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Suspension experts please get in here (discussion about springs)
Hi guys,
The C5 corvette obviously has a leaf spring suspension but spring rate is not often talked about until you start introducing coilovers into the discussion.
After doing some searching on this forum, I found that the stock C5 Z06 spring rate is:
- 526lbs/inch front and 714lbs/inch rear
When we load those springs by lowering the car on stock bolts, how is the effective spring rate affected?
When we move on to a coilover, it becomes difficult to compare the stock leaf spring rate to the coilover spring rate because you have to consider wheel rate before you can do an apples to apples comparison between the two.
Also, it’s interesting that a front engine car would have stiffer rear springs. I notice that for many of the guys who road race, they transition towards more spring rate in the front and less in the rear. It’s not uncommon to see 700lbs/inch front and 600lbs/inch rear for the more serious racers (for the coilover users).
For the sake of argument, let’s ignore the leafs and focus on the three brands of coilovers:
- PFADT (discontinued but ran about $3,000/set): 425lbs/inch front and 575lbs/inch rear
- LG GT2 ($2,000/set): I am not able to find any info on spring rate for this coilover set
- STANCE ($1,200/set): 7kg/mm front and 10kg/mm rear (that translates to 392lbs/inch front and 560lbs/inch rear)
The PFADT/LG are proven and have a great reputation but I won’t buy PFADT because the company is out of business and I can’t easily replace a shock cartridge for example if I needed to down the line. The STANCE coilovers are considered to be a mid-level coilover and they have a decent reputation in the import world. Those are very attractive at $1,200/set. Has anyone used the STANCE coilovers on this forum? If so, what sways are you using and what’s been your impression and would you recommend them?
The C5 corvette obviously has a leaf spring suspension but spring rate is not often talked about until you start introducing coilovers into the discussion.
After doing some searching on this forum, I found that the stock C5 Z06 spring rate is:
- 526lbs/inch front and 714lbs/inch rear
When we load those springs by lowering the car on stock bolts, how is the effective spring rate affected?
When we move on to a coilover, it becomes difficult to compare the stock leaf spring rate to the coilover spring rate because you have to consider wheel rate before you can do an apples to apples comparison between the two.
Also, it’s interesting that a front engine car would have stiffer rear springs. I notice that for many of the guys who road race, they transition towards more spring rate in the front and less in the rear. It’s not uncommon to see 700lbs/inch front and 600lbs/inch rear for the more serious racers (for the coilover users).
For the sake of argument, let’s ignore the leafs and focus on the three brands of coilovers:
- PFADT (discontinued but ran about $3,000/set): 425lbs/inch front and 575lbs/inch rear
- LG GT2 ($2,000/set): I am not able to find any info on spring rate for this coilover set
- STANCE ($1,200/set): 7kg/mm front and 10kg/mm rear (that translates to 392lbs/inch front and 560lbs/inch rear)
The PFADT/LG are proven and have a great reputation but I won’t buy PFADT because the company is out of business and I can’t easily replace a shock cartridge for example if I needed to down the line. The STANCE coilovers are considered to be a mid-level coilover and they have a decent reputation in the import world. Those are very attractive at $1,200/set. Has anyone used the STANCE coilovers on this forum? If so, what sways are you using and what’s been your impression and would you recommend them?
I have this information from posts over the years on CF. I also read that the wheel rate ratio for COs is:
F - 0.441
R - 0.373
which is multiplied times the listed CO rate. I can't swear to this but you can also run the numbers from the screen shot information shown.
The wheel rate for OEM leafs is:
F - 0.302
R - 0.160
which explains why the rear leaf rate is so high.
Lowering your car on the stock bolts will not really change the spring/wheel rate. There maybe some very slight change but I'll leave that to others to comment.
- STANCE ($1,200/set): 7kg/mm front and 10kg/mm rear (that translates to 392lbs/inch front and 560lbs/inch rear)
The STANCE coilovers are considered to be a mid-level coilover and they have a decent reputation in the import world. Those are very attractive at $1,200/set. Has anyone used the STANCE coilovers on this forum? If so, what sways are you using and what’s been your impression and would you recommend them?
