If you look into the front wheelwell you can clearly see a urethane foam bumper above the dust boot. It appears scalloped to make it more progressive, and squeezing the dust boot reveals there isn't much travel before contact.

Honda likes to hide them underneath the dustboots. I've seen them in both Type-Rs and various Si models, and one must be careful not to leave them on the old strut or the new ones will explode. They are made of urethane foam.

If a higher rate is desired for a particular application (eg, track use), the bottom may be trimmed. If it already sits on the stop at rest, this transition will only be apparent on jounce after the suspension has extended. As it is not always possible to cut the top, the cut bottom may easily be reshaped to resemble the part that was cut off.

I have to admit I've retrofitted a lot of older cars with the cut-off bits from these nifty high-tech bumpstops, with excellent results--so I am very happy to have friends who lower cars professionally.

 

Like you guys have been saying, the bump stops do give the suspension a progeressive rate. We are still tuning my Civic Si, but Koni makes a bump stop that might end up on the front of mine. We'll see after we get some data after next event. Race teams don't use progressive rate because they don't know how to for the most part. There are a few who aren't allowed to, like your NASCAR guys, who also aren't allowed to use any bump stops.

 

BFG9000

The more I think about this subject, the more I wonder about how lucky I was; I simply threw the old bumpstops away. Every new kit - mostly Koni - came with new bumpstops.

Orthomini Jr

What model year is your Si?

The problem with these types of bumpstops, from a racing or street modification perspective is, when the springs are changed the relationship between the progressive bumpstops and the springs change - they were designed to work together. Race teams may simply discard these for this reason alone...their new set-ups are more than likely not compatible...one would think.

 

It's a '91

What we'd be doing is using the bump stop as a spring to make the front more progressive. The Vogtland kit for my car uses a linear front spring. We'd be making it progressive while saving money that would be spent on a stiffer spring.

 

Okay, call me dense. I still do not understand the intimate relationship between bumpstop, spring and damper. How does a bumpstop make a linear rate spring progressive when it really controls the damper's movement? I wrote in a previous post, progressive damping. I was quite literal with my choice of words.

I'm not disaggreeing with anything, I just, well...don't get it yet Perhaps there is something more subtle at work here.

Michael

 

The spring rate of the spring itself did not change. If it was linear, then it's sill linear. However, the effective spring rate that is used by the car is from the combination of the spring and the bump stop. Therefore the effective spring rate is linear for the first portion of compression, then it becomes progresive when it contacts the bump stop.

 

Do you have to change anything else in the suspension system if u get the M7 springs? This is the only thing I don't want to have to do!

I don't really know what a swaybar is or what it does?

Mikey

 

Forget the bumpstop for a moment.

Visualize what a spring does for a dampener. It controls the dampener's movement. A stiffer spring is "stronger" and will move that dampener much more strongly. A weaker spring does not move the dampener as strongly (notice I didn't say the word "quickly", but used the word "strongly"...BTW, is that even a word??).

Now visualize what a dampener does for a spring. Internal to the dampener is valving and some sort of medium that passes thru the valving: oil, inert gas, etc. Changing the dampening via valving or changing the medium will affect how quickly the spring can collapse and expand.

Now think for a moment how a car would handle if either the spring or dampener was removed from the car. With just springs the car would have a rideheight, but would be exteremly "bouncy" like a pogo stick, moving from extreme compression to extreme extension. With just dampeners, the car would fall to the ground collapsing the dampeners.

OK. So think a moment about the bumpstops. They're external to the dampener and they're not changing the valving or medium the valve moves thru. The bumpstops are exerting pressure onto the movement of the dampener just like springs exert pressure on the movement of the dampener. So bringing this together, the squishy bumpstop has the same effect as a quishy spring.

p.s. If this helps make more sense: the bumpstop doesn't make the overall spring rate progressive, better stated, it causes the overall spring rate to become dual-rate.

 

matma92serI'm confused perhaps by the words being used...then it becomes progressive...by it you mean the damper?

dominicminicoopers

Yes, I'm beginning to understand. I'm very keen about matching spring and damping frequencies. But I've neglected in my thinking, the two-way relationship between spring and damper - thanks for isolating these, big help; a strong damper with a light spring rate will cause very sluggish responses. A light damper with a heavy spring rate will cause an unsettled condition - essentially one of your points; the frequencies of each must work with some degree of sympatico. I've only written the previous a half dozen times, employed it for twenty odd years...you would think I would remember.

So a spring of a given rate, presumably well matched to a proper damper, will yield different compression and rebound characterisitcs due to how the damper is allowed to move thru its compression and rebound stroke...characterized by the bumpstop. So, as always, a spring is controlled by a damper, whose movements (frequencies) are further refined by a progressive rate bumpstop.

I can see where this would make for a comfortable riding car; indeed, lighter spring and damping rates can be used with equal or greater control of a less civilized set up. But, a question still remains; these 'systems' are designed to work together...their frequencies are matched. As soon as one of these is changed - the spring comes to mind - the system is upset. I only throw this out there because this system is apparently delicate. Indiscriminate spring and or damping rates will affect more than ride. Hell, just changing the bumpstop will alter how this system works.

