I just had the opportunity to get a sweet deal on some koni adj koil overs. Not only do I get to play around with ride height, but also rebound dampening .

However, my knowledge as to what rebound does for a MINI is quite limited. There's posts here on NAM where people have posted what settings they're running. Most are running more rebound (stiff) in the front and less rebound (soft) in the rear.

Can anyone comment as to how stiff vs. soft rebounds relate to the car's handling in the front? in the rear?

 

I'm not experienced with car suspension, but on a mountain bike you would adjust more rebound dampening so you don't rebound upward after absorbing a bump (the return of the shock coming back too fast). Too much dampening and you would reduce the ability to absorb repeated impacts like wash-board bumps (the return on the shock would be too slow).

 

Simply, rebound is how fast the shock returns to its normal position after compression due to surface abnomalities and/or cornering force. Being adjustable means you control the speed of the rebound. By opening up the valve, the return is quicker. Too quick will have the vehicle bouncing off bumps (not good while cornering as you'll lose grip). Too slow and the suspension stays compressed too long (relatively speaking), which could affect the suspension doing its job again if called upon before fully rebounded. Compression adjustments and rebound adjustments are not independent of each other. Adjusting one affects the other. Also, I'm assuming coil over shocks are nothing more than spring preload adjusters that happen to affect ride height? Is that true? If it is, that defeats the purpose. Ride height should be independent of preload. Preload should be set according to the weight of the vehicle (sag) to maximize suspension travel, not external appearance. I think people are buying coil overs because they think they're better. My 1975 Kawasaki H1-500 had coil overs. Doesn't mean they were any good (which they weren't). My 1997 Ducati (sold recently) had an Ohlins gas charged coil over rear shock ($1000) which was fully adjustable for preload, compression, and rebound. Great shock. Ducati's also have rear shock linkage that makes ride height adjustable without affecting the spring's preload (ability to do its job...that's the way it ought to be). Once I got my Ducati's suspension dialed in (took a lot of experimentation), I never touched it. I would imagine most people who install coil overs don't adjust them after some initial fiddling, or ever. What you want is a suspension that keeps the wheels planted over surface abnomalities while allowing the full range of the suspension travel, regardless of how hard you're pushing the car. I don't think coil overs are required for that in most street situations. In fact, their characteristics may work against your desires. BTW, "hard" and "soft" are typically used to describe compression, not rebound, although too quick of rebound could be considered hard I guess. So if I understand the coil over preload/ride height adjustment, a lowered ride height is due to lessening preload? That could be good if you're after a lower height and a softer ride. I'll admit I know far more about motorcycle suspensions than car suspensions, so if I dorked this up let me know. My .02.

Cheers!

 

Yes, this concept I understand. However, how does this relate to the MINI? What's the difference between having them set for higher rebound on the front vs. lower rebound on the rear? What does it do?

Koni's technical support has not been helpful at all! When I told them the 12+ pages of instructions that came with kit were in German and I asked for english, they said they didnt' have a translation. I also asked them what were the best starting point settings for the MINI (I asked this because they tout this kit as being specially designed for the MINI with testing on the Autobahn in Germany), but again, they had no answer for me. Huh? Designed and tested on the Autobahn? I'm beginning to think Koni is full of crap. I mean, they don't even know the spring rates of their springs! What type of company doesn't even know what their own spring rates are!! Funny how they tout this kit as being specially designed for the MINI, yet they have no starting points for me nor knowledge of their own systems.

 

i don't have pictures of the shocks you guys are talking about (maybe that would clear up my question), but what is this preload you're talking about?

if the top of the spring is resting against the car (through the top mount) and you try to "compress" the spring by moving the lower perch "up," aren't you just jacking up the car higher?

wouldn't you have to be at the restrained extended limit of the damper stroke to be able to compress the spring? is that what your "preload" is?

