Jeff M

I'm in the research phase of installing the Van Steel Coilover system on my 92 LT1 Coupe. Car is not my main transportation nor a daily driver however it will see considerable time on the street. Most of it's time will be competing in local road course events. Unlikely any strip runs, never been a 1/4 mile guy.

I realize while "ride" is a very subjective term, I'd like to have the ability to soften it up a bit while on the street. Not looking for a Cadillac ride but also don't want bruised kidneys after each drive. From what I've learned here the QA1 shocks will provide that flexibility.

Which brings me to my question... what are you running for spring rates? I was leaning towards 375 front and 300 to 325 rear. Thoughts?

Car has all Urethane Bushings, ZR1 30mm front and 26mm solid sway bars, Camber Brace, Harness Bar, and will soon have the Vette2Vette's Frame Stiffeners.

gerardvg

Hi

The QA1 coilovers are a great choice.

However the spring rate determines the ride, if your car is used on the street buy the street single adjustable street kit.

The shock absorber controls the spring, they are a matched set.
I recommend going to a street version, I have a track setup with around 400+ springs that give a very harsh ride.

Just some advice, see what others who run coilovers have to say about the ride. I had set my car up for track but am considering changing to a softer street setup as the ride is grueling on bad roads.

Have already gone from -1.5 camber to zero camber, is tiring having a car that is great on the track. To something unstable on the roads, wanting to dart to one side or the uneven roads.

A car setup for track work is really annoying to drive on poorly maintained public roads.

l98tpi

I dont run a coil over set up on my car. I have a 1200lb front transverse and a 800lb rear transverse spring. I can corner balance the car good with the set up. Not sure about coil overs but I know if you wanted to spend a lot of time you would have a lot more control of the corner weights at each corner of the car. But like I said, you will spend a lot of time doing this and you will need to get your own set of scales unless you want to spend a lot of money having alignment shops do it all them time.

MatthewMiller

My experience has always been that damper rates contribute more to harsh ride than spring rates. When the car goes over a bump, stiff dampers send momentary loads into the chassis that are much higher than the spring rates (like 10x higher). That's why I always thought it was funny that some people worried about their shock towers on strut cars when converting to coilover suspensions. My new-to-me C4 has high spring rates along the lines of l98tpi's, and it can still be made tolerable on the street with lowered damping rates. It's not as smooth as stock, but it's not nearly as bad as most people would predict. I had an SN95 and had the same experience. OTOH, I've had misadjusted adjustable dampers on a stock-suspended car (accidently went full-hard when I intended to go full soft) and it felt like the suspension was literally locked up solid.

Since I'm new to C4s, can anyone tell us the motion ratio for the stock spring setup? That is, where does the spring link to along the line between the inner control arm pivot and the lower ball joint up front? Same question for the rear, too. Then we need to know the motion ratio for the shocks, too. That's what we need to know before we can compare transverse spring rates with coilover spring rates. I don't think you proposed rates of 375 and 300-325 are off the mark, though, if the shocks are close to a 1:1 motion ratio.

Edit: Here is a short but good thread on the subject. Post #5 tells you what you need to know. Just keep in mind that the chart he links to measures rates in Newtons/milimeter, not lb/inch. So per that post, we get "leaf spring motion ratios of approx 0.57 front and 0.80 rear" and "motion ratios for coilovers of 0.74 front and 0.98 rear." Remember that you must square those motion ratios to get he wheel rate for a given spring, and now you can make a direct comparison between transverse springs and coilovers. So doing the math, to equal my front VBP Extreme spring's (1150lb/ft) wheel rate with a coilover, you'd need a coil spring rate of 681lb/inch. So your 375lb/in front coils would not be all that severe.

The only way to know what spring rates you find acceptable in ride quality is to ride in cars with similar rates and with dampers similar to what you will use, or to try some different springs yourself. The beauty of coilovers is that it's easy to swap springs to try some different rates.

Jeff M

Thanks everyone for the replies! Gives me more to think about but definitely good advice all.

whalepirot

I agree with Matthew for this reason:

Driving the roughest riding stock Corvette '84 Z51) with NO rubber in the suspension got old on these relatively decent streets. I'd changed to a standard rear transverse, with little real change. It broke so the Z51 was reinstalled.

It came time for shock replacement and after two sets of leaky Monroes, I had Bilstein revalve the stockers to challenge spec. the car is very pleasant to ride in without diminishing handling.

I was surprised, in a good way.