I have mentioned in the past that I put some DGR coils on my car about a year and a half ago.
They have gone up in price a little since that time, but they were fairly inexpensive ($900 for the set???) and I could get them from a Cdn. supplier which meant I didn't have to fool around much with customs or insane shipping charges from the U.S. Also, my biggest concern at the time was not so much performance, but I wanted to be able to raise the car in winter, otherwise I bottom out in our poorly cleared alleys (which, BTW, I did early this winter because I didn't raise the car enough. no damage though). Performance was a consideration, but 2 things made it less important to me at the time.
1. I had never autocrossed before and barely even knew what it was.
2. Since I'd never put coils on a car, I had NO idea what spring rates might be acceptable, so I didn't see much point in spending more money only to find out I'd made a poor choice anyway.
DGR coils, by default, some 13kg/mm front, 9kg/mm rear. Those values are close to the 14kg/mm front, 10kg/mm rear numbers I see bounced around fairly often here.
So, if you have checked the <revalve thread,> you'll see some calculations I did which indicate that based on the length of the lower suspension arms front rear, we should be putting stiffer springs in the REAR and softer in the FRONT.
To recap, the lengths I measured are
Front ... 14.5 ........ 11 ....... 0.76
Rear .... 17.125 ..... 11.75 .. 0.69
where the numbers above, in order are
length of suspension arm
length from body mount to shock
I didn't remove them from the car, nor did I have jacked 3 ft. off the ground, so don't send me death threats if the numbers turn out to be a bit off. The front in particular is measuring to a ball joint, so it is a bit of a guesstimate.
Any way, with those number and have 13kg/mm and 9kg/mm springs to work with, I calculated the nat. freq. to be
front 2.1 Hz.
rear 1.6 Hz.
but, from what I have read, rear should be 0.1 or 0.2 Hz higher than front, though I do recall seem to recall someone saying it should be difference between front and rear, and not necessarily a higher rear freq.
Also to that, I checked the numbers to see what they would look like if I used the 9kg/mm in front and the 13kg/mm in the rear. Then the frequencies come to
which is pretty close to what you want.
So a week ago, I decided to swap the fronts and rears. Obviously you have to move over the top mounts and lower part of the shock as well (whatever you call it. The part that spins down and mounts to the lower suspension arm), or they won't fit.
I really only decided to give this a try because I had to redo the preset anyway, and I was adding in some camber arms in the front, so I was going to have things apart anyway. I also wanted to adjust height so that the lower susp. arm in front is more or less level and so is the rear axle. This is supposed to give better handling than just lowering the car more.
Having had a look, I can tell you one reason to have the front stiffer, if you are going to lower the car, is that upper suspension arm comes very close to the top of the wheel well if you lower your car much. Mine isn't lowered very far and I still only have an inch or so to play with.
So I have been driving the car like this for about a week. It feels different, that is for sure. Rear feels too stiff to me. It doesn't take the bumps as well as I'd like. The front actually feels pretty decent.
I can't speak much to handling yet. There is still so much gravel and sand on the roads that any loss of traction can be attributed to that rather than to bad spring rates, and I really don't want to slide around so I'm taking corners too easily to really check the handling. But it doesn't feel that bad!! It did take a day or two to get used to it. The front isn't that low, but is lower than stock. I have 245/40/18 on the front with a 40mm offset and I haven't rubbed yet.
A couple of points on DGR coils.
1. I don't like the damping much. I may revalve in the fall. I think the dampers are too stiff for me.
2. The paint on the coils is in terrible shape after 1 1/2 yrs (2 winters, 1 summer). If I revalve, I'll get some new springs also.
3. Other than the coils themselves, the rest of the shock is in pretty good shape. Cleaned up pretty easily, paint (or coating) has endured. Dust boots are in good shape and the piston rod looks smooth and shiny.
They only have probably 7500 miles on them.
First autocross in a couple of weeks. We'll see then how this holds up.
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