 

 

In this thread, I'd rather learn about adjusting the rebound settings on Konis... But for you're edification, I've posted a pic above. :-)

 

Preload is the loaded weight on the springs (car plus contents). The springs are slightly compressed by this. On coil overs, you can increase or release the compression, even though some preload will always exist due to loaded weight as well. By releasing compression, the spring is softer, which helps the suspension to soak up bumps, but decreases turn in (front). Suspension at best is always a compromise between certain variables. You want it to soak up as much as it can while allowing the suspension to travel to near maximum. If you're suspension was totally adjustable, you would want to pick the spring force (rate) that gives your shocks full use of the shock's travel (therefore, soft as possible), and set preload/compression to give you all that travel minus about 5~10mm at full force (i.e, very hard braking for the front). Then you want to set up rebound to bounce the suspension back up at a quick but controlled rate so as to not bounce back too hard causing the tire to loose grip. Of course with non coil overs, manufacturers have chosen the compromise for us. The sring rates they choose are strong enough to let the shocks do their job without bottoming out. Compression and rebound in the shocks is pre-selected to give an optimum average. That's why when you buy aftermarket springs and shocks the end result is typically stiffer for better turning, but at the compromise of soaking up bumps (ride quality). As for the MINI S, seems Koni's FSD shocks are the best solution to the stock MINI's inherent lack of ability to soak up bumps to most everyone's standard, and still give you great cornering ability. A lowering spring on top of that will slightly increase the cornering capability and slightly decrease the ride quality. The lower you go, the more the extreme effect because you're narrowing the shock's travel fairly significantly.

 

i saw the pictures; thanks.

stevie B, your comment is impossible. if the car is resting on the top of the springs and the botton of the springs are resting on the perches, you can't change the load on the springs; it is determined by the weight on the springs as long as one end of the spring is free to move. you have to change the weight on the spring.

i'm starting to suspect that this term "preload" is being sort of misused. i DO understand the whole idea of corner balancing by jacking the various corners up and down until you get the weight on each to what you want; it is this "tipping" of the center of gravity around by the jacking that actually changes the WEIGHT on each corner. if this is preloading ok, but i get the idea that some people think you can change the load on the spring WITHOUT moving the cg; that's what you can't do.

 

meb- please clear up this thread in simple terms.

there's too much reading and not much direction.

 

Please, can anyone comment as to how stiff vs. soft rebound rates relate to the car's handling in the front? in the rear? Is generally a softer or a stiffer rebound good for the MINI's front suspsension as compared to the back, or should they be the same? Why?

 

Look at the coil over. The spring isn't just resting in there, it's under a force (load) which is alredy compressing it. That's preload. It is possible to adjust so there's no force on the spring while the shock is unmounted, but then when mounted the weight of the vehicle will compress it slightly. That's also preload. The first concern is getting the right spring based on the weight of the car loaded so the suspenison can do its job. Clear?

 

Did your sweet deal come with setup information? Koni should have already determined a starting point for both front and rear (which should be different). If they didn't, just set them in the middle and drive the car and determine where you need to adjust. Driving on a bumpy road will help during experimentation. If the car is not soaking up the bumps, the rebound is too great. Can you adjust compression too? Too much rebound and the suspension will bounce back too quickly, which may make the car skiddish in cornering and lose grip, lose drivability and ride comfort. Too little rebound and the suspension compresses and stays that way too long; therefore, possibly causing the suspension to bottom when called on to compress again. Also, drive the car with the suspension set to each extreme. That'll give you an idea what the extreme of the affects are. What you want is to set the suspension up so that it's as soft as possible without bottoming. Frotn and rear will differ (theoretically) as the F/R weight distribution of the car is different. However, Koni may have allowed for that perfectly in their valving. I think you need to take it somewhere and have it set up by people with experience. Good luck.

 

Dampers are sort of a very difficult thing to figure out. Here's why; "it's a black art." Words spoken to me by an individual who does nothing but design dampers all day, every day. Further, I'm told, the actual force used to measure the resistance in dampers is not a good judge at all for what a damper can or cannot do; three different dampers may dyno with the same specs, but the difference in feel and control has more to do with the relationships between valves - leaf valves, and shime thickness etc. It's like saying three different cars corner at 1g. But how each behaves while getting to 1g and how easy each is to control at that threshold can be very different.

So why the long winded paragraph above? The "black art" comment sort of applies here. Ya gotta go out and experiment. Yes, I know you are not designing the dampers, but there will exist a relationship between bound (compression) and rebound that works for your Mini. Your job is made easier by the fact that this Koni adjustable coilover is an in-house design. I would expect all the damping qualities to be complimentary.

