and do you know it?

This has not been a topic before on NAM, but some of us feel that it is deserving of such, so here it goes...

First, the inspiration (and concern) came from page two of this thread:

https://www.northamericanmotoring.co...t=68819&page=2

There is much I can say, but it would take a fair amount of time, and since I've already shared some thoughts and experiences previously, let me provide another a link. This thread is quite interesting, particularly with post 14 onward:

https://www.northamericanmotoring.co...ight=leda+bump

Lowered MINIs, particularly those with some types of camber plates, are more apt to maxing-out travel. Some shocks/struts seem to be more accomodating...

The reality is that in certain situations, experiencing this can be quite dangerous. As I mentioned in a post provided within one of the above links, a simple putty test is an easy and cheap way to see if one is bump-stopping. Under extreme, unique conditions, this is to be expected, but otherwise not...

I know a few of you bump-stop, and I hope you'll chime-in with your set-up and experiences. Besides being a safety concern, it must not be good for the shocks, nor the strut towers; especially when durometers are not in place.

I have a feeling, and I hope that I'm wrong, that many are bump-stopping and not knowing it...

 

Tony,
I personally do not have a problem with this in spite of running my H&R c/o's excessively low.
I did have a bit of an issue when running RDR camber plates with H-Sport springs and stock struts. Very scary. Part of my motivation to switch to the c/o setup.

 

Joel, thanks much. I'm guessing that the vast majority who lower their MINI's do so with springs... YES, it can be very scary. I wish I could remember the details (it's been almost 2 years), but my heart rate must have tripled in a split second! Funny in retrosect maybe, but not at all given what could have happened...

 

im sure im bump stopping on the HUGE dips and bumps. but under
normal driving conditions, i doubt it.

im running the H-Sport bumpstops that came with the springs. one of
my previous cars was 'riding' the bumpstops as there was no way to
cut the bumpstop without cutting the dust boot (was molded together).
it drove like shiit over bumpy roads. i then tried my buddy's car with the
same setup except he was using the Koni progressive rate bumpstops
and new dust boots.

felt 10x better.

 

Agreed. The cost vs benefit ratio of coilovers for most owners just isn't there initially. I know Ken and others have had excellent luck with springs and stock struts and it has been debated to no end in regards to strut life. This is really an ancillary issue though compared to bump stopping and safety.

The "thrust and lunge" as I refer to it when you hit the stops on an off camber, or reducing radius turn, can be catastrophic in regards to vehicle control.

I do think it is a bit of a testament to the vendors who are making springs that this is not a huge issue with our cars. In the VW world many more people have bump stop issues and bottoming issues due to very excessive/style related drops with springs only.

 

Some cars are tuned to ride the bumpstops from the factory. These usually have very tall stops that are very soft and progressively get harder. These just act as springs and aren't a bad thing.

In a car not designed this way (like the mini), you end up with instant spring rate increase when the car hits the bump stops. If the front suspension hits the stops before the rear suspension, you have instant understeer. If the rear hits before the front, instant oversteer. It's not a smooth transition and would not be very controllable.

I've tuned stops on my Spitfire racer so I thought I'd chime in even though my coop is stock.

Cheers

 

All,

Want to thank Tony for starting this thread and to Spitfire and others for their sage observations on the topic.

I think that we MINI drivers may be "bump stopping" more frequently than we realize. I wonder how many of those mushroomed front strut towers, those cracked out front strut bearings, and I don't know what other suspension component failures are the product of impulse damage caused by the suspension hitting the bump stops. Don't know. Also, wonder how many scary driving incidents, situations where the rear end pitches and yaws violently, are the result of the front end hitting the bump stops? I know that incidents of this type materially slowed down my own track driving development until I was able to figure out was it MINI, me, or the track surface and start to "trust" MINI again.

I'd like to suggest a matrix of sorts that could help identify the combination of suspension modifications and driving situations most likely to cause MINI to hit the bump stops. Until I thought through a matrix of this type, I was clueless about my suspension problems. Maybe this information will be useful to identify or prevent bump stop induced handling or component failure problems by others.

Suspension Modifications:

1) lowered suspension using stock struts with unmodified bump stops, or aftermarket struts not designed for lowered suspensions.
2) any replacement springs with lower than stock spring rate at the limit, e.g. "soft" springs, non-progressive springs.

Driving Situations:

1) significant front weight transfer, e.g. really heavy braking, steep down hill segments.
2) huge front weight transfer, e.g. heavy braking combined with steep down hill segments.
3) significant front weight transfer combined with significant spring compression, e.g. the outside front tire hitting a pot hole or FIA curb in a cornering situation.
4) significant static suspension loading, e.g. MINI carrying a full complement of adult passengers, sacks of concrete, or my wife's luggage.
5) massive suspension loading and spring compression, e.g. landing after being airborne, or hitting a world class pot hole at speed.