 

Yes, changing the bumpstop will alter how the system works. However, it only affects the system when the system is compressed enough to where the shaft of the dampener is compressed enough for both ends of the bumpstop to come into contact with something, otherwise the bumpstop is "along for the ride". The question arises is how often during driving does the bumpstop get "used" in the suspension equation? 5%, 50%, 95%. I dunno since I haven't measured it (my guess for a stock MCS that it is a low percentage). How about for an MCS with the typical ~1" drop we have in aftermarket springs? Certainly it must be a higher than stock because there's less distance the dampener has to compress. But how high of a percentage of use, I'm not sure. What if we lower the suspension but use heavier springs than stock? So to be able to answer your question of how upset the system becomes by changing the bumpstop, will greatly depend on on it's usage percentage.

p.s. I asked my dealership's techs about the bumpstops and the tech actually said the MINI doesn't need the front bumpstops whatsoever. The tech recommended even removing them. Wierd huh?

 

The whole idea behind progressicve rate lowering springs is that they won't bottom out the suspension any earlier than stock springs would. Now if the shock is not able to handle the harmonics of that spring then thats a different story.

A normal, round bump stop will make the setup dual-rate. What shape is going to make a bumpstop progressive? There is a trick on weight transfer between the corners that I don't think I'm allowed to discuss unless someone is paying me to tell them. We (R&H) like to overshock cars most of the time, we also exclussivly use Bistein's in our setup's. In our experiance on shorttrack, asphalt or dirt, Bilstein's are good for about 0.15 seconds over anything else, and a digressive rate bilstein is good for 0.3 seconds over a linear Bilstein. On a 1/4 mile track three tenths is the difference between the pole and not making the field.

The suspension as a whole.

 

Not progressive damping (a bumpstop has no damping) but progressive springing. Imagine those Japanese cars that already sit on their bumpstops at rest and can have 4" of wheel travel by compressing the bumpers further. Or just think of the springs as being too light to control roll (to grossly oversimplify, a one ton car with ground level roll center would need 1000lb/inch springs to limit roll to one inch at 1G), and the car always cornering on the bumpstops as its normal mode of cornering. Changing springs to only slightly stiffer ones would have no real effect except if they are lower they put the bumpstops further along into their progressive spring rate. Remember the rate of the bumpstops can progressively go to 1000lb/inch. This rate is added to the rate of the linear springs.

The shock rate must match the bumpstop+spring+bar rate, and it's not a big deal if you have adjustable dampers.

 

Or Bilsteins

Sorry if I'm a little biased, but that's what happens when you're trained by the man that Earnhart Sr. nicknames Mr. Bilstein

 

Bilsteins are 'adjusted' by removing them and replacing with a different model Bilstein: TC (OEM soft) HD (medium) or SP (hard). IMHO they are very well matched with their own springs but once people start tinkering with bump stop lengths and antiroll bar rates, adjustability becomes a plus.

On the original topic: as meb pointed out, most aftermarket "progressive" springs are dual-rate springs. You see the softer coils stack solid and then the rate changes to the stiffer rate of the remaining coils, much like the tender spring on coilovers. OEMs like Ford on the Taurus actually use evenly spaced coils with costly variable thickness wire and/or variable diameter coils; those are truly progressive in rate. Smaller diameter coil=higher rate, same effect as thicker wire. Beehive/barrel shaped springs for the Mini may therefore actually be somewhat progressive after all...

Heh, I'd like to see them do that to their own car. Even if there was a backup bumpstop inside the strut, the car is already so low at full jounce that it might drag the bottom of the car on the ground after a bump. That's what I'd call "bottoming.":smile:

 

Imagine those Japanese cars that already sit on their bumpstops at rest and can have 4" of wheel travel by compressing the bumpers further.

This seems like a perfect way to fine tune the suspension - sitting on the bumpstops at rest. Why don't we see more of this within the aftermarket world? Expensive?

orthomini jr

There is a trick on weight transfer between the corners that I don't think I'm allowed to discuss unless someone is paying me to tell them.

Do tell! I can imagine that using different types of bumpstops ( length and progressivity - is that a word?) might help with weight transfer...


Thought of something else too; the 4" bumpstops in the above example seem to me to work thru the entire range of suspension movement, giving one what appears to be a tremendous amount of design control. I would think this would be a much lighter set-up as well??? I know I've danced around that comment above a few times, is this true?

 

When we're setting up a Late Model on dirt we don't/can't go with a Bilstein that is made for a certin car. We're using a 46mm Bilstein with the valving that we need. For instance a ZV, which is a digressive rate, I think a 3530.

The TC is a Twin Tube shcok that doesn't even get mentioned to us. Otherwise, on a normal car, if you're running sticky race tires then we're going to put you on the sports. If that doesn't work well enough then you'll have to pay the $65 to get the shcok revalved the way we want it.

We don't use bumpstops for weight transfer, we use shocks.

 

agreed, but i chose eibachs because they appeared to NOT be this dual rate wind design, but instead a true progressive wind in which the distance between the coils changes constantly top to bottom...i wish some spring/damper company engineers would also chime in on this thread.

 

Agreed. But, spring and damping rates are closely guarded by manufacturers...makes this subject appear as a black art.


We don't use bumpstops for weight transfer, we use shocks. I simply thought you were referring to bumpstops, given the subject matter, and, what appeared as an innuendo to me.

 

aye