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      06-04-2019, 02:14 AM   #1
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A Look at Bump Stops

Bump stops often come up as part of the discussion when people talk about lowering springs. From what I've seen here, most people only know that a set came with their car from the factory, and that Dinan offers a set to be used with lowering springs.

Bump stops can/are used for a couple of reasons. First is to do what they're called, stop/soften the bump when you hit a feature that would cause the damper/shock to bottom out. It does that by offering resistance by increasing the spring rate since it has a spring rate of its own. Some bump stops are linear in nature and others are progressive. Some manufacturers/tuners also use the spring rate increasing property to provide body roll resistance. Tuners typically do this with "packers" or shims that reduce the damper travel before engagement, and OEs do this by making long bump stops that engage after not too much damper travel.

Front Bump Stops


Here are a couple of front bump stops. On the left is my OE F3x bump stop, middle is F8x, and right is an E39 bump stop, the same one Dinan includes in their kit. The F3x bump stop is about 3.25" long and progressive (hence the tapered shape), the F8x one is about 2.5" long and also progressive. The E39 bump stop feels more linear and is much softer than the F3x and F8x stops. Both the F3x and F8x stops get really stiff pretty quickly.

Rear Bump Stops


Here are the rear bump stops from the same kits, F3x left, F8x middle, and "Dinan" (E60) rear. The F3x one is about 3.5" long, F8x 2.5" long and E60 2.25" long. Once again the F3x and F8x ones are progressive and much stiffer than the E60 one.

From this we can see that the F3x and F8x bump stops were designed to engage somewhat early on and add a significant amount of rate to the soft OE rates. I did a bump stop travel test on my rear dampers with Eibach lowering springs and found that at static ride height the damper was already engaging the OE bump stop. I try to aim for at least .75" of damper travel before engaging the bump stops so the suspension can absorb modest road features without adding additional spring rate/bounce.

When I had my OE adaptive dampers and Eibach springs I had the E39 front/E60 rear "Dinan" kit. They worked fine and I didn't have any complaints about them. With my existing damper setup I've run all three sets in the rear (the fronts have internal bump stops). Since the OE bump stops already engaged the dampers at resting ride height this caused more jolt when the rear hit bumps since the stop was so stiff and adding to the spring rate early on. The rear of the car felt like it danced/squirmed around with this. The next bump stop I went to was the E60/Dinan one. This smoothed the rear out and I was pretty content, but I was curious about the F8x rear bump stops and decided to throw that on there to see how they would feel. In normal driving I don't notice any difference, because they're weren't really being engaged or only being engaged lightly, however when cornering at the limit I could feel the stiffer rate and it felt like the rear of the car stopped rolling earlier than it normally would've. I was pleasantly surprised by this and decided to stick with the F8x rear stops.

So for folks looking to lower their cars, you might want to consider the F8x bump stops in addition to the E39/E60 "Dinan" ones.
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      06-04-2019, 12:14 PM   #2
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Great write up! Thanks for sharing.
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      06-04-2019, 02:04 PM   #3
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Nice post, Farkle. Thanks for making it easy for the next guy to figure out.
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      06-04-2019, 05:58 PM   #4
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Do you have part numbers for the F8x bump stops and do they need any shaving or modification to fit on the F32? Would they be a better match with Dinan springs than Dinan's offering?
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      06-04-2019, 06:56 PM   #5
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Great read! I am considering suspension options but I'm pretty new to this conversation. I'm leaning towards a setup that retain the oem shocks( and edc functionality) since the shocks are 500 each and mine only have 21k miles on them. If I were to do anything it would probably be the Dinan springs /bump stops/ shockware tuning. Lots of great info from you and others on this forum. I'm just wondering how much I would feel the difference outside of a track day setting. ride is only 10mm lower than my current rwd m-sport setup although it will also be stiffer
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      06-04-2019, 07:38 PM   #6
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This topic peaked my interest, so I ended up pulling out the OEM bumpstop that came with my 2014 328i xDrive.

