Prin

I just installed the prokit on my car and now when I hit a bump, the rear seems to "bottom out". It hits very hard. Is there something I can do? I had to cut the bumps in half so the car would not be sooo bouncy.

Xsta Z 28

iTrader: (2)

Buy better springs . . .

trackbird

iTrader: (4)

Yes, you need shocks to damp the rear and slow it down so it won't hit the bumpstop so hard. That bumpstop is a progressive "spring" to slow the car "gently" so you don't get the big impact. You cut that down and you will now get the big impact. This is why we've always stressed that you should do shocks and springs. The shocks will help remove the "bouncy" and allow the bumpstops to prevent the "bang".

Hayrab

I have Koni SAs on all 4 corners and I still bottom out with the prokit. I still wonder this kit is so highly rated among members here, it makes the back sag alot too.

trackbird

iTrader: (4)

As I said earlier:

I didn't say you wouldn't bottom out (hit the bumpstops).

You will bottom the car on stock springs, you will bottom the car (bumpstops, not chassis) with lowering springs. It's a compromise you have to get used to. I have run 200 in lb rear springs and I spent lots of time hitting the bumpstops. It's just the nature of the beast.

Xsta Z 28

iTrader: (2)

I have never "highly" rated the ProKit . . . but for some strange reason it is touted . . . People love it for some reason . . Unfortunately another great instance of the blind leading the blind.

Eibach is a big name in suspension so many feel "you can't go wrong" with a big named co . . .

I have two different types of Eibach springs on my cars, and both with upgraded shocks (Bilstein and Koni) and I still can't stand them . . .

Sam Strano

iTrader: (41)

Nobody said suspension tuning was easy. But that doesn't stop the internet mechanics from always popping up and making absolute statements like "this product X kick ***".

Like Trackbird said, any f-body is going to contact the bumpstops in the back. Here his rear springs were like twice as stiff as stock and he does it.

Can you explain where and when you experience the "bottoming out"? Also you need to fill in blanks like how much weight, if any you carry in the car. What works for one might now work for you. EVERY SITUATION IS DIFFERENT!!!!! You need to build your suspension appropriately for the job. And you can't rely on what you hear online. You can use it as information, but speak with someone you know who can explain why and what changes and that you can discuss your needs with.

You made the issue worse with cutting the stops. The WS6 stops are very square and when you hit them, it's very abrupt. Cutting them in half made it worse. You have more travel (barely) before you hit them, but when you do it's even a more violent change. Hence the reason I recommend non-SS/WS6 rear stops, they are a lot more progressive in their addition of spring rate.

Xsta Z 28

iTrader: (2)

Intersting info, any part number or info on where to buy non-SS bumpstops?

THX!!!

mitchntx

iTrader: (14)

Hitting the bumpstops is a bad thing altogether. Get enough spring under the car to keep them off of it ...

Here is a laundry list of spring choices to accomplish just that ...

http://www.pitstopusa.com/searchresu...ategoryID=3599

I am running an 11" spring and a 225 rear rate. When fuel gets low, it picks up a loose condition, but with a fuul load it appears to be neutral, according hot tire temps.

FWIW, I'm running
700 fronts (half-assed coil-over kit for 1/2 the price of the common ones). Considering 650s for a rough track
32/21 sway bars (dictated by rule)
Bilstein HDs up front (you know the ones that will vaporize on anything other than a stock spring)
Koni SAs in the rear (wanted some adjustability for fine tuning.

I tried 200, 225 and 250 rate springs in the rear and found the 225s gave me a more even tire temp for an extended period of time (25 minutes). It makes a difference if you are running for 90 seconds and then go cool everything off vs 20 minutes of hard running.

Sam Strano

iTrader: (41)

That notion that hitting the bumpstops it bad it completely untrue and unfounded. But based on the fact you think of them as bumpstops. Try thinking of them as bump rubbers instead (since the Z28 parts that I recommend are not square and abrupt like the SS/WS6 parts).

As a matter of fact, if you read Carroll Smith's stuff, you'll find that he likes playing with bump rubbers to tune the chassis. There is NOTHING wrong with a progressive stop or rubber. You run more spring than I do to avoid them. And your old car was a WS6 with the shitty square stops, so I can see that you'd want to avoid them. But using a nicely progressive one adds wheel rate when you need it, stays out of the way when you don't. And when you do contact one like that, it's smooth and doesn't return energy like a spring does. Which requires less shock valving.

An F-body is NO different than a pick-up truck. Light in the back, solid axle. Just like trucks, the more spring you add with the light weight, the more the rear wants to slide and skate around. Just compare a 1/2 ton truck to a 1 ton. Or use the same truck with an without a load.

