Hey everyone, im thinking of getting a rear sway for my MCS and just have a few simple questions. As i am really new to the driving world and its definitions, i would like to know exactly what is understeer and oversteer. I've read that having the stiffest setting (ie: H-sport comp) would be the most dangerous for a regular street driver, why is that? Again, i am new to the performance driving world and would just like to learn the basics first. Thanks a lot!

 

Oversteer is when the rear end looses traction before the front; usually causing your rear end to swap positions with the front. Under steer is when the front wheels loose traction before the rear causing you to plow straight instead of turning.

For the average driver, understeer is preferable because the first thing most people will do when they loose traction is to get off the gas and/or on the brakes. This will actually help an understeer situation by transfering weight to the front wheels (which have lost grip). If you try to do this when your oversteering, it's all over and you end up looking in the wrong direction.

The MINI is set up stock to understeer in nearly all situations. A stiffer rear bar will increase the tendancy to oversteer AND reduce the tendancy to understeer by forcing the rear weight to transfer to the front tires. This means you will oversteer with less force on the brakes than the stock bar would allow. It also means you can keep your foot into it much longer through the corner without the need to brake because your front tires will still be gripping.

For a race car, a stiff rear is alright because the driver will rarely have to hit the brakes hard through a corner unless purposely. On the street, if someone hits their brakes in a corner and your right behind them, then you need that extra margin of safety of a softer rear bar. It doesn't mean that you shouldn't get a stiffer bar than stock but just don't go out and set it at full stiff.

I have the H-Sport comp on the softest setting and the MINI still understeers if I go into a corner with neutral throttle position. If I'm off throttle and braking hard, the rear and will break loose. I just don't follow people close in corners when it's raining and you'll be fine

 

That makes the picture a lot clearer now. Thanks a lot . Now i just have to choose which rear sway to get.

 

Understeer is when you see what you are crashing into. Oversteer is when you don't, because you crashed back end first. I would recommend that you get some miles under your belt with the stock suspension before you go making any changes that you may not like & may even be dangerous if you don't have much driving experience. While I don't have any experience with that rear sway bar, I do have lots of experience with oversteer. With a stiff rear bar the car is going to be tail happy. Many folks don't like a tail happy car & some do. I do! It's best if the car has a good balance between the two.

 

the easy way to remember is:(edited from original thanks Eric)

understeer = front hits tree/guard rail

oversteer = rear bumber hits tree/guard rail

 

City slicker. Out in the back woods we substitute 'tree' for 'guard rail'.

 

OT, I was just in Santa Cruz.... what a town.....

My nephew has a place on the beach...... big Grey House w white trim

ate at some place where the guy is into Einstein

back OT..... if your not pushing your car too hard the sway bar in the middle setting is pretty neutral and really not very tail happy...... IMO it just makes the car seem "right".... I did not go to the front bar until I went coilovers and they/it were/was way too prone to roll for my taste.

 

i rather hit a gaurdrail

 

you sick puppy but I like the way you think. I do wish they had a spell check for us semi literates who rely on them like crutches

 

Do yourself a favor and find a car control clinic / advanced driver's skill school. The BMWCCA (BMW Car Club of America) puts on a good one. It will explain understeer and oversteer to you, and let you experience them (if your car is capable of entering into an oversteer condition) in a safe setting.

 

I bought my rear sway bar and put in the stiffest position and I love it.
You have to get used to it, but once, you are not coming back.
Anyway, the MINI is fun!

 

...not every swaybar size is suitable for every venue and every setup...28mm might be great at an autoX event, but not at most tracks on an otherwise stock car. Swaybars tranfer weight and in doing so remove weight from the rear of the chassis. When the inside rear wheel leaves the ground, weight transfer comes to an abrupt end. A 28mm bar will, under most situations, get to this point much quicker than most folks need or can use on public roads or on road race track for instance. And you won't know until you've pushed the car at 9/10 - 10/10 on a track...and likely, you'll find it doesn't work.

Too much rotation can most definately be a bad thing. Managing weight transfer is ultimate goal in setting up a car. It takes much more than a big rear bar to get it right.

 

^^^ +1 i would stick with the stock bar if you're a "beginner in the performance driving world."

 

Me too, even throughout the winter in Wisconsin. Go with what you can comfortably handle.

Driving school pays dividends every day on the street.

 

Yeah, that's the other thing... on a high speed track, you don't want too stiff a rear bar because you just won't be able to recover at 100+mph like you can at 30.

 

what size rear swaybar should someone use if they are sick of the natural tendency to understeer, and just want a neutral car for sprited street driving. I don't want a totally understeer free car. I want a car that can do both depending on my discretion. My car is VERY difficult to oversteer at the moment...

20mm adjustable? or 22mm adjustable

 

22mm alta.

 

Weight transfer is avery complicated matter if being considered at an engineering level. On the flip side, we over simplify the affect of swaybars here. The real answer is, it depends upon what else you've done and where you drive.

A little more bar in the rear of an otherwise stock MSC is not a bad idea; it'll promote a little more weight transfer and actually help to keep the front inside wheel on the ground a little more. The same philosophy applies to powerful rear wheel drive cars but in reverse; adding a bigger front bar helps to keep the inside rear wheel on the ground so that one can accelerate quickly out of a corner. Too much in either case causes either too much oversteer - mini, or too much understeer - rear wheel drive example.

And, weight transfer is not simply a kg or lb figure, it is also relative to time. A really big bar will transfer a lot of weight right now! Whereas a smaller bar will transfer less weight over a longer duration. Longer duration is relative to steering angle. Think about the two scenerios here driving into a turn...if you change steering angle by say 60 degrees in both cases in .5 seconds, the bigger bar will rotate the mini much quicker.

