No, the bump stops area essentially a progressive spring. They are an integral part of the suspension and used frequently on a lowered car.

I'm not slamming into the bump stops (except for pot holes) but am compressing them enough to send my spring rate very high in hard corners and cause a loose condition.

I definitely need better shocks, but that is not going to keep me from compressing my springs in a hard corner. As I already have stiff springs, it seams I need to increase suspension travel and allow the springs/shocks more room to work before getting into the bump stops. At the very least, this should decrease how much I compress the bump stocks and thus how much I increase the effective spring rate in a corner.

I still don't think that's the right way to tune..

When you transfer weight on those rear shocks, assuming they are Bilstien HD's they probably lack the rebound control. The rear probably swings from one side to the other faster than you'd like, causing more of a snap oversteer. If you just trim the bumpstop, wouldn't this condition be worse if you end up on the bumpstop anyway?

That is my point, they shouldn't be used frequently on a lowered car unless you have a mismatch of spring rate and dampers.

They don't ride bumpstops from the factory and shouldn't w/ lowering springs either.

Why not just a quality shock that will dampen the spring in its available travel rather than trying to move the bumpstops and compensate for shitty shocks that you are trying to make do something they weren't designed to do?

The idea of gaining travel with modifing the bumpstops has some problems. To keep the suspension working properly the bumpstops are used, And they need to be the Z28 ones, not the SS/WS6 or the aftermarket poly ones. I have tried all and the only ones that work are the Z28 ones.
If you were a fabricator you could relocate the bumpstop , in its entirety, up higher. This looks to be the solution, but then you run into the issues that the axle and related parts are now up higher into the body tub than desired, suspension angles are affected and parts start to hit. One of the parts that can get hit is the gastank, not good.
with the proper springs and shocks and stops the car behaves as it should. It may not look as "cool" as we would want, but that was a issue that the GM designers stuck us with. Unless you back half the car and totaly redo the frame, floorpand tubs etc, dont mess with the stops they are there for a reason. I agree with the arguement that a proplerly designed suspension should not contact them, but that is not what we are working with.
I have tried many different spring, shock and stop combos with 10 bolt, 12 bolt and 9in rearends and found that the rear is much harder to get correct than the front, and the only 2 springs that worked well for me were the 1LE ones for stock ride height and sams for the lowered height. I have used V6 springs, prokit, sportline, slp stage 1, slp stage 3, global west, and various customs with spring jacks.

Exactly JamRWS6, exactly.

Lowered car's do ride the bump stops and I am pretty positive I have heard Sam say this himself. Something about his Mustang is sitting on them at a stand still.

However, I agree they SHOULDN'T.


I do not believe shocks wil fix the problem. The problem is the physical overall compression of the spring. A damper does not, or atleast should not compensate for this.

The spring is compressing enough that the axle makes signifcant contact with the bump stop, effectively increasing the spring rate, and causing a loose condition.

The way I see it, I could run stiffer springs (not much out there stiffer than Hypercoils), give the springs more room to compress before hitting the bump stops by raising the rear ride height, or accomplish the same thing by trimming the bump stops.

I am talking long high speed (65-70mph) corners particularly with a decreasing radius. I notice the lose condition when the radius decreases and maximum compression is put on the outer rear wheel.

Again, I do not believe this to be a dampening issue as this is related to spring compression in a long corner, not oscillations, vibrations, quick weight transfer, etc.

Isn't the same thing accomplished by trimming the bump stop and then re-shaping it to match stock? I am talking everything from angle of taper, to height of taper, and footprint at the axle. As I explained before, this would be like removing 1/2" where the bump stops mounts to the car, an area that is virtually uneffected (deformed) by even the greatest spring compression.

That all depends on the springs you have. My car certainly does not ride the bump stops. Someone with something like sportlines on the other hand will be.


What you are missing here is the shock controls how quickly the spring compresses, or how quickly/abruptly your axle is hitting the bump stop, and then controls how the suspension is behaving when you do hit the bump stop. This "looseness" is either springs that are too stiff (over steer) or shocks that cannot control the spring (snap over steer), or both.
Another thing to add, your hypercoil springs are progressive arn't they? Is it not possible that what is making you loose is the spring going into their 2nd, much higher rate when you are cornering like you describe?

But wouldn't you impact your full suspension travel quicker when turning at those higher speeds? I at least feel like my car wants to roll more when turning at those speeds as compared to turning at 10 mph. I would think that a better rebound spec in your shocks would only help you more in the situation you are explaining above.... slower weight transfer... easier impact to the bumpstop... faster weight transfer... hard snap into the bumpstop...

I'm still not saying that people shouldn't modify their bumpstops. If they do then it should be on the right setup. And I think its smarter to tune the roll rate first before you increase your suspension travel.

I am no physics expert when it comes to this stuff... I'm only describing my own experiences from what I've picked up at the track. What kind of racing do you do or driving do you do to experience this? Typically in a decreasing radius when I mess up, I experience understeer anyway. Though this is in autox.. I have no road race experience.

Good convo by the way... it appears possible after all to have a technical convorsation without people taking stuff personally :)

Your main issue is controlling your springs enough to keep from hitting the bumpstops, or at least hitting them as hard and as often.
Springs hold the car up, shocks/dampers control the springs. Guess what you need?

You may not believe it, but I have known people who didn't seem to believe gravity is constant. Guess what? Reality is reality, whether you or I believe it or not.

If you want to go through the exercise, knock yourself out, it may be a fun learning experience. At the end, at some point, you'll figure it out and likely wish you'd listened and just gotten good shocks and instead spent that time modding more, or working for more mod money.

Some (most) people don't listen to good advice and have to learn the hard way. I've been there as demonstrated by the fact that I did tons of suspension shit before shocks - DUMB!