As for you tire temps. Great, but see solid axle cars don't have camber curves. Nothing you do with the rear springs is going to make you temps change do to camber. Only due to sliding and balance. I'm betting you 250's gave higher temps (because you were sliding the rear around), and the 200's gave low temps because the car tended to push and the rear wasn't working as well. Given your stiff springs and weak for the springs you have shocks, I'm not at all surprised.

Yet again, you miss the big picture. You base everything of your experience. That in itself it fine, but you have to understand your experience is limited, and all you are doing is burying your head in the sand when you don't explore other avenues or condemn them based on what you think you know.

MeentSS02

iTrader: (11)

And where do you find these magical bump stops (or rubbers)? I'd like to get some since I've hit them a couple of times and don't really like being jarred...

mitchntx

iTrader: (14)

Now Sam, be nice. Don't be hating. Let's keep it civil ...

I like your analogy about rear spring rates cause when I hit the bump stops the *** end certainly wanted to skate around ... the spring rate went through the roof ... immediately! Wouldn't that constitute "experience"?

Having the spring rate jump several hundred pounds almost instantly takes quite the driver to control. I applaud your Schumacher like reflexes. I don't think the general population has them, though ... my big picture and your buying demographic ...

And I don't have a WS6, rather a regular old Trans AM ...

Sam Strano

iTrader: (41)

the magic parts are under any normal Z28 or Formula. You can get them as near as your local dealer...........

Mitch, again you missed the point..... Wasn't your old car a WS6????? That has the square stops that spike you rate when you hit them. The standard stops don't, they are pointed and much more progressive in nature. You are basing what happended to you on hitting the stops, which I agree with. But the trouble wasn't just hitting the stops, it was that you were hitting poorly designed stops. Use a better stop, you don't need as much spring to try and avoid them. Your experience is limited to what you had only. So how can you say the problem is with all the stops? You can't. Now you have normal stops in this car, but you have already decided that you need X spring based on before. But this isn't this same as what you had before. And you didn't explore all the options of reasons before.

trackbird

iTrader: (4)

These are the more progressive (Z28) ones (they may be a different color these days. I remember someone telling me they were white or something now). Just sharing information objectively.

mitchntx

iTrader: (14)

Nope ... My car has always been just a regular old TA ...

Sam, I DO see what you are saying ... if you are gonna hit the stops, then use them FOR you and not AGAINST you and make the best of it.

But having enough suspension under the car to never get to that point makes for a more predictable transition into and through the turns, IF you are allowed by rule to change the rear spring ...

Granted, I was on the stops when I had the Eibachs on the car. When I went to the G2 springs, it happened quite a bit less frequent, usually only in a heavy transition like when coming off the banking at T1 at TWS at 140mph ... I can't imagine being on the bump stops at that speed and trying to "drift" the car through T1 and T2 ...

I wonder if our differing philosophies boils down to driver venue and style, more than anything ...

Sam, I have a lot of respect for you and your accomplishments. They are admirable indeed. But if my limited experience has shown me ANYTHING is that "handling" is in the "seat" of the beholder.

We could most likely switch cars ... I would hate yours and you would hate mine, each having ideas on how to make each other faster. I'm not saying I could ever be as fast as you, rather our styles differ so much and the subsequent setup is so radically different, that we couldn't be fast in the other's car. We have agreed in the past that there is more than one way to make a car handle.

I don't have a horse in this race ... you do. So, I will voluntarily stop participating in posts that you are in as I'm afraid it might confuse folks, question their purchases and in turn, it might hurt your business.

I can't believe my humble opinion would carry that much weight, but I get 2 or 3 PMs a day asking for information. I have let my inbox fill and I'm not gonna empty it. So, the playground is yours ...

Eugenio_SS

iTrader: (2)

what shocks you have ? and if adjustable, what settings are they at ?

Eugenio_SS

iTrader: (2)

would you by any chance have the jounce spacers ?
if so, have you considered removing them for extra suspension travel ?

absolut_speed

iTrader: (1)

Just for comparative purposes, here is the SS/WS6/Firehawk bump stop (after I removed the spacer.)

Prin

I have the factory installed shocks

Eugenio_SS

iTrader: (2)

imho, that's the major culprit.
The stock deCarbon shocks already have a hard time handling stock spring rates. The prokits are in the order of 25% stiffer springs... yet nothing has been done for compensating for the damping side.
Getting some Bilsteins revalved for the front and some HDs for the rear should make things much better... but then depends on your budget as well... you might also want to go with Koni adjustable shocks.