EP 914-6 How low can I go? Options

[neilca]

--------------------------------------------------------------------------------

I am setting up an EP 914-6 for SCCA regionals. I have 22mm front torsion bars and 350# springs in the rear. How low can I set the ride height? I have found the bolts that hold in the front sub frame to be the lowest point of the car and I can adjust the bars till it hits the ground. The rear I use the jack points on the back corners of the tub. I can lower these down to 2" off the ground.

I have a set of the 23mm front bars also and can get heavier rear springs if needed. Any suggestions? I am runing cantilevered slicks from Goodyear.

I will be running tracks like Road Atlanta, Barber, Roebling and CMP. How low can I go?

Thanks,
neilca.

[neilca]

Terry,

Thanks for the spread sheet. You are correct the bars have to work harder with the longer arm. I need to spend a little time with your sheet. Is the effective wheel rate the same as the spring constant of a coil over?

Truth is I lengthened the lower arms because I didn't want to spend the money for wheel spacers. I am an engineer so, I am very cheap. Once I did that my camber went way out of wack. I always planned to make my own struts so I went with the radical angle. I was shocked, pardon the pun, to find I was now gaining negative camber. Plus I had the zero scrub radius.

When i worked on a national GT4 car we used plastic ties on the shock shafts to moniter travel. I think I will do this before I start changing springs.

Since Blake was restricted to 5 inches I guess anything lower is goodness. As for having the lower arms parallel to the ground I understand the reasoning however does a lower CG offset the low roll center?

[stewteral]

Terry,

Thanks for the spread sheet. You are correct the bars have to work harder with the longer arm. I need to spend a little time with your sheet. Is the effective wheel rate the same as the spring constant of a coil over?

Truth is I lengthened the lower arms because I didn't want to spend the money for wheel spacers. I am an engineer so, I am very cheap. Once I did that my camber went way out of wack. I always planned to make my own struts so I went with the radical angle. I was shocked, pardon the pun, to find I was now gaining negative camber. Plus I had the zero scrub radius.

When i worked on a national GT4 car we used plastic ties on the shock shafts to moniter travel. I think I will do this before I start changing springs.

Since Blake was restricted to 5 inches I guess anything lower is goodness. As for having the lower arms parallel to the ground I understand the reasoning however does a lower CG offset the low roll center?

Hi Neil,

I built the spreadsheet when I was working out what my car needed. I started with the basic spring rate calculations and then modified to the 914 application.

1) To answer you question: NO, the actual WHEEL RATE of the rear suspension is HIGHER than the Spring Rate!!! Due to the fact that the spring is mounted on a LONGER moment arm than the axle moment arm. The SHORT conversion is to multiply the SPRING RATE by 1.17 to get the WHEEL RATE.

2) After seeing your pics on your suspension: 1st: NICE WORK!!. Secondly, please take time to understand the values in my SWAYBAR Rate calculator: I made the ASSUMPTION that while you lengthened the lower arm 2" to 16"length,
I left the STOCK swaybar to suspension input at a distance of 7". It appears the right number would be something like 9".

I'm a business major, but SCOTTISH and "CHEAP" is my way of life!! So we are on the same page there. I lengthened my front arms by 1/2" so I could get the camber adjustment range I wanted. Having done so, I've REDUCED the static front camber as the car got stiffer and believe 3/8" would be a better number.
My current setup is -2.0 degrees camber all around.

-I'm thinking that the 1 degree camber GAIN could work to your advantage: This will allow you to set your static camber at a low 1 - 1.5 degree number and when the car rolls into the corner, it will gain the camber it needs. However, as I learned the HARD WAY, the ONLY way to know what is going on is to buy a TIRE PYROMETER!!! I got one from eBay and THEN the true chassis tuning started.

As far as the Zero-scrub radius, while it has benefits, it does not appear to be a major focus in chassis tuning.....but get a 2nd opinion!

Checking the suspension travel in the corners with spot ties is a great idea....engineers and others, also with a brain, KNOW there is nothing like hard data!!! From the photo, I can already see that in the rear, you suffer from "burning paint" on the wheel arch sheetmetal. So it appears you are already as LOW as you can go...unless you RAISE the sheetmetal arches.

CG vs. Roll Center: THE GREAT QUESTION, from what I have experienced, the Roll Center is the more important issue and the LOW roll center will continue to give you handling problems.....but I would recommend getting a 2nd opinion. Sorry, as a Business Major, I DON'T have THE KNACK!

Hey ANDYZ, would you like to voice an opinion here?

Best,
Terry