semicycler

Normally the sway bars have no tension in them when the wheels are straight. The stock drop links are designed to be the proper length for this to happen at the stock height. No tension allows each wheel to move somewhat independently going over bumps in a straight line. As you turn the steering wheel the sway bars through the drop links tighten up the suspension between the left/right side of the car helping maintain those tight corners. All is well. Stiffer sways help cornering even more up to a point of diminishing returns.

If you drop the car the drop links are no longer the proper length. This adds some pretension to the sway bar while driving straight. Each wheel is no longer completely independent as this point. The up/down motion on each side is limited depending upon how much tension exists in the neutral position. Turning does similar things. Tension between left/right is higher at each angle. Too much pretension at neutral and when you turn you can get strange oversteering or understeering effects (depends upon a lot of suspension effects including front to rear sway bar stiffness ratios). In extreme cases you can get a snap steering effect coming out of a turn. If feels like the car suddenly steers on its own in an unexpected way. It can be quite scary and very dangerous at high speeds.

So what to do? Adjustable length drop links. When installing match the length to roughly the OEM length and install. Then with weight on both wheels on the same axle and the steering pointing straight, lengthen or shorten just one side until the tension is released, then lock the length in place. Technically you only need one side to be adjustable. But practically you buy adjustable ones in pairs. They're sturdier than stock in addition to being adjustable in length.

For mild drops the OEM drop links are fine. They add a minor amount of preload that is mostly unnoticeable. Going to higher alignment specs along with drop? Adding aftermarket sway bars? Dropping mid to high amounts? Feeling funny steering effects coming out of a tight or increasing radius turn? All good reasons to check if your sway bars are preloaded.

How do you check for preload? With your current setup and weight on the wheels climb under the car. Ramps work well testing one axle at a time. Or if you are lucky with access to a drive on lift it's even easier. Remove the lower nut on one drop link only. Then try to remove the lower end of the drop link from the sway bar. If you can easily remove it then there is no pretension. If you need to push up or pull down on the sway bar to remove the bolt, there is pretension. If you need to muscle the sway bar to remove the drop link you definitely need adjustable length drop links.

jglaze

I'm not 100% sure what failed either, I do need to talk to the shop a little more before I drop significant money. It's too easy to go to the Bilstein website and drool, but always nice to hear from folks with firsthand experience.

Regarding stock replacement, that is a fair point, and I'd considered that route as well utilizing some of the saved funds for replacing some other aging suspension parts. I'm under no illusion that I'll be outdriving the stock setup at this point, but wanted to make sure I was considering all my alternatives.

And, thanks again to Semicycler who has posted on a number of these suspension threads and has been more than helpful in the past with talking me through some of the finer points of suspension tuning with regard to the GT3 LCAs and lowering the car!

Alexandrius

There's so much that goes into suspension as well.

keep in mind, if you run 18' wheels you will have more ability to soak up potholes with your much taller tires fat rubber, and can get away with perhaps a bit more agressive suspension on street and track.

id go 18" wheels with taller tires to maintain proper ratio, then go ohlins road and track, and add all the peripherals needed to support, so lcas, drop links, etc

jglaze

18"s are on my list - and I prefer the look, frankly.

Alexandrius

yeah I have 18's with track tires on them. I drive to and from events. I absolutely love them on street feel-wise.

The downside ? Noisy as hell. Seriously loud resonance from those tires (r888).

but for me the trade off is worth it.

cars are always about trade off, just have to find what you want yours to do the most heh.

lowbee

So is 19" really just for looks ? Don't 19" at least give you better steering respond on the track ? I am curious (or need to be schooled on) why you choose to run 18" on the track....please help me understand..

