Hey guys, it's been a while!

Can anyone tell me all the pertinent dimensions and numbers for the suspension on the MINI? I'm trying to calculate the Roll-Center on the MINI, and I dont really have a place where I can get under the car to make all the right measurements. If anyone has them, or can point me to a diagram i'd be incredibly grateful.

I also need the stock spring-rates, and the number of active coils while you're at it (that one's easy to check if nobody has the number off-hand). Basically any information on the stock suspension would be wonderful.

 

These are dimentions I've been meaning to measure for quite a while. Changing what's there, however, isn't an easy task unless you're up for making your own subframes, suspension bits, etc.

I can only imagine MINI wouldn't be too enthusiastic handing out geometrical blueprints to the suspention, so we're on our own here.

Let me know if you get data before I do!
Cheers,
Ryan

 

the best i've found so far:

http://members.***.net/btonnesen/suspension.jpg

http://members.***.net/btonnesen/front%20suspension.JPG

http://members.***.net/btonnesen/rear%20suspension.JPG

 

Trying to do something like this?

http://forums.vwvortex.com/zerothread?id=1363022

 

here is a tid-bit:

the axis of the mini strut is not in the same line connecting the upper fender mount bearing center and the lower ball joint (steering axis). the result is the strut axis precesses about the steering axis, causing considerable movement in the upper strut bearing carrier rubber element.

 

that the roll center actually moves...somewhat un-intentionally, and, undesirably. Same is true for double wish bone suspension systems but more a function of geometry rather than flexing bushings.

 

from what i have garnered (Puhn "how to make your car handle", p37), you figure out the roll center for McPherson strutted front ends as follows:


draw a line (L1) between the top of the strut (center of the bearing) (point A) to the steering axis ball joint (point B) (as note above, this is close to, but not the axis of the strut)

draw another line (L2) perpendicular to L1 toward the center of the car and originating at A.

draw a line (L3) from B through the inner control arm ball (C) and extend it to intersect L2 (Int 1)

from Int1, draw a line (L4) to the tire contact patch on the ground. (almost done...)

the roll center for the front of the car is where L4 intersects a vertical dropped down on the car centerline.

a few notes:
lowering the car will lower the roll center
more neg camber will very slightly raise the roll center

 

should that be:
draw a line (L3) from B through the inner control arm ball (C) and extend it to intersect L2 (Int 1)?

I made a few measurements on the car and made a couple drawings for
the front suspension level, and with the inside strut extended 2" and
the outer strut compressed 2".....

the roll center for the front seems to start at the midline about 3" above
the ground, and as the car leans, it scoots to just under the inside tire
contact patch.

the rear is a little harder for me to measure and draw, maybe later...

 

oops...i guess a pic is worth more than a few words, eh?


edit made

 

Seems the rear roll center is about 12 inches above the road and moves
down and toward the inside wheel contact patch a couple inches as the
car leans. correct me if i'm wrong.

 

if you guys send me dimensions, i'll lay this out parametrically on my cad system at home. then just by changing the numbers for the height of the top strut, we can play lots of what ifs. i can screen dump the sketches to .jpg and post them.

i have carrol smith's series of books. the roll center examples in them are all for double wishbone designs, but i'm pretty sure about what jlm is describing in terms of finding the instantaneous roll center.

 

While you're at it my flux capacitor needs some cleaning and I'm all out of Dilithium crystals for the warp drive..



Seriously... That would be cool if this were done....

 

here is something interesting:
http://www.circletrack.com/techarticles/4637/

the point (Int 1) is the instantaneous center.

the roll center in on the line connecting Int1 to the tire contact patch, but I'm not yet sure where along the line. (I think intersecting the vertical line dropped from the car centerline ain't right) I think what you do is draw L4 for LS and RS, and where L4 left intersects L4 right is the roll center.

maybe I'll make up a little drawing...

duh! just realized intersecting the vertical centerline will give the same thing as intersecting LS and RS L4's due to symmetry.

 

i just realized that i might be hijacking grinder's project. i'll give him first dibs on doing this...............

 

Are you guys so caught up with roll centers? There are, as I'm sure you know, easier ways to make this car handle better. Changing the role center is a big deal; you may end up making things worse, assuming you take on this daunting task. But first ask why. Are you trying to keep the roll centers from moving around? Are you trying to change its postion with repsect to the ground? ...keep in mind that weight transfer is a complicated and perhaps designed in element. If you lower the roll centers too far, weight will transfer as easily. One extreme, a solid rear axle; the roll center is the center of the diff as it intersects the center line of the axle. Although the roll center in this application does not move, it is fairly high off the ground...one reason solid axle comfigurations fish tail so easily. Lowering the front roll center in this configuration will create an oversteering condition worse than stock. At the other end of the spectrum is the double wish bone system. Roll centers vary from just above the ground to below the ground with this type of suspension. Touring cars for example might have their roll centers below ground for any one of the following reasons; reduce weight transfer fore and aft - more stable - and potentially creating a set-up that naturally eliminates lean so that softer spring and damper rates can be used so long as CG is low too. But, this is just one isolated part of suspension tuning. Great talk, but WOW, if you wish to fiddle with this stuff. More than a few suspension engineers get this stuff wrong. And, RC has a strong relationship to CG. The farther apart these two become, the more roll.

I would be very surprised to see the roll center for the rear of the Mini 12" above the ground, very surprised. That is quite high...