My theory is that any combination of suspension modifications and driving situations from this list creates a high probability situation where MINI could hit the bump stops with the resultant consequences.

These are my thoughts. What do others think? Am I way off, exaggerating? I understand that there are advances in bump stop technology that might actually solve some of these situations. Don't know what these solutions might be and am interested.

Regards,
John Petrich in Seattle

 

H-sport springs with Koni FSDs - No problem with bump stopping. Car is lowered 3/4 inch and I am using the H-sport bump stops.

 

Larry,

Glad that you are not experiencing any problems with hitting your bump stops.

According to the formula outlined above you are in a risk category from the modifications; the lower spring rate H-sports (see: https://www.northamericanmotoring.co...ad.php?t=39371) and the Koni FSD's which are "full body struts" not designed for lowered applications.

The H sport bump stops are in the "altered" category and look like they are relatively short and will permit significantly greater strut travel before compressing. This is a good thing for you.

The other variable in the bump stop equation is the driving situation. If you don't get into any of the listed driving situations, you wouldn't expect bump stop problems. Do you do any track or autocross driving? Suspect that you are describing spirited street driving.

So, a complete response from you would not only characterize your suspension modifications, as you did, but also your driving habits. One without the other isn't enough to use to judge.

Regards,
John Petrich in Seattle

 

When Randy Webb installed my Ledas, bump stops were not used. I honestly think that if they were, it would have been more difficult to discern that I was impacting upon compression; at least in most driving situations. And given that I was hitting without them (at like 5-10 mph), I would have been virtually riding them full-time, if installed (the durometer bump stops)...

Like John, I truly feel that many are bump-stopping, and just not really knowing it; and/or that the unsettled character is normal, or expected with such a set-up. If thrown into a track situation (I don't qualify here), or some serious canyon carving (I know about this), it can feel like a bucking bronco!

 

My experience:

1-Hsport progressive springs and OEM shocks....Mini would hit bump stop whenever there was a sudden change in road surface

2-Hsport progressive springs and Koni Yellow...better but still bottom out on occasions...springs too soft

3-Megan coil-over with higher linear spring rate...no bottoming out yet

 

Sid,

Wow! A lot of bump stopping. Seems to fit the formula, except, what type of driving are we talking about here. Just don't know of your habits.

Your experience and Tony's are sobering. My personal quest on this whole bump stop thing started when my Instructor made a casual comment that MINI's front end didn't dip much under heavy braking. We were hauling at that point. This was with H&R's and stock struts and the stock unmodified bumpstops. MINI has some anti-dive geometry, but I had already undone a little of that with the roll center correction. I know that I had been careful with the brakes because I had learned to watch my braking to avoid "incidents". But, little to no front end dip with braking didn't sound good to me. So, I cut my stock bump stops way, way, down and am saving my money for some real struts for Y2007.

Looking back, I was probably gently transitioning on to the bump stops with my relatively cautious braking technique and didn't know the difference. On those "special" occasions like steep downhill heavy braking and being airborne (Thunderhill) I couldn't control the transition on to the bump stops, and that's where the fun began.

I keep repeating myself, but now I can "trust" MINI and drive closer to it's potential and not feel suicidal.

Anyway, under what circumstances were you bumpstopping?

John Petrich in Seattle

 

a bit more data:
When i received my first set of Leda's, they incorrectly shipped me a special mini set designed for longer travel with a lowered car, addressing rhe loss of travel upon lowering in this manner. As i understand it, the Megans can lower the car independently from shortening the travel.

H&R's have some sort of built in bump stop for the fronts, but require that you use the stock bump stops in the rear.

Eventually, with the leda's, i adjusted my ride high up to bring back more travel. With the leda's, i used the stock bumps, slight modified to fit. this was after carefully test driving on the crap roads of NYC where, without the bump stops, there was frequent bottoming. While I never 'shroomed a tower, it was unnerving. I was using P&D camber plates with the nylon monoball, no forgiving cushions. the few track days and autocross events worked great, no bottoming. Ralleying would be a problem, similar to NYC city driving. Ultimately, this suspension issue in my daily driving was a major reason I sold the car.

At one point, a forum member from the Bahamas trashed his stock upper mounts, so i made him a monoball set, no rubber, with no camber adjustment (his racing rules). this guy was getting airborne, so his towers must have gotten a workout, but i didn't get much feedback.

 

John,

Nice to hear from you again. Your experiences seem to fit the theory. Bump stopping is one of those "extras" that can come with MINI suspension modifications.

BTW, I dearly love those P&D plates you sold to me. No compliance. Who needs it? We are running rubber tires aren't we?