The very fact that you think the title of this thread needs a question mark shows how much fundamental stuff you're missing. My friend, you are getting good advice, from some pretty savvy people (not me), do yourself a favor and listen.

I couldn't agree with jmilz28 more. I am not the only one with the opinion that your shocks are the main issue followed by the spring you are using. I stated what I thought about the bumpstops being an "integral" part of the suspension and will leave it at that. I think you are on a wild ghost chase with the bumpstops chasing something that isn't your problem.

In that sustained G example you had you do realize shocks and springs will also determine how the axle is reacting when it does contact the bumpstop A LOT more than the shape or depth of a bumpstop.

If you do all this and it fixes your problem then good for you; otherwise I think its a waste of time.

I am going to jump in here and give an example of what happened to me
my ws6 has 100 + k on the clock. After getting over the novelty of having the car. I noticed that when the car went over bumps it was jarring to say the least. so after some internet searching I found some info and asked some questions and settled on koni's and strano springs. Well I recieved the shocks tuesday installed them last night. Walah! Instant difference.I've only installed the rear shocks and no bump stop issue. Remember no springs just rear shocks and they are set a touch off of full soft.I would highly reccomend the koni's but if your wallet doesn't allow then get a quality shock or save up for them like I did. I would give sam a call and read some of the posts across different boards they've all lead me in the same direction and I'm happy with my purchase. so to end a long story shocks shocks shocks

To add to what Black-n-sleek said (since I talked to him earlier today), he didn't have stock shocks... he had Sensatrac's, which ironically are supposed to ride better above any sort of performance. Even though that's the stated case, clearly it is not reality.

To the point, his car went from crashing-bashing and not much fun to completely different with a damper change--and the damper here isn't meant to be a ride damper like the Monroes that were on it before, but it still rides significantly better aside from being more stable. I believe Vinny's first word was "wow"......

I really appreciate all the comments and the good discussion guys.

First let me clarify a few things.

jmilz28, I did not start this thread. I know lowered cars need different shocks which is why I have stated from the beginning of this discussion that my Bilstein shocks are inadequate. They were on the car when I bought it and I know they need to be replaced. They WILL be replaced soon.

A little background on myself and the car:
I have a masters in mechanical engineering, including taking a vehicle dynamics course which included a track day at the Michelin Proving Grounds in Laurens, SC including wet road coarse driving, wet skid pad, and with different tire pressures and tread depths. The car is used solely for joy rides and HPDE events. This is actually experienced like clock work on one of the windy roads near my house which is part of my "loop" or drive I like to do. I know, not the best place to test, but its convenient. A similar phenomenon was experienced at my last track event in Savanah, GA at Roebling Raceway in Turn 3.

All great points and possibilities. Yes, the Hypercoils are progressive. I am thinking that the much higher rate is being compounded greatly in the corner by the spring rate itself coupled with contacting the bump stops. While shocks would slow the rate of spring compression, they would not limit the overall spring compression. Hence, if this is indeed my problem, shocks will not fix it.

This is related to the mock spring rate tables I posted earlier and may be why linear springs that lower the car less seam to have better success. For example, 150 pound linear springs that lower the car 1" instead of 160-210 pounds springs that lower the car 1.5-1.75".

This gets to the heart of my thinking. Obviously a set of 1" linear lowering springs are going to allow more suspension travel before contacting the bump stops than my Hypercoils. They are also going to allow the bump stop to make them progressive in nature, whereas the bumps stops negatively effect (drastically increase) the Hypercoils spring rate.

Hypothetically, if I could eliminate the bump stops I could allow the progressive design of the Hypercoils to work as intended and have a similar setup to the linear springs. I am basically wondering if a 1/2" trim will get me close enough.

Maybe. The Z28 bump stops are progressive and I am contacting them in a rather progressive fashion (i.e. not a slalom). It is certainly a valid point and a possibility.

Am I the only one who saw "high speed decreasing radius corner" with "loose" and thought of "What is the driver doing"?

Roll out of the throttle for the decreasing radius and the rear unloads. Do it while cornering and the car oversteers. *shrug* Happens all the time and a good autocrosser often uses that to his/her advantage in order to point the car.

Chop the throttle suddenly and / or be too quick with the wheel and you'll likely be enjoying your surroundings through the side window. Now the driver complains of oversteer and looks at changing the car.

Therefore, my question is (and I may have missed it earlier in the thread) "What is the driver doing when this occurs"?

I'm off the throttle before the decreasing radius and do not start to pick it back up until the rear settles. This is not a progressive slide of the rear, it's like a little stuttering side step. I can try running it a different way though, what do you suggest and why?

I'm not complaining. I'm diagnosing, tuning, thinking, learning, etc.

You guys have 70mph turns in autocrossing? Damn, that sounds awesome, the ones I have done are always very tight and slow.

I'm definitely going to do Koni's in the rear first and then see what happens, will decide where to go from there. I will try to remember and post back in this thread.

I'm merely suggesting that the driver plays a very large role in how the car behaves. Without actually being in the car, we can't say for sure what is going on. In such a corner as you are describing, it's not surprising that the rear of the car slides and is loose. It's only logical and natural that it will act that this way.

A "little stuttering side step" would seem to be expected in this situation and your choice of line, throttle control and wheel input can help the situation or exacerbate it. Two different drivers can drive the same car on the same day and come away with very differerent opinions about that car. Why do you suppose that is?


Of course shock settings, suspension hardware and tire pressures will also affect driveability and balance as well.....

No, there are not usually 70 mph turns but they are not all slow and tight either. The ability to dance with the car and get it to change direction in the blink of an eye at something that sometimes approaches highway speeds is needed for success. Occasionally that requires what I mentioned in my earlier post.

You need to run some bigger events. :D