Gnd Control coilover spring rate opinions? (long)

Greg200SE-R · Mar 30th, 2003, 03:47 PM

Hey all,
I have a 98 200SX SE-R and am looking at the Ground Control coilovers for KYB AGXs. I currently have Progress drop springs at 180/150 and this is too soft. For the GCs, keeping ride comfort in mind, what are some good spring rates for a car that sees no track use? But, handling is important because lots of my performance driving is done on narrow windy mountain roads with a variety of sharp/sweeping 25 - 60mph corners. Potholes aren't uncommon. And, understeer is the main problem in my car's handling. Considering this, what would you guys suggest as spring rates? I heard 300fr/200rear was a good compromise between track/street. Should the rear be 100lbs lower than the fronts? I have a friend with a B15 Sentra riding on Tein SS coilovers at 336/280. I know that the B15 is about 1000 pounds heavier than my 200SX, but his Sentra's ride is PERFECT. NOrmally I see the B14 200SX spring rates suggested as roughly 50lbs less than the B15 Sentra's. So going by these suggestions, would 275/225 give me a similar ride? Compared to 300/200 though, 275/225 would bring the rear rates only 50lbs less than the front and increase the rear's stiffness relative to the front. To reduce understeer, would this help? Or do our cars perform better with a 100lb difference between f/r? anyone know through experience how all of these settings would work as far as performance and ride quality? I am also thinking of removing my front stock anti-roll bar to further help the understeer problem. Should I consider different spring rates in front to compensate? Thanks in advance.

spdracerUT · Mar 30th, 2003, 05:06 PM

well, how good of a driver are you? Can you catch oversteer? I'm running 300f/250r and the rear stays planted. I've spun out twice at the track and that was due to lift throttle/trail braking. There are some guys who are running 300/300 with the adjustable stillen rear bar and that appears to make the car fairly neutral in the high speed stuff, still understeers at lower speeds (auto-x). try searching sr20deforum.com

spdracerUT · Mar 30th, 2003, 05:08 PM

oh yeah, the ride is tolerable though you'll feel the white paint lines in intersections!

Greg200SE-R · Mar 30th, 2003, 05:55 PM

I consider myself a knowledgeble driver. A high speed crash caused by understeer about 11 years ago prompted me to do a lot of research into suspension/handling characteristics of FWD/RWD cars. I have not ever felt oversteer on a FWD before tho. I don't usually drive fast enough to worry about understeer, and when it does happen it's usually power-induced understeer, revving pretty hard in 2nd or 3rd gear. It's this last bit of understeer that I want to eliminate and increase the car's handling limits. I assume that even if I had 300/250 springs without the front anti-roll bar, that I would not drive it hard enough to induce oversteer (I'd still probably have to worry about understeer before oversteer). So, 300/250 is tolerable? Not too stiff for normal roads with potholes and rough surfaces? 90% of the time, my car will be a daily driver so as long as the suspension isn't bone-jarring on real world roads, I'd be happy. Thanks.

wickedsr20 · Mar 30th, 2003, 09:20 PM

My suggestion is either 300/300 or 300/250. Either one gives a tight feeling, yet streetably comfortable ride. As a finishing touch, I'd keep the stock front sway bar and get an adjustable rear sway bar. Best of both worlds w/o spending too much $$$.

98sr20ve · Mar 31st, 2003, 10:03 AM

Keep the front swaybar and go 300/300 with no added rear swaybar. If that is not enough then add the rear bar. For autocrossing 300/375 is the way to go from what I have seen.

bahearn · Apr 1st, 2003, 12:10 PM

For a Classic, 250/150 is more appropriate for a street car. I have 300/200 on AGX and the rear is just too stiff. It's pretty nice on the track, though.

Sway bars will do wonders for adjusting understeer.

Greg200SE-R · Apr 1st, 2003, 09:13 PM

Thanks for all of your replies and all of the great information. I think I'm gonna go 300/250 and pick up a sway bar a little later on. It's not easy for me to cough up $360 for Ground Controls, so another 2-hundred-something bones for a sway bar just doesn't fit in right now, since its effects would not be felt often enough for me to justify the cost. It is definitely on my lists of future mods, tho!

bahearn, I heard that in stock/mildly modded form, classics turn and rotate better than a comparable B14 when driven in track/autocross situations. Maybe there are suspension or weight differences between a classic and a 200SX that may account for your rougher ride than a B14 with 200lb springs in back. Thanks for your input man.

kev · Apr 7th, 2003, 03:14 PM

I've got 300/250 GCs. I don't think the rear is too stiff. For street use I run 1/1 settings on my AGXs.

