Coil Over spring rates VS coventional coil spring rates

[CastleWorks]

I currently have 620 lb coil springs in my 67 Firebird. I am considering moving to coilover setup. My question is most coilover setups I see are offered in spring rates anywhere from 350-550 lb springs. Is there a difference in comparing the spring rates on a coilover setup vs a conventional coil spring / shock suspension?

I appreciate any input you have. The car is primarily used for track days and autocross.

Thanks

[j-rho]

It depends on where the coilover mounts to the lower control arm. If it mounts roughly in the middle of where your conventional spring was, the "motion ratio" is kept about the same, so an equivalent rate would result in similar handling.

If the coilover ends up mounting further outboard on the arm (closer to the ball joint), then it will improve the motion ratio, and the chassis behave effectively as if the spring had been stiffened. In general that outboard movement also helps your shocks control things better too.

[CastleWorks]

Jason,

I appreciate the feedback, that does help.




It depends on where the coilover mounts to the lower control arm. If it mounts roughly in the middle of where your conventional spring was, the "motion ratio" is kept about the same, so an equivalent rate would result in similar handling.

If the coilover ends up mounting further outboard on the arm (closer to the ball joint), then it will improve the motion ratio, and the chassis behave effectively as if the spring had been stiffened. In general that outboard movement also helps your shocks control things better too.

[CastleWorks]

If anyone here is running a first gen Firebird or Camaro with coilovers, I would love to hear what spring rates you are running and how the car is used.

Thanks

[bret]

I currently have 620 lb coil springs in my 67 Firebird. I am considering moving to coilover setup. My question is most coilover setups I see are offered in spring rates anywhere from 350-550 lb springs. Is there a difference in comparing the spring rates on a coilover setup vs a conventional coil spring / shock suspension?

I appreciate any input you have. The car is primarily used for track days and autocross.

Thanks

This will answer all your questions on spring rate: http://www.ridetech.com/tech/spring-rate-calculator/

[SSLance]

Why have I never seen that page before Bret? Looks like a great way to calculate the perfect spring rate for one's application.

To the original poster, springs for coil over setups are available in just about any spring rate and length you may want. Don't limit your package choice just by the spring rates offered with a particular package. I run 600# springs on my fronts with front corner weights around 1000#s on each corner, but there are many factors that go into that equation including suspension theory in general.

[bret]

[QUOTE=SSLance;1159701]Why have I never seen that page before Bret? Looks like a great way to calculate the perfect spring rate for one's application.

Lance, you need to visit us more often! That page has been up for a couple of years. It's been tough to get people to use it...not sure why. All it takes is a minimum of effort to get accurate info on corner weights and control arm measurements. It take no special equipment. We worked intensely with Hyperco to develop the algorithm to get these rates right. The better your data, the more accurate the spring rate. As you saw, we even give you three choices for driving styles...cruiser/daily driver...performance driving...and racing.

Another item to note...we stock coilover springs in rates ranging from 125# to over 1000# in 25# increments [50#increments above a 600# spring] You do not have to settle for a limited choice of a 350#, 450#, 600#, or 800# spring. We can get you the RIGHT spring for your application and driving style.

[j-rho]

Bret,
That is a beautiful page/app you guys put together for spring rate advice, kudos for that. It's definitely the most easy-to-use version of that sort of thing I've seen on the internet. I bet if you check your logs, don't be surprised to find the IP addresses of your competitors trying it out!

If I had one suggestion though, is I think the targeted ride frequencies could be a bit more spread apart, especially on the upper end for the "race" suggestion. For my 850lb. sprung, 90lb. unsprung, 9" out on 16" arm @ 90 degree angle typical first-gen Camaro, it suggests 600,650,700 lb. springs @ 8" for cruise/mixed/race. Those ride frequencies work out to 1.57, 1.64, 1.7.

IMO 1.3-1.6 is a good modern cruiser range, and 1.6-1.8 is a good compromise for a dual purpose car. But for the race setting, I think you can/should go quite a bit stiffer on modern tires. In the old days 2.0 was about the "reasonable limit" for a production car, but tire technology has come a long way and these days the good street tires (like BFG Rival-S, Bridgestone RE71R) are just fine at frequencies of 2.3-2.5 and above. On actual DOT race tires like Hoosiers A7s or slicks, 3hz is really not unreasonable.

I ran my Camaro with ~1400lb. front springs (~2.4hz) and a big front bar, and it handled pretty well for what it is/was - no understeer anyway. Rode fine on the street too, but as we all know, that has more to do with shocks than springs. I tend to run the rear about 20% softer to help the car be more compliant in putting down power.

I had built many cars for autocross before the Camaro and some since, but starting out at 2.3-2.5hz front and 1.9-2.1 rear (the less powerful the car, the closer were the front and rear frequencies), has always put the stiffness in the ballpark for where I ended up for something front-engined/rear drive. In surveying many other successfully tuned and campaigned street tire cars, those frequencies are pretty much the norm.

Just a suggestion, again - great job on the cool app!