Technical White Paper: Lowering Springs and Bump Stops, Take Three

Since you already have ZCP, the only thing I would do is to get a high-end coil over... at least KW CS or equivalent. Don't bother with the lower end set ups. The M3's suspension, while somewhat soft, is very competent and predictable, and you haven't experienced its true potential until you've taken it onto the track.

Sorry for getting off topic - PM'd

Let's take this discussion offline as it's a different topic. Feel free to PM me.

rzm3 wrote

Since you already have ZCP, the only thing I would do is to get a high-end coil over... at least KW CS or equivalent. Don't bother with the lower end set ups. The M3's suspension, while somewhat soft, is very competent and predictable, and you haven't experienced its true potential until you've taken it onto the track.

Good quality coil over - do you mean replace the stock shock or retain EDC/stock shock and get a sleeve-over system?

Replace the stock shocks.

quick question... ive heard alot of people going on the e36 bumpstop route.... is it the same if you just cut your oem bumpstops???

pardon my ignorance, but are people pairing lowering springs with e36 bump stops because they are shorter and the car wont be constantly riding on the oem bump stops?

how does the ride quality/handling differ between a car lowered on springs with and without modified bump stops?

thanks!

OP sorry to steal your thread but im going to do the same process, do I only need the bump stop in the front (e36)?

I wish we had a definitive answer. I'm looking at Swift springs and can't make up my mind on the e36 bumpstops.

Alan292 wrote

pardon my ignorance, but are people pairing lowering springs with e36 bump stops because they are shorter and the car wont be constantly riding on the oem bump stops?

how does the ride quality/handling differ between a car lowered on springs with and without modified bump stops?

thanks!

Emm Tree wrote

I wish we had a definitive answer. I'm looking at Swift springs and can't make up my mind on the e36 bumpstops.

I have the swifts and I did buy the e36 at the time with it but didn't install it. Been driving with the swifts for almost a year and I can tell you that they do not ride on the bump stops or hit it as frequently, as everyone assumed.

2 potential reasons why they don't:
- The drop isn't as low as the H&R or RD sport etc
- Swifts are linear springs as opposed to progressive like most of the ones available for our cars

Another reason why I stuck to the e92 bump stops is that BMW builds modern cars to ride on bump stops. There is a lot of technical details about it on this site and others. So I had to consider the fact that there must have been some advancement in the quality/material/condition of the current bump stops versus ones built for the e36.

Since this thread starts off talking about bump stops, I thought I'd share my research on this topic with the community.

While its been well documented that the E9x M3 stock suspension engages the bumpstops after just a small travel, I hadn't found any hard data on the bumpstop spring rate or what the force-compression curve looks like. For the hard core track folks who's stiff springs keep them mostly off the bumpstops this won't matter so much. But for those of us considering tweaking our street cars to still be primarily street cars, knowing the bumpstop rates helps us understand the stock suspension baseline better.

I bought a fresh new E92 front bumpstop to measure it (and not be thrown off by tired 10-year-old foam). My measurement system was a hydraulic press, a dial indicator, and a bathroom scale. The bathroom scale tops out at 350lb so that's the limit of my data but that turned out to be enough. To get the bumpstop to behave properly the center needs to be supported with a shaft as it would be on the car (otherwise the bumpstop folds over), so I fashioned a support shaft, then a top plate with a hole for the shaft to pass through and a larger collar to press down on the top plate to compress the whole thing.

I took two passes up and down in travel. I had a lot of stiction between the shaft in the center and the inner surface of the bumpstop which caused the offset in force for one of the passes. But I show all the data including this because the slopes are consistent despite the offset. Here's the data



I was actually a bit surprised to see the initial rate is so low at about 100 lb/in. Then after about an inch of travel the bumstop starts to stiffen up a lot, reaching about 700 lb/in by 1.5" of compression

From this data I'd say the stock bumpstop makes an effective progressive spring, the first half-inch or so (on my car it measures a bit over 3/4" but others including Steve Dinan reported only 1/2") of travel without engaging the stop is about 160 lb/in (stock front springs), then the next inch of travel adds 100lb/in for total 260 lb/in rate, and after that the stop starts to get rigid and becomes truly a "stop".

I also acquired an E36 bump stop to compare. The stop is slightly shorter as others have reported, but the initial rate is very similar. The transition to the stiff 700 lb/in rate occurs a couple tenths of an inch sooner, similar to the overall shorter length of the E6 vs E92 bumpstop. These characteristics make it a good option if you're looking to retain the stock bumpstop behavior but need it slightly shorter.

A+ post would read again

Thanks for doing the legwork