Time to settle things - lowering springs and bump stops

[TypeRx]

Ok so I just looked at my P3D- OEM shocks and you really can't even fit a finger between the shock & the OEM bump stops in the rear - the front doesn't seem much different. No clue how they're not "permanently engaged" for you guys lowering, but I've never lowered a car using springs before, so maybe there's something I'm missing.

View attachment 538244

Awesome post - thanks for looking into it. Can you confirm if the suspension is loaded or unloaded in your pic?

I think the reality is that these cars on lowering springs with stock bump stops are riding them very frequently.

But, these cars seem more like BMWs where the stop is truly an integrated part of the suspension...not just there to prevent bottoming out. So, unless you REALLY compress the stop, it maintains reasonable comfort and shock rebound. That is my theory at least.

Cutting the stop gives you more headroom but also changes the “spring rate” of the stop, risking a much rougher ride when you do contact them.

If my setup becomes uncomfortable over time I’ll just use that as an opportunity to move to adjustable coils.

 

[HP Autosport]

Awesome post - thanks for looking into it. Can you confirm if the suspension is loaded or unloaded in your pic?

I think the reality is that these cars on lowering springs with stock bump stops are riding them very frequently.

But, these cars seem more like BMWs where the stop is truly an integrated part of the suspension...not just there to prevent bottoming out. So, unless you REALLY compress the stop, it maintains reasonable comfort and shock rebound. That is my theory at least.

Cutting the stop gives you more headroom but also changes the “spring rate” of the stop, risking a much rougher ride when you do contact them.

If my setup becomes uncomfortable over time I’ll just use that as an opportunity to move to adjustable coils.

If that was unloaded, we are in trouble. That added rate can't be controlled by the dampers. The car will feel like a pogo stick!

 

[Dolemite]

Awesome post - thanks for looking into it. Can you confirm if the suspension is loaded or unloaded in your pic?

I think the reality is that these cars on lowering springs with stock bump stops are riding them very frequently.

But, these cars seem more like BMWs where the stop is truly an integrated part of the suspension...not just there to prevent bottoming out. So, unless you REALLY compress the stop, it maintains reasonable comfort and shock rebound. That is my theory at least.

Cutting the stop gives you more headroom but also changes the “spring rate” of the stop, risking a much rougher ride when you do contact them.

If my setup becomes uncomfortable over time I’ll just use that as an opportunity to move to adjustable coils.

Totally unloaded as an OCD-owned car should be. Bog standard P3D- suspension. I’ll be installing my MPP Sports soon.

Like I said though, I’ve never lowered a car using only springs - always gone the coilover route so maybe I’m not getting something? I’m just peeking through the wheel well and lifting up the rear boot. Tried to do the same with the front but it’s a much bigger pain in the ass - all I could do was shove a finger in there and it felt about the same.

 

[TypeRx]

Totally unloaded as an OCD-owned car should be. Bog standard P3D- suspension. I’ll be installing my MPP Sports soon.

Like I said though, I’ve never lowered a car using only springs - always gone the coilover route so maybe I’m not getting something? I’m just peeking through the wheel well and lifting up the rear boot. Tried to do the same with the front but it’s a much bigger pain in the ass - all I could do was shove a finger in there and it felt about the same.

haha, ok, let me be clear here. When I said loaded I basically meant wheels on the ground...suspension is actually supporting the weight of the car. Unloaded = fully jacked up in the air; nothing acting on the suspension but gravity. Because is you are fully unloaded and there is only that much clearance...yeah, my guess is we are riding on our bump stops 100% of the time when it is loaded.

i, like you, have only used purpose built coilovers on my prior cars. My Porsche and Audi both had Ohlins/HyperCo based setups with gobs of adjustability. That is overkill for my current/planned use of the P3D so I am trying just springs out. So far it’s working out just fine, but uncertain how happy I will be in the long term or over very harsh roads (where I live road conditions are generally excellent).

 

[Dolemite]

haha, ok, let me be clear here. When I said loaded I basically meant wheels on the ground...suspension is actually supporting the weight of the car. Unloaded = fully jacked up in the air; nothing acting on the suspension but gravity. Because is you are fully unloaded and there is only that much clearance...yeah, my guess is we are riding on our bump stops 100% of the time when it is loaded.

i, like you, have only used purpose built coilovers on my prior cars. My Porsche and Audi both had Ohlins/HyperCo based setups with gobs of adjustability. That is overkill for my current/planned use of the P3D so I am trying just springs out. So far it’s working out just fine, but uncertain how happy I will be in the long term or over very harsh roads (where I live road conditions are generally excellent).

Yeah that’s an important clarification - good call:

The suspension is loaded. Car is just sitting there in my garage.

Car itself is unloaded. Nothing in the trunk etc. that would shorten the gap.

 

[HP Autosport]

Yeah that’s an important clarification - good call:

The suspension is loaded. Car is just sitting there in my garage.

Car itself is unloaded. Nothing in the trunk etc. that would shorten the gap.

How is the suspension loaded? Just jacking up that one corner of the suspension?

 

[Dolemite]

How is the suspension loaded? Just jacking up that one corner of the suspension?

