This can sometimes be very important. For example, Hyperco did not have a 7k or 400lb 7 in 60mm ID spring in their catalog. We purchased thousands of these in order to offer them because this was a critical rate for many of the Subaru applications that we build coilovers for.

We offer springs with application specific R&D behind them which is something that virtually no other coilover manufacturer is doing. We purchase these springs thousands at a time in order to get the best price on them then pass the savings onto you. We put our time and money into sourcing and developing the best possible components to get you the best possible results. We don’t spend money on advertising. We don’t spend money on wholesale distributors. We don’t spend money on a complicated dealer network. We sell our suspension directly to you, so when you buy suspension from us you get more for your money than you do with any other brand.

– We Are Here To Help –

If you have any questions about springs, spring rates or anything else please feel free to contact us anytime!

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