swapped my coilovers, front to back
04-15-15, 04:26 PM
#1
Pole Position
Thread Starter
swapped my coilovers, front to back
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
motion ratio.
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
front 1.76
rear 1.99
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.
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
motion ratio.
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
front 1.76
rear 1.99
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.
Last edited by scott1256c; 04-15-15 at 09:45 PM.
05-22-15, 11:49 AM
#3
Pole Position
Thread Starter
I've put off updating this thread long enough, I guess.
Since the orginal post, I've done 3 autoX sessions and 1 high speed driving school at the track.
After my first autocross, I prepared to swap the shocks and springs back the way they were. I'm glad I held off. I've come to like the feel of this setup better. First autoX was NOT smooth driving, and I felt the front end dig in too much. Mostly, I think, as a result of hammering the brakes and unsettling the car, but also because I left the dampers in the softest position. Correcting both of those, well, the smoothness thing is ongoing, has left me feeling like the car is handling pretty well. I haven't adjusted my sway bars yet, and maybe I should, since going from 9kg to 13kg in the rear, and opposite way in the front would sure justify some change, but I'm not disappointed with how it handles at the moment and I'm going to leave well enough alone. I feel the car handles bumps on the street better, but I think the rear is a bit too stiff. The rear seems to jump up a bit more than I'd like when I hit a bump. Front actually rides over them pretty decently.
I'm still thinking I'll try a revalve and changing the springs in the fall. DGR look like a BCR knock off to a degree, so I think those bilstien parts kene used to revalve his shocks will fit me also.
Final note here, after looking at the lower suspension arm and trying to level out by adjusting ride height has left the car lower than last year. I AM getting some rubbing now. Note that I'm running a 245/40/18 up front. My track session actually wore through the plastic liner in a couple of spots and the tire seems to have hit one of the tabs which bolts (or screws actually) some part of the wheel well to the front fender near the upper front of the wheel. This is where the wheel wore thru the liner. I haven't decided how to handle this yet. For now I'm going to bent that tab out of the way and see if at least that part of the problem goes away. It didn't dig into the tire any appreciable amount, so the tires haven't been compromised (yet).
Since the orginal post, I've done 3 autoX sessions and 1 high speed driving school at the track.
After my first autocross, I prepared to swap the shocks and springs back the way they were. I'm glad I held off. I've come to like the feel of this setup better. First autoX was NOT smooth driving, and I felt the front end dig in too much. Mostly, I think, as a result of hammering the brakes and unsettling the car, but also because I left the dampers in the softest position. Correcting both of those, well, the smoothness thing is ongoing, has left me feeling like the car is handling pretty well. I haven't adjusted my sway bars yet, and maybe I should, since going from 9kg to 13kg in the rear, and opposite way in the front would sure justify some change, but I'm not disappointed with how it handles at the moment and I'm going to leave well enough alone. I feel the car handles bumps on the street better, but I think the rear is a bit too stiff. The rear seems to jump up a bit more than I'd like when I hit a bump. Front actually rides over them pretty decently.
I'm still thinking I'll try a revalve and changing the springs in the fall. DGR look like a BCR knock off to a degree, so I think those bilstien parts kene used to revalve his shocks will fit me also.
Final note here, after looking at the lower suspension arm and trying to level out by adjusting ride height has left the car lower than last year. I AM getting some rubbing now. Note that I'm running a 245/40/18 up front. My track session actually wore through the plastic liner in a couple of spots and the tire seems to have hit one of the tabs which bolts (or screws actually) some part of the wheel well to the front fender near the upper front of the wheel. This is where the wheel wore thru the liner. I haven't decided how to handle this yet. For now I'm going to bent that tab out of the way and see if at least that part of the problem goes away. It didn't dig into the tire any appreciable amount, so the tires haven't been compromised (yet).
07-01-15, 03:27 PM
#4
Thank you for posting this information. In your post you mentioned that your rear seems to jump quite a bit more than you would like when hitting a bump. I had the exact same problem before on my '94 GS300. It was like a bucking bronco in the rear when I would go over a speed bump at a medium-slow speed.