Ok let's try this another way -

When I took that pic, my car was empty (no cargo, etc.), just sitting there, in my garage with all 4 wheels on the ground. I didn't do anything crazy - just shoved my arms in the wheel well, lifted the shock boot, and took the pic.

 

[TypeRx]

Just FYI -- With my car parked in my garage a few mins ago, I squeezed my arm behind the rear wheel (its a tight fit!) and lifted up the shock boot as far as I could. I wasn't able to get it to compress enough to even visualize or feel the bump stop. Basically, the farthest I got was just about to the top of the shock cartridge housing. Now, my suspension is lower 1.3" in the rear than stock so that is part of the problem of me not being able to compress the boot enough. Also, there is such limited room I couldn't get any leverage. No way would I be able to do this while also taking a picture. Maybe I'll try again at some point later.

 

[skrtskrt]

As someone who's new to all of this, what exactly does this mean? We should've cut the bumps?

 

[tlr1000]

Thanks for going to the trouble of taking that photo Dolemite.

As someone who's new to all of this, what exactly does this mean? We should've cut the bumps?

In the picture that Dolemite posted he has barely 1/2" clearance on oem springs. If he lowered his car with a set of springs that decreased ride height by 1/2", he'd be constantly touching. As far as I know there should be at least some gap for travel and not constantly resting on the bump stop. If Dolemite installs Eibachs then the instructions would tell him to cut the bump stops which would appear necessary. If he installs some of the other springs that don't ask for trimming of bump stops, then his car would just be sitting on those stops. Not sure if all variations of the model 3 are the same in this clearance regard but definitely very little clearance for the P3D. Long story short - cut the BS (I mean trim the Bump Stop )

 

[rukawa005]

Question: after lower and trimming bump stops, what if I want to go back to stock springs? are there any negative effects of stock springs riding with trimmed bump stops? Thanks in advance.

 

[Mash]

Question: after lower and trimming bump stops, what if I want to go back to stock springs? are there any negative effects of stock springs riding with trimmed bump stops? Thanks in advance.

In both cases shorter bump stop means much harder hit at full compression. But with shorter springs that happens more often and even harder.

 

[MountainPass]

We still get this question often, so we went ahead and measured the rate at every increment of compression of the OEM bump rubbers. The piece that is getting trimmed off does nothing except locate the bump rubber before it is compressed, so we can definitively say that it doesn't matter whether you trim it or not. The effective spring rate of the bump rubber skyrockets with compression too.

More info here: Suspension Tech - Firmer But More Comfortable? How Can That Be? | Mountain Pass Performance

 

[TypeRx]

Thank you MountainPass for providing this information to the community. No doubt, the best solution remains a good set of matched coilovers like you all provide. For those that use lowering springs only, this info is really helpful but also shows the limitation of lowering springs since they do increase the risk of contacting the bump rubber.

 

[MountainPass]

Thank you MountainPass for providing this information to the community. No doubt, the best solution remains a good set of matched coilovers like you all provide. For those that use lowering springs only, this info is really helpful but also shows the limitation of lowering springs since they do increase the risk of contacting the bump rubber.

We figured this could save you guys from worrying about whether to trim or not trim!

 

[tlr1000]

If the manufacturer of the springs you installed says to trim the bumpstops and you decide not to and subsequently you have a warranty issue and asked by the manufacturer if the instructions were followed and you tell them no, I wonder what the manufacturer would say?

For example, Eibach springs are covered by factory warranty against factory defects in material and workmanship. However, the "warranty does not apply to any products that have been improperly installed..." Not following their instructions would likely be considered "improperly installed".

 

[MountainPass]

If the manufacturer of the springs you installed says to trim the bumpstops and you decide not to and subsequently you have a warranty issue and asked by the manufacturer if the instructions were followed and you tell them no, I wonder what the manufacturer would say?

For example, Eibach springs are covered by factory warranty against factory defects in material and workmanship. However, the "warranty does not apply to any products that have been improperly installed..." Not following their instructions would likely be considered "improperly installed".

I'm not sure they would have any way to really verify that.

 

[tlr1000]

I'm not sure they would have any way to really verify that.

Absolutely agree that they couldn't verify any problem was caused by not trimming bumpstops. However, too many manufacturers look for an excuse to not warranty things and I just rather follow manufacturer's instructions and not take that risk even if, as you say, it really doesn't make a difference technically speaking. Saves a potential argument and takes away a potential excuse that could be used.

 

[MountainPass]

Absolutely agree that they couldn't verify any problem was caused by not trimming bumpstops. However, too many manufacturers look for an excuse to not warranty things and I just rather follow manufacturer's instructions and not take that risk even if, as you say, it really doesn't make a difference technically speaking. Saves a potential argument and takes away a potential excuse that could be used.

Best to play it safe. Don't be like one of our customers who sent me a photo of his suspension improperly installed, then another photo after he fixed it with the impact gun he used for the damper right beside it!

 

[tlr1000]

Best to play it safe. Don't be like one of our customers who sent me a photo of his suspension improperly installed, then another photo after he fixed it with the impact gun he used for the damper right beside it!

Exactly. I am almost 100% certain you prefer all your customers to follow your installation instructions as well.