I say leave the front sway bar alone! I also have the Stillen Rear sway bar, and its quite nice

I do autoX, so I am considering going with the 375 lb springs for the rear. I know nobody is made of money, but it's only $60 to order a pair of springs from GC. So if the 300/250 doesn't suit your needs...it's only $60 per pair of springs to experiment

hpro123 · Apr 8th, 2003, 01:49 AM

Quote:

Originally posted by bahearn
For a Classic, 250/150 is more appropriate for a street car.

Bruce, I know there is no formula that may actually let us figure how exaclty the car is going to behave but I would like some input on your opinion on spring selection.

Some suggestions (although proven? in practise) defy logical explanation.

Stock classic spring rates are 123/112.

Now, going to 250/150 means that we stiffen the front by 103% and the rear by 34%. Wouldn't this alter the behaviour of the car towards way more undrsteer? Or is there something that actually does not let that happen?

I mean,, even by going to the "common knowledge" 300/200 rates the actual stiffening front/rear is 143%/78.6%.

What gives?

I belive the original post in this thread raised a lot of interesting issues but we have failed to produced a reasonable answer to the questions posted.

Chris

myoung · Apr 8th, 2003, 02:58 AM

300 lb./in front and 200-lb./in rear springs, makes for a good all-around setup for both street and track.

PatScottAKA99XE · Apr 8th, 2003, 07:57 PM

By the end of the week Ill be able to tell you how 336f and 280r feels. No track or sprited driving data will be availible though. Still running snow tires here in VT..

bahearn · Apr 8th, 2003, 08:00 PM

Chris, you have two opposite goals to achieve with spring rate on a street car: good handling and good ride.

The farther you swing to the good handling side, the worse the ride gets. I really believe 300/200 is too stiff for a daily street Sentra. Go with softer rates and speed up weight transfer with sway bars; with the new Progress adjustable bars, it should be easy enough to dial in as more or little understeer as you desire while maintaing some semblance of a nice ride. This is the Herb Adams school of suspension design.

You young guys are more tolerant of a bone-jarring ride than I. Truthfully, I thought 300 lb/in front was pretty good but 200 lb/in rear was too stiff. To keep understeer in check, you have to soften the front in step with the rear (there's only so much sway bars can do for you).

Also, don't forget that B13 and B14 are rather flexible, so that has to factor into the computations.

hpro123 · Apr 9th, 2003, 06:20 AM

Thanks for the comments Bruce.

I have no problem with going to softer rates for comfort. My main concern was the im-balance that may result from a 300/200 pair or even more a 250/150.

Judging from past experience and comments, something like 250/200 or 225/175 would be a more reasonable compromise.

As for the progress bars, as much as I admire adjustability in anything, I sincerely believe that US$520 MSRP for the pair is way expensive.

And since we mentioned them, a few thoughts:

I believe that they are more oriented towards the hard-core racer rather than the daily-driver enthousiast (price is a strong indicator here too!!!).

Their diameters are 30mm front and 21mm rear (stock SE-R are 28mm and 18mm respectively).

This means that they are roughly 50% stiffer up front and 85% on the rear. BTW, the fact that the rear is (compared to the stock pair) stiffer than the front is a nice start and certainly obtains the original goal of a less understeering setup.

Now, I assume that the lightest setting on the bars corresponds to the "diameter" stiffness. I have no way of knowing what the other 2 positions mean in terms of stiffnes. A similar product from Whiteline in Australia has the 3 positions "spaced" by 2mm of bar thickness, so their 18mm rear adjustable can act as a 18-20-22mm bar. If this is the same with Progress, then we are looking at a sway bar that will be 100% stiffer than stock up front and 170% stiffer on the rear.

Certainly in line with the 300lbs front spring suggestion and definitely worth a look! Now, if it was not for the small US$520 matter.......

Chris

PS. Thanks for the "you young guys" comment, much appreciated!!!

spdracerUT · Apr 9th, 2003, 07:01 PM

Hmmm... i guess when we talk about springs rates, we should also say what kind of car they're on! Apparently, the rear of my car rides a bit rough but I don't notice it from the driver's seat