That written, and as was intimated a few times above, the compression stroke should be firm enough to control unsprung weight movement. In real world commuter practice this is quite difficult as you do not posses a purpose built race car driven on race car smooth roads. The compression stroke should not be set so strong it causes your car to bounce and hop over bumps - written above. If you were to watch your car driving along a curvy undulating country road in a video, you would want the motion of the car to remain glass smooth as each tire impactsa compression type bump. The suspensions moves up without upsetting body motion - which is another way writing/say, this will not upset the motion at the other three wheels. See, if the compression energy is not absorbed, but transferred, the other three wheels will be forced into contrary oscillations...some subtle and some not so subtle.

If you can establish the strong and weak values for compression and rebound, begin by setting compression at 1/3 to 1/2 rebound. You may start by setting rebound at full strength. Set compression at 1/3 to 1/2 this. There is a relationship between rebound and compression, but it begins by determining rebound characteristics. Then go drive the car.

More compression damping will not make the car corner flatter by the way. A strong setting will only allow the car to take more time getting to its complete roll position. A strong compression setting may make the car feel very darty.

Think of it this way - and this is partially true; the compression stroke controls unsprung weight(weight os suspension wheels tires brakes, suspension arms ) and rebound controls sprung weight(you and everything else).

Adding to the already complicated subject is the matter of balance and weight transfer. The Mini is nose heavy - 63% of its weight sits over the front axle. The damping forces must be stronger up front in an effort to control moving mass. But, you'll also want to make sure your car can rotate a bit around a corner. The bulk of this should be determined by the springs, by the way - you cannot control these here so we'll move along.
Adding too much rear rebound damping can help the car to rotate, but may also cause it to skid across bumps in tight turns. Avoid going that far on the street.

Also, if your rear swaybar is really big, you'll more than likely need more compression control; if you allow the body to compress quickly, the swaybar will work faster. Again, springs should determine gross handling balance, not the dampers or swaybar(s).

I just thought of another way to desocribe the differences...I'll write it, but I need to think about it for a while. Springs and swaybars and rebound affect wheels rates. Compression should not.

My brain is not very organzied today...sorry for jumping all over.

 

What Meb is saying is this:

1. stiffer front setting= understeer
2. stiffer rear setting = oversteer
3. stiffer rear setting will affect comfort more than stiffening the front

You should start out med and med setting first and see how your car
handles. If it understeers, stiffen up the rear. If it oversteers, soften
up the rear. if it's too firm, soften the rear and firm up your rear
swaybar setting. you have to play around both the damp and
swaybar settings together to get both straightline and turnability
dialed in. also, don't forget your tire pressure settings too.

will take a few weeks and several days of playing around.

have a nice day.

 

Thanks meb and kenchan for the info!

In regards to some of the info meb writes: Unfortunately there's no way for me to determine the compression setting, so getting the ratio correct for rebound to compression will have to be trial and error.

Also, since the dampeners are infinately adjustable from their softest and firmest settings, getting the left and right sides equal will be problematic at best.

I have a stock swaybar, so its adjustment will be fixed. But now I know that if I do get a different rear sway bar installed, I'll need to readjust the rebound setting (I presume it will be softer, right?)

Understanding that more weight is forward on the car makes sense as to why some people are setting the fronts to have stronger/stiffer rebound settings than in the rear.

I guess I'm going to need to become a "black-art" warrior in training. :-)

 

>I have a stock swaybar, so its adjustment will be fixed. But now I know that if I do get a different rear sway bar installed, I'll need to readjust the rebound setting (I presume it will be softer, right?)


KEN: rebound setting for the rear damper can be softened up if you are not happy with the firm straightline ride. then you firm up your rear swaybar
setting to dial-in your turnability.


>Understanding that more weight is forward on the car makes sense as to why some people are setting the fronts to have stronger/stiffer rebound settings than in the rear.

KEN: it depends on the overall setup and what you want from the car;
it is not necessarily just because of the extra weight in the front. when
you stiffen up front too much not only do you get understeer, but also
wheel hop over uneven roads.

for street it's better to keep the sus soft and provide adequate bump
stroke so that your tires do not lift from the uneven roads especially
while turning. then you play around with camber and toe settings and
do the final run down of your 'dial-in.' but that'll come later.

there's always a give and take....

 

Wow! I re-read my morning post...I needed more coffee, talk about being all over the place.

A couple more thoughts; keep track of your adjustments on paper. Keep a log of how your car 'feels' when driving a particular set-up on a particular road.

