Time to settle things - lowering springs and bump stops

[TypeRx]

Guys:

It looks like there is conflicting info out there on whether or not to trim the bump stops while installing lowering springs. Some say they don't and there are no ill effects. Some say they do to help prevent their shocks from bottoming out and to comply with manufacturer recommendations. And others have said that the model 3 OEM shocks have such little clearance that the bump stops are essentially an integrated part of the suspension and need to be left as-is.

If you have lowering springs on stock shocks on your model 3 (doesn't matter what trim or brand/version of lowering springs), please complete the survey below. Please don't complete the survey if you haven't installed lowering springs on your stock shocks yet!

Post a comment below if you are unhappy with your decision (as noted in the survey)

 

[XLR82XS]

I have built custom cars for 20 years. Any vehicle owned by myself, or a customer vehicle, with lowering springs on stock shocks the bump stops have not been trimmed/modified. No problems.

My model 3: Eibach pro-kit with OE shocks - bump stops not touched. Ride quality has not been sacrificed.

 

[TypeRx]

^^appreciate the feedback. Please click "NO" survey button (if you haven't already) so when other members come here in the future they can quickly glean results.

More voting guys, let's build a reasonably sized sample

 

[XLR82XS]

^^appreciate the feedback. Please click "NO" survey button (if you haven't already) so when other members come here in the future they can quickly glean results.

More voting guys, let's build a reasonably sized sample

NO clicked before post.

 

[skrtskrt]

bump

 

[tlr1000]

Seems some lowering spring companies recommend trimming (Eibach, Tein, some H&R) while others are silent (UP, T-Sportline, and others). I have Eibachs and the instructions say to trim 25mm in back and 20mm in front. Did Eibach include this instruction when it's actually not necessary? Why do they give a different spec for front and back? All BS? Maybe - but I assume a reputable suspension company would add that into the instructions for a reason. If you look at some Eibach instructions, different trimming amounts are recommended for different cars and even whether you trim the top or the bottom. Again, I don't believe it's random.

Here's a good write up from the Tein website:

So, in regards to trimming bump stops- why is this important? If we find that aspects, other than damper stroke length, seem to be very generous, we know that we can make a lowering spring that will work with a shortened bump stop. So we include a chart by vehicle application that shows how much you will need to trim for front and rear when installing our lowering springs.


Some cases may require a different type of trimming style for the bump stop. Typically it is just trimming the bottom portion of bump stop and retaining the top piece (A Type). Sometimes it’s the reverse (B Type). In other cases, you may need to trim a middle section and retain the top and bottom piece (C or D Type). See below the different style cuts we recommend, depending on the vehicle:








We know several customers skip the bump stop trimming step. This can cause several issues. We’ve added this measure so that you can retain a bit more stroke length at the newly lowered ride height. This also helps improve ride quality. Because the bump stop is made of a high durometer polyurethane material, it is like a secondary spring, but a really stiff secondary spring. Since the dampers are not valved to handle such a stiff secondary spring, it can make rebound feel really harsh. Some may say bouncy. Constantly hitting the bump stop can cause the damper to prematurely wear or potentially blow out, too.​

At the end of the day it's up to you on what your comfort level is. I'm sure based on driving styles and road conditions many will never run into a situation that maxes out the stroke to hit the untrimmed bumpstop so in those cases trimming or not will not matter. Note that Tein says not trimming "can cause several issues" rather than will cause several issues - meaning you may never experience any problem if you don't trim them. What ever amount your spring lowers your car by is the same amount you will lose in damper stroke.

Best bet is to follow what the engineer states to do. Less chance of a problem and if you have a warranty issue it's one less argument that can be used against you. Only thing lost is a bit of extra effort.

 

[bryanbruin]

Bump stops are trimmed on my Eibachs. No regrets at all.

 

[skrtskrt]

So by removing the bump stops, it helps us not bottom out and a more comfortable ride. Am I reading that right? What are the cons to that?

What are the pros of keeping the bump stops on?

 

[TypeRx]

Bump stops are an integrated part of your suspension. Removing them completely provides no buffer for your shocks if fully compressed and will result in a much greater likelihood of a blowout. You won't find any spring mfg recommend removing the bump stop completely. This might be different for some (not for the model 3) racing coilover setups where a bump stop is engineered out of the equation.

If you are talking about just trimming, the disadvantage of doing this is that the bump stop is essentially a progressive spring. Removing the softer bottom portion will leave the harder top portion in effect -- if you end up contacting that it will be a more significant jolt. The pro to leaving things as-is is that you maintain the full progressive nature of the bump stop, so even if you are riding it it doesn't have as much of a jolt. But but leaving it full length on lowering springs your chance of riding it are higher.

Still, its amazing to me the diversity here on bump stop trimming. I was 100% set on trimming mine per the Eibach directions but am really re-thinking it now. I figure if it really contributes to an uncomfortable ride (which people don't seem to be indicating), I will simply dissasemble and trim (PITA though) or maybe use that as an opportunity to toss on a properly matched shock/spring set. Down the road....

 

[tlr1000]

Bump stops do not impact ride on a normal basis. If you trim, you have more stroke before hitting the bump stop. If you don't trim, the chances are higher that you engage the bump stops (but even then you may never hit them). Safe to just follow what the manufacturer says to do as I'm sure they've looked at all the pros and cons and have decided the pros outweigh any cons for bump stop trimming specs they provide. Companies like Eibach and Tein have more experience to base their instructions on compared to most of us.

