I did on the set I put on a Saturn SC2 over 20 years ago. God I'm old. I did not on the M3P. UP did not state, but they are progressive, and should get more firm as they compress. Now I don't know what the curves on the OEM springs versus UP are, but it is possible that if the rate is high enough that the car could hit the bump stop on an OEM spring in situations where it would not with an aftermarket spring, even if not trimmed. Given the risk that the dampers could bottom out, since I didn't remove springs, and put everyuthing through its full course, I left them alone. Figured if I were hitting the stops, I could go back and trim them, possibly without removing the assembly again. But if I HAD trimmed the, and did too much, I'd be looking at a damaged set of dampers, the inability to add back to the stop, and the certainty of the need to pull the assembly to install a new stop.
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Time to settle things - lowering springs and bump stops
- Thread starter TypeRx
- Start date
Either you leave them stock length and they are engaging most of the time and making the ride harsh, or you cut them and the suspension compresses at full speed into the remaining piece of bump stop rather than slowing progressively. Neither is really ideal.
If you are getting Eibach springs, trust their directions and trim accordingly. Asking a vendor that doesn't sell Eibach springs for an opinion if you should trim Eibach bump stops will likely get a response that leads you down the path of buying their product.
Easy solution, cut half the dimension of the instruction, then you will have the best of both worlds? 
I am just chiming in to prevent misinformation about our products (people seem to think it uses OEM bump stops). He really wanted to pry an answer out of me so he got one. We made this post exactly 2 years ago, so our position on this subject has never been a secret.
Suspension Tech - Springs vs Coilovers | Mountain Pass Performance
Great idea! lolEasy solution, cut half the dimension of the instruction, then you will have the best of both worlds?
To digress a bit, I think it's a no brainer that coilovers are preferable to springs (let alone a discussion on whether to cut bump stops or not) but for what I paid for my Eibachs, it would be 5 to 8 times more money for coilovers. Personally, I would not get a 5 to 8 times benefit but some would. At the end of the day, money is important or we would all have the performance 3. Whole other discussion.
Finally got off my butt and lowered my P3D+ with Eibach Pro-kits. Finished 1” lower in the front and 1.4” in the rear exactly as advertised. Didn’t trim the bump stops. Ride quality is just like stock..I swear it is almost feels smoother. Handling overall felt fine -- no noticeable benefit or detriment but its not like I really put it through the paces yet either.
What a great change!
What a great change!
XLR82XS
D M C
I used a local shop that has previously worked on my Porsche/Audis. Pacific German. Although I generally DIY, I'm losing interest in doing this sort of work. I had PG order the springs, install, and conduct an alignment. They are a great crew.
Good article. Just to clarify, it says "as soon as you lower the car, you are engaging the bump rubber AT ALL TIMES" whereas above you mention, "...leave them stock length and they are engaging most of the time. So is it all or most? Also when the article says 'lower' is this true of every spring that reduces ride height regardless of spring rate and amount of ride height reduction?
I've never heard of any aftermarket coilover kit retaining factory bump stops - is there such a thing?
It depends on how much you lower the car. I haven't heard of it either, but it hasn't stopped some people from trying to install their stock bump rubber on our dampers when they don't read the instructions!
That makes sense. I can't imagine that if someone lowered their car a "mild" amount - say less than an inch - it would cause them to be engaging un-trimmed bump rubber at all times.
Anyone going through the expense of buying a well-engineered coilover kit such as the MPP ones would be, dare I say, foolish to reinstall the stock bump stops over the included ones. Surprising someone would do that.
I think we can definitely agree it is best to follow manufacturer's instructions. So in the case of aftermarket springs that say to trim the bump stops then do it. I'm sure there are pros and cons of doing so but assuming that the engineers weighed this all out and they know more about their own springs than anyone else.
I think your advice is sound but the anecdotal experience of others swayed me to try without trimming. So far so good. If I end up unhappy with the ride quality I will bite the bullet, uninstall, and trim the stops (or more likely just upgrade to adjustable coilovers with matched shocks/springs).
Good plan!
Wonder what the response would have been if you asked the question more generally like, "When installing after-market parts, do you follow or ignore the manufacturer's directions?"
Look, the reality is that all of us interested in modifying the suspension (or any part, really) on our cars is already ignoring "manufacturer directions". As adults, we all have the ability to weigh risk-benefit and make decisions on our own. And deal with the consequences and hopefully grow individually as we gain experience. :thumbs up:
I meant manufacturer of the part being installed, i.e., Eibach, H&R, MPP, etc., rather than Tesla. Absolutely agree we are all free to make our own decisions. Strictly my opinion but if you buy something from a parts manufacturer I believe it is safest to follow the instruction of the manufacturer designing the part. Obviously there are many that have their personal reasons to not do this and that's perfectly ok.
Dolemite
is my name
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.
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