Front: 3133 679 1507-01, 3" tall
Rear: 3353 6854701-01, 3" tall
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      06-04-2019, 08:44 PM   #7
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Quote:
Originally Posted by dr.roro View Post
Do you have part numbers for the F8x bump stops and do they need any shaving or modification to fit on the F32? Would they be a better match with Dinan springs than Dinan's offering?
Front F8x bump stops: 31336859768
Rear F8x bump stops: 31337847662

No modifications are required to fit F3x applications.

I can't say whether they'd be a better match for Dinan or not. Dinan probably recommends their softer bump stops because their springs are so much stiffer than stock, so they don't need as much support/boosting from the bump stop. That said, if you look at the F8x competition pack springs they have a front spring rate a bit softer than the Dinan front, but equal to the Dinan rear and uses stiffer bump stops, so I don't really think there's a "wrong" answer when choosing between the two.

Quote:
Originally Posted by Jvac View Post
I'm just wondering how much I would feel the difference outside of a track day setting. ride is only 10mm lower than my current rwd m-sport setup although it will also be stiffer
You can notice the difference when doing any hard cornering. If there's a cloverleaf, hard corner in your daily driving, or some tight twisty canyons you do, you're probably getting bump stop engagement.

Stiffer bump stops boosting the rear spring rate on roll can help the car rotate just like if you had stiffer springs to begin with. This is why you sometimes see auto crossers user packers to shim their bump stops (and then take them out afterwards for stock ride comfort).

Last edited by FaRKle!; 06-04-2019 at 08:53 PM..
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      06-04-2019, 09:22 PM   #8
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Awesome, thanks again. The f80 bump stops are pretty cheap (~60 for a set of 4) considering Dinan sells their fancy "handling kit" for like 200$. That's quite a markup
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      06-04-2019, 10:03 PM   #9
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Quote:
Originally Posted by Jvac View Post
Awesome, thanks again. The f80 bump stops are pretty cheap (~60 for a set of 4) considering Dinan sells their fancy "handling kit" for like 200$. That's quite a markup
If anyone's interested, I have a set I acquired when buying some F8x suspension sets to play around with I'll sell for $50 shipped. I also have my previous E39 front / E60 rear "Dinan" kit I'll let go for the same.
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      06-05-2019, 08:28 AM   #10
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You are the man, FaRKle! I've been hoping that someone would do this for the past year. Great work! Beers on me the next time that we run into each other!
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      06-05-2019, 02:34 PM   #11
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Hello BMW Experts!

Interesting how our suspensions are tuned with chunks of foam rubber!
The F30 330i LCI has different bump-stops for the rear drive (2 of them) & X-drive:

https://www.realoem.com/bmw/enUS/sho...diagId=33_1607
https://www.realoem.com/bmw/enUS/sho...diagId=33_1607

Murf
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      06-05-2019, 06:17 PM   #12
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Quote:
Originally Posted by Littlebear View Post
Hello BMW Experts!

Interesting how our suspensions are tuned with chunks of foam rubber!
The F30 330i LCI has different bump-stops for the rear drive (2 of them) & X-drive:

https://www.realoem.com/bmw/enUS/sho...diagId=33_1607
https://www.realoem.com/bmw/enUS/sho...diagId=33_1607

Murf
RWD and xdrive have different springs, ride heights, and dampers, so it's not unusual they might have different bump stops too.
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      06-05-2019, 06:46 PM   #13
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Quote:
Originally Posted by FaRKle! View Post
RWD and xdrive have different springs, ride heights, and dampers, so it's not unusual they might have different bump stops too.
Yes, two in the rear for the 330i LCI, & add the 328d (?) #s in your pic, and the #s given by 'thisismikeyb' for his 328ix, and it looks like we have lots of bumpstops for the F30!