 

[fritzner]

Trimmed front and rear per Eibach's instructions and the ride quality is great on my SR.

 

[SDM44]

No for both on my Eibach springs, on my SR+ using the correct 004 springs. So a 1" drop isn't going to really effect the shocks and factory bump stops.

Driving-wise, the car feels a little bit smoother on the road and on the freeway that it did before with the factory SR+ springs. Hitting bumps on the road doesn't really feel any different than before.

If I really need to, it's easier to take the wheels off and reach in there with a serrated knife to trim the bump stops later, than it is to cut them now and pull everything apart to put some new ones back in.

 

[XLR82XS]

No for both on my Eibach springs, on my SR+ using the correct 004 springs. So a 1" drop isn't going to really effect the shocks and factory bump stops.

Driving-wise, the car feels a little bit smoother on the road and on the freeway that it did before with the factory SR+ springs. Hitting bumps on the road doesn't really feel any different than before.

I feel the same scenario. Smoother on the freeway - no change when hitting bumps on non-freeway.

 

[HP Autosport]

Guys:

It looks like there is conflicting info out there on whether or not to trim the bump stops while installing lowering springs. Some say they don't and there are no ill effects. Some say they do to help prevent their shocks from bottoming out and to comply with manufacturer recommendations. And others have said that the model 3 OEM shocks have such little clearance that the bump stops are essentially an integrated part of the suspension and need to be left as-is.

If you have lowering springs on stock shocks on your model 3 (doesn't matter what trim or brand/version of lowering springs), please complete the survey below. Please don't complete the survey if you haven't installed lowering springs on your stock shocks yet!

Post a comment below if you are unhappy with your decision (as noted in the survey)

It may be time to remove the dust boot and measure how much bump travel there really is before the bumpstop is engaged. Depending on the intended design purpose bumpstop may be used as a secondary spring for chassis tuning, it's not just really a hard stop for the suspension. Engaging the secondary spring or the bumpstop allows the vehicle to react to the added spring rate in the corners. A good example is BMWs, their chassis engineers use progressive bumpstops/secondary springs to tune the chassis while maintaining ride quality using traditional springs.

 

[TypeRx]

It may be time to remove the dust boot and measure how much bump travel there really is before the bumpstop is engaged. Depending on the intended design purpose bumpstop may be used as a secondary spring for chassis tuning, it's not just really a hard stop for the suspension. Engaging the secondary spring or the bumpstop allows the vehicle to react to the added spring rate in the corners. A good example is BMWs, their chassis engineers use progressive bumpstops/secondary springs to tune the chassis while maintaining ride quality using traditional springs.

So do you guys trim the bump stops or not when installing lowering springs on model 3s?

According to MPP, there is ~10mm of travel (OEM suspension) before the shocks contact the bump stops (assume this is for the fronts..who knows on the rears). They stated that the bump stops are intended as a secondary spring, like your mention. Eibach recommends removal of 20mm on the front and 25mm on the rear bump stops when installing their ProKit springs (on a P3D). So, with that info in hand...what would you do?

 

[skrtskrt]

So do you guys trim the bump stops or not when installing lowering springs on model 3s?

According to MPP, there is ~10mm of travel (OEM suspension) before the shocks contact the bump stops (assume this is for the fronts..who knows on the rears). They stated that the bump stops are intended as a secondary spring, like your mention. Eibach recommends removal of 20mm on the front and 25mm on the rear bump stops when installing their ProKit springs (on a P3D). So, with that info in hand...what would you do?

So in this case would MPP recommend keeping the bumpstops?

 

[TypeRx]

So in this case would MPP recommend keeping the bumpstops?

MPP doesn't really weigh in as their approach it to do it right from the start and match the shock/spring properly. When you do that you don't typically need to modify the bump stop.

Suspension Tech - Springs vs Coilovers | Mountain Pass Performance

 

[HP Autosport]

So do you guys trim the bump stops or not when installing lowering springs on model 3s?

According to MPP, there is ~10mm of travel (OEM suspension) before the shocks contact the bump stops (assume this is for the fronts..who knows on the rears). They stated that the bump stops are intended as a secondary spring, like your mention. Eibach recommends removal of 20mm on the front and 25mm on the rear bump stops when installing their ProKit springs (on a P3D). So, with that info in hand...what would you do?

We have yet to trim any bumpstops. That said, you should always follow the manufacturer's instructions.

If the ~10mm is true, any lowering springs will put the suspension on the bumpstops/secondary springs. However, none of the vehicles we installed the springs on felt that way.

We just recently did Eibach springs on M3 AWD. During the road test, we like to hit this section of the street that medium to high brake force must be applied to slow the vehicle down for a 90-degree turn with a bump in the braking zone. Most lowered vehicles without proper dampers will bottom out the front suspension. The Eibach and M3 AWD combo did not experience this.

 

[MountainPass]

So in this case would MPP recommend keeping the bumpstops?

Our coilovers come with their own bump stops that are made for the application so it doesn't really apply in this poll!

 

[TypeRx]

We have yet to trim any bumpstops. That said, you should always follow the manufacturer's instructions.

This is always the conundrum LOL. Anyways, thanks for your contribution/info - it actually is quite helpful!