Next year I want to revise MINI's suspension. This revision will include coil overs with up rated struts and increased spring rates. A static analysis wil show all the forces to be the same. But, what about a dynamic analysis - a real world track situation - are the forces the same?

My question is this: Will I gain any better front end tire contact at the track if I run a softer front anti-roll bar with significantly increased front spring rates to help chassis roll control?

The reason I am asking is that when the chassis rolls, those anti-roll bars crank in a lot of spring rate to resist the rolling forces. Is this increased spring rate from the anti-roll bars any different, have any different impact on tire / road compliance, than just installing much stiffer coil springs on the struts? I think I know that a way stiff anti-roll bar will make a front end just "skate" across the track and not "hook up" like it should.

Any thoughts will be of interest. meb where are you?

Pondering in Seattle,
John Petrich

 

All I can say is that you are very much on the right track with your thinking. Go with it

 

Onasled,

Cryptic to say the least. My thinking:
1) asking the set up question?
2) stiffer springs and up rated struts?
3) herfy front bar?
4) wimpy front bar?
5) some combination of #1 thru #4?

Please make a suggestion.

still, Pondering in Seattle,
John Petrich

 

Yes, this is what I meant to show that I was agreeing with.
If you are setting up a track suspension then yes, stiffer spring rates all around. With stiffer rates come softer bars, especially in the front.
What rates? Well that will really be up to you on just where you drive the car, mostly street or track?
Also none of these mods should come before front camber plates as I suspect you know already.

 

Hi Greg,

I have PS9s if you were to change the spring rate to be more track like but still on the street is there a recomendation that you would make.....

 

Only IMHO, but if it were me I might only bump the rates up another 50 lbs all the way around and also go linier with them all. Actually the springs that come with the PSS9s are very track worthy. Might think about going back to the factory front bar at this point also. Next would be a Cooper front bar.
The PSS9s have a good rebound adjustment which make this a very do'able upgrade.

 

A few random thoughts.

The more rigid the chassis the better the platform to tune the suspension.

Lowering CG to control roll is more desirable than just putting in stiffer springs.

If the springs don't stack now they may be of a high enough rate. Stiffer springs, weaker bar or weaker springs, stiffer bar? I don't know I'm hoping you guys do.

Where is the roll center in a MINI and can it the suspension be tuned to make it more effective in reducing body roll?

You asked [QUOTE-Petrich]The reason I am asking is that when the chassis rolls, those anti-roll bars crank in a lot of spring rate to resist the rolling forces. Is this increased spring rate from the anti-roll bars any different, have any different impact on tire / road compliance, than just installing much stiffer coil springs on the struts? I think I know that a way stiff anti-roll bar will make a front end just "skate" across the track and not "hook up" like it should.[/QUOTE]

The one advantage to the bar I can think of is; it adds to tire loading and compliance mainly in cornering. Stiff springs will pound on the suspension all the time. Maybe to the point where traction is affected. Like say a rough corner exit. A softer spring with a well tuned bound rate will ahndle this better than just a stiffer spring.

I've watched these boards for a long time and don't recall seeing thorough testing and data posting on spring rates.

Cool thread John

 

You won't see much of that here on NAM, but you will find it at the track.
Some full race Minis are running up to 600 front and 1000 rear. In fact Koni makes a spec shock for some European Mini series with this rate.

I was lucky enough to sit with the Moton tech for over an hour of one on one discussion about this topic. I did learn a bunch, but at this time some of that will remain as my little secret, though none of it is really a secret.
Gaining knowledge on this stuff is best sought out by asking those who do it every weekend. Finding real good facts will be tough here on NAM.
I'm not saying that there aren't some here that really know there stuff on suspension, because there are. I personally have had many discussions with Michael (meb) over the phone and in person about the theories of suspension and always value his opinion, but at this time they are mostly just theory and also some past experiences with other cars. Even meb is trying something new soon and I look forward to his thoughts on the results.

Personally I am also only going on information that is second hand. But soon I will really have some good first hand feedback as we will really be doing a good amount of testing with springs and bars when the car is finally done.

 

... also it's important to note that racers change spring rates per track and per weather conditions. I know of some GT1 cars that drop rates as much as 500 lbs in the rain.
So, I guess this brings up some real problems with making the right choice for a street driven car. What may be a sweet setup on the far west coat may suck on the far east.

 

When I went from Hsport springs and yellows to the PSS9s I experienced way to much body roll... the front bar cleared that up..... I don't want to go back to that.....

 

... but I see it as 'Band-Aiding' a problem. Going with a stiffer front bar is something I did also and I was never able to get back up to my track times after doing so. It's just not what the fast cars are doing by any means.
Anyway, I think if you went with a Hypercoil replacement you might find that the bar was not the issue.

 

please explain "Hypercoil replacement"

 

http://www.hypercoils.com/



You would have to measure the PSS9s to see which size you needed. Also, especially for someone like you, check out the hydraulic perches

 

I sent them an email....just curious

 

Well that's something I appreciate it.

Looking forward to whatever turns up.