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      06-05-2019, 09:10 PM   #14
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Quote:
Originally Posted by FaRKle! View Post
If anyone's interested, I have a set I acquired when buying some F8x suspension sets to play around with I'll sell for $50 shipped. I also have my previous E39 front / E60 rear "Dinan" kit I'll let go for the same.
I read another thread where someone claimed that the bump stops in the Dinan kit were trimmed/shortened to a specific height, not just standard oem stops. What say you?
And why would the stock f30 be setup to engage the bump stops so early in the shock's range of travel? Seems like a lot of unnecessary impacts get transferred to the structure of the car like this, making for a harsh ride, am I wrong?
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      06-06-2019, 12:36 AM   #15
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Quote:
Originally Posted by Jvac View Post
I read another thread where someone claimed that the bump stops in the Dinan kit were trimmed/shortened to a specific height, not just standard oem stops. What say you?
And why would the stock f30 be setup to engage the bump stops so early in the shock's range of travel? Seems like a lot of unnecessary impacts get transferred to the structure of the car like this, making for a harsh ride, am I wrong?
You can see from their pictures that the stops aren't cut. If you were going to cut bump stops you'd cut the top portion (side that doesn't engage the damper).

Stops can be engaged earlier on to provide a progressive spring effect where you have a soft OE spring initial rate, and then the stop boosts the rate when it comes into play. If the bump stop is too stiff/hard then it can transmit too much force into the body, but its spring characteristics can be tuned just like swapping to stiffer/softer springs themselves.
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      06-06-2019, 07:21 AM   #16
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Yes yes obviously yours have not been trimmed but I don't know if you got them from Dinan or just sourced them yourself. Anyway thanks for all the good info you provided.
Quote:
Originally Posted by FaRKle! View Post
You can see from their pictures that the stops aren't cut. If you were going to cut bump stops you'd cut the top portion (side that doesn't engage the damper).

Stops can be engaged earlier on to provide a progressive spring effect where you have a soft OE spring initial rate, and then the stop boosts the rate when it comes into play. If the bump stop is too stiff/hard then it can transmit too much force into the body, but its spring characteristics can be tuned just like swapping to stiffer/softer springs themselves.
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      06-06-2019, 09:47 AM   #17
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great post! I am planning to do a drop next, like another member said I have the the EDC and dont want to waste the shocks so I might go the Spring route rather than coils (for now) hoping to get a few good years in before I do coils.

I know this post was mainly for Dinan Springs, would the same application work for Eibach springs?
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      06-06-2019, 10:03 AM   #18
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Quote:
Originally Posted by CRAMAZIN View Post
great post! I am planning to do a drop next, like another member said I have the the EDC and dont want to waste the shocks so I might go the Spring route rather than coils (for now) hoping to get a few good years in before I do coils.

I know this post was mainly for Dinan Springs, would the same application work for Eibach springs?
The bump stop philosophy should be the same with Dinan and Eibach springs since there drops are almost identical.

I'm assuming that you have an xdrive. The Dinan springs are about 30% stiffer than stock and claim a drop of .75" all around. The Eibach springs (-06 part number) are about 10% stiffer than stock and claim a drop of 0.8" front and 0.6" rear. Xdrive come with a bigger wheel gap in the front from the factory so this is by design to even things out a bit.

I don't have electronic damping but I have the Eibach springs with Koni Special Active dampers which have been described as having a similar ride to the EDC. I've been very pleased with the Eibachs. They were just the right improvement over stock for me.
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      06-06-2019, 10:16 AM   #19
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Quote:
Originally Posted by johnung View Post
The bump stop philosophy should be the same with Dinan and Eibach springs since there drops are almost identical.

I'm assuming that you have an xdrive. The Dinan springs are about 30% stiffer than stock and claim a drop of .75" all around. The Eibach springs (-06 part number) are about 10% stiffer than stock and claim a drop of 0.8" front and 0.6" rear. Xdrive come with a bigger wheel gap in the front from the factory so this is by design to even things out a bit.

