Front and rear spring rates

[dukeboy_318]

Working on finishing up my 4 link design. I'm running 375 lb springs on the front coil overs, is there a ratio to start with to pick the rear spring rate? I was thinking about going a tad heavier, to maybe 400 or 425?

[bret]

I think you will find that specific "readers digest" answer hard to come by for a couple of reasons:

1. There are many varied theories on spring rate vs sway bar vs shock force vs low roll center/high roll center vs tire traction.

2. There are many varied performance criteria...ride quality? handling? racing? tire size and traction? style of competition?

3. The suspension manufacturers here have all gone to a great deal of effort to develop a complete package that considers all of these inputs. They may not be eager to spit out their recipe...or even part of it.

Having said all that, we have developed [along with Hyperco] a very accurate online spring rate calculator. http://www.ridetech.com/tech/spring-rate-calculator/

Yes, it does take some work on your part to provide accurate weights and dimensions to make this tool work correctly, but it will offer you a very accurate starting point for your project. I will say that if you are building a very light [under 2000 lbs] or a very heavy [over 4500 lbs] vehicle...or you intend to engage in an extreme form of racing [NASCAR, Indycar, F1] you will need to do some testing and tuning beyond this in the real world. For the rest of the 99.5% of the world, it is spot on.

[dukeboy_318]

Originally Posted by bret

I think you will find that specific "readers digest" answer hard to come by for a couple of reasons:

1. There are many varied theories on spring rate vs sway bar vs shock force vs low roll center/high roll center vs tire traction.

2. There are many varied performance criteria...ride quality? handling? racing? tire size and traction? style of competition?

3. The suspension manufacturers here have all gone to a great deal of effort to develop a complete package that considers all of these inputs. They may not be eager to spit out their recipe...or even part of it.

Having said all that, we have developed [along with Hyperco] a very accurate online spring rate calculator. http://www.ridetech.com/tech/spring-rate-calculator/

Yes, it does take some work on your part to provide accurate weights and dimensions to make this tool work correctly, but it will offer you a very accurate starting point for your project. I will say that if you are building a very light [under 2000 lbs] or a very heavy [over 4500 lbs] vehicle...or you intend to engage in an extreme form of racing [NASCAR, Indycar, F1] you will need to do some testing and tuning beyond this in the real world. For the rest of the 99.5% of the world, it is spot on.

Awesome. I'll check it out. Thank you very much. I figured the test/tune thing would come into play, I was just curious if there was a general rule of thumb.

[dukeboy_318]

Originally Posted by bret

I think you will find that specific "readers digest" answer hard to come by for a couple of reasons:

1. There are many varied theories on spring rate vs sway bar vs shock force vs low roll center/high roll center vs tire traction.

2. There are many varied performance criteria...ride quality? handling? racing? tire size and traction? style of competition?

3. The suspension manufacturers here have all gone to a great deal of effort to develop a complete package that considers all of these inputs. They may not be eager to spit out their recipe...or even part of it.

Having said all that, we have developed [along with Hyperco] a very accurate online spring rate calculator. http://www.ridetech.com/tech/spring-rate-calculator/

Yes, it does take some work on your part to provide accurate weights and dimensions to make this tool work correctly, but it will offer you a very accurate starting point for your project. I will say that if you are building a very light [under 2000 lbs] or a very heavy [over 4500 lbs] vehicle...or you intend to engage in an extreme form of racing [NASCAR, Indycar, F1] you will need to do some testing and tuning beyond this in the real world. For the rest of the 99.5% of the world, it is spot on.

Thanks again bret. You saved me a headache. I had it bass backwards. I was thinking you wanted heavier springs in the rear, but it's actually supposed to be lighter.

[bret]

Originally Posted by dukeboy_318

Thanks again bret. You saved me a headache. I had it bass backwards. I was thinking you wanted heavier springs in the rear, but it's actually supposed to be lighter.

A couple of reasons for this...

1. the rear of the car is typically lighter

2. the rear suspension on most of our cars is a stick axle as opposed to an independent. The IFS multiplies the load on the front spring by approx. double [the exact amount will be calculated via your dimensional input on our spring rate calculator]

If you were to weigh and measure a C5 Corvette for example, you would find the spring rates comparable, or even heavier on the rear because of the rear independent suspension.

[dukeboy_318]

Originally Posted by bret

A couple of reasons for this...

1. the rear of the car is typically lighter

2. the rear suspension on most of our cars is a stick axle as opposed to an independent. The IFS multiplies the load on the front spring by approx. double [the exact amount will be calculated via your dimensional input on our spring rate calculator]

If you were to weigh and measure a C5 Corvette for example, you would find the spring rates comparable, or even heavier on the rear because of the rear independent suspension.

Sweet. Too bad you didn't offer a kit for the old A body Mopars....