longer springs vs. shorter springs

[kilgojr]

Okay, so school me on springs. I am specifically looking for arguments with longer vs shorter 'free' spring lengths on a coilover setup for an autocross car. If I am running a 2.5 inch inner diameter spring, and I can have the same ride height with an 8 or 10 inch length spring vs a 5 or 6 inch length spring, is there any foreseeable advantage to either?

1. weight, it is assumed the 5 to 6 inch spring is lighter then an 8 to 10 inch spring


other then this assumption, what arguments are there?

[JohnW8]

Okay, so school me on springs. I am specifically looking for arguments with longer vs shorter 'free' spring lengths on a coilover setup for an autocross car. If I am running a 2.5 inch inner diameter spring, and I can have the same ride height with an 8 or 10 inch length spring vs a 5 or 6 inch length spring, is there any foreseeable advantage to either?

1. weight, it is assumed the 5 to 6 inch spring is lighter then an 8 to 10 inch spring


other then this assumption, what arguments are there?

8-10" spring would tend to coilbind depending on the travel. Miata?

[kilgojr]

8-10" spring would tend to coilbind depending on the travel. Miata?

Yes, for the Miata. I'm using a Koni Race damper, in the factory location, but not on the factory mounts, spherical on each end, with adjustable mounting locations, not just adjustable height. I'm not set on the ride height yet, but I will have a good idea of height, and travel shortly. The shocks, IIRC, have about 6 inches of stroke available. The price of the springs is pretty much the same longer vs. shorter, just wondering if there is a benefit to either.

[TouringBubble]

If I understand you correctly, suspension travel would be the limiting factor.

Assuming you have a 6" spring and a 10" spring with identical rates, you would adjust the suspension lower for the longer spring to get the same ride height, limiting the travel of your damper.

If the 6" and 10" are different rates, allowing for the same ride height at the same perch adjustment, the longer spring is a lot softer and you have the general comparison of stiff v soft springs, as well as the coil bind that John mentioned.

If somehow you can get a 6" and 10" spring that are the same rate and give the same ride height at the same perch adjustment (I don't see how it's possible), then coil bind and weight would be the difference as mentioned already.

I'm guessing you have scenario 1, and the reason the different springs exist are for different ride heights. You might need more height than the short spring provides so a longer one is offered.

[Chuck Baader]

Assuming no coil bind at full travel. The two springs will have different harmonics that can or cannot interact negatively. Always start with a sorted kit, as I did, but instead of 6" springs on the front of my car, I now run 10". cB

[kilgojr]

If I understand you correctly, suspension travel would be the limiting factor.

Assuming you have a 6" spring and a 10" spring with identical rates, you would adjust the suspension lower for the longer spring to get the same ride height, limiting the travel of your damper.

If the 6" and 10" are different rates, allowing for the same ride height at the same perch adjustment, the longer spring is a lot softer and you have the general comparison of stiff v soft springs, as well as the coil bind that John mentioned.

If somehow you can get a 6" and 10" spring that are the same rate and give the same ride height at the same perch adjustment (I don't see how it's possible), then coil bind and weight would be the difference as mentioned already.

I'm guessing you have scenario 1, and the reason the different springs exist are for different ride heights. You might need more height than the short spring provides so a longer one is offered.

The dampers have 3 "scenarios" for placement of the adjuster. So I can run the adjuster at a very low setting for shorter springs, or a very high setting for long springs, or a medium setting for somewhere in between. This allows the travel to stay the same, and adjust for different length springs.

The adjuster is not on the shock body, it is a separate threaded sleeve that goes over the body and is locked in place by retaining rings on the shock body.

30series.JPG

[TouringBubble]

I know what you mean. Spring length/adjustment doesn't affect shock travel, but shock travel affects the usable range of the spring. If you plan to use the different springs all within the range of the shock then what Chuck and John said is right. But if you need a longer spring for increased travel then shock travel must be considered. I may be thinking to deeply in to it.

[JohnW8]

Not only shock travel must be considered but wheel travel. You can a 2 foot of travel but if the wheel is jammed into the fender or the control arm is hitting subframe at 3 inches the long travel is a no-go.

Wait,.. you do have fenders,.. right?


If you set the spring perch on the rear shocks to low with 2.5 springs you get awfully close to the axles on a normal Miata. (I polished a groove in my axles from a spring perch, and always wondered what that vibration was) Not sure on the Abnormal Miata you got going.
(Can't wait to see it)

[jledford]

How technical do you want to get? Here's a guy from back in my DSM days that goes into a LOT of detail on suspension (along with just about every other topic concerning auto-cross): http://www.farnorthracing.com/autocross_secrets.html

[Cholewa]

How technical do you want to get? Here's a guy from back in my DSM days that goes into a LOT of detail on suspension (along with just about every other topic concerning auto-cross): http://www.farnorthracing.com/autocross_secrets.html

[JohnW8]

How technical do you want to get? Here's a guy from back in my DSM days that goes into a LOT of detail on suspension (along with just about every other topic concerning auto-cross): http://www.farnorthracing.com/autocross_secrets.html

Excellent link! Now if only I knew what the heck he was talking about.

[bimmertech]

@#$%! That site is supposed to be on the secret internet! Actually, I've been using that site as a reference for a long time. I think everyone should do some research there before purchasing suspension for a competition car.

[jledford]

A lot of the information was secret for a while, he posted up many of those "articles" on a private site that I'm on before he put them on his website. Now that he's retired from racing I guess there are no more secrets.