I don't have electronic damping but I have the Eibach springs with Koni Special Active dampers which have been described as having a similar ride to the EDC. I've been very pleased with the Eibachs. They were just the right improvement over stock for me.
Yeah I do have the xDrive which is why I was more interested in Eibach to even out the drop. Then I thought about going to do coils with KW but I figure I can save some money now and still use my EDC for a few more years (currently 25k miles) and then decide if I wanna do coils or add dampers later. Good idea?
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      06-06-2019, 11:12 AM   #20
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Quote:
Originally Posted by CRAMAZIN View Post
Yeah I do have the xDrive which is why I was more interested in Eibach to even out the drop. Then I thought about going to do coils with KW but I figure I can save some money now and still use my EDC for a few more years (currently 25k miles) and then decide if I wanna do coils or add dampers later. Good idea?
Great idea! That's exactly what I would do if I had EDC with 25k miles. Not sure what else you have done already but here are a few suggestions depending on your interests and priorities:

Handling/Ride: Put on summer tires and save your runflats for winter until they wear out. No need to buy a new wheel set just have them switched onto the stock wheels, assuming 18" wheels? Michelin Pilot Sport 4S are the best and will make it feel like an entirely new suspension both in handling and ride comfort. Switch to 245/40-18 for best handling or 245/45-18 for best comfort (and 245/45 fillup wheel well more so car looks dropped)

Brakes: Hawk HPS 5.0 pads and StopTech Stainless Steel hoses (about $106/set of four, minimal labor during brake fluid flush) This will increase your braking, your brake pedal feel and much less dust than stock. Dust is lighter and not sticky.

More Power: BootMod3 Stage1 is an extremely easy to install in 20 minutes sitting in the car in your driveway. Stage1 doesn't require any hardware upgrades like intercooler or high flow downpipe as needed for Stage2. Only $50 to upgrade to Stage2 later if you make those hardware changes.

Also drop-in a new aFe Pro Dry airfilter for about $75. It breathes better to add a little horsepower and you can clean and reuse it forever. If you don't already have the plastic M Performance intake box holding your air filter, (it has a hole in the bottom piece facing the front and its trimmed in bright red plastic) you can either add it for about $200 or cut holes in the same location. It allows more air into the intake for more power.

Replace the plastic N55 charge pipe with a metal aftermarket pipe that fits well that the Evolution Raceworks chargepipe. Plastic pipe tends to break right at the 90 degree elbow near the throttle body. Labor cost wise it makes sense to install the charge pipe and the intercooler at the same time. I'd recommend the Wagner Competition EVO1 or EVO2 for reasons explained in other posts that I have made.

Hope this helps you or someone else! Take care!
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      06-06-2019, 11:50 AM   #21
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When I Lower with my new coilovers I'm planning on swapping rear bump stops to the f80. You can find them for pretty cheap through a wholesale bmw parts store. That will help increase the rear suspension travel once lowered.
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      06-06-2019, 02:09 PM   #22
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Quote:
Originally Posted by Jvac View Post
Yes yes obviously yours have not been trimmed but I don't know if you got them from Dinan or just sourced them yourself. Anyway thanks for all the good info you provided.
What I meant was look at the photos from Dinan's website/product page. You can see the bump stops they supply aren't cut.




Quote:
Originally Posted by CRAMAZIN View Post
I know this post was mainly for Dinan Springs, would the same application work for Eibach springs?
I would change the bump stops with any set of lowering springs. With springs that are similar in rate to the F8x springs, I think F8x bump stops will pair well and follow the design intentions BMW had better than the E39/E60 "Dinan" bump stops. With springs stiffer than those on the F8x cars, the softer E39/E60 "Dinan" ones might work better since bump stop stiffness probably doesn't need to be as high.

Last edited by FaRKle!; 06-06-2019 at 04:34 PM..
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