I believe I posted that my natural frequency I the rear was either 2.3 or 2.1Hz. It was waay too high. So I removed the 12Kg/mm swift springs in the rear and replaced them with 6Kg/mm in the rear. This gave me a natural frequency of 1.64Hz. The bucking bronco problem was solved completely. The rear has a bit more sway now when compared to the 12kg/mm spring, but is definitely controlled when making 90 degree right turns at 20-25mph.
I was thinking about trying an 8kg/mm in the rear, but I may hold off until after I swap in the revalved BC dampers with bilstein internals in the Rear (front is complete and love the handling so far).
Also this may help your rear natural frequency issue as well. This was taken from Farnorthracing - Autocross to win
http://farnorthracing.com/autocross_secrets5.html
The guy running the site used to work for a few race teams I believe... its some good stuff. According to this, you may be in dedicated autocross territory with that rear Natural frequency.
"Spring Selection
A spring change to a stiffer spring limits the amount of motion that the suspension undergoes in reaction to a particular acceleration (so does a change in CG height and track/wheelbase, but those are much harder to change than springs and for most practical purposes less effective too)
But there are upper limits on how stiff we can go with the springs, so we need a measure of "stiffness" to set the boundaries.
That number is the natural frequency of the suspension - it is worked out for you in the Dynamics Calculator. Rule of thumb is rear NF slightly higher than front (by a tenth of a Hz or two - it keeps the sprung mass from pitching too much because the front wheels encounter bumps first so the rear needs to react a little faster) Street car: 0.8 Hz. Occasional autocrosser: 1-1.5 Hz. Full-bore autocrosser: 2.2-2.5 Hz."
I believe I posted that my natural frequency I the rear was either 2.3 or 2.1Hz. It was waay too high. So I removed the 12Kg/mm swift springs in the rear and replaced them with 6Kg/mm in the rear. This gave me a natural frequency of 1.64Hz. The bucking bronco problem was solved completely. The rear has a bit more sway now when compared to the 12kg/mm spring, but is definitely controlled when making 90 degree right turns at 20-25mph.
I was thinking about trying an 8kg/mm in the rear, but I may hold off until after I swap in the revalved BC dampers with bilstein internals in the Rear (front is complete and love the handling so far).
Also this may help your rear natural frequency issue as well. This was taken from Farnorthracing - Autocross to win
http://farnorthracing.com/autocross_secrets5.html
The guy running the site used to work for a few race teams I believe... its some good stuff. According to this, you may be in dedicated autocross territory with that rear Natural frequency.
"Spring Selection
A spring change to a stiffer spring limits the amount of motion that the suspension undergoes in reaction to a particular acceleration (so does a change in CG height and track/wheelbase, but those are much harder to change than springs and for most practical purposes less effective too)
But there are upper limits on how stiff we can go with the springs, so we need a measure of "stiffness" to set the boundaries.
That number is the natural frequency of the suspension - it is worked out for you in the Dynamics Calculator. Rule of thumb is rear NF slightly higher than front (by a tenth of a Hz or two - it keeps the sprung mass from pitching too much because the front wheels encounter bumps first so the rear needs to react a little faster) Street car: 0.8 Hz. Occasional autocrosser: 1-1.5 Hz. Full-bore autocrosser: 2.2-2.5 Hz."
Last edited by kene; 07-01-15 at 04:50 PM.
07-01-15, 11:08 PM
#5
Pole Position
Thread Starter
Yes, at the time I did feel it jumped in the back end a bit, but I don't feel that way any more. Now that I have driven on them like this for a while, they feel just fine. In fact, I like it better than I did with the springs/dampers the other way around.
I read that far north racing site quite a while ago. Like you I thought it had some great info. My current freq. is ~1.7 front, and just < 2 in the rear. So it is still a little stiff. I'm still planning to redo the valving and get new springs over the winter, but we'll see.
I read that far north racing site quite a while ago. Like you I thought it had some great info. My current freq. is ~1.7 front, and just < 2 in the rear. So it is still a little stiff. I'm still planning to redo the valving and get new springs over the winter, but we'll see.
Thread
Thread Starter
Forum
Replies
Last Post
ndk83
Suspension and Brakes
15
09-22-09 06:49 AM