AutoXing requires, dare I write, a right now turning response. big bars help to accomplish this. Road courses are completely different. Velocity is much higher and steering wheel inputs tend to magnify chassis movement and weight transfer. Public roads are different from the two above.

Every other consideration, spring rates, damping rates, rollcenters and therefore roll couple, tire and bushing comliance camber, caster and toe values all affect one another and ultimately swaybar size. For a race track or autoX track, one can give up a lot of comfort. Big springs and strong dampers are a great beginning. On the road, comfort must be considered. Here you can gain wheel rate by increasing the size of the bar, and not the springs and dampers. But you have to be carefull; as I wrote above, weight transfer is a kg/lb AND time thing. Soft springs with a big bar allow the big bar to come on line very quickly. On the other hand, big springs will contribute to a greater proportion of wheel rate and weight transfer, leaving any additional contribution to wheel rate and weight transfer to the swaybar at steering angles closer to lock. Another really simplified way of looking at the last example on a raod course with lots of long sweepers with a few tight or closing radius turns; the springs will perform the lion share of work during the long sweepers where a lot of weight transfer is not needed. but when you ask the car to tighten its line thru the closing radius, the swaybar comes online contributing to overall weight transfer and wheel rate. (wheel rate is a not so techical subject. A 400in/lb spring for example may contribute to only 300in/lbs of wheel rate due to suspension geometry. Why? Most springs and dampers cannot sit directly over the center of the wheel, in other words, in a vertical position above the wheel's center line. So then, actual damping and spring rates are really less efficient in action than they are on a bench. The real determining factor here is suspension MOTION RATIO - or the suspension's mechanical advantage or leverage.)

Just keep in mind, springs dampers and swaybars are also designed to limit weight transfer...very tricky business. Kinda why I get riled about about wild swaybar suggestions. There are a number of suspension engineers working at the F1 level who do not believe in swaybars at all. They have there place in passenger cars for sure.

etalj,

So what was the question? Oh, yes! A 19mm rear bar on an otherwise stock MSC should be all you need for the street. Dialing in a little more negative camber up front, and or, dial a bit out in the rear will also help the front end to bite more, but don't remove too much neg camber from the back end, total grip is still important. For a stock MCS on the street I would personally opt for 1.5 degrees neg up front, 1 degree neg in the rear, front toe as close to zero without being zero or toe out, rear toe 1/16 in and a 19mm rear bar. Leave the front stock swaybar bushings alone and use poly or delrin in the rear...yes, you can really fine tune swaybar efficiency with bushings too. Keep tire psi same front and rear for the street. This is a repsonsive but stable, tire friendly, easy to drive set-up.

 

I gotta agree w/ Snid. Before you put anything into your car, the best investment is driving school to find out what the car is actually capable of.

I was all set on buying the larger swaybar, all my older cars would have benefitted from it.. but after some schools.. I have to say, the minimal oversteer can be easially controlled by tire pressure adjustments.

IF you're going to track the car regularly or want purely POSER status, then get the larger bar. but you really don't need it for regular roads.... and i've pushed it pretty damn hard in the NH and VT mountains...

My 2 cents.. read what people have.. larger bars and lower pressure on the rear tires.. I've been running about 3psi higher on the rear, and have had very neutral handeling. This is a short wheelbase car, if it start to come around you better be ready to correct it.

 

Wookie,

Higher psi in the rear causes more understeer. More psi up front where the 63% of the Mini's weight resides will counter understeer. You wrote both??? I'll assume you meant 3 psi higher in the front since you previously wrote "lower pressure on the rear tires"

And, I believe you're spot on about DE events. I had a hoot in my completely stock MSC last season. This year will be different, but I know the car's stock limitations pretty well.

An addition to my long winded post above that included a brief note about bushing compliance; as scrubing forces increase due to cornering, one of the first places compliance can be measured is in the bushings. Bushing material can have a sobering affect on comfort. That written, I would begin by replacing the steering rack bushing - from Powerflex - first. I would then consider the front lower control arm bushings. All else stock, these two changes will also cure some undetsteer.

 

I agree - a 19mm rear bar is all you need...

 

meb, you've got me thinking about the steering rack bushings. How easy is it to replace them? Any good instructions?

 

I'm also considering a rear sway bar, and the information on this thread has been very helpful. Any specific suggestions on 19mm sway bars? Also, I have an MC (non-S)...are the aftermarket bars suitable for both?

Dave

 

Yup... I've got the 19mm H&R rear bar - best feature are the bushings, which don't require lubrication!

Mine's been on for 3 years now, quiet as ever... It's been through countless track days and 2 seasons of autocrossing to boot, as well as daily driving...

 

I did some psi experiments last weekend. I found that any additional psi on the front above standard caused the steering to lighten up considerably and with it an exponential increase in understeer. The lightened steering is an indicator of a smaller contact patch caused by the overinflation. With the smaller contact patch you get less grip. It's that simple. My norm on my 16" wheels is 30 psi all around. On a roundabout close to home, 32~35 psi up front caused a massive loss of front end grip. At 35 psi I could not hold my normal line as the fronts only would slide outward under the same use of throttle and same corner speed. Therefore, went back to 30 psi and all was correct with the world again.

With my 19mm rear sway bar, I have just a tad bit of understeer. I also tried 2 psi more in the rear and it seemed to remove some more understeer as the smaller contact patch in the rear now makes for less grip. It also makes the rear a bit louder over bumps, so I'm convinced that 30 psi is perfect for my street use.

The fact I have my winter tires on right now helps the experiments as they tend to grip less in the dry anyway. Therefore, you get to the limits much faster.