The tech very very insitant that I should not cut the bump stops. He said that the suspension will be operating outside of it's designed perameters.

He pointed me to an article about Micro Cellular Jounce Bumpers (formerly known as bumpstops) but they are now a progressive part of the suspension.

Here is the article straight from H&R, comments ...

"Attention - calling all bumpstops.

Well, we call them bumpstops because we always have. It is what we are used to calling them. But in the age of specialized tech-talk they are "bumpstops" no more; now they are micro-cellular progressive jounce bumpers. - What? ... That was a double decafe Mocha, skinny, no whip!
"The song, "Head out on the Highway, look'in for adventure" keeps ringing in my head. Where was I, oh yeah, trying to avoid the dreaded bumpstop (dumpstop)."
Most people think of a bumpstop as a black rubber snubber hanging down from the frame above the axle to protect against metal-to-metal contact. Just like my dad's 1974 Chevrolet Caprice station wagon. You know, the one with the big block 454 and the hide - away tailgate. The Caprice was the cruising wagon of choice when highway 5 between L.A. and San Francisco first opened and gas stations were few and far between. The song, "Head out on the Highway, look'in for adventure" keeps ringing in my head. Where was I, oh yeah, trying to avoid the dreaded bumpstop (dumpstop). The thing was, no matter where you went in that wagon; you rarely came into contact with the bumpstop.

The micro-cellular progressive jounce bumper, or simply put, the foamy bumpstop, is actually a supplemental spring. It works to make the suspension progressive, allowing a smooth transition to full compression. What most people don't realize is that the foamy bumpstop is an active part of the suspension. Let's say you're sitting in your M3, 996, Accord, Golf, S4, or Civic. (Hmm I can't decide). They all use the foamy. Ok, you're in your brand new Integra, just drove it off the showroom floor and are sitting at the stoplight waiting for the green. The foamy is actively engaged even while waiting at the stoplight.

Car manufacturers use this brilliant piece of high-tech engineering for many reasons. By using an almost zero-weight supplemental spring, you can build the main (steel) spring with a reduced spring rate for a comfy ride. The softer spring uses less weight, and, saving weight is a number one priority of new car manufacturers. Cars have thousands of parts. A little weight saved here and there really adds up. When the manufactures save weight they also save costs, less material=less cost. So we now know why these foamy gems are used. But how do they really work?
As mentioned earlier, the foamy bumpstops are an active working part of the suspension. They work in harmony with the springs and the rest of the suspension components allowing the ride to be comfortable while cruising. When the car is in a handling situation, such as in a turn, they make the car feel firmer for better handling. Think of the foamy as a little progressive spring over the shock rod. All car manufacturer bumpstops have a specifically calculated spring rate and compressed height. (block height).

When a spring is designed the spring rate must be calculated with the rate of the progressive bumpstop in mind. Otherwise the spring will not work in harmony with the bumpstop and the frequency of the suspension will be out sync. The human body interprets a certain range of suspension frequency as comfortable or uncomfortable. Frequency in an automotive chassis is like chords in music. If two or more notes are combined in a pleasing combination you have harmony, otherwise you have uncomfortable dissonance. The same thing happens in suspension tuning. A balanced suspension is important for correct function. This is why it so critical to understand the true effect of the pro-active foamy and the spring. Everything must work together in harmony!

The compressed height is what limits the wheel travel and controls how far the wheel and tire move up into the fender well. Aftermarket suspension designers must consider that enthusiasts will be upgrading the tires and wheels. Therefore, it is vital that these designers take into consideration the needs of tire and wheel fitment. By trimming the bumpstop you allow the tire and wheel to move further into the fender. This can cause the tire to rub where it did not before. If your application does not require bumpstop trimming and you are concerned about tires rubbing, just load up your car with your buddies and drive over some dips and speed bumps. If your tires do not rub with a full load in the car, they should not rub with lowering springs installed.

So, what has little Johnny learned today? There is no such thing as a bumpstop in a modern suspension. The bumpstop has been replaced by a supplemental, active foam rubber spring, which is one of the essential components in the suspension."

 

The fact is like so ... there's about 1" of suspension travel space w/ the OEM spring before the lip of the shock hit the OEM bump stop then you install the spring that is more than 1" drop/lower/less so that pretty much eat the space available for the suspension to travel and sit on the bump stop.

DrLev99 already proved that his car sittin' on the bump stop in fact after he cut the bump stop the car dropped some more. You have to remember the OEM bump stop is a taller non-sport version so it's thicker if you don't want to cut it you should swap it w/ the sport version since by design it's thinner.