There is no right or wrong here, just compromise. And I'll let you in on a secret, it's a compromise for anyone anywhere designing and settting up. That means you and me and Ferrari's team as well.

One other point to be made. We speak, or write, about balance. But balance is an animal that changes thru the arc of a turn. Some set-ups oversteer entering a turn and understeer out and some vise versa. The best place to get this sorted out is on a track. But the combo of compression and rebound can also help define how a car moves thru transitions areas. Try to set your car up for as dynamic a situation as possible. Perhaps you have a long high speed curve followed by a closing radius turn in the other direction. I find this type of condition very helpful when it comes to setting up cars. The speed is important because time allows the suspension to compress. Then you have to get on the brakes and set up for the next turn in the opposite direction. I'm also saying that braking will affect your set-up too and you NEED to consider this as part of your setting up! Perform this run in the opposite direction too; the slow speed turn into the high speed turn in the other direction. This experiment will tell you how your car transitions on throttle, off throttle and on braking. too often handling is thought of as hammering a constant radius turn. Your car needs to be your wicked accomplice everywhere! It shouldn't spook you at any point.

If you feel your set-up is just about perfect everywhere, except off camber braking into a turn, add a little toe-in at the rear. This is not an autoX suggestion by the way. If you have a 22mm rear bar with your final spring/damper set up biased to a tad oversteer under tigh conditions, a little toe-in will not even bother slow speed oversteer. Toe-in will help to save your back side on fast off-camber turns. I believe rear toe affects stability more so than the front.

If you have the time, remove both swaybars, and then take a careful but sprited ride. I write this because springs are the most fundamental part of your suspension, then the dampers. If you can get your set-up really close without the use of swaybars - I mean balance in, thru and out of turns, you can then employ swaybars to tweeak oversteer a bit...or tweak understeer a bit...or keep the balance exactly the same but improve responsiveness by upping swaybar size so each contributes proportionately to wheel rate. Let me explain the last one a different way. Say you like the balance of the stock Mini, but it just doesn't respond fast enough for you. Simply up the current size of each bar EQUALLY. Balance will be the same, but the car will respond quicker to inputs.

Let us know how you've done. And really, don't get discouraged if things don't work out real well the first or second or third time. And if you are feeling a bit down about the time, think about how much time and money a gazillion folks take to sort out an F1 chassis. A front wheel drive, strut type set-up, IS a compromise. Most of these built-in compromises cannot be altered, only masked.

 

Thanks again for the info.

Will do. Probably won't be able to get to it until a few more weeks. :smile:

 

See post #4 above. I don't read technical German very well.

It might be in the German instructions somewhere. But I saw no mention of MINI in the wording, so I think they're generic instructions....

 

Allow me to clear up a point written in one of my replies above regarding sprung and unsprung weight.

The compression stroke does indeed contribute to controling sprung weight. Rebound controls sprung weight, unsprung weight, and, the springs rebound energy. FYI

I did not tie up my explaination properly above.

 

This is why coilovers with bound and rebound adj are better left for people who race on the track...for the average mini driver , spring and swaybar will get the same job done cheaper =)

 

Being the average MiNi driver, I've put tons of miles on my car already and the shocks probably need to be replaced.

Just changing the springs would not be good since all aftermarket performance springs for the MINI also lowers the car, causing shorted shock absorber life, so I'd need to get shocks right away too. I opted to get the Koni Adj Coilovers because I don't like to have my car lowered at all times and also for the fact I would get new shocks along with the performance springs.

However, one thing I didn't want to have to deal with was rebound adjustability. I would have preferred the manufacturer (Koni) to have tested their set-up and determined a default rebound setting that gives overall good balance for their particular spring rates on the MINI. I mean, they already provided and set the compression settings, why not the rebounds too? So that said, I started this thread to be more knowledgeable on how rebound settings affect the MINI and what to do and what not to do.

 

Listen, there is no right or wrong as I wrote. Every opinion made here is valid...for someone. You have to decide if you're willing to invest the time to get it right. And by the way, possesing the ability to adjust bound and rebound is a good thing. You're learning curve may be a bit steeper in the beginning, but in the end you'll have a set-up that is closer to your needs, ie fewer factory compromises or assumptions.

Enjoy the learning process!

 

great input, mebBerk