Alexandrius

theres a lot of good reasons for both. I will explain the pros and cons.

tires being equal, on stock alignment, the 19's are faster. Why? Thinner tires with stiffer sidewall = better turn in. This was proven by best motoring on the 997 specifically.

now, let's say we have a stock setup with 19's and Michelin pilot super sports, versus an 18" setup with toyo r888s. The r888s will be faster just due to being an R compound and having much more grip, but turnin will still be a bit compromised. Advantage here is to r888 ( which are cheaper in 18, and our cars have many good cheap 18 inch wheel options for track wheels).

now, if you can afford to make suspension changes to accommodate 18 inch wheels, you can have an overall faster car on track, with a much less comfortable on-road experience (car will be twitchy in a straight line even).

i hope this answers your question, the point being all of these variables are interconnected. Could I track on 19s just fine? Of course. And with r888s probably with about the same time. But the 18s would at least be cheaper.

lowbee

Thanks Alex, that make sense.....

semicycler

It's a trade off of strength, weight, and cost. Strong lightweight wheels are less expensive in 18". The same make/model of tire is generally cheaper in 18" sizes with many more options on the market. It's easier and cheaper to find a 18" setup with track tires than a comparable setup in 19". And since tires wear fast on the track, the ongoing costs to replace the rubber is important. So using R-compound on the track in an 18" setup generally weighs less, cost less up front and has less ongoing costs than a comparable 19" setup.

Ignoring cost differences, if you find a 19" comparable setup then perhaps sidewall stiffness becomes a factor. But chances are it will still weigh more. This means more unsprung weight and less acceleration. Sure you might be able to turn in faster but will be handicapped on acceleration.

Unless of course money is no object on the track in which case run ceramic rotors too

himself

I19's fill out the wheel arches better, but in terms of track time, you'd probably need a pro to quantify the difference. For me, I doubt there would be any appreciable difference between 18 or 19 on the track in terms of feel. Any differences regarding steering input are driven more by alignment than tire.

Just be sure there is enough room for the caliper and you aren't reducing tire width. Then go with the cheaper tires (There are a lot of choices for 18" tires and they are typically cheaper).

-td

jglaze

Going back to the original question, it looks like the B4s and B8s for PASM are roughly the same cost, though with the B8s I'll need to factor in new springs (and droplinks/toe links/etc which I've already started sourcing), though the stock springs have 90k miles in them anyway... The B16s are significantly more expensive and seem like overkill.

I'm leaning toward the B8s because I think I'd like a subtle drop and despite needing to replace additional parts, due to the age/mileage of the car I figure it doesn't hurt to replace the major wear items in the suspension anyway. So it looks like:

B8s
Eibach springs
F/R adjustable drop links (may not need with Eibachs?)
F/R GT3 sways (tbd...)
Rear adjustable toe links (have)
DSC (have)
GT3 LCAs (have)

Anything I'm missing that I should be replacing while I'm doing the work?

semicycler

Earlier on you said 90K miles on the car. Find the Bilstein B8 install instructions online somewhere and see what OE parts are supposed to be reused. If any of them have rubber bits to them then plan on refreshing them with new pieces. Your existing ones are likely shot or close to it. And since you have to remove them while installing the B8's, now is the time to refresh them (strut tops, bump stops, maybe the front shock tower bearing although it can be cleaned and regreased).

jglaze

Good point. Incidentally, Elephant Racing has a good interactive diagram for helping to figure some of this out, though they seem slightly higher priced that I've seen elsewhere. I need to dig up that thread about where people source their aftermarket parts...

As I think about it more this morning, do you (or anyone) know roughly how long the stock suspension should last or when you should expect to start replacing things? I know it's dependent on driving style, location, etc, but I'm wondering if 90k is early for this car (a lifelong CA car until me...)?

semicycler

Good question. Age, mileage, driving style, tracked or not, weather conditions where the car is used all play a factor. So it's not a simple X miles or Y years. Instead go back to basics. Your pre-DE tech inspection failed the suspension. That's what started you down this route for new shocks. Chances are more than just the shocks are gone or close to gone.

For reference my LCA pucks starting leaking at around 75K miles on a car that saw track time. And front tie rod ends had too much play at 85K miles. I've since replaced just about every suspension component while removing all the rubber bits for monoballs. The rear strut tops where fine, the fronts looked aged. The rear bump stops where in really bad shape. 2006 C2S Texas car that saw moderate track time. So hot weather, age, and tracking more than mileage in my case.

Bruce recently change his leaking shocks out. Don't remember the details but thought the mileage was around where you are.

ColoradoMark

I had a blown rear shock after 74,000 miles.