 

This is another interesting read on their design and purpose.

http://www.simulia.com/locations/india/dow...ptimization.pdf

 

Maybe it's H&R new design ... well ... if you are not gonna cut it which I'm pretty sure it'll be on the bump stop so let us know how's the bump stop riddin' feel like ... GL!

 

+1

The purpose of the bump stops is a fact, and everything you stated above is true. I didn't want to cut the stops either for all of those reasons, but the fact is that the OEM struts were not meant to be used with the H&R springs. If you want to use this setup, you have to give up something up in the process....the length of the stops and the ride quality.

You can try the Sport stops, like Blastiwi said, or you'll HAVE to cut the current ones. I don't want to say I told ya so...

 

When I originally was going to drop my xi, I had pm'd Rudy to see if he knew anyone in Pittsburgh who could do the job. He mentioned a local guy who was a true BMW enthusiast and BMW mechanic for decades here. So I emailed the guy re: the drop. This is the thesis he sent back to me....sound familiar??
____________________________________

Thank you for contacting me. Your message raises several concerns about what you are attempting to do.

First of all, when it comes to modifying BMWs, we are a tuning shop for these cars. I've been competing and modifying BMWs for more that thirty years now. In that time, my experience has allowed me to learn quite a bit of how to modify BMWs. It also has allowed me to learn from mistakes made in the past as how not to modify BMWs. My clients seem to appreciate that. Proper BMW tuning requires a well-thought-out engineering approach when selecting components to modify these cars. Buying random parts "off the shelf" more often than not results in a car that performs far less well than the stock vehicle, or will actually damage the car. Damage from lowered springs will void parts of the warranty on your car.

Secondly, suspension systems are just that- SYSTEMS. BMW is very careful when designing the springs for that car. When ordering replacement springs from BMW, the springs are so specifically designed that the vehicle needs to be entered in the parts system to select the proper spring dependent upon the equipment built on the vehicle. Even the weight of the stereo system is calculated when they specify spring rate. For example, if you have a Hardon-Kardon stereo with heavier speakers-you may get a different OEM spring from BMW! Shock absorbers and springs are designed to work together, and to work properly must be matched to perform properly. A properly tuned suspension has spring rates that are carefully matched to the shock's dampening characteristics. In other words, when you install a sports spring the shock must match that spring. Installing a "sport" spring with a standard shock will most likely result in a mismatch of components. The stronger spring will overpower the shock and your car will be "oversprung." That means that the strength of the spring oscillations will not be canceled out by the too-weak stock shock. That mismatch will be doubled, since the shock has a rate for compression and one for rebound. The resultant performance AND ride from your selection of springs will SUCK. Firming up the springs and installing sport shocks to match will give you a harsher ride, that'll be fun for about three days until you realize that you screwed yourself. Adding the lower-profile tires will add stiffness to the ride as well. The tires also contribute their own spring rate to the equation.

Properly engineered shock absorbers used with lower springs often have a different bottoming cushion system than the original shock. The bottoming cushions are usually located internally inside the shock on sport shocks, and are shorter to prevent bottoming. In other words, when you alter the suspension travel by lowering the springs, you need to alter the shock travel to accommodate the reduced travel of the spring. Lower springs may cause bottoming of the shocks that break or damage suspension or chassis components. Perhaps if you stand back and look at the lowered car with the plus-sized wheels it'll look cool, but how will it perform in the real world? Nobody engineers a better spring/shock combination than BMW does.

Frankly, as stated above I have concerns about modifying your car as you have proposed to do. If I can't fully stand behind the work and feel good about it, I don't do it in the first place. What we do is to provide carefully thought-out and proven BMW tuning solutions for our clients who have numerous competition championships or years of satisfying street enjoyment from our approach. I think that my approach to servicing and modifying BMWs is working. I'm sure that someone will be happy to install your sport springs onto stock shocks, but I'm not comfortable doing that. I hope that you benefit from me sharing my experience.

 

It sounds like that guy does not recommend any shock and spring combination other then factory. Unless you spend millions in R&D, increased performance and comfort do not go hand and hand. Its one or the other. Pick your poison.

 

I have XI model which come with non-sport suspension, if i order sport bumpstops for I model, will it fit my XI?

anyone know the part number for sport bumpstop for LCI 535 model? thanks

 

Do not cut the bump stops!

Yours Truly,

The XI Master

 

Then you shall ride on it ...