Bump stop cutting

[pshirley]

Bump stop cutting. I recently replaced the factory shocks for Bilstein Touring shocks because the ride was rough. The car already had BavAuto springs. Even after the new shocks the ride was harsh. I read that you need to cut down the bump stops, so I removed about 1.5" from the front and back. It helped a bunch but the larger bumps still seem a little hard. Do I need to remove more of the bump stop, not much left, maybe an 1"? Are the springs bottoming out? They springs are 4 years old. What about the shocks, could they be bottoming out? I have BF Goodyear RS-A tires, are they known for hard side walls? What should I try next? Thanks for the help. Paul

[Jon K]

Bump stop cutting. I recently replaced the factory shocks for Bilstein Touring shocks because the ride was rough. The car already had BavAuto springs. Even after the new shocks the ride was harsh. I read that you need to cut down the bump stops, so I removed about 1.5" from the front and back. It helped a bunch but the larger bumps still seem a little hard. Do I need to remove more of the bump stop, not much left, maybe an 1"? Are the springs bottoming out? They springs are 4 years old. What about the shocks, could they be bottoming out? I have BF Goodyear RS-A tires, are they known for hard side walls? What should I try next? Thanks for the help. Paul


P Shirley wallabee way sydney...

sorry your name reminds me of Finding Nemo.

As for the suspension. It is VERY common that BavAuto springs bottom out. You should have used Bilstein Sport or HD shocks though, because they allow for the lowered ride hide with less chance of bottoming the shock. Essentially, if you've cut the bump stop down already, you're more than likely bottoming something. The BavAuto springs are so sloppy sometimes that they bottom over dips and such. I think you have the wrong shocks for that spring application.

[Kalevera]

The BavAuto springs are garbage. I just pulled a set from my car after 1000 miles and I'm glad to be rid of them.

According to Don Gale, they sag over time, so after 4 years of service, an already shitty spring is probably even shittier...explaining why it's bottoming out all the time.

Hopefully you've still got some tread on those tires after all of the negative camber. I would change them out for a different spring altogether. Chances are that the bilsteins are okay, but it'd be wise to check them out, regardless.

Do a forum search...you'll find oodles.

Best, whit

[Brandon J]

BavAuto springs are known to bottom out. Bilstein HD shocks are NOT right for sport or lowered springs. The Bilstein Sport and the Konis are the right ones for the sport springs as they are made for the shorter springs. BTW, IMHO Konis are much better than the sports. They have a longer travel, have rebound adjustability, and allows the user to cut the external bumpstops to best length. Bilstein Sports have internal bumpstops (so no adjustability by cutting), have a shorter travel (so less compliant), and do not have any adjustability.

[632 Regal]

the travel with a lowering spring is only about 3 inches max, the Bavautos with a V8 will bottom out on anything larger than a cigarette butt. With the 6 you will get some more travel but still is limited by the shocks bottoming. I have the Eibachs now and they still bottom out on everything too. You should get the Bilstein sports with the internal bumpstop so you dont have to worry about cutting them things and them popping out and having a direct bottom and break stuff.

[pshirley]

the travel with a lowering spring is only about 3 inches max, the Bavautos with a V8 will bottom out on anything larger than a cigarette butt. With the 6 you will get some more travel but still is limited by the shocks bottoming. I have the Eibachs now and they still bottom out on everything too. You should get the Bilstein sports with the internal bumpstop so you dont have to worry about cutting them things and them popping out and having a direct bottom and break stuff.


Thanks for all the feedback, I really appreciate it. If I don't want to give up the stock comfortable ride should I go back to the stock springs or is there a set that are too much stiffer than stock, but not as low as the Bavautos? This is my daily driver and I want a smooth quiet ride. Thanks again and look forward to your replies. Paul

[632 Regal]

M-tech only lower it about a half inch...why bother.

[Brandon J]

the travel with a lowering spring is only about 3 inches max, the Bavautos with a V8 will bottom out on anything larger than a cigarette butt. With the 6 you will get some more travel but still is limited by the shocks bottoming. I have the Eibachs now and they still bottom out on everything too. You should get the Bilstein sports with the internal bumpstop so you dont have to worry about cutting them things and them popping out and having a direct bottom and break stuff.
I would still disagree with you. With bottoming out, you are mainly comparing the loaded ride height to it compressing. You are still forgetting when the springs extend, you want to keep the wheels on the ground. A very good way to get a compliant ride out of a sport suspension is to increase travel. That's how the e34 M5s are. Have you ever seen the travel on a Nurburgring suspension? They travel a lot.

Again, the benefit of the external bumpstop is that you have adjustability by cutting the bumpstops to the length that best works. I did this by keeping them on and cutting a little by little until I thought they worked well. Remember that if you shorten the bumpstop that you increase the distance the shock has to work. So, it has more room to dampen before it bottoms out and hits the bumpstop. That is why travel is important. Finally, if the shock can extend further, then the wheels are more likely to stay on the ground. Just imaging going over rough roads and a wheel does not reach the ground.... a la pothole. Now imagine the wheel just drops to the ground as the car drops. There is a moment where tire and road do not meet because the shocks can't travel that far. Now if there was more travel, then the wheel would stay on the ground and dampen as soon as the car goes down. Make sense? Again, more distance to cushion.