What car projects are you working on now. Any MINI related?

Regards,
John Petrich in Seattle

 

Errm... I can't seem to be able to find the "How to tell if you are hitting your bumpstop" bit in the above links...

Any chance of someone describing the experience? The sounds it creates... the feeling of bump stopping... etc etc...

I've got a "feeling" I'm bumpstopping... Will PSS9s solve it?

Thanks!

 

with h-sports i could definitly tell when it hit the bump stops in the rear when you would go over a big bump/dip the suspemsion would go down then you would feel it get really hard int he rear then soft again.

 

John...these are the perils of Detroit area street driving...I'm a very sensitive driver who nearly stops traffic at railroad crossings and approach driveways at an angle so the rough encounters are almost always unexpected.

That said, road repairs are around here are notorious for their cave men technique Rather than properly filling in gaps/holes, they (MDOT) create speed bump worse than before The roads have a lot of crown so if you are crossing a major intersection, you'll nearly get airborn and then come crashing down over the other side.

Under these circumstances, the Hsport with their progressive short springs and weak kneed OEM shocks just give up and slam into the bump stops. Considering they have lost an inch of travel, that isn't hard to expect.

The addition of Konis helped the situation a bit through a stiffer damper support but the Hsport's progressive springs just keep giving up under the same shocks.

Megan's on the other hand, are higher rate linear springs with matched adjustable dampers. Another big advantage is the coil-over's height adjustment is independent of the spring preload. This enables the ride height adjustment to be at any level while retaining full damper/spring stroke (fender clearances limited)...the damper/springs are one unit while the lower mount tube is threaded on It also has nice hefty bumpstops (not the thimble sized Hsport type)...if I have hit the bump stops on these, it's hard to tell...I've caugh small amounts of air a few times and the landing is a solid, secure "thud"...

BTW...do you still have the H20 injection on?

Sid

It goes "BANG!!!"...your glove box pops open...your sunglasses goes crooked on yo face...your radar detector falls off the windshield...you scream "MOTHA@#$k!!!":impatient

 

That is definitly the best description of "bump stopping" that I have ever heard.

 

Alright! I think there were a few instances! Anyways, PSS9 are on its way due to scraping of my fender well after changing rims...

 

I have the crashing and violent outbursts as well, but I don't think it is the bump stops or dampers bottoming out. I think it is the spring bottoming out.

I should say that I never have this problem during hard, bumpy backroad driving only over potholes and those awful "road repairs". I noticed it with the h-sport springs/bump stops and stock shocks. When I changed to bilstein sports I took a good look at shock travel as the bilsteins didn't come with bump stops and the h-sport's won't fit the larger rod on the bilstein's.

I compressed the stock and bilstein shocks to max travel to be sure I wouldn't bottom out my new shocks. It looks to me that it would be impossible to fully compress the shock while driving (even with the h-sport bumpstops) and that the spring would bottom out first. I did notice that the springs had wear marks on them. Not just the "helper" coils, but between the lower 2nd and 3rd coils (number 1 being the coil on the lower perch).

After seeing that the shock can completely compress without any issues, I see that the bump stops are there to keep the spring from bottoming out, not the shock, as the collective concious has implied.

Bottom line is that I need more spring travel. Looks like I will ends up with coilovers after all. Wich sucks because I just got everything installed. I haven't even done the final alignment yet because I can't keet my shock towers in one position long enough to do it.

The real kicker is that with the bilstein's, camber plates and rear madness bushing (don't even get me started with these beauties) I am almost back to stock ride height, but with the crashing of a lowered car.

Excuse the long post. Live and learn, I guess I'll put the bilsteins and camber plates on my stockish mcs when I can get money together to redo my recently redone suspension.

 

It sounds to me that, depending on the installation, either the coils or the struts can bottom out. Hadn't thought about the spring part, but your post sure illustrates what can happen with the springs.

In my case, it was the struts, not the springs.

There are a lot of pitfalls with aftermarket suspension additions. Have been following the thread about Megan coil overs. Much the same thing that you describe.

Regards,
John Petrich in Seattle

 

Are you sure it is the shocks? The rear maybe, but the front shock can be competely compressed up to the mounting bolt without binding. I just double checked this on a spare stock shock.

Edit: I didn't see if you were using the stock bumpstops or not.

 

Yep, sure as sure can be. Cut down the front bumpstops and it all went and stayed away. Cannot even make it happen anymore.

John Petrich in Seattle

 

Ok. I never used the stock bumpstops with my lowering springs. Maybe I'm am not experiencing it to the same degree as everyone else. It hits really hard and seems beyond what the spring rates are. I had a really low and stiffer bmw that never felt this hard. I'm sure the tires don't help either.

 

It has happend to me both on and off the track. On track is quite scary