 

Hey guys, I'm back again...for a while.

Cristo,
Can you post your pictures/diagrams/numbers or whatever you have? Thanks.

jlm,
with all the work you've done on the MINI and its suspension, do you have any pics, numbers, diagrams, etc...?

meb,
I cant answer for everyone else about why they want to know about the roll center, so I'll just say what I'm interested. I'm a college student, and last year I convinced one of my professors, who happens to race semi-professionally, to teach a class about cars. The result was MSCI 615 - Automotive Engineering, Materials and Dynamics. In this class, one of our assignments was to measure the roll center of a car, and as the semester progressed we'd end up calculating the ideal ride height, spring rate, etc for whatever car we chose (after making a few more measurements, like corner balancing it, etc...). So, it'd be easy to go find a Mustang, or some other car with a live rear axle, but I'd rather figure out more about the MINI.

This is only semi-related, but I'm excited about it and I thought I'd share. Well, the original reason for starting the MSCI 615 class is that I'm the president of the Society of Automotive Engineers (SAE) at my school and this year we're actually going to take two cars and prepare them to compete in the One Lap of America event in May. Right now Audi is looking at possibly donating two A4 or S4s, and we've already got a bunch of other sponsors lined up. HP is going to provide laptops and digital cameras, Bell Engineering is going to donate a turbo and intercooler and help us figure out the plumbing if need be, PPG is gonna make our rides look great, Yokohama is giving us tires, Koni (I think it's Koni) is going to give us coilovers, etc... I'm really excited about all this. I just had to let it out!

 

hey, where do you go to college? ive been considering going into automotive engineering and im lookin around at different colleges... just went to Auburn last weekend... Seems like your program is pretty cool..

 

If you end up going with the Audi (or other VAG product), contact me privately about diagnostic equipment.

 

Grinder,

Didn't mean to appear as though I was attacking the idea, sorry. Perhaps buried within my question is knowing the kind of frustration we feel when we decide to take on a daunting task such as finding roll centers, and, then try to somehow alter such things. I was trying to ask why so you might ask yourself why. But, alas, you are onto some very exciting places with roll center. Good luck and keep us posted about your experiences. Wish I were riding shotgun!

Ciao,

Michael

 

I just took some measurements with a tape measure, and used a piece of
graph paper and a pencil with a good eraser, and got out my copy of
Puhn's book to double check the theory. I then shortened and compressed
opposite sides of the struts on paper and saw how it shifted things and
redrew. It's not rocket science, and if you're a little off on the exact
center of the ball joints and pivot points, it only makes a very small
change in the location of the roll center.

If I have the time and energy, I'll do a more formal sketch sometime and
scan it, but I bet someone else could do a neater job than I could.

 

Here's the sketches of the rear suspension flat, 3" compressed (lowered),
6 degree roll, and 3" extended (raised) this one will
go on the next post. Flat, the roll center is 10" above the ground in the
center....At 3" compressed, it's 5" above the ground. At 6 degree roll, it's
9 inches up and 1 1/2" to the side. The camber of the tires is not precise in these diagrams.

 

At 3" extended, the roll center is 13" from the ground in the center.

 

Thanks, thats perfect. If anyone ever gets any info on the other end of the car, I'd love to see it!

Ok, back to my off-topic topic:

{OT}

So Audi backed out, but we already got a Alfa Romeo Milano donated. However, we're looking for at least one more car. The requirements:
1) Affordable (We're probably talking in the <= 5K range because we've got a $2000 entry fee for each).
2) RWD (or AWD. Oh hell, beggars can't be choosers. Just make sure it meets #4)
3) Sedan (need to carry 4 people + stuff, so if it can and isn't a sedan that's cool),
4) Capable of performing on the track after some light-to-moderate tuning (turboing is an possibility).

The list so far: A4, BMW 3, Alfa Milano, and uhh, that's all I can think of. (edit my friend just said a Datsun 510?)

So, any suggestions? ALSO, where else should I post this question (both on NAM and otherwise) to get more answers and to keep this thread on topic?
{/OT}

 

Hey guys,

You said to keep you updated so here I am again.

The Society of Automotive Engineersat Rice have been working hard all semester to prepare our two cars for the One Lap of America event. We've been working on an Alfa Romeo Milano and an Isuzu Impulse Turbo. Unfortunately most of the work has been to get these cars back into working condition, rather than the pimp them out for racing, but thats not to say we haven't done anything to make them faster. The Isuzu already has a great suspension (it was done by Lotus) but we did replace all the shocks, we ported and polished the heads, and even put a bigger turbo on it. For the alfa, we've got race cams, a slightly increased displacement, high performance air filter, and a few other goodies. Hopefully next year we can really get serious and look into turboing it, etc...

We leave for the event in only 9 days! Our website is here if you want to check it out. Will any of you be participating in the One Lap of America or attending any of the races? If so I'd love to finally meet some of you guys and be able to put faces with some of the names on here.

 

You must be excited, I would be! Good luck. Any TV coverage?

Don't forget to warm those brakes up! Just a little joke I shared with a racer friend of mine before each of his races; he forgot to perform this warm up before a hill climbing rally in Canada years ago and rolled the car around the first turn - actually he was oing down hill, not a climb. He was so glad he added the center brace in the roll cage....saved his life.

Anyway, have a great time.

Ciao,


Michael