Now with the konis, add the adjustability of compression. Konis are the way to go.

[liquidtiger720]

I think I would have went with koni's/h&r's if I didnt life in san francisco. Even with the sachs sporting kit (which is great by the way)...its pretty rough driving around.

[JonE]

Paul,
Ask Whit Lowell if he still has his stock springs, if that's what you're going to do...

[Craig]

Bumpstops are part of your suspension so I personally don't like cutting them. They act as a "second spring" of sorts and prevent massive blunt trauma from occuring to your strut towers.

BavAuto springs are crap, I have them on my car and will be swapping them out in the next month or so for better ones.

[632 Regal]

and it still bottoms conciderably. I realize that the V8 is heavier (how much we dont know yet?) and attribute it to that for the time being.



Bumpstops are part of your suspension so I personally don't like cutting them. They act as a "second spring" of sorts and prevent massive blunt trauma from occuring to your strut towers.

BavAuto springs are crap, I have them on my car and will be swapping them out in the next month or so for better ones.

[Kalevera]

Yeah, I've still got those suckers. You can HAVE them for the cost of shipping -- I just want them off my front porch :)

Best, Whit

[Kalevera]

Hey Josh...What kind of wheels do you have on your car? I just put my 17" 235/45 Kuhmo Ecsta Supra-wrapped BBS SPORTS from an E39 on the front (rears haven't shown up yet), and I've been kinda disappointed with how harsh the ride has become versus the stock BBS 15" 225/60. And the roads here in NC are pretty good...I can only imagine what it'll drive like in Cleveland (pothole city).

Best, whit

[pshirley]

Yeah, I've still got those suckers. You can HAVE them for the cost of shipping -- I just want them off my front porch :)

Best, Whit

I might take you up on your offer. Do you know if the 530 springs will fit my m50 95' 525i? How many miles on the springs? I assume they don't hold up for ever, how do think they will work?

I was just looking at Racing Dynamic Springs......your thoughts? Stiff, moderate, soft? How low will they drop the front and back?

thanks again for all the replies, you all have been very helpful. Paul

[liquidtiger720]

Hey Josh...What kind of wheels do you have on your car? I just put my 17" 235/45 Kuhmo Ecsta Supra-wrapped BBS SPORTS from an E39 on the front (rears haven't shown up yet), and I've been kinda disappointed with how harsh the ride has become versus the stock BBS 15" 225/60. And the roads here in NC are pretty good...I can only imagine what it'll drive like in Cleveland (pothole city).

Best, whit


Im on the stock 15's for now. Once these tires wear out...Im hoping for 18' mparallels or breyton insiprations or the 17in throwing stars =).

[billy in slo]

From my experience, 5 different older bmw's w/stock springs, cut springs, R.D. springs, bav-auto springs, koni red, sports, H.D.'s, touring. The biggest culprit for bottoming was the shocks. Either mis-matched i.e. short springs w/H.D.'s or more commonly just worn out. I know everybody rags on the bavauto springs but I have them on my e28, e30 and e34 and am satisfied with the combination of ride height and comfort and handleing, none of which is outstanding but that is the comprimise. As far as a harsh ride, I think a plus 2 and especially a plus 3 in wheel/tire combo will cause this more than a spring/shock combo. Just my .02 worth.

[Brandon J]

Bumpstops are part of your suspension so I personally don't like cutting them. They act as a "second spring" of sorts and prevent massive blunt trauma from occuring to your strut towers.

BavAuto springs are crap, I have them on my car and will be swapping them out in the next month or so for better ones.
That's why you don't get rid of them. With bumpstops there are different ones with different "hardness". One may only cut half and inch from the bumpstop total. I did it in quarter inch increments. Bumpstops are still a vital part. I have run different length bumpstops on my Sachs kit and a RD spring set-up. Cutting is really the way to get the full travel of the shocks. Sachs now includes their own bumpstops, so that you don't have to cut the bumpstops (however I would question not cutting if you run ther lower rear spring perch setting). I do know exactly how it is to drive without bumpstops. I did some work on a M5 where we replaced the 535i HD front shocks that the previous owner had in there with with konis. We did not have the bumpstops at the time, so we ran the konis full hard to prevent bottoming out to the strut mount.

Bumpstop cutting has been done for years and years. It is a common practice when the supplier does not supply a replacement bumpstop to their suspension kits. There are different "hardness" or "plushness" to different bumpstops and if you do your homework or have seen different ones on different cars, you will notice which ones best suit your needs. Many magazines have written about cutting bumpstops when lowering your car and how to do it right. Just remember that cutting increases shock travel and the amount of distance that the shock can dampen, inturn can een help reduce bottoming out. Do a search on google and you will see many references saying the same thing about cutting bumpstops.