 

Swaybars actually pull down the inside wheel while transfering weight - tis why endlinks are said to work in tension, and why they do not need to be so darn big. But, there comes a point where roll forces are great enough to cause the inside wheel to lift off the ground. At this point the sway bar contributes nothing - zero - to weight transfer. Whatever the cornering attitude is at that point, is the perpetual at limit cornering attitude for that cornering force for that setup in that corner.

Springs, springs, springs. I've written this a bunch of times on the past, but it becomes a little hard to press this concept when most of us drive on the street a fair amount of the time - me included...I'm on the constant lookout for that perfect compromise...and still looking as Greg wrote. On the track however

Roll center location can be changed with lots of work and I questioned this about two years ago in a thread. However, if you lower the car, increase the spring rates and make the track wider...a wider track lowers the center of gravity and helps to restore roll couple. Springs help to control roll. And swaybars contribute nothing to fore/aft weight transfer - a complicated part of cornering; too often we think of cornering as a very easy to describe side force. But in reality it's a combination of roll, yaw and pitch - three directions of movement must be controlled; front to back, side to side, right rear to left front and vise versa.

 

How do you know when you have reached the point where springs stop helping and you need an anti roll bar?

Also, I have a minimal graasp on how to find the instant center and with that the roll center on a conventional rear drive but haven't a clue how to do this in the MINI.
Links, book titles or verbage would be appreciated.

 

I faxed a drawing to Greg a while back...not sure if he still has a copy??? Mine is not to be found. All you need to know is the location and angle of the strut towers - for stock- and the deviation if camber has been altered ( becasue camber is really what affects this angle), the location and orientation of the lower control arms, and the center of the tires at the contact patch. Then you can find the instantaneous centers which define the roll centers. Wheel offset will change these as well as a few other things - read below to find out. One way of controlling bumpsteer - which is not a biggy with regard to the mini - is to always make sure the tie rods point to the instantaneaous centers.

Ride and roll rates depend upon many things, but the quality of the road or track is a major consideration. In theory, you don't need antiroll bars. In practice, they're helpful because they leave room for some amount of comfort on the road or track. However, Collin Chapman (Lotus) did not like roll bars - according to what I've read...I never met the man He designed some of his earlier F1 cars with a roll couple relationship that allowed a precise amount of roll center migration - in the rear - without the use of a swaybar. The roll center was at that near perfect realtionship with the center of gravity - roll couple; the roll center moved just enough to cause some weight transfer without becoming too high with respect the the CG, afterwhich additional roll center migration causes a jacking effect. But these types of relationships are possible when a single purpose built car is being considered. The Mini is not.

So, the answer...there isn't one. You can establish wheel rates by performing motion ratio calculations to form a baseline - with the stock car. Then, thru experience you can develop a sense for spring and damping rates. Engineers perform a lot of these calculations in a computer, but the human side is still very important. Engineers are given a problem and expected to deliver results to the marketplace in the shortest time frame. Since I'm not an engineer, I simply experiment...sometimes at great cost to performance and pocketbook

Another point here about motion ratio; wheel offset will affect damping/spring rates. My 45mm offset track wheels with Toyo RA1s are actually slower at the track than my 38mm offset BBS wheels shod with Michelin Exalto PE2s. A wider wheel offset lowers the center of gravity, reduces the amount of roll, and reduces the effectiveness of the damping system. So, the car feel quite a bit stiffer with 45mm wheels than it does with 38mm wheels and this is because the motion ratio is different - the portion of the control arm that extends beyond the point where the damper/spring attaches is now effectively longer because the wheel's centerline is farther away from this point. So one can look at this in two ways; if the track is made wider, the car will roll less and requires less damping for the same affect. Or, if the track is wider, one must increase damping. A little hint here; the mini's front track is more narrow than the rear...

So when we consider comfort and and handling, wheel offset is a very important part of the equation. I wrote this somehwere in the past here.

 

I got out my book by Puhn las night to try and once again make sense of al of this as it relates to my car...... I will try and digest it later today

 

I got out my book by Puhn las night to try and once again make sense of al of this as it relates to my car...... I will try and digest it later today

 

I just finished a couple. One by Herb Adams and an old book by Carroll Smith.

Learned some, understood a little and forgot a bunch

 

Sometimes you think you're doing pretty good when something as simple as a picture makes you realise that there's a bit of work left to do....Hint: Look at the LR wheel

 

I have those as well

 

Just posting for the "subscription"

 

In that picture there is no more rear swaybar contribution to handling. However, if that's as far as that wheel comes off the ground on that track, and hopefully this condition doesn't occur thru every turn, that setup is basically nailed. It's easy to suggest a little more roll stiffness from springs or dampers...

There was this fellow at LRP last spring who drove a very well setup CRX - for racing. When I was behind him in the left hander, his inside rear wheel came off the ground ever so slightly but never left the ground anywhere else - an obvious compromise. He was very very quick.

As an aside, Onasled and I were at LRP yesterday. It was very interesting to see just how dainty the swaybars are on some of the Can Am Porsches, GT40s and other pure race cars...and the endlinks are quite long ans thin. I also met SRTtech and Octaneguy - who drove from California with the GPs to be part of the Mini/Vintage Festival.