No. These fall squarely into the category of all the cheap OTS asian CO's that import guys use to slam their cars and then believe because it feels like it is on rails that they have a race suspension...
Despite what most owners of OTS CO's will tell you about how great their CO's are, most can be proven on a dyno to be unmatched, poorly valved, and non-repeatable (for the single/double adjustable type). Cheap CO's are going to be worse then a properly setup stock C5Z suspension. Even OTS "high-end" CO's are likely no faster then a well valved/dyno'd set of quality dampers matched to springs/bars/tires and setup with proper ride height and alignment.
Sorry if I come across a bit harsh, I went down the cheap CO path and learned the hard way (hitting the wall out of T5 at Road Atlanta) and cringe every time I see posts about "what CO's should I buy". I am no expert here and I know that I am no expert. What I do know is that when it comes time to invest in CO's for high performance driving, take it to an expert that specializes in building/tuning suspension systems. I did and only regret not going down that path first. What is really amazing is that you can get high-quality custom built and valved CO's fully dyno tested and matched to your specific car setup and driving application (Auto-X, HPDE, competition, ...) for the same price as "high-end" OTS CO's.
Dan,
Thanks for sharing your spring info.
Tom,
I'm no expert either. I've done some reading, the book "How To Make Your Car Handle" was recommended on CF, does some explanation of how the various components work together, lots on geometry, etc. Since I'm not an expert and after reading the mentioned book, I'm even more gun-shy about making suspension changes. My stock GS handles pretty well, seems well balanced and I plan to stay on street tires. I'm sure GM spends way more money trying to get these cars to be well balanced than what I can spend, so talking to the experts about it, even though the components may be a bit more expensive, seems to me is the better path to go.
Along this line of thought, I also wonder about going to Coil Over suspension systems is staying on street tires for track use. If the comp spring is capable of keeping the tire contact patch flat at various angles, what is the advantage of going to CO's? From the previously mentioned book, you do most of your suspension tuning with the spring, fine tuning adjustments are made with shocks and sway bars. So if you are using your daily driver for a few hpde sessions per year, it seems a good starting point would be to upgrade the springs to Z-06 levels, high performance 2-way adjustable shocks and adjustable sway bars (at least for the rear) would give you (at least me anyway) more combinations to adjust for than my current driving skill can take advantage of.
A great off the shelf coilover in my opinion is the LG G2 Bilstein setup. I've had it on my racecar for 2 years and recently upped the springs from 700/600 F/R to something closer 4 digits. I know other racers that go north of 4 digits. I ran the car on the G2 kit as is for 2 years and was very competitive in NASA ST1. Since I had them apart to put new springs on I had them re-dyno'd. They were spot on after 2 years of racing and abuse (curbs etc). The dyno's showed minor variance right to left: so good in fact the shock guy said it was hard to get symmetrical curves closer on new shocks! I'm at the point where yes I'd like to do some tuning at this 10/10ths level with adjustable compression and rebound but we are talking a couple of tenths per lap possible improvement.
A great off the shelf coilover in my opinion is the LG G2 Bilstein setup. I've had it on my racecar for 2 years and recently upped the springs from 700/600 F/R to something closer 4 digits. I know other racers that go north of 4 digits. I ran the car on the G2 kit as is for 2 years and was very competitive in NASA ST1. Since I had them apart to put new springs on I had them re-dyno'd. They were spot on after 2 years of racing and abuse (curbs etc). The dyno's showed minor variance right to left: so good in fact the shock guy said it was hard to get symmetrical curves closer on new shocks! I'm at the point where yes I'd like to do some tuning at this 10/10ths level with adjustable compression and rebound but we are talking a couple of tenths per lap possible improvement.
We ran the G2 Bilstien on our car also. More than likely the best non adjustable shock out there IMO. We ran 850/750 F/R. Car was very fast in thee twisties.
06-27-2014, 05:30 PM
Suspension experts please get in here (discussion about springs)
