Coil-overs or Leaf Springs–That be the Question.

[lbszr]

Originally Posted by Hib Halverson

I wasn't aware of any C4 front springs with C5-style adjustment screws. What company makes them?








Russ addresses that above and I bet there are others making heim-jointed stabilizer bar links. You can even do it the po-white-trash way and just use washers between the stock end link spacers and the seats the link cushions sit on, but, yeah...heims look much cooler and sharpen bar response.

Great write up. Thanks,

I use the vbp front leaf leaf with adjustable ends, like the c5.

Oh well, I guess the secrets out, what I am . I did the shim procedure, but I did try for a little better look with body shims for the front bar, and made aluminum shims for the rear bar, hopefully the poly bar bushings are sharpening the response.

[batchman]

Originally Posted by RussMcB

I recently bought a pair of adjustable links for the rear of my car here

Wow Russ, great find. I was thinking of installing only one/side since they do appear heavier than the stock parts, and they ain't cheap - but are cheaper than the Guldstrand parts I was choking on buying .

Originally Posted by Hib Halverson

The post I made got kind of long so I decided not to cover that. My gut feeling is there might be a problem with loading on those parts but I really had not information to support it. In defense of C4 coil-over conversions, I'm not aware of anyr reports of fatigue failures of C4 shock mounts on cars converted to coils.

I'm not aware of any failures either and I'm probably just over-cautious given I'm running huge and sticky slicks and sometimes on bumpy courses. Again that rear knuckle looks stout but I figure I'm probably north of 1.5g's and also need to space the shock inboard, making the "lever" more effective.

Oh and thanks to lbszr catching and fielding the Q on the VB&P spring setup, although as I recall I had to specifically ask for this style adjuster and they did have a significant lead time (for the inserts I think) when I called. I thought everyone knew about them on this, in fact I thought they were the only source with non-factory spring rates.

Originally Posted by XfireZ51

My car came w coil overs and overall I am pleased w them. I won't convert back but I am interested in the comment of increasing the stab bar rate. Is there a guide to what this should be given the spring rates chosen, i.e. 425F/300R?

I'm sure your C/Os are fine but I would suggest adding an annual inspection on that rear mount, or after any big "pothole in a puddle" type incident. You undoubtedly have a well matched system in your spring/shock combo, there's a lot to be said having the spring and shock sharing mounts.

For your bar question you'll have some math to do if you want to home in on the factory spring/bar ratios - your wheel rate vs spring rate will be a little different than with the factory spring seat location. For things like bars though I put a lot more stock in tuning by SOTP. Of course it's very difficult (and in fact unwise) to get steadily close enough to limits to find the front/rear balance on the street. Here's a good excuse to get comfortable on an autocross course! Luckily there are a number of bar sizes from the factory and the aftermarket, they're not expensive and they're relatively easy to change - easy enough to try a few combos at a typical test-n-tune event.

Speaking of which, anybody have a 19mm rear bar lying around? I think my next spring will be high enough rate I should soften what I have, and I'm running the smallest one I have in-hand.

Best,
- Jeff

[XfireZ51]

Originally Posted by batchman

...

I'm sure your C/Os are fine but I would suggest adding an annual inspection on that rear mount, or after any big "pothole in a puddle" type incident. You undoubtedly have a well matched system in your spring/shock combo, there's a lot to be said having the spring and shock sharing mounts.

For your bar question you'll have some math to do if you want to home in on the factory spring/bar ratios - your wheel rate vs spring rate will be a little different than with the factory spring seat location. For things like bars though I put a lot more stock in tuning by SOTP. Of course it's very difficult (and in fact unwise) to get steadily close enough to limits to find the front/rear balance on the street. Here's a good excuse to get comfortable on an autocross course! Luckily there are a number of bar sizes from the factory and the aftermarket, they're not expensive and they're relatively easy to change - easy enough to try a few combos at a typical test-n-tune event.

Speaking of which, anybody have a 19mm rear bar lying around? I think my next spring will be high enough rate I should soften what I have, and I'm running the smallest one I have in-hand.

Best,
- Jeff

'Thx Jeff,

Overall the car corners very flat. I don't feel a tendency to over or understeer but I'm not driving at 8/10 or < either. Frankly, it feels stiff enough already to the point where the addition of the rear spare tire carrier calms down some of the rear end "bounciness".
I've added the DRM trailing arm brackets this winter along w 345s in the rear. I am hoping that will further plant the rear end.

[batchman]

Originally Posted by XfireZ51

the addition of the rear spare tire carrier calms down some of the rear end "bounciness".

Does a full tank of gas behave differently than near-empty?

Bounciness in my experience indicates a bit of a mismatch between spring and shock. The shock is not fully able to control the spring. This can be due to age (loss of gas pressure or an oil leak, internal or external) or a just a (somewhat common) original mismatch. This points to either rebuilding or re-valving the shocks, or reducing the spring rate.

The other thing that can feel like a bounciness is reaching the end of the shock's travel. If adding the spare, a full tank and maybe some heavy luggage or something improves things, that's where I'd look - if you can get a small zip-tie around the shock shaft that can tell you about the maximum compression you're seeing, and measuring tire-to-fender lip at rest vs when jacked up by the body can tell you about where you are with respect to droop travel. If it's a travel thing you may be able to improve it by changing your ride height.

I hope this helps some - but take my advice with a grain of salt. I'm sitting here with most of my front end apart for months, the rear not apart yet, and the season's first event looming large. At the moment I feel more like an internet race engineer than an amateur one .

Best,
- Jeff

[XfireZ51]

I haven't noticed a diff between full/empty tank, but I definitely felt the difference once I removed the spare tire carrier and associated hardware.
I have the tire carrier on again, but that's because I have it holding insulation which is dampening the resonance from the exhaust as it crosses underneath the hatch area. The rebounding appears to be controlled but the rear end is stiff.

[mike100]

I was just talking to a well known member over at the C4 area on CF that said he wants to go back to transverse leafs after running coil-overs for the last 5 years on his 96. Outside of optimizing a C4 for a particular smooth road course, sometimes just going back to stock is the best choice on the street- especially for spring rate, travel, and ground clearance.