Coilovers: How do I go to stiffer springs without forcing the shocks to top out?
Posted by Cessnaporsche01@reddit | askcarguys | View on Reddit | 21 comments
Okay, so I just put coilovers on my C5Z. The kit came with 550lb springs in the rear, but the car only compressed them less than 0.75" of their 3.10" stroke, resulting in top-out and snap-oversteer when cornering. I bought some 450lb springs instead and got myself another ~0.375" of down-travel, which solved the snap-oversteer issue, but these springs are awfully soft and still allow for more weight transfer than I'd like.
So how do I increase spring force without just dropping droop to nothing and picking up the inside wheel? Do I need a heavier swaybar or stronger front springs just to prevent the car from lifting that wheel?
Equana@reddit
Stiffer spring with the same free length will increase ride height and use up the droop travel. Coil overs are on threaded bodies...screw the spring seat down until the ride height lowers and gives you more droop travel. The threaded spring seat is there to set the travels closer to the middle of the stroke.
Cessnaporsche01@reddit (OP)
That 0.75" is at 0" of spring preload. I can only reduce the droop travel from there, not increase it. Loosening the spring seats just releases the spring.
Equana@reddit
Loosening the spring adds droop travel. If you don't want the spring to go loose, you add a tender spring.. a very light spring with flat wire.. to insure the spring doesn't rattle loose.
And the higher spring rate in the rear promotes more oversteer. Not as much as topping out but more. The weight is going to transfer anyway...that is just physics.. the spring just supports the body from pitching as much.
When you run it the way you have, how does the ride height look? Rear high?
Cessnaporsche01@reddit (OP)
Now that might be the answer I was looking for! Never had heard of those.
With the square springs (450lb/in on all corners) and zero preload all around, the rear is a little higher than the front. With the stiffer rear springs that came with the kit, the rear is closer to an inch higher than the front.
MoparMap@reddit
Was going to suggest the helper/tender springs as well. I have them on my Viper as my springs were only maybe 6" long, but the shock was something like a 7-8" body. They are more like spacers with my current preload setup, but that's basically what you're looking for.
Gunk_Olgidar@reddit
Spring is too big for the car.
Cessnaporsche01@reddit (OP)
Too big as in spring-force, or too big as in length?
Gunk_Olgidar@reddit
Well both in reality, but I'm talking length here.
F=KX
Stiffer springs have higher spring constant ("K") and deflect less ("X") under the same weight ("F"), so they need to be shorter than the stock springs for the same vehicle weight.
Leaf springs have been used in Vettes since forever for packaging reasons. Spring constant increases with deflection. And in the Corvette that is done to avoid bottoming out with the very low total travel distance in the rear. So to get your C5 at proper ride height, you may risk bottoming out on large bumps.
And since it's been like that forever, you're obviously not the first and won't be the last to do this. So spend some time on corvette specific forms and they can guide you to the best choices for your coilovers.
Make sure you have good bump stops and keep an eye on them. And take it easy on the rough stuff.
Cessnaporsche01@reddit (OP)
Right... but let's set aside ride height (and thus spring length) here, since that can be adjusted by manufacturing alternative mounting hardware. My problem is lack of spring travel between 0 corner load and static/resting corner load.
Like, if it only takes ~400lb to hold up the corner, I'm never going to get more than 3/4" of shock compression on 550lb/in, etc.
This means that car can only roll a hair under 1 degree without topping the inside shock out. Going up to shorter, say, 600lb springs would reduce body roll, but also make pickup happen at just 0.85 degrees (approximately, not simulating the dynamic system) and that would probably be under higher G-loading which is not exactly desirable to me.
Considering, from factory, the car has the capability to roll over 5 degrees while keeping all wheels planted (8 inches of wheel extension!) this sub-1-degree roll limit before the rear suspension simply gives up road holding seems incredibly diminutive.
The more I think about this, maybe I really do just need swaybars...
Gunk_Olgidar@reddit
https://www.shredjesse.com/1999-c5-corvette/c5-corvette-sway-bar-sizes-leaf-coilover-spring-rate-research-notes
Cessnaporsche01@reddit (OP)
Oooh! Not that is a very good resource. Bookmarking.
Over_Pizza_2578@reddit
Do your shocks have separated preload and ride height adjustment? If so, only minimal preload, like one or two rotations of the nut, just so the spring cant bounce around
Cessnaporsche01@reddit (OP)
They do not. Not that it matters anyway - zero preload gives me enough ride height; I just have too little spring-force to counter body roll and too much spring-force to allow the shocks to be properly compressed
hatred-shapped@reddit
Stupid question. Did this kit require you to remove the leafsprings? And did you?
Cessnaporsche01@reddit (OP)
lol fair ask. Leafsprings are removed
hatred-shapped@reddit
Sorry, I had to ask because I've seen them not removed. Have you tried adjusting the damper settings? Most coilovers I've used were super stiff in the rear. Both the spring rates and the valving in the dampers. And did you get the car corner weighted? Remember coilovers are meant to adjust the weight distribution of the chassis.
Cessnaporsche01@reddit (OP)
I've played around with the dampers a fair bit. The car seems to like relatively moderate damping front and rear, although the rear needs a bit more than the front to stay stable over rough or uneven surfaces. Have not corner weighed the car though.
doctorsnarly@reddit
Does the spring bottom out? You should be able to get a spring at a higher rate with less coils of that's the case.
Cessnaporsche01@reddit (OP)
It does not. But am I thinking wrong, or would that not simply compress the same amount? It's not like the spring can be allowed to float until a certain point in the shock travel...
doctorsnarly@reddit
The spring should compress until it binds. What is stopping it from binding?
Cessnaporsche01@reddit (OP)
I don't have enough weight on it. It's a 7" spring, and binds at around 3". Tbh, the shock would probably hit its bump stop before the coil spring was bound up.
But in any case, adding preload increases ride height and reduces droop travel, which